OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions on Other Engines Suzuki 2-stroke: When to use OS Pistons and Rings?

Dear Gents,

Looking at some the photos over in Mark Electric's current thread on his Suzuki 2-stroke Rebuilds (https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=59526#Post59526) has got me wondering about the circumstances in which the oversize pistons and rings that are available for this motor are deployed...(?)

I ask the question because I have never really heard of a removeable cast iron sleeve on any motor being re-bored out to an OS size. I guess it must be possible, because they obviously must bore the centres of them at the factory when they are manufacturing them. But out here in the real world, removeable sleeves are usually just removed and replaced with a new specimen of the original-sized item when they start to wear, aren't they?

Trouble is - neither Suzuki nor GA seem to have ever offered replacement sleeves as a spare part. If they did, I suppose they wouldn't need to offer OS pistons and rings now, would they(?)

So the following questions beg (in my mind at least...)
1) Has anyone ever successfully re-bored one of these Suzuki sleeves out to the OS size?
2) If the answer to (1) is "no", is it normal for the sleeve of a low-compression specimen of this motor (with good seals, let's say) to wear uniformly enough to tolerate the available OS pistons and rings without squeezing them in and out of shape during each cycle? (possibly until they eventually break...)

I guess some measuring with a Bore Guage is going to form part of the answer, but any general or specific comments about the when's and the why's relating to this issue would be most interesting to hear.

Best Wishes and Many Thanks in advance,
Moby Mick.

Hi Moby Mick

Suzuki recomond a maximum wear of .10mm (.004") between the standard piston and bore which is 58mm and from standard the piston clearance to the bore is .042 to .055mm (.0017" to .0023") which is measured from the bottom 25mm of the piston and 110mm down in the bore using a bore gauge, anything over this Suzuki recomend reboring to the next piston size which is .25mm (.010") oversize.

In answer to your question 1 is yes these engines have been successfully been bored out and they get machined on a small engine boring machine as changing the sleeve would be difficult because you really have no way of pressing it out from the top through the bottom because of the one piece casting of the block.

In answer to question 2 if you had any more than .25mm (.010") wear in the bore and you could fit the oversize piston in the bore then I would be throwing out the block because I would say it is well past it's used by date, if you could put a oversize piston down the bore then it will not be running true and would probably cause some serious damage to the piston and the bore.

Ther are a few small engine reborers around and even some of the Go Kart shops do rebores for small engines.

I hope that is of any help to you. Steve

Very helpful indeed Steve - Good reply!

I suppose one of the things that was confusing me was the sleeve-retaining-ring that Mark E pointed out in one of his photos of a disassembled motor, leading me to surmise that the sleeve was somehow meant to be removeable. Righty-oh, so you're meant to bore them out in-situ. I guess the holes in the crankcase-half for the mounting-plate would be used to somehow bolt the crankcase-half to a block sitting on the bed of the boring machine. All makes sense now.

Many Thanks,
Moby Mick.