Suzuki 2 Strokes

hi all
i'm just checking the gap on my piston rings as the cymer manual says there should not be more than 1mm between the tips of the piston rings, when you push them into the top of the pots. But i wanted to ask the members whether they meant the 'lower' part of the ring, or the upper part (the tips) as many of you will know that these rings do not end flatly but resemble more a motorway bridge when you silhouette them.

thanks for that.

I also noticed that there were some scuff marks on my pistons. Any real reason to clean them up? Other than just feeling good? I mean, would it help if they were cleaned up?

best
MJ

Tips - not the gap to fit around the locating pin.

thanks for that. And what about the bores? Two are 54 mm but one is 53.5mm. WOuld you put new rings on that one?

WHen the pistons are at TDC, they move a tiny, tiny bit when you push hard on them. Something like less than 1mm. I'm guessing this is not enough play to justify new rings (?)

MJ

I'd measure that again. They should all be close to 54mm but you will need accurate measuring equipment to measure the pistons and bore. I tend to use a quick and dirty approach and slide thin feeler gauges in between the front or rear of the piston and the bore to get a quick idea of whether there's too much clearance. Do it at the bottom though. The top of a piston is smaller than the bottom of the skirt to allow for thermal expansion.

feeler gauge in between the pistons/piston rings and the side of the chamber?

And if you can get one in? Does that mean it's bad? What gauge measurement do you use?

I checked the bores with a slide rule type measuring ruler. (Don't even know what you call them).

thanks

MJ in Beirut

Hi!
I found an old sketch which I had put into my Haynes-manual

Not the rings. That's to measure bore wear. Start with the thinnest one in the pack and see what fits in there, but do it from the bottom rather than the top if possible. I don't have the real numbers in front of me, but let's say that stock clearance is .0025" and service limit is say .0050". If you can get a feeler gauge thicker that the service limit between the piston and bore, it needs to be re-bored and new pistons fitted.

The measuring stick you refer to is a vernier caliper and it's not easy to get consistent and accurate measurements with one.

The feeler gauge trick is only a quick and dirty method because it doesn't tell you if the piston is OK or the bore or if both are worn out, but it's a good indicator of the situation.

TZ - tell me what you mean. Are you saying that you stick the feeler gauge down the side in between the piston rings and the bore? Or the piston and the bore?
thanks mate
MJ

Two different measurements.

Ring end gap you do by placing a ring in the bore, square it up and measure the gap across the narrowest part with a feeler gauge.

Piston to bore clearance is typically measured by measuring the bore with a bore gauge (expensive tool) and the piston with a micrometer and subtract one number from the other to get the gap. The quick and dirty method is to take a barrel and turn it upside down. Insert the piston and then slide a feeler gauge or two between the bottom of the piston skirt and the bore. Piston to bore clearance is typically in the .002" to .003" range, so we are not expecting to get many of the thinnest feeler strips into that gap.

Do that on the front or rear face of the piston skirt, not the sides which are sightly smaller.

Is that clearer?

yes, much, much clearer. Thanks!
i already did the piston ring test and the gap was much less than the 1mm clymer reccomended limit.
But i wll have a go at the bores now...
cheers
MJ