When to check your timing, Lessons learned Pt#2


Here is a story about when to set and check your timing.  Over the years, I have written many stories about timing Corvair engines. Many of these stories point out that 1/5th of the flying Corvairs have never had their timing set. I suspect that builders think I am exaggerating. I am not. Here we will examine the case of a Corvair powered plane that has been flying for several years, and has never had the timing set or checked, in spite of having many annuals, being destroyed and rebuilt, wasting the engine on a poor installation and rebuilding it, and flying the airplane to two colleges. There are several lessons here please read carefully. My point is not to condemn the owner, it is to get people to take airplane operation, maintenance and ownership more seriously.

Above is Gardiner Mason’s plane, the focus of this story.  Just to be clear, I like the guy, but I really need builders to do better on timing, and I am going to use Gardiner’s case as a specific example in hope that more builders take this issue seriously.

Above is a n early 2007 photo of Gardiner’s engine running on our test stand at the old Edgewater hangar. It was started at CC#10. That was eight years ago. Anyone who comes to a college understands that I set the timing statically to get the engine to start, and teach builders how to set the timing and check it when the put the engine in the plane. I do not set it for them because in the transportation, storage and installation, it might get bumped and altered, and I want them to check it. Besides, the College and the building process are aimed at teaching builders, not doing things for them.

Gardiner flew his plane to CC#27 in Barnwell 2 months ago.  He came a day early. he later told me he was cold and fatigued and off his game on arrival. His landing was hard enough to break an axle off the plane. By luck, it wasn’t severely damaged, and the local crew provided the assistance to fix the plane in one day. I only briefly got a look at the plane. On the way back to Georgia, Gardiner had the oil pressure drop off to 10 pounds….twice. After the first time, he landed and found the engine 2 quarts low; he refilled and noted an improvement, but not the restoration of normal pressure. He elected to take off, and the next leg brought a repeat of the same. He called me when he got home and told me that the plane now had no compression in several cylinders. He removed the engine and drove it to my shop. While he was here, he said to me that he had never set the timing on the engine. Not once that he could recall.

Let’s cover some basics:

1) The timing needed to have been set on installation and checked at least at each annual.

2) The oil pressure in an engine never drops until it runs out of oil and sucks air. A Corvair with 3 quarts in it will have the same exact pressure as one with 5. Low oil pressure is the sign of internal damage, and it has nothing to do with the number of quarts in the crankcase.

3) NEVER take off in an engine that has just given signs of failure, like dropping oil pressure. There is no excuse. In Gardiner’s case, “get home itus” was a factor.

4) an inspection of his engine showed that it had been detonated to death from having the timing too far advanced. The low oil pressure is bearings that were beaten by the pounding, the low compression is having the head gaskets blown out. When it was landed the first time, rotating the prop by hand, which I tell people to do on every preflight, would have confirmed the lack of compression on several cylinders.

Here is a vital point I want to make clearly: Gardiner has flown more than 20,000 hours. He has had some issues with his plane and engine. Many new guys seeing this ask themselves “if that guy has problems, why can I, a rank amateur expect to do better?” Here is why: Because a guy with 100 hours of experience who exercised good judgment is going to have better results than a 20,000 hour guy who thinks “it will be alright.” If you are a new guy, read this story:

Risk Management, Experience vs Judgement.


How often should I set or check the timing on my Corvair?

On installation, at every annual, after any unusual operational event, after any engine removal and reinstallation. If I add these up on Gardiner’s plane, he missed about 10 points where he needed to check the timing. There is some validity to checking it at oil changes. If you change the oil, you are going to do a run up test to make sure you have no leaks. I can combine this with a timing check, and I will literally be adding less than 4 minutes to the oil change.

Above is a famous photo from Sun n Fun 2011. It is three Pietenpols smashed by the tornado. It is hard to see, but Gardiner’s plane is at the bottom of the pile. I admire the fact he aggressively went to putting it back together, but he has recently told me that he never checked the timing on the distributor after salvaging the motor out of this wreck. Common sense says that any of the airframe part could have smashed into the distributor body, or the salvage crews that moved the planes with front end loaders could have altered it, or it just could have gotten bumped putting the engine in and out of the plane. Gardiner flew the plane about 30 hours since rebuilding it, but did not verify the timing.

The tornado was not the only issue Gardiner had in the last 8 years. This link is to a long story about how I worked with him to fix his engine after he damaged it with cooling issues: http://www.flycorvair.com/pietengineissue.html . Below, in color, is an excerpt from the story, written almost 4 years ago:

“This is severe detonation. Many times, people ask me if high oil temp can cause a loss of power, etc. Here is the absolute bottom line: If you lose more than 50 rpm,  immediately suspect detonation, and take action. I have actually had a builder try a take off when his engine was down 500 rpm from normal on a take off roll. (He had an “expert”  set the timing for 55 degrees of advance.) If I see 75 rpm low on a plane on take off, I abort the take off. Any noticeable reduction in power on a Corvair is detonation.  You can run the engine with the oil at 300 degrees, and it will actually make slightly more power on the dyno; likewise, a high CHT that isn’t detonating will have little  effect on power. Running on five cylinders, the engine will lose only about 250 rpm on take off. I point this out so that people can understand just how much violent force the engine  is absorbing when it is detonating bad enough to lose 700 or 800 rpm.”

After the issue, in May of 2010, I helped Gardiner put his engine back together and we ran it. Last month, Gardiner said he assumed I set the timing then, and never bothered to check it, not at any of the annuals, not after the tornado, not after the reinstallation.


How hard is it to check the timing?

Here is a link to the set of instructions that come with every distributor we make, which are also on our webpage, which I also use as a guide to teach builders at Colleges:


Below is a photo from the instruction sheet, the process isn’t just described, it is fully illustrated.


Developing your own inspection Checklist:

Below is the FAA’s basic check list for engine inspections during a 100 hour or annual inspection. They are the very minimum. Engine manufacturers can, and do make further specifications. In short, you can ask any A&P or IA, and they will tell you that the timing, differential compression, spark plugs and the inside of the oil filter are checked at every single annual.  If you meet any A&P who disagrees with this, have him put it in a one paragraph email with his name and license number, and I will forward it to the FAA, and we will see who is right. Use the notes below and develop your own detailed list.

Each person performing an annual or 100 hour inspection  shall inspect (where applicable) components of the engine and nacelle group as  follows:

(1) Engine section – for visual evidence of excessive  oil, fuel, or hydraulic leaks, and sources of such leaks.

(2) Studs and nuts – for improper torquing and obvious  defects.

(3) Internal engine – for cylinder compression and for  metal particles or foreign matter on screens and sump drain plugs. If there is  weak cylinder compression, for improper internal condition and improper internal  tolerances.

(4) Engine mount – for cracks, looseness of mounting, and  looseness of engine to mount.

(5) Flexible vibration dampeners – for poor condition and  deterioration.

(6) Engine controls – for defects, improper travel, and  improper safetying.

(7) Lines, hoses, and clamps – for leaks, improper  condition and looseness.

(8) Exhaust stacks – for cracks, defects, and improper  attachment.

(9) Accessories – for apparent defects in security of  mounting.

(10) All systems – for improper installation, poor  general condition, defects, and insecure attachment.

(11) Cowling – for cracks, and defects.


Thoughts on reasonable responsibility:

Last year, I had a guy who called me up and said he was having some issues with the ground runs on a Corvair he had put on his plane. I asked him if he had set the timing or checked it. Answer “No.” He went on to explain that The engine was one that I had built in 2005 for a former owner, it had been shipped around the country, resold, etc. His comment was that he assumed that the timing was correct because I “would have set it.”  OK, let me put this in simple terms. If you bought a gun from a guy who told you he bought it from me eight years earlier, would it be safe to assume it was unloaded now? Maybe a prudent plan would be to simply check to make sure.  If you learn only one thing about flying this year make it this : Maybe 1/3 of the people killed in aviation were done in by something that they just assumed someone else checked for them.  Want a foolproof way to avoid that? Get out of the mentality that says you count on anyone to have done something that you can easily check for yourself. You are building a plane to be in Command of every aspect of it you can.  This means that you do not trust the line boy to have filled the tanks when you can just look, you do not trust another pilots opinion of the weather when you can walk over and look at the computer, and you do not trust that your timing has never changed because you don’t want to buy a $39 timing light.

Above, one last look at Gardiner’s plane after the tornado. Can you see a single part that you wouldn’t carefully inspect and verify before flying? The conservative approach would be to assume that every part was 100% garbage until proven otherwise by detailed inspection. That would be exercising good judgment. -ww.

5 Replies to “When to check your timing, Lessons learned Pt#2”

  1. WW, I just checked mine and it was slightly advanced, 37 degrees at WOT. It is now 32 degrees because we had an almost 40 degree weather last week. I thought setting it at idle and knowing the distributor,( I ran it on a distributor machine), would give me good results, WRONG! The conversation we had was most enlighting when you said the vibration of the airplane application messes with the logic somehow and you need to set the timing at WOT. Needless to say this has been another humbling learning experience. I remember telling you I don’t like to do it that way, but now I know better from having seen the 5 degree variance from what the math and logic stated. Feel free to share this with others. This small change gave me another 50-75 rpm in static run up.

  2. After reading this story and thinking back to a recent blog on oil changes I have to wonder if anyone who is receiving a repairman certificate for a plane they built actually take the annual (and 100 hr) inspection seriously. If they have not changed the oil or checked the timing on the engine at the annual then it sounds like it was just pencil whipped, i.e. signed off without actually performing any work. I hate to make such a suggestion but maybe these owner performed Annuals need to done under at least the supervision of an A&P so that someone with a license on the line will ensure that the work was actually done. In the case of a Corvair flight engine I would be afraid to let an A&P touch it due to the differences from typical flight engines but at least he/she could provide the assurance that the owner did indeed do all the work that was required of them. When an A&P / IA does such work they risk their license if anything happens and it was found that they lied on the log entry, what risk does the owner face other then the risk to life and limb. One would think that would be enough but obviously it is not. Maybe some minimum training would help but this is a scary situation and I fear in the current climate it could spark calls for tighter requlation and who knows what a mess that could make of things.

    1. Sarah, Keep in mind, we do have many builders who do effective condition inspections on their planes. IMHO, industry is diluting standards for maintenance on things like S-LSA aircraft, so I think the pendulum is swinging away from tighter standards. I think the most beneficial thing we can do is to work within our own small community and set a better standard. Corvair builders should compare their own inspection lists and encourage those operating without one to adopt or adapt one from an experienced builder/flyer. Good subject to cover at colleges.-ww.

  3. William,

    As a professional A&P/IA I will verify that at any annual/conditional inspection(or various other times) that my shop conducts, magneto timing is ALWAYS verified. We allow no more than a 1 deg difference between what the manufacturer specifies and what we read using our timing tools. We commonly see magnetos several degrees off and the effects on idle, throttle transition, spark plug fouling and WOT performance are instantly detected. Doing a timing check is very easy and I fail to understand why a person who can build an entire engine/airframe would not make sure that this critical item is not verified. It’s difficult to understand.

    Arnold Holmes
    Av-Mech LLC

  4. William,

    Thanks for the great article. As a non-gear head it helped me to understand more about timing and when to do it.

    As an air line pilot, I have passengers ask me about ticket pricing and seating. And I half-jokingly say, “I don’t ticket them. I fly them.” The same is true here.

    Just because I have many flying hours doesn’t mean I can build an airplane and/or maintain it. Only by utilizing good practices such as AC 43-13 and the Conversion Manual can I hope to have success in this arena. Thanks for reminding me.

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