using oversize rings on stock pistons?

[Billy]

Hello All,

Thanks in advance for all the help. This is my first time posting, but I have kept my self busy for some time now, rebuilding my basket-case '82 XS650, with all the info from the tech section and previous posts.

My question now, which I have seen discussed briefly in other threads, involves the use of oversize piston rings on stock pistons.

My situation: I ordered some used "stock" cylinders and pistons to replace the originals that had been seized. It appears that they have been worn / honed to the point where a new set of piston rings do not fit within maximum spec - the end gap is too wide. The end gap with new standard rings in the cylinders measures about 1.15mm.

Is this a situation where I could use oversize piston rings filed to the correct gap? Or should be looking towards oversize pistons aswell?

 

[Patches]

Maybe someone else will chime in here but here's my opinion.

It's tricky, because you have a specified piston clearance dimension (distance between the piston and cylinder wall). Unfortunately I don't remember what it is at the moment, and my manuals are out at the shop. You may be able to get away with putting in 1 OS rings and file the ring gap to the proper spec. I would suggest measuring the bore and pistons and see how far off you are. If its close you should be ok, but if you're wanting to be o. The safe side you can always take in a new set of OS pistons to the machine shop and have the cylinders bored accordingly to the proper clearance dimensions.

 

[gggGary]

I think one issue is that the bores do not wear evenly, they become oval, with the front and rear taking the loads and the most wear. The wear will vary up and down the cylinder as well. Honing does not correct the uneven wear. I cannot see the wisdom in having an engine apart and then doing a stop gap repair like this. Have it measured, buy the necessary oversize pistons and rings and bore the cylinders to match.

 

[Max Midnight]

The simple answer (IMHO) is of course you can BUT......probably not a good idea.

That gap is 0.15 mm over the max and 0.55 mm over the standard spec. You don't say if the measured gap is consistent down the bore or if it tapers (max is 0.005mm).

I would also measure the piston to bore clearance (0.05 - 0.055 mm, maximum clearance is 0.1 mm).

I suspect that you are over the wear limit for the bore and suggest that you have it measured so you know what is required.

 

[Billy]

I am going to try to get the bores measured today to check the taper and piston clearance, but it seems like the consensus is that oversize rings are not a good way to go about this. Guess I should have just bored out my seized up cylinders and not messed around with these replacements. Thanks for the input.