Topic: Piston size

[Ooops]

Hi,
not been on here for a good few month's other things to sort out.
I was going to strip and rebuild the engine in my 1976 550F, but have now decided just to go with a top end rebuild. As far as I can tell the main bearings etc are OK.

I've got the head and barrels off, removed the piston's and the bores are in good condition.
From what I can tell the piston's are still standard size and they did have the standard rings replaced once by a former owner(paperwork to support this)

Do I now fit the next size piston's and ring's, will they slot straight in or will I need to have the barrels re-bored. As I mentioned before the barrels are very clean and smooth.
What would be the best way to measure the fitment before hand. I have read in one manual that inserting the piston back into the barrels and using a feeler gauge. If it can pass between the piston and barrel then use the next size piston/rings.
Any advice would be greatly appreciated.
Tim

[Blasbo]

Hopefully some one with more experience will chime in, but the shop manual will give specs for piston and bore size.

[Grey]

Depends on how accurate you want to be. The best is to find a machinist with a bore gauge that knows how to use it. You said the cylinders looked smooth. Did you see any cross hatch in them? If not then they were worn badly. Which may mean a bore job is needed. The machinist should be able to tell you what you need. Take the pistons and specs with you.

If you run an engine to rich and the fuel washes the oil off the cylinders they will wear the cross hatch off. That's not a good thing.

[KJ790]

You need to measure your cylinders and see how worn they are. If they are out of round, out of taper, or worn to too large of a bore diameter, then you will need to bore them back into tolerance and get the appropriately sized pistons (most likely first oversize). If your cylinders are still within original spec then you can use standard size pistons and rings.