Builder ‘Eddie Easy’ is going to work with Roy of Roy’sgarage.com. Roy has his own 5th bearing design, and it is now flying on about a dozen aircraft. The bearing design requires builders to send their case and crank to Roy so that he can line bore his bearing to the case and he has to process the crank to install his 5th bearing journal on it.
Builders selecting Roy’s bearing design almost always have Roy assemble their bottom end for them. Also, Roy’s bearing design requires a special safety shaft and custom-made hybrid studs. (Dans 5th bearing uses parts straight from our catalog) For these reasons, an exact head to head price comparison isn’t possible, but we can come up with a reasonable comparison for builders. Since Roy’s set up utilizes a Moldex processed 8409 GM crank, It isn’t a fair match to compare it to ‘Davie Dog’s’ engine with a Billet crank. It is a better comparison with ‘Chas. Charlie’s’ short block. After we go through the numbers I will do some notes and comparisons at the end.
( CC stands for Clarks Corvair parts, SR stands for Summit Racing, ELS stands for Ebay Larry’s Corvair parts, and ECA stands for Ebay California Corvair parts.)
Crank group (1000)
1000- 8409 crank, no gear ($500 )
1001- Crank gear (new, $150, installed in crank processing)
1002- Crank gear key (Included in crank prep)
1003- Crank gear gasket (Included in crank prep)
1004- Rear keys -2-(CC-#5858, $1.50, $3)
1005- Fuel pump eccentric (used, from core engine)
1006- Spacer (used, from core engine)
1007- Bronze distributor drive gear (used, from core engine)
1008- Oil slinger (used, from core engine)
1009- Main bearings (From Roy, $120)
1010- Connecting rod bearings (ELS-$59)
Cam group (1100)
1100- Cam ( CC, part 8800, $235 )
1101- Thrust washer (new installed by Clarks, $12.60)
1104- Hydraulic lifter set -12 total- (Summitracing.com $2.99each, $36)
1105- Cam lubricant (comes with OT-10 cam)
1106- ZDDP oil additive (SR,$16)
Case Group (1200)
1200- Case -2 halves with studs- (used, from core engine)
1201- Main case bolts -8- (used, from core engine)
1202- Pipe plugs for oil galleries -2- (used, from core engine)
Special Items required in a Roy bearing closed case: The bearing itself; $1695, Hub modification $60, Difference in price for custom HS and SS; $30. Roy needs the case to be very clean, and he charges $120 for this service. It is not required, but Roy will assemble the lower end for the low price of $100. (during the bearing installation process he has to bolt the case together several times.)
The total of Eddie Easy’s engine parts on the chart above are $1252.10. To this must be added the bearing price, $1252.10 + $1695 = $2,947.10 . Add in the typical $120 case cleaning, and $90 for modified parts and the total comes out to $3,157.10. (Raise this to $3,257.10 and you get it back assembled.)
Chas. Charlie’s engine is identical, except it has a Dan Gen 2 bearing and it comes in at $2,770.10. $387 difference in the un-assembled form. There is some cost for shipping things back and forth, but it isn’t a deal breaker. For a builder who is looking for an assembled case, it isn’t the least expensive method, but it isn’t astronomically expensive either. There isn’t really a low-cost do it yourself option, nor a pay as you go approach that a guy like Allan Able can employ, but Roy’s product isn’t aimed at those builders.
Two things to frankly discuss: Roy has a very long waiting list, It has run over one year. Because of the hand done nature of the bearing, he can’t just phone up the CNC shop and order up another dozen bearings, and this leads to a long order time. Second, Roy has a background in working on things like Mercedes cars. To his perspective, applying the mercedes standard to the main bearing bores on a Corvair case means that 1/3 of cases are out of tolerance. This means you could need a whole new core case if he ‘rejects’ it.
To my perspective as an aircraft mechanic of 22 years, the GM tolerance is fine, and there is no need to arbitrarily cut it in half. Aluminum case opposed motors are traditional built a lot looser that Cast iron car blocks. Roy works with .0005″ as the limit of out of round on the bores. I have my doubts that all Corvairs passed this on the day they were made. The Gm new spec is .001″, twice as much. I have built many flight motors that were .0015″, They worked great.
For a reality check, Kevin and I once had about 20 140hp Corvair engines between us. These are Chevys high rpm/ high output engine. Inspecting many of these cases coming from 6,500 rpm engines which had 100,000 miles of beating on them, revealed that the main bores were often .0035, or seven times Roys tolerance. Yet none of these engines spun a main bearing. Thus I don’t agree that a Corvair between .001 and .0015 is in any danger of spinning a bearing or wearing out. You can ask any builder who has attended a number of colleges and seen 100 different engines that were torn down if he has ever seen one with a spun bearing, he hasn’t. In 20 years of working with Corvairs, I have seen two or three spun bearings, but they were all in engines that were literally run without oil.
At Embry-Riddle it was drilled into our heads that if the book said the allowable torque range determined by engineering was from 50 ft/lbs to 75 ft/lbs, then putting the item anywhere in that range made it air worthy. Mechanics that spent a lot of time trying to hit 62.5 ft/lbs were wasting effort and trying to prove something about their ego. If they would only be happy if it was between 55 and 70 because they were not sure about the torque wrench, then they were to get a new wrench. Guys who though they were making something ‘better’ by torquing it to 75 every time, were living under some illusion. In short, any mental justification that the mechanic used to put his own ‘custom’ touch on tolerance was to be frowned upon, because it probably indicated that the mechanic thought of himself as smarter than the engineer, or he did not trust the book. arbitrarily applying standards from one machine to another was really frowned upon. Less clearance isn’t always better, Closer fit in aircraft engine components isn’t always better, and neither is any arbitrarily set standard. The real issue with that kind of thinking is that you end up believing that you have a system that is ‘better’, and you stop looking at the field data that might suggest otherwise. No one gets smarter that way.-ww.
About William Wynne I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at www.FlyCorvair.com and in more than 50 magazine articles.