Ixion FAQ

How do I put new piston rings on two-strokes?

On Jul 22, SMITH_DOUG/HP1600_00 wrote:
Subject: 'New pistons / rings on TZR'

But seriously....

| Well, the TZR had a partial seizure on the right hand cylinder, so I
| thought I'd get a full rebore, new pistons etc.  I got the new rings and
| pistons, and went to put them in... the bottom rings move quite freely,
| but the top ring won't move (or compress) at all.  I've tried both rings
| in the top groove, both ways up, in both pistons, but it's still the
| same... is this normal?  I've had suggestions about putting a piece of
| card around the piston, and using a jubilee clip to force the ring in,
| which sounds reasonable... any others?

Back in the "good old days" when the people who sold you spares wore grubby brown coats, it was not uncommon to have to "dress" the rings or grooves to make them fit the pistons. Important things to remember are: OL> Get the rings in the right grooves. The "springy" ring is almost certainly an oil ring, and will go in the lower of the two grooves. Get the rings the right way up. They are not symmetrical. There is a "Top" and a "Bottom" to a ring, sometimes it's even marked. The main difference is that the side of the ring that touches the bore, should be at a slight angle (usually the ring is wider at the bottom, to "scrape" the oil back down the bore, hence "scraper ring".) The ring must "float" in the groove, tolerances vary but "enough to rotate smoothly, but not enough to rattle around" is a good guide for me. If it sticks, it's probably due to some imperfection in the casting, this can be rectified by gentle dressing using a swiss file, but of course, go easy! The ring gap must be the correct gap when the piston is in the bore. i.e. Pop the ring on, and then put the piston in the bore enough to compress the ring. Check the gap that's left. Many problems occur because the ring doesn't have enough gap left to allow for the sometimes considerable differences in bore diameter. Machining the ring gaps is a fairly standard job most workshops will undertake. Make sure the ring gap is in the right place. For four strokes that's usually just a case of making sure they _don't_ line up with each other. On two strokes it's critical, the gaps *must* avoid the ports. In all the strokers I've dealt with, the grooves have had raised lands for locating the gap. Well, I hope that's been of some use, remember my standard two-stroke disclaimer: "hey, I don't even *like* two-strokes!"

--

Cheers, Richard.

I would guess that the springy ring is an expander and should go in the bottom groove before the bottom ring.

If the locating pins in the piston are not central in the groove this will indicate which way up the rings should go.

Hope this helps in some way.

Les.

>  boxes) as I once spent a very long time trying to fit rings from a
>  larger overbore size onto a smaller piston.  It turned out that the
>  dealer had bought them separately and had got two different sizes.
>  Just an idea!

You can get these at just about any brit bike shop in all sorts of sizes and They ARE worth it. Even if you can compress the ring easily, you got to ease each individual ring into the bore when refitting the piston and the clamps help a lot.

Do check you have correct top rings though, before forcing it with a clamp.

> 4. The ring gap must be the correct gap when the piston is in the bore.
>  i.e. Pop the ring on, and then put the piston in the bore enough
>  to compress the ring. Check the gap that's left. Many problems
>  occur because the ring doesn't have enough gap left to allow for
>  the sometimes considerable differences in bore diameter. Machining
>  the ring gaps is a fairly standard job most workshops will
>  undertake.
>  

> multiply by pi to see how worn your bore is. If you get more than 5 thou
> then it's time for a rebore.