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NFS pistons and gapless rings?

K

kcameron

Well Known Member
I've decided to scrap my plans for a big performance upgrade to my RV-4's IO-360A1B and just do a top overhaul. The engine is currently fitted with Lycoming 10:1 pistons (supposedly from a helicopter engine according to the builder). From a quick borescope inspection, it looked to me like the pistons may need replacement due to significant pitting. I'll know more after I remove the cylinders this weekend.

If I need to replace the pistons, I'm considering using Lycon's NFS brand of forged pistons. Has anyone here used them? Do you have any thoughts on the quality relative to stock Lycoming units? I spoke with Lycon but it's sometimes hard to separate sales pitch from reality.

Lycon is also offering "gap-less" piston rings. I wasn't able to get much info about them. It seems like they might significantly reduce blow-by and oil consumption. Anyone here know about using gap-less rings in a Lycoming?

One of the stranger recommendations from Lycon was that, if I go with gap-less rings, I should get my intake valve guide machined for elastomeric seals to reduce oil consumption. They said the increased suction caused by gap-less rings will cause the engine to draw excess oil through the intake guides without the extra seals. I've been racking my brain to try and understand this. It seems to me that the effects of the ring gap would be very small and would therefore have a small effect on intake guide oil leakage which is supposed to be very small to begin with. Is this something real or just another aviation superstition?
 
kcameron said:
I've decided to scrap my plans for a big performance upgrade to my RV-4's IO-360A1B and just do a top overhaul. The engine is currently fitted with Lycoming 10:1 pistons (supposedly from a helicopter engine according to the builder). From a quick borescope inspection, it looked to me like the pistons may need replacement due to significant pitting. I'll know more after I remove the cylinders this weekend.

If I need to replace the pistons, I'm considering using Lycon's NFS brand of forged pistons. Has anyone here used them? Do you have any thoughts on the quality relative to stock Lycoming units? I spoke with Lycon but it's sometimes hard to separate sales pitch from reality.

Lycon is also offering "gap-less" piston rings. I wasn't able to get much info about them. It seems like they might significantly reduce blow-by and oil consumption. Anyone here know about using gap-less rings in a Lycoming?

One of the stranger recommendations from Lycon was that, if I go with gap-less rings, I should get my intake valve guide machined for elastomeric seals to reduce oil consumption. They said the increased suction caused by gap-less rings will cause the engine to draw excess oil through the intake guides without the extra seals. I've been racking my brain to try and understand this. It seems to me that the effects of the ring gap would be very small and would therefore have a small effect on intake guide oil leakage which is supposed to be very small to begin with. Is this something real or just another aviation superstition?
Click to expand...

1. I'd be really concerned about pitting of the piston faces.

2. TotalSeal makes gapless rings, the 2nd groove on the pistons will have to be cut on a lathe because gapless rings don't work with keystone grooves. I have a friend running these on his Mustang2 and he says they work great. I'd go with Combustion Technologies pistons which are forged (they all are) and they're fairly inexpensive. Send the pistons to Total Seal and have them cut the 2nd ring groove and fit the rings.

3. Most pushrod engines have stem seals, and I've heard of just a few engine builders using them in on Lycomings. The purpose of the valve stem seal is to prevent coking of oil on the valve stem, and of course to reduce oil consumption. If you think about it, it only takes a tiny amount of oil leakage past the valve to have high oil consumption. Lets say it takes a drop of oil every ten revolutions, X 2400 rpm, that would be 240 drops of oil...times four cylinders now you're talking about a significant amount of oil.
 
Thanks for the response, Bob.

I checked the TotalSeal website but they don't show Lycoming or any rings for a 5.125" bore. Are you suggesting I get them to make a custom set for me?

I've done enough valve jobs on car and motorcycle engines to be very aware that an intake valve guide leak can cause significant oil consumption. My point is that Lycon claims gapless piston rings create enough of a change to make intake stem seals a necessity. Still seems like voodoo to me.

Kev

rocketbob said:
1. I'd be really concerned about pitting of the piston faces.

2. TotalSeal makes gapless rings, the 2nd groove on the pistons will have to be cut on a lathe because gapless rings don't work with keystone grooves. I have a friend running these on his Mustang2 and he says they work great. I'd go with Combustion Technologies pistons which are forged (they all are) and they're fairly inexpensive. Send the pistons to Total Seal and have them cut the 2nd ring groove and fit the rings.

3. Most pushrod engines have stem seals, and I've heard of just a few engine builders using them in on Lycomings. The purpose of the valve stem seal is to prevent coking of oil on the valve stem, and of course to reduce oil consumption. If you think about it, it only takes a tiny amount of oil leakage past the valve to have high oil consumption. Lets say it takes a drop of oil every ten revolutions, X 2400 rpm, that would be 240 drops of oil...times four cylinders now you're talking about a significant amount of oil.
Click to expand...
 
Lycon pretty much does know their stuff. But what are you trying to accomplish? 10:1 pistons in an angle valve is already pushing it on a stock engine (I prefer no more than 9:1 for non-racing applications). Do you know the vintage of your cases? The angle valvers had a lot of case cracking issues with early cases. Later ones were beefed up, but that isn't widely advertised.

If you are just looking to reduce oil consumption, then the whole thing may be voodoo, or it may work. I know of stock engines from the same rebuilder that burn a quart every 4 hours, and some that burn a quart every 20.
 
Gapless rings----Total Seal, have been around for a long time.

The first exposure I had to them was in hot rod VW powered dune buggies, and they always provided a benefit to the engine.

The improvement in the piston/cylinder seal will cause less blowby, and also higher vacuum in the intake system, thus the valve stem seals are a good idea.

AFAIK, this is now pretty standard for most really high perf engines, really helps out with a blower.
 
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