ring's gap

Hello,

I received a piston, rings and cylinder today. I checked the ring's gap. I was able to insert the filler gauge of .3mm into the gap once the ring was inside, but I have exert quite a bit pressure with my finger in order for it go through and there was snap metallic sound accompainying it. Does it sound ok, or do I have to regap the ring?

Thanks for any help

pedro

Re: ring's gap

Check this site out. It's for scooters but the principles are the same with any piston ported design.

http://www.scooterhelp.com/tips/engine/lam.piston.install.html

Re: ring's gap

Thanks for the link. I checked the gap of old ring (the one that came with the engine and it has a gap of approx. .4mm).

ALso, I have a ring that is a little bit thicker but they both are for the same piston. Do you believe that it would ok to use them together? Could I use a new ring with an old one of the same type?

Thanks a lot

pedro

Re: ring's gap

I would say that if you use one of the old rings in the lower ring groove and a new one in the upper groove, you will probably be ok. Compression might be down a bit, but it will most likely run.

Re: ring's gap

On second thought...if your piston and cylinder are new (as in un-used NOS), I would suggest new rings. Why settle for a half-baked job?

By the way, in your description, are you talking about the measurement of the end-gap (ring in cylinder) or the side-gap (ring in piston groove)? If you are talking side-gap, you might want to find out the specs for that. The link I gave you only comments on the end-gap.

Re: ring's gap

Yeah, you are right; I will order new rings.

I am talking about the end-gap (ring in cylinder). I was told by the mechanic from the dealer that the end-gap should be of between 0.4mm to 0.5mm; but it seems too much for me. I heard that it should 0.3mm, and the website whose link you sent me says that the end-gap should 0.2mm.

So I took the old ring and inserted it into the cylinder, I could measured the up to .35mm. I am assuming that the filler gauge has to go in smoothly, so that there should not be a snap when I insert the filler gauge into the gap.

thanks!

Re: ring's gap

The 0.2mm end gap in the scooter link is the minimum gap, (the maximum tolerance will be in the repair manual). If your ring gap is currently 0.35mm I'd say that is most likely within tolerances. But don't take my word on this. Do some further digging to get the actual specs.

Re: ring's gap

I measured the gap of the old ring, and found out something like .40mm. I bought a pair of rings, but it seems that the new bigger ring has tiny small fissure in one its extremes (the extreme of the ring fits the groove's peg). It difficult to, but if I pay attention I look closer I can see it. I tend to believe that compression would escape through it. And the old bigger ring is ok (no fissure).

I know that it is a half-baked job, but I will have to wait 2 weeks until I receive new rings. Couldn't I install the old bigger ring together with the new thinner ring, and afterwards install the new big one? So that I can ride until the new bigger one arrives.

thanks!

pedro

Re: ring's gap

In general, gap should be .003" (0.08 mm) to .004" (0.1 mm) for every inch (25.4 mm) of bore. As much as .008" (0.21 mm) gap is acceptable. If your bore is 39.5 mm, it is about 1.5 inches and requires about .006" (.15 mm) gap. Up to .012" (.3 mm) is acceptable.

You can probably run one old ring and one new one until the second new one arrives, but it will probably not have full compression which will cause some power loss.

http://www.dol.net/~dave.reed/tips.htm

Re: ring's gap

Thanks a lot for your explanation! But now I am very confused, based on what you are saying my rings should have a max gap of .3mm and a minimum of .15mm. The mechanic told me that it should have between 0.4mm to 0.5mm. And I read somehwere that it should 0.3mm.

thanks

pedro

Re: ring's gap

And I already gapped one of the rings to approx. 0.4mm. I could insert a filler gauge of 0.4mm in the gap of one of the original rings. So, I am really confused now.

Re: ring's gap

The information that I've given is from Otto Engine Works who have been doing custom piston/ring work for a long time.

What is the bore of your cylinder?

Re: ring's gap

Mine is a quinqj (quinqj is a licensee from Suzuki, I believe). It is 49cc, 2-stroke, clone of the Suzuki turbo. It is made in China.

I measure the diamter of the bore of the cylinder with a caliper and I could not have a precise measurement. But it seems to be around 39.96mm to 40 mm. What do you think?

thanks

pedro

Re: ring's gap

So that's about an inch and a half, which requires between 0.15 mm and 0.3 mm gap.

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