Parts List, Pt #2, Example: Zenith 750

Builders:

OK, lets look at an example. I am just calling this a 750, but in reality it is also a potential Panther, Waiex or Cleanex engine also. What I am getting at; this is a big bore engine (3,000 cc) with a Heavy Duty Group 2800 oil system. The Conversion parts going into the engine are highlighted in blue in the chart below.

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Above, Greg Crouchley and I stand with his 3,000 cc engine in my hangar, after it’s break in run. Note the reverse oil filter housing. We do not install the HD oil system for the test run because we want to have the oil temp come up early. The engine is now in Greg’s Waiex.

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We have written stories about engines like this. For 750s look at: 3,000cc Engine Running for a Panther look at:Panther Prototype Engine 3,000 cc/120 hp to OSH and for a Waiex look at:World’s Strongest 3,000cc Corvair, built by Greg Crouchley. Between the there engines above, the only difference in the Conversion parts sets is that the Waiex uses a 2601(R) Reverse Gold oil filter housing instead of a standard one.

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Note that the Conversion parts set doesn’t change with either a GM or a Weseman Billet Crank, or even if the engine has a Gen 1 or a Gen 2 bearing. Listed below are the conversion parts that a common to all 3,000 cc engine with Heavy Duty oil cooling systems. Each engine still has some custom choices in the rebuild parts that each builder can make. Below the part number we have some discussion and a look at budget totals. In part #3 of this series we will look at a 2,700 engine with a standard oil system.

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Part description         Part Number              Pricing          Notes

Drive end

Hybrid Studs                2502                              $79

Safety Shaft                    2503                              $79

Short Gold Hub            2501(B)                       $579 

Front Starter kit          2400                             $566  

Ft Alter. Brackets         2901                              $99

Oil Systems

Gold Oil Filter housing   2601(S)                  $239 

Gold Sandwich                 2802                        $169 

Hi-volume Oil case          2000HV                   $289 

Billet Oil Pan                      2201(B)                    $289 

Deep oil pick up kit         2202(A)                     $59

Ignition

E/P Distributor                  3301E/P                   $349 

External items

Valve Covers                       1900PC                    $149

Pushrod tubes                    1602PC                     $60

Piston, Rod, Cyl. Kits

2,850 cc Kit                           2850CC                 $1,800   

3,000  cc kit                          3000CC                 $2,200 

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In the front end category, I left out the 2901 front alternator brackets because many of these engines going in 750s and all of the ones going in Panthers use the Weseman’s rear alternator bracket, which is Group number 2950 in my numbering system ( but you get these direct from Dan and Rachel).

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In the oil systems, The Heavy Duty system uses all the parts listed. Additionally many people use a block off plate part number 2805 it is $20. The Welded pans are slightly lighter and $40 less expensive, but on 3,000 cc Corvairs the Gold Billet Pans out sell them 5 to 1.

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Every Flying 3,000 cc Corvair I can think of has an E/P style distributor. Only a few of them, like the Panther prototype are E/P-X models, a $40 upgrade. Almost all builders use our Valve Covers. They look good, but they have important mechanical features like being able to see TDC on the engine by removing the oil cap and looking at the #1 rocker arm instead of pulling a plug out. Zenith installations must also have the oil fill in the valve cover.( the stock filler neck hits the cowling.)

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The price of the 3,000 cc Kit includes the machine work to the case and heads to fit the larger cylinders. The 3,000 cc pistons are specifically designed and made for Corvair flight engines. They work with both 100LL and auto fuel.

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Price totals:

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If you add up all the parts above, except for the 3,000 cc kit, you are looking at $2,906. If you add the 3,000 cc kit, you are up to $5,106. Make the distributor an X model, add the block off plate and the total is $5,166. Keep in mind that most builders buy the components slowly over time, but I have the total here because we have lately had a number of requests for a total price from people who wish to buy the parts at one time.

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Obviously this isn’t the total price for a 120 HP /3,000 cc engine. This number does reflect the Conversion parts cost, and a big part of the internal engine parts. The list above is the part of the budget that builders spend with us on their project. As I have pointed out many times, we try not to resell anything we can simply direct builders to acquire for themselves, such as the Weseman parts and Falcon heads.

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There are a lot of different options on building the rest of the engine, and if you would like to look at them, read this link,Getting Started Reference page. Specifically look at the links to parts #5 through #9 at the bottom, it gives every specific examples of the cost of different levels of bottom ends on the Corvair. -ww.

Engine conversion parts list, Part #1

Builders,

Below is a table listing the most common parts we offer. They are easier to see at a glance in this format compared to studying our catalog in depth. In part two of this series, I will give several typical examples based on popular airframes.

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If you would like to get a very detail look at how each of these parts fits in our numbering system, click on this link: http://www.flycorvair.com/products.html.

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Note: The first two digits of the part numbers are the group number in which the full description of the part can be found. ie, Hybrid studs, 2502 are in The Hub Group (2500).

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At the very bottom are  numbered notes that address the right hand column.

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Part description         Part Number              Pricing          Notes

Drive end

Hybrid Studs                2502                              $79

Safety Shaft                    2503                              $79

Short Gold Hub            2501(B)                       $579               (1)

Front Starter kit          2400                             $566              (2)

Ft Alter. Brackets         2901                              $99

Oil Systems

Gold Oil Filter housing   2601(S)                  $239               (3)

Gold Sandwich                 2802                        $169              (4)

Hi-volume Oil case          2000HV                   $289            (5)

Billet Oil Pan                      2201(B)                    $289            (6)

Deep oil pick up kit         2202(A)                     $59

Ignition

E/P Distributor                  3301E/P                   $349            (7)

External items

Valve Covers                       1900PC                    $149              (8)

Pushrod tubes                    1602PC                     $60               (9)

Piston, Rod, Cyl. Kits

2,850 cc Kit                           2850CC                 $1,800          (10)

3,000  cc kit                          3000CC                 $2,200          (11)

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(1) This is the hub used with a 5th bearing. 2501(A) is for no 5th bearing

(2) Front starter kit includes the 2401 starter, the 2402 brackets, the 2403 tail bracket, 2405 top cover, 2406 gasket and the 2407  hardware. We are glad to sell it as a kit or by the part, the kit is slightly less expensive.

(3) this is the standard part. For a reverse model (Sonex-Waiex) the part number is 2601(R). The part can be seen at: http://www.flycorvair.com/goldoilsystem.html

(4) This is for HD oil cooling systems. See the above link for more info.

(5) This part number is for the remanufactured rear case with our CNC high volume pump already installed. Includes at parts in the 2000 group. Read more at this link: High Volume Oil Pump

(6) This is the Gold machined part. The welded pan is 2201(W) for $249. It uses the same 2202 pick up kit.

(7) For more info, and the E/P-X option read this link:                                      E/P and E/P-X Ignition systems, (3301E/P and E/P-X)

(8) These are modified with the filler and breather ports, they come in several colors. Read more here: E-mail
Now: Custom Valve Covers Available Through Monday

(9) These are stock GM steel tubes that have been cleaned and powder coated white.

(10) This kit has Remanufactured rods with ARP bolts, Forged dual fuel pistons and new Clark’s full fin cylinders. A look at the parts can be seen here: Complete Engines for Sale

(11) This kit has Remanufactured rods with ARP bolts, Forged dual fuel pistons and new Custom machined, full fin cylinders. Price includes machine work to case and heads. A look at the parts can be seen here: Complete Engines for Sale

E/P and E/P-X Ignition systems, (3301E/P and E/P-X)

Builders:

Below is the story on our standard and optional ignition systems. The E/P stands for “Electronic /Points” , as it utilizes both. The E/P-X model is internally identical, it just has a few external features to make a slightly nicer installation. We have been producing E/P distributors since 2006. In our numbering system Group 3300 is the engine ignition group. the specific part numbers are 3310 E/P and 3301 E/P-X.

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Above is a photo on an E/P-X distributor. The features that make it an -X model are the Weatherpack quick disconnect plug system, the studs holding the cap on (instead of screws) and the fiberglass jacket on the wires. Other than these items, both E/P models are identical.

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We looked for a long time before finding the Crane module that is the heart of the E/P ignition. There are many electronic ignitions on the market, but for flight use they have two critical Achilles’s heels: They use many amps of power and they do not work at reduced voltage. The made in the USA crane unit has neither of these issues.

 There’s  a lot of great automotive electronic systems that work fantastically as long as there’s more than 11.5 volts available and  a steady flow of 10 amps to power it. In the world of flying, where you could have an alternator or voltage regulator failure,  and be reduced to the amount of electrical power stored in your battery, these electronic systems are not acceptable. Electronic ignitions with computers on other alternative engines have demonstrated as  little as 20 minutes flight time after a charging system failure. Many alternative engines that are converted modern car engines have this defect. Most of the people who fly them have never run them at cruise power with the charging system disconnected to know just how short their window is.

A Corvair  engine running one of my ignition systems will run for hours on the battery that started it. The points system will work all  the way down to the 9 volt range. My Electronic/Points  system utilizing the Crane module is a very low power consumer and additionally has the unheard of quality of producing stable  sparks well below 9 volts. No other electronic ignition that we tested demonstrated this. The power wire to the crane unit is a tiny 22 gauge wire. When testing distributors on the machine you can run the Crane unit for an hour and it is still cool to the touch.

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In the above photo, an E/P ignition running on our machine. This uses the same coils and systems as our Dual Points  Distributor with the exception of eliminating the condenser on the electronic ignition’s coil. The photo is from 2006. We have since produced more than 200 E/P units and retrofitted more than 100 D/P distributors with E/P plates.

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 Success can sometimes come from pioneering work, but it always comes from emulating what has proven to work. Virtually every flying Corvair powered airplane built in the past 15 years has one of my ignitions on it.  No aircraft has ever had any type  of a forced or precautionary landing made on our ignition system. It works. Period. The only issue builders have has are reversing the red and yellow wires while installing it (this instantly burns out the Crane unit at a cost of $75; bad, but not like burning out a $1,600 Rotax 912 ignition) and we have had 3 people pinch a wire carelessly putting a distributor cap back on. This said, no one has had one of these units fail while flying, and they have been airborne for thousands of hours.

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Above is a wiring diagram that shows the basic layout of my ignition system. This page is taken from our 601 Installation  Manual, so it includes some of the wiring associated with fuel pumps. This drawing shows the D/P wiring, but the E/P only has two minor differences. The key elements of the design are redundancy, low  power consumption and low voltage tolerance.

With our system, notice that you can fail one of the coils or one set of points and still have 100% power available through  the backup system. Once every few months, a builder will propose a system that has three pickups and a wasted spark system using  three coils and two plug leads from each coil. I know these systems well, and they’re not safe to use in Corvair engines  because with three coils and three pickups, you’re statistically more likely to have a failure and when you do, you’ll be  immediately down to 66% power. However, the dyno shows that dragging two dead cylinders means you’re really down to 50% power  and most Corvair powered airplanes will not climb on half power.

Our EFI page contains a photo of Mark at Falcon’s EFI engine. Note that it actually has  six LS1 coils which have built in modules. This is acceptable because a single coil failure will bring you down to 83%  theoretical power; about 75% power on the dyno dragging one dead cylinder. This illustrates the point of why it’s acceptable to  have single plug ignition on a six cylinder engine. The performance loss of one cylinder on a six is not catastrophic like losing  one cylinder on a four cylinder engine. Corvair powered airplanes have taken off and flown on five cylinders on three occasions  that I know of without incident. This was due to a missing plug, blown head gasket and missing rocker stud, respectively. You would not get away with this on a four cylinder engine.

The shot of the workbench above shows 85 Distributor bodies neatly stacked. Over the years, I’ve reworked  hundreds of  Distributors. I’ve had the opportunity to examine many of them after they’ve put in years of flight service. We’ve  continuously had running Corvair vehicles to test all types of ignitions in the ground environment. Many of the theories I was  taught and believed 25 years ago proved inaccurate or inapplicable to our situation. All that counts in the aircraft arena is what you have proven. Theory is fine for ground debate, but people going flying need proven systems.

D/P Ignition Systems, (P/N-3301D/P)

Builders:

Here are some notes about our oldest ignition system, the Dual Points distributor. I made the first of these models nearly 20 years ago. We went on to produce several hundred of them. In the last seven years there have been superseded by our E/P and E/P-X distributors, which themselves are evolutions on this basic design.

Dual Points distributors served the Corvair flight community very well. Many thousands of hours have been flown on these ignitions, and there has never been a single forced landing nor accident attributable to the design. (we have had people fail one side because of pinching a wire putting the cap on, but they flew on the other side) The design uses two sets of points from a Corvair mounted 180 degrees apart. either one can run the whole engine smoothly.

We mount the condensers remotely on the coils. When I introduced this, there was a giant debate on the internet claiming the condensers being on the end of 20 inches of wire would case some sort of ‘delay’ in the ignition, even though I pointed out that electrons travel down wires pretty much at the speed of light, and 20 inches vs 186,000 miles per second is a very short interval, the debate lasted years. Meanwhile, many happy people went out and flew countless enjoyable hours without noticing.

In the 1960s, companies like Mallory made dual point distributors for racing Corvairs, but these had three lobes not six, the goal being much shallower ramps on the point cam that would allow 7,500 rpm operation. such a distributor can not provide redundant ignition.

Today, we sell only a handful of D/P distributors a year. They are a special order item, but the remain popular with some very old school builders and some builders Down Under. They work well, but I highly encourage all builders to use E/P series distributors instead, they run smoother and have comparatively little maintenance. (D/P points need cleaning or replacing every now and then, but on the E/P the points are a back up and pass no current normally and may go 1,000 hrs. of operation without adjustment.) All the engines we build and sell are equipped with E/P series ignitions. Read all the articles and decide which system you like, they are all well flight proven.-ww.

In the above 2006 photo, a Dual Points distributor P/N 3301(D/P). The screwdriver points to one of the two 8/32″ screws that hold down the Points Plate. Two things I tell builders relentlessly, but are sometimes not heeded: 1) Never adjust the points to make the gap .019″, the gap on all distributors come from us pre set to a specific dwell, not a gap, and if you let anyone talk you into jamming an old feeler gage in the points, you will upset the pre adjusted timing. I have had 40 or 50 people do this and then rationalize it by saying “the gap looked small.” If people want to do this, I will fix it, but it does tell me who reads directions and who wants to argue rather than learn and understand. 2) Never take the two plate screws loose for a look inside, it will have the same effect as doing #1. Builders can replace points on these in the field, but it is done by matching the existing preset gap on the original points, not by using some book value.

The above photo shows a Dual Point Distributor in the machine. If you look closely at the 11:00 o’clock position you can see the illuminated arrow pointing at the degree wheel. the distributor machine was made in 1950. The items piggybacked on the top row  allow the simultaneous operation of the electronic side of the Distributor while superimposing the EI picture on the scope. Every single distributor we ever send out the door is test run in this machine.

When running a Distributor on the machine, I can vary the rpm it’s turning and observe its advance directly. When your  Corvair engine is idling, the advance weights in the Distributor are held shut by springs. The advance at this point is referred  to as the static timing. I set the Distributors so they have little advance below 900 rpm. As the engine comes off idle, the  mechanical advance inside the Distributor’s body makes the spark occur earlier. This is the mechanical advance at work.  All the mechanical advance needs to be in by 2,400 rpm or so. This way, you can tie the tail of your airplane down, run it to  full power and check what the total advance is at the propeller’s full static rpm. Total advance for engines running on 93 octane  fuel should not exceed 30 degrees. For engines on 100 low lead, 32 is the limit. Beyond these numbers, the engine could be aggravated to detonate.

Each of our Distributors is marked on the underside with its mechanical advance and the beginning and ending rpm of its curve.  Thus, if you have an engine you’re going to run on 93 octane fuel, and your Distributor says “18-1,000-2,400,” use a timing light to  set the static timing to 14 degrees below 1,000 rpm. With the plane tied down, raise the rpm above 2,400 and verify  that the total advance does not exceed 30 degrees. A dire warning: Never touch the ignition wires while the plane is running  and turning a propeller. There is a remote possibility you’d get a high voltage shock and inadvertently flinch into the propeller.  It’s a very remote possibility, but a builder in Australia did it and was lucky to keep his fingers.

For a better understanding of ignition timing please click on this link:

Ignition Timimg on Corvairs.

We also have more information on this link:

Engine Operations reference page.

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The above photo shows four point cams. Occasionally people ask if they can recurve distributors at home. It would be a very  difficult process, and while you might achieve some results, a lot of the fine tuning we do to distributors is very difficult  to see. Off the end of the screwdriver is the part of the point cam that the counterweight touches. Notice the four different  profiles shown here. There are six different common Corvair profiles. The upper two are ground to match templates we’ve  developed to produce ignition curves that suit aircraft use. The upper two point cams appear shinier because they’re nickel plated. We later switched to chromed ones we use now on all models.

Above is a wiring diagram that shows the basic layout of my ignition system. This page is taken from our 601 Installation  Manual, so it includes some of the wiring associated with fuel pumps. The key elements of the design are redundancy, low  power consumption and low voltage tolerance. It’s also immune to voltage spikes and high temperatures.

With our system, notice that you can fail one of the coils or one set of points and still have 100% power available through  the backup system. Once every few months, a builder will propose a system that has three pickups and a wasted spark system using  three coils and two plug leads from each coil. I know these systems well, and they’re not safe to use in Corvair engines  because with three coils and three pickups, you’re statistically more likely to have a failure and when you do, you’ll be  immediately down to 66% power. However, the dyno shows that dragging two dead cylinders means you’re really down to 50% power  and some Corvair powered airplanes will not climb on half power.

The above 2001 photo shows the firewall mounted electrical box from our test mule at the time, The Skycoupe.  We put this together so all the electrical components and flow cool air over them. The Wagabond has something similar. This function is done on aircraft like Zeniths by having the coils and the MSD 8210 behind the firewall. The only difference in today’s  method is the use of Bosch Blue Coils, readily avaiable from Great Plains Aircraft. The Accel coils shown above must have external  ballast resistors, which are internal on the Bosch Blue Coils. The top shelf houses the MSD 8210 coil switch. There’s some  discussion about the use of the Mallory equivalent of this part. The system will work with either; it does not care. If you look at the wiring diagram above, you and identify most of the parts in the system.

Engine Operations reference page

Builders:

Here are links to a great number of stories on operations. Many companies have no such data on their website. Their goal may be just to simply sell engines, and that is easiest if the potential buyer is never brought into a mechanical discussion. On the other hand, we have data because we are in the business of teaching builders to be the master of their engine, and this involves some reading.

If your goals are those of the traditional home builder, to learn, build and fly, to be the master of your plane not just the guy that owns it, then read on. All of the stories below are written by myself, and reflect my 25 years of working with Corvairs. Contrast this experience with the fact that more than 50% of the engine sales people at Oshkosh have never put a wrench on the inside of an engine, not even the one they are selling.

In the 100-120HP range, just 3 engines have a 50+ year track record of flying: Lycoming O-235, Continental O-200 and the Corvair. I have worked with the Corvair since 1989, and slowly evolved it to the engine we have today.  Along the way, we learned a lot, both about the engine and the needs of builders. The stories below are a reflection of this knowledge that we stand ready to share with any builder who has set his goal on learning and mastery.

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 Above, a winter 2005 photo of our 601XL, N-1777W with hangar cat “Whobiscat” warming herself on the Cowl. We have been working with Corvairs a long time.  Gus Warren in the cockpit at the end of a long day of flying.

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Click on any color link to read the story:

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Shop perspective: Mastery or ?

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Operations:

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Thoughts on cold weather operation, minimum oil temps, etc.

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Starting procedures on Corvairs, 2,000 words of experience.

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Engine oils and oil systems:

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Notes on Corvair flight engine oils.

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Corvair Oil Change interval….. Lessons part #1

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Corvair Oil System, information on oil pressure gauges.

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High Volume Oil Pump

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Ignition and timing:

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 Aircraft wiring 101

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Ignition Timimg on Corvairs

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When to check your timing, Lessons learned Pt#2

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MGL vs Corvair ignition issue

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Cylinder Head Temperature:

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Cylinder Head Temperature measurement

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Corvair CHT, letters and notes.

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CHT part #3, Letters, notes, sources and inlets.

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CHT Part #4 more notes

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CHT part #5, flight data from Zenith 750

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Measuring Cylinder Head Temps on Corvairs.

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Cowling Inlet Area, marketing, accident stats, Darwin where are you?

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Spark Plugs:

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Spark Plug Installation

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A Tale of Two Spark Plugs……

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Spark Plug Issue resolved…..

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Cowlings:

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Cooling with J-3 style cowls. (Pietenpols, Cubs, Biplanes, etc)

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Corvair Cooling, Three 2007 examples from our hangar.

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Corvair Cooling, something of a human issue…..

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Corvair Cooling

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http://www.flycorvair.com/pietengineissue.html

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Ignition system, experimental “E/E-T”

Builders,

Below is a distributor system that has been in the works for about 3 months. We had a free hour on Saturday night so we did some test assembly to check the fit of the sub components. It is a specialty item with two Crane units in it, and no advance. It is something that we may use in the future on Turbo engines, thus the working title E/E-T.

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Above, as you see it, this is a non-running model, but it has a serious purpose. The red parts you see are plastic, and were made for us by Corvair/Panther builder Paul Salter. They are very accurate, because they went straight from the CAD model we worked up on his laptop to his 3D printer. There are 3 red parts: The large base plate will be made from 3/16 aluminum, the reluctor wheel and the rotor drive will be made of steel to be affixed to the main shaft. The small parts were printed in 5 minutes each, the plate took an hour. They allowed us to check the fit of all the parts without sending anything in to the machine shop. The cap and rotor are Ford V-6 parts.

The spark retard on this system will be controlled by a small USA made brain box that is for off road ignitions. The controller also takes into account MAP, so it will work great on a turbo engine. (when these engine go into boost, they need a lot less ignition advance, or they are prone to detonation) If you look at the rotor, it has a very wide contact nose, typical of new designs with purely electronic advance. This system may also have a handful of application for naturally aspirated engines at very high altitudes. such engine need a lot of extra advance to completely burn the mixture when the pressure is down. Either way, we are now having the metal parts made, perhaps we can do a demonstration run of this at CC#28 or #29.

Above a 2007 photo and caption from our webpage. It highlights things we looked at and considered using. “Many Internet commenters falsely assume that I have only looked at one way of doing things. The photo  above shows various ignition parts, some considered, some tried, some still in the works, sitting on the  shelf next to my distributor machine. Seen in the photo are a low profile crab-style cap with a corrected  firing order from an import; a ball bearing distributor housing from the same engine machined to fit in the  Corvair case; distributor shafts from small block Chevys that have identical diameter and oil pump drive;  HEI ignition system from 4.3 liter V-6, Pertronix points eliminator; Mitsubishi optical trigger; and  miscellaneous other parts. We build and test an awful lot of stuff that does not make it to the discussion  level. Just because we have one way of doing it that has proven to work well does not mean we don’t  understand how to do it many other ways, and have considered, tested and perhaps rejected ideas brought up as  new discussions on the Net.”

Ignition Timimg on Corvairs

Builders,

One of the things that sets our work apart from other engine options is the amount of direct interaction we have with builders. A salesman can spend all day talking to a guy about buying something and still have no real measure of what that guy’s understanding of the product is. Conversely, I can spend 10 minutes showing a single step to a builder, and then ask him a few questions. I will then have a good gage on his understanding, and tailor the delivery of information to his level. Although we have several hundred builders, I am an ‘idiot savant’ when it comes to perceiving and remembering our builders development of mechanical skills and understanding.

In conversation, one of the things I have consistently seen is that many builders don’t have a good picture of how ignition timing works on an engine. There are three levels of understanding on this: 1) being able to follow the directions on our website and use a timing light. 2) Knowing a little more about the why of timing in our engines, and 3) having a grasp on the factors affecting the behavior of combustion chamber reactions.  With the help of the graph below, I want to move a number of builders from 1) to level 2).

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Above is an ignition graph I ‘borrowed’ off the MSD ignition website.  Although this timing ‘curve’ is not an exact match for a Corvair flight ignition, it is close enough to support a good explanation and aid builder understanding.

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First, some language translations: What they are calling ‘initial’ timing is what I call ‘static’ timing. On a Corvair we usually start with 8 degrees to get the motor to fire up on the stand. But this number isn’t important, ‘total’ timing, or what I call total advance is. This is the number that your engine will fly around at, and it is the one you must check with a timing light. Also, people use the term “ignition curve” to describe the advance section of the graph, because theoretically it would graph as a curve, but in practical reality it graphs as a straight line.

When an individual cylinder is coming up to fire at idle, the spark takes place about 10 crankshaft degrees before the piston gets to the top of the bore. This allows the peak pressure and the effort of the cylinder to take place after the piston passes over top dead center onto the power stroke. As the engine rpm comes up, the spark needs to happen sooner because there is less physical time for the combustion to take place. This change in timing is called ignition advance, and in the Corvair this is done with mechanical flyweights inside the distributor body. Cars have a very complex set of running parameters, but airplanes do not. With fixed pitch props the power required by any rpm is fairly consistent. Thus the mechanical weights can cover the task that cars must have complex systems like vacuum advance (then) and computers (now) for. Airplanes like ours can use a very simple timing setting where the engine stays at one setting most of it’s airborne operation.

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Total advance on a Corvair flying on 100LL is 32 degrees. On 93 auto fuel it is 30 degrees.  Total advance is Static + the Mechanical (centrifugal).  Cars have both mechanical and vacuum advance, but in planes we just use mechanical advance. The engine makes it best power at these settings, with a good margin protecting it against detonation. Why not leave it at these all the time? It would be very hard to start.  While you can say we ‘advance the timing for full power’, you can use different language to say ‘timing is retarded for starting.’  It is saying the same thing.

Here is the critical point to understand: Having the timing set too far advanced, to say 38 or 40 degrees, is the easiest and fastest way to destroy the engine. This isn’t just true for Corvairs, it is true for all gasoline engines. The specific number has a lot of variables, but on any engine where you advance it too far, it will detonate. On a Corvair, the first thing to go are the head gaskets. (This is actually a good thing. On most car engines, it is the cast piston that breaks up first, leading to a stopped engine. A Corvair will run with several blown head gaskets and make about 60% power. the forged pistons we use will suffer detonation but stay in one piece. )

Why do some people get away without setting the timing for a while? How fast the engine is damaged is a variable. Lets say a guy never checks the timing and it is accidentally set to 42 degrees. On his first flights he uses 100LL and it is 50F outside. 180 seconds after starting the take off roll he is at pattern altitude and throttling back. the CHT is only 285F. He will get away with this. Change one variable, and bets are all off. Make it 80F outside, add a passenger and lengthen the climb to 300 seconds at full power, or worse, load the tank with auto fuel, and it will start detonating. Now, it isn’t likely to do it in the first 60 seconds, it is going to wait until the CHT climbs through some threshold. This is how people can fly the first 20 or 30 hours on a plane with the timing never checked, and then one day scare the shit out of themselves (and their passenger) when the engine suddenly starts losing power when they are at 300 feet climbing out. This is entirely preventable by just checking the timing with a light. If the same guy just took 10 minutes to set the timing back to 30 degrees total, he could run the engine at full power, fly at gross weight, at any OAT, any time he liked with no damage to the engine. Seems simple, but 1/5 of builders will not do this. I would like to tell you why they don’t, but I can’t. My expertise is aircraft maintenance, not mental illness.

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Above a 2008 picture from my shop. on the left is my 1950 Allen distributor machine. I actually first used this machine to build drag race distributors at Speed World of Union, N.J.,  from 1982 to 1986 when Englishtown was my Oshkosh. After I got into aviation, I went back to my original ‘alma mater’ and bought the machine  from Speed World’s owner Ron Murphy. I have been working with distributors for a long time.

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Second critical point to understand: The engine must reach total advance BEFORE it reaches the static rpm of the propeller.  If you tie the tail down and run the engine to wide open throttle (WOT), you will be at ‘static rpm.’ All the distributors we build are internally modified and test run to make sure they have all of their advance in effect before 2,600 rpm. (The exact number is written on the bottom of each distributor after it is tested.)  Go back and look at the graph above. If a KR-2 builder used a car “curve” like the one pictured and he set the timing to 32 degrees at the plane’s static rpm of 2,700, he would then take off and have the engine wind up in flight, but the actual timing would advance to 40 degrees and the engine would be in the detonation zone. Although I warn people against doing this exact thing in my manual, a KR-2 builder from out west, used a regular car distributor destroyed his plane on the very first flight doing this. I later confirmed this by testing the distributor. Believe it or not, the guy wanted it back unmodified, because he was building a second plane and was going to use it again. As I said before, I would like to tell you why they thought it would work better on round two, but it isn’t in the scope of my expertise.

Third important point: Every distributor we sell has three numbers on the bottom that you need to know. They typical look like 700-20-2350. The instructions explain this also, but many people don’t read them. Maybe 10% of they builders I visit with a running engine or a flying plane have these numbers written down in their log book or notes. A great number of builders actually paint over them before reading the instructions, which requires sending the unit back to me so I can run it through the distributor machine to reestablish the numbers. Here is a hint: if a builder calls me up with a running engine and wants to know how to set the distributor, all I have to do is ask him what his three numbers are to know if he read the 9 pages of installation instructions or just threw them out. (It also gives a lot of insight to how closely he followed other directions.)

If we made 3 numbers for the graph above, they would be 1250- 18- 3750. Our first number is the highest rpm that you can have with no advance. The second number is the degrees of advance, and the third is the rpm where all the advance is in by.

Fourth important point: The static advance and the high rpm that all the advance is in by are not critical, only the total advance is.   OK, lets look at some samples; A 750-16-2200 distributor would yield 16 degrees of static when it was idling below 750 rpm, if the total was set with a light at 32 degrees with the engine running above 2200 rpm.  What about the 8 degrees static? That was just to start the engine the first time and get the break in run done. If the guy never when back and set it with a light, he would only have 24 degrees total, and he would make his 100hp Corvair into an 85 HP one, maybe shaving 300 FPM off the rate of climb. I have only seen that done 40 times or so. At least the engine is in no danger of detonating. I have actually had people decide their didn’t make enough power and remove it from the plane without setting the timing. I have also had people cut down their wood props until the static rpm came up, and only then set the timing with a light and were now greeted with a prop that over sped. Timing lights cost money, but not reading instructions can cost a lot more.

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Above, a closer look at an E/P distributor in the machine ( circa 2008). The machine has a large electric motor inside that spins the distributor. The silver degree ring is fixed, but the spark is projected onto the inner black rotating disc. The motor is variable speed from 0-6,000 rpm. I can easily see the exact advance at any rpm. The machine is equipped with coils and plugs, so the ignition have a load on them. The machine is fully instrumented for dwell, and the points in every distributor come pre-set. Using this machine I can make sure that the two systems fire at exactly the same time.

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Next example: 650-24-2400. This is a good hand prop distributor for a retrofit on a Pietenpol with a blower fan. The engine will be easier to prop because if the total timing on this distributor is set to 30 degrees, it will only have 6 degrees static when the owner is propping it.  Once the plane starts, the idle will typically be 750-800, and some advance will come in, and the timing will be 8 or 10 degrees and smooth out. A Corvair will idle good at 8 degrees better at 12-16. The number is not important, only the total advance is critical. Likewise, it doesn’t matter if the full advance comes in at 2000 or 2650 rpm, just as long as you set the timing with a light to the total advance ABOVE that rpm.

Why not make every distributor the same? Inside the distributor their are 6 different pin holes in the plate, 9 different advance weights, 12 different advance cams, and 3 different springs that can be used in several combinations. If you didn’t get an “A” in statistics, let me share:  it is over a million permutations. With 24 years of experience on the distributor machine I have it down to 60 effective and useful combinations we use, but this is why every singe one of the is verified on the machine by me personally.

If a builder reads and follows the directions, he has mastered level 1). If he reads, considers and understand this story, he has moved his understanding up to level 2). Does he need to know more than this to effectively use the engine? No, but if he would like to know far more, it is one of the things I have a good understanding of in engines. This did not come from years of being a mechanic. The further understanding came from a number of years in Engineering classes at Embry-Riddle, Particularly the Chemistry classes. While the subjects we studied were academic examples for almost all of my younger classmates, I was 26-28 years old then, and the information was enlightening when I had a sudden understanding of combustion dynamics that I had observed for years in automotive racing, but didn’t have a detailed view of how the factors worked together, far less that you could make calculated and predictable changes.

Many factors are at work in the cylinder as the piston comes up to the ignition point. RPM, Charge temp, Density, surface area, compression ratio, the rate that the mixture is being compressed at, the octane of the fuel, how well it is atomized, how homogeneous the mixture is, hot spots in the chamber, angle of the plug, and the big one, how turbulent the flow in the chamber is. All this comes into play before the spark ignites the mixture. As the flame front propagates, a complex new set of variables happens as the pressure in the cylinder and the heat goes up, but the mixture becomes diluted by byproducts of combustion. These are interesting to the design of the engine, but you need not be conversant in them to use the engine and be its Master.

Over the years, modifications we have done and recommendations we have made have come from this category 3) understanding. These tests verified on our own dynamometer, confirmed many of the things we do today as common practice. For example, the tight quench area of 2,850 and 3000 cc pistons was solely to improve the turbulence in the cylinder, which in turn raised the rate of reaction, and gave us full power with far less ignition advance. The dished pocket on these same pistons was to lower the static compression to suppress detonation. This type of work is a very good example of why I like to call the Corvair an “Automotive Conversion engine”  It is far more than a car’s engine plucked from a modern wreck or a roll over. Yes, the origins came from the labs of General Motors, the worlds largest corporation, but we have gone to great lengths to tailor this engine to make it an outstanding aircraft power plant. It makes todays aircraft builder the beneficiary of a tremendous amount of work. All he has to do to utilize this is read the directions and use a timing light. -ww

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