Engine Balance

[thad14433]

Recently received my Aerovee Kit. As I was going along I decided to weigh the parts, the connecting rods were very close but then I found one piston 2 grams lighter than the others. This got me wondering if this was very significant. Tech support informed me that 5 grams was the “manufacturers variance standard” and I was well within that and I believe that is absolutely true. But after reading Tom Wilson and R.S. Bob Hoover they seem to see the variance builders should accept and manufactures variance as 2 different things.

Wilson addresses balance issues on page 45 of his book “How To Rebuild Your Volkswagen Air-Cooled Engine,” recommended in the Aerovee instructions booklet, and indicates he accepts no tolerance just says they must weigh the same, I interpret that as an ideal. Hoover in his rather extensive blog on the subject states there should not be a weight variance greater than 0.5 g. As best I can determine balance shops work to 0.01 g. maximum, but normally less and most to 0.0 g. which is really not that difficult, for them.

While the Aerovee is pretty much a rather bulletproof design and will run balanced or not, being balanced would seem, both in weight and volume, a good idea. I have not been able to find any other discussion of this as it relates to the Aerovee and was wondering if anyone can enlighten me on this subject or point me in the right direction?.

P.S., If you haven’t read Wilson’s book, you probably should it is a LOT more detailed in the steps to take in building your engine.

[kmacht]

It is not very common to find a set of pistons that are exactly matched. What you need to do is find the lightest one and remove material from the others to make them match.

Keith
#554

[thad14433]

That might help but without the whole rotating system combined in the balancing it's possible you could make the balance worse rather than better. If you somehow knew balancing the weight of the pistons would be positive where would you remove material, it's complicated. My experience trying to get help from Mahle doesn't happen using their contact system. Thanks for your reply!

[DCASonex]

Reminds me of when overhauling my old Jabiru, my copy of the manual stated to balanced within .3 grams, and I was fighting to get close to that. Only when about done did I see that (.) was a spec of dirt on my copy.

David A.

[thad14433]

Dealt with a machine shop to balance my unassembled Aerovee, the estimate was $150, certainly less than expected.

[RodgerC]

If you balance your AeroVee it will push you along at a nifty 120MPH @ 3100 RPM and if you don't, it will only get to 105KTS @ 3100 RPM

[thad14433]

Wouldn't have expected an increase in speed but will surely enjoy it. I'm mostly interested in doing everything I can to prevent a failure and fully intend to fly it to a prop shop as soon as allowed and have the prop dynamically balanced. Everyone knows what happens when your car tire is out of balance. With your engine its unlikely you will ever notice that the rotating internals are not balanced but there are consequences of that and one day in the future it could bite you in the butt. The Aerovee is the best engine on the market for the money, both initial and to maintain down the road. The engineering starting with VW and going through with Sonex is first rate, including the support material, like plans, instructions and bulletins, etc. in my opinion. But, if you are like me and do not have a engineering or engine builder back ground and probably even if you do and even though the Sonex material is great, I would not just read Wilson's book and the blogs online by R.S. (Bob) Hoover but study them, A LOT.

[XenosN42]

If you balance your AeroVee it will push you along at a nifty 120MPH @ 3100 RPM and if you don't, it will only get to 105KTS @ 3100 RPM

Thanks for the laugh Rodger. I love subtle humor and this doesn't get much more subtle.

-- Michael
XENOS N42XE
Onex N169XE

[Rynoth]

If you balance your AeroVee it will push you along at a nifty 120MPH @ 3100 RPM and if you don't, it will only get to 105KTS @ 3100 RPM

Nice, that one took me a second.