I'm sure these people here that have used aftermarket uncertified pistons in their engines and I'm curious what your thoughts/experiences are. Lycon has been using such pistons for 20+ years and a few other companies have been selling them for several years also.

A engine builder friend said a modern pison/ring pack would be far superior to a factory CMI piston and it would be redicilous to spend $330/piston for one when I can buy a whole set with pins and rings for $900. I tend to agree but I've never heard anything from anyone that has used forged pistons instead of the factory cast ones.

Anyone have first hand experience?

Not in an airplane engine. I put used pistons out of a 1959 Oldsmobile 4" bore into a 1932 Ford four banger. It had the deck height that I wanted. They worked fantastic. We never told the pistons that they went into an old Ford. I have heard (around a campfire) of somebody putting 8 to 1 pistons out of an IO470 (Bonanza) into an O470 (Skylane) that originally came with 7 to 1 pistons. He was sill using Mogas and had over 500 hrs on the setup.

If you do your research properly, you should have no problems. I know of an O-235 engine flying with perfect circle brand rings that were sold for use in a Case diesel tractor engine, the dimensions are the same. If you can find someone with a stack of very old "sport aviation" magazines, back before 1970 they printed an article about which Ford and GM parts could be used in various airplane engines. They listed part numbers for pistons, rings, bearings, and some valves. Just make sure you verify EVERYTHING before you assemble the engine, little things like ring end gap become very important and may be different between a water cooled engine and an air cooled engine.

In an experimental? Why not? It's not like forged pistons are new technology... And if Lycon is doing it for their experimental engines, that's one more vote for the "Yes" column. The only disadvantage would be that your engine would no longer be a "certified" engine (and if I understand correctly, could never really be reverted to one). So maybe a few bucks lost when it comes time to sell the engine (??), and about 15 additional hours of "Phase 1" test flight required. Only certified engine/prop combinations get away with the 25-hour fly-off, any other combo and you'll have to fly the full 40-hours. (Go ahead, throw me in that briar patch! I'm fairly convinced that a full-on flight test program would take pretty close to the full 40 hours anyway... Besides, I love to fly, and can't wait to fly my Patrol...)

Ring tension and piston expansion are the two things I'm most concerned about but the two outfits I've talked have said it's not an issue. Compatible rings are available and the pistons won't expand anymore then the cast ones.

whee wrote:Ring tension and piston expansion are the two things I'm most concerned about but the two outfits I've talked have said it's not an issue. Compatible rings are available and the pistons won't expand anymore then the cast ones.

Just to clarify and not being nit picky.-Just info to add to the conversation. Forged pistons definitely expand more than cast pistons. Almost always are run with larger piston to bore clearance. Probably with the clearances that our overpriced antique air cooled tractor engines run it may be a moot point.

I agree RockHopper and I was surprised when the manufacturer I talked to said theirs don't. Perhaps I misunderstood or maybe they are using a different alloy than the forged pistons I'm familiar with. But I think your right, with the loose piston/cylinder clearance tolerances on these engines I don't think it matters.

These lighter pistons available from a couple different suppliers are significantly lighter than the factory pistons. Does anyone think that will effect engine/prop harmonics? Maybe worth noting; I have two different sets of Continental pistons and one set is a couple hundred grams lighter per piston that the other set. Both engines are approved for the same props.

I would suggest talking to Hal of Zipper kit fame and my hangar partner.

http://zipperbigbore.com/

He uses forged pistons in the Zippers and likes them way better than cast. Our Cont's and Lycs are different than Rotaxs of course, but Hal will be able to fill you in on the benefits of forged and any potential pitfalls in our engines.

67 Cougar...Built a 351C ... went with ford motor sports forged pistons. Piston to wall clearance was a thousandth and 1/2....


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blackrock wrote:I would suggest talking to Hal of Zipper kit fame and my hangar partner.

http://zipperbigbore.com/

He uses forged pistons in the Zippers and likes them way better than cast. Our Cont's and Lycs are different than Rotaxs of course, but Hal will be able to fill you in on the benefits of forged and any potential pitfalls in our engines.

Yea... the pistons in my zipper run only 1.5 thou of clearance, which is really tight for a forged piston. I used to run 0.005 or 0.0055 in turbocharged car applications (more HP intense by far, but only used for short bursts). Air cooled is of course the big difference here, but from what I was told by Hal and crew when I ordered the pistons and cylinders, is that they are using a certain type of forging that doesn't expand as much as 'traditional' forgings. maybe 4032 alloy? That is not supposed to expand as much as the traditional 2618. I had not really run across any other forgings while in the car world, but I'm sure there are other things out there I'm not aware of. Anyway, whatever material they are made from, they are running them tight, and we push them hard of course, and there hasn't been an issue there that I'm aware of.

The strength for the weight of forged pistons, and the higher heat capacity definitely makes them desirable IMO