Exhaust Valve lapping

mslindstrom · Post by **mslindstrom** » Mon Oct 07, 2002 6:18 pm

Need advice/opinions/experience with lapping the exhaust valves with out removing the cylinder. I have two cylinders right at 60lbs with hissing through the mufflers.

Post by **GAHorn** » Tue Oct 08, 2002 2:44 am

The correct way to fix this is to remove the cylinder. Keep in mind that merely "lapping" the valve in-situ will not allow you to inspect for a cracked seat or a cracked/worn guide. It will also not maintain the correct seat-width which contributes to burned valves.

zero.one.victor · Post by **zero.one.victor** » Tue Oct 08, 2002 3:59 am

I'll betcha that the reason the exhaust valves are leaking is that the guides are worn. Continentals are notorious for this,from the A-65 to the C-145/O-300. I don't know if the 470/520 series engines also have this weak spot or not.
It's my theory that the geometry of the rocker arm/valve stem is such that a side load is put on the valve,causing excessive wear to the guide. The exhaust guides seem to be worse,maybe the heat involved causes faster erosion of the guide than on the intake side.
I talked to a long-time 170 owner who had his engine fitted with "roller rockers" that supposedly eliminate this problem. Anybody here have experience with them?

Eric

Post by **GAHorn** » Tue Oct 08, 2002 5:05 am

I've forgotten which ones, but one type of "rocker rollers" have an AD against them and they must be removed. Since they cost about $1500, and since you have to install them,......and now remove them and buy the originals again, ....they are not worth the money, in my opinion. Also, TCM and most aftermarket cylinder mfr's don't think they are necessary. The newer valve guides have sufficient length and area to handle the rocker geometry just fine thru one engine TBO run.

mslindstrom · Post by **mslindstrom** » Tue Oct 08, 2002 2:35 pm

Thanks guys. George, I know that the "lapping" is a stopgap effort and not the correct or long term fix for the leaking valves. I'll check the engine logs and see how long these cylinders have been on the engine and then decide.

Curtis Brown · Post by **Curtis Brown** » Tue Oct 08, 2002 8:27 pm

I have two cylinders with compression in the sixties with the hissing in the exhaust. It really makes one upset when they have only 78 hours on an overhaul. Anyway, they are still under warranty. I continue to be amazed at what price we pay for aviation equipment/parts and the limited reliablity/life they seem to have.

wa4jr · Post by **wa4jr** » Thu Oct 10, 2002 2:17 am

Hey Curtis, you hit the nail right on the head

I've stayed awake at night wondering the same thing. We only have ourselves to blame however, for the obscene prices charged for things with "airplane" stamped on them...we always open our wallet and pay while the manufacturers and suppliers laugh in our faces. Sometimes I dream that we in the GA community should launch a "just say no" effort when it comes to unreasonably high prices and then see how fast those prices come down. Oh well, I can dream, can't I