Head + Cylinder replacement?

[Anonymous]

I've got a '79 GS750E, and I'm experiencing lower-than-normal compression. The engine's upper end is apart at the moment, so doing additional compression testing is out of the question in the immediate future

anyway, my question is this: i have an extra cylinder set with pistons from a motor that had normal compression. it's from the same year and is of the same size as this engine. would swapping the cylinders require any other items to be replaced or repaired? (are they like a matched pair or anything..?) any suggestions in this regard?

thanks a lot,

Chris

[Steve]

If it was my engine, I would have the cylinders checked for straightness, honed, and install new rings.

Might also check the valve seals and have the valves lapped.

[fgh]

Seems to me the only parts that might not like there new home would be the wrist pins. The ones from the motor being repaired might be worn differently than the new pistons or the ones from the spare pistons might be worn differently than the connecting rods. I would probably use the ones from the spare engine as I'm sure they are fixed to the connecting rods and pivot on the pistons. I can't see where anything else could matter as long as the engines were the same.

Of course its always good to have the parts machined and rings and seals replaced but it costs more. I don't mind doing repair work so I would reassembly it as is as long as everything looks good and try it out.

LOL

[Anonymous]

like i said, i've got motor parts. if it would be better in the end to just re-ring the engine, then i guess that's the route i'll take. it was just a thought, since it wouldn't cost me anything to take parts from the other engine

[duaneage]

If you work rework the head you run the risk of having the engine burn oil past the rings. The rings are slightly beveled after a bunch of miles and restoring compression by redoing the head can cause the rings to leak oil and blow past.

If you have good cylinders handy get some rings and hone the cylinders. Fresh rings are not too much trouble since you have the top half off anyway, that is the hard part.

[Anonymous]

where would you guys recommend getting the rings and/or any associated engine parts?

[fgh]

Don't! You've got good cylinders, pistons and rings. If you can't find any flaws then put them in. A honed cylinder and new rings require breakin and might not seat.