Re: K&B greenhead .35

Ken Cook Wed Jun 26, 2024 6:21 pm

Hey Drew, keep in mind that Ski's swap meet fun fly is July 12 at New Jersey. I've come across some greenheads in that crowd. They don't share the popularity as most engines. I have to ask, but have you had any of the gaskets replaced in your greenhead? These used fiber gaskets and if the originals are still in there, they certainly could leak causing low compression as your experiencing.

Droobie Wed Jun 26, 2024 7:30 pm

Unfortunately that swap meet is on 7/13 and I have a big anniversary party I’m throwing the same day.

Yes- new gaskets, I’ve had it all apart, cleaned up the liner on a sheet of glass with 400 grit, etc. The piston has some scoring, I think it ingested some dirt at one time or another. The liner actually doesn’t seem too bad. I tried heating the piston up a bit to see if I could “anneal it”; not cherry red but hot. Put it all back together and no improvement on compression. It will fire up on the E-starter and run fairly well on the stand but I don’t fly engines that won’t flip start.

ffkiwi Thu Jun 27, 2024 12:07 am

Droobie wrote:Unfortunately that swap meet is on 7/13 and I have a big anniversary party I’m throwing the same day.

Yes- new gaskets, I’ve had it all apart, cleaned up the liner on a sheet of glass with 400 grit, etc. The piston has some scoring, I think it ingested some dirt at one time or another. The liner actually doesn’t seem too bad. I tried heating the piston up a bit to see if I could “anneal it”; not cherry red but hot. Put it all back together and no improvement on compression. It will fire up on the E-starter and run fairly well on the stand but I don’t fly engines that won’t flip start.

If you want to do this you DO have to heat the piston to cherry red-to achieve the phase transition that results in a larger diameter when cooled. its an all or nothing approach, you can't do it proportionately-and it works on SOME types of cast irons, not all-a lot depends on the treatment of the raw material stock as it was processed during manufacture of the bar-not the subsequent machining of said bar into a piston. If the approach works-you can generally expect the piston to grow by a couple of thou-which will allow you to lap it back to fit-and this is a one off treatment-once you've done it, that's it-you cannot do it a second time....or rather you can-but you won't get any growth.....nor can you simply buy a random piston an expect it to fit. Given the production techniques of the era-selective fitting was the norm-pistons graded in 10 thousanths-or even smaller increments-and selectively fitted to ground and/or lapped liners that matched.[unlike British practice which was to lap a piston to fit a specific liner. There is a good reason why-unless you're LM Cox Mfg-that pistons and cylinders are sold as matched sets.

ChrisM
'ffkiwi'

ffkiwi Thu Jun 27, 2024 12:09 am

Droobie wrote:Unfortunately that swap meet is on 7/13 and I have a big anniversary party I’m throwing the same day.

Yes- new gaskets, I’ve had it all apart, cleaned up the liner on a sheet of glass with 400 grit, etc. The piston has some scoring, I think it ingested some dirt at one time or another. The liner actually doesn’t seem too bad. I tried heating the piston up a bit to see if I could “anneal it”; not cherry red but hot. Put it all back together and no improvement on compression. It will fire up on the E-starter and run fairly well on the stand but I don’t fly engines that won’t flip start.

If you want to do this you DO have to heat the piston to cherry red-to achieve the phase transition that results in a larger diameter when cooled. its an all or nothing approach, you can't do it proportionately-and it works on SOME types of cast irons, not all-a lot depends on the treatment of the raw material stock as it was processed during manufacture of the bar-not the subsequent machining of said bar into a piston. If the approach works-you can generally expect the piston to grow by a couple of thou-which will allow you to lap it back to fit-and this is a one off treatment-once you've done it, that's it-you cannot do it a second time....or rather you can-but you won't get any growth.....nor can you simply buy a random piston an expect it to fit. Given the production techniques of the era-selective fitting was the norm-pistons graded in 10 thousanths-or even smaller increments-and selectively fitted to ground and/or lapped liners that matched.[unlike British practice which was to lap a piston to fit a specific liner. There is a good reason why-unless you're LM Cox Mfg-that pistons and cylinders are sold as matched sets.

ChrisM
'ffkiwi'

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