2011 Sherco 2.9 Ring End Gap

[b_42woody]

What is the ring end gap wear limit on a 2011 Sherco 2.9?

My piston and cylinder look quite good but I have the following approximate ring end gaps:

Lower Ring 0.045 inches (1.143mm)

Upper Ring 0.047 inches (1.194mm)

These gaps were measured with the rings positioned about 10mm from the top of the bore.

My piston-to-bore clearance is about 0.003 inches (0.076mm)

Thank you.

[copemech]

Not sure there is a published limit. However, from my recall, yours sounds about twice new limit on both accounts.

I think if it is a rattler, you will not fix with rings, otherwise, throw some in just to freshen it up.

My 250 rattled like hell at .002 piston clearance!

[bilks]

Well for the 2009 2.9 piston/cylinder tolerance is 0.0270- 0.0325 mm

Edited September 5, 2014 by bilks

[dadof2]

Bilks, those clearances don't look right either in metric or imperial. If they are metric they look very very tight.

I would expect piston to bore to be between 0.0015 and 0.0025 inch

which is 0.038 to 0.0635 mm

In answer to original posters question your ring end gaps are far too big but I don't have correct info to hand.

[bilks]

Well the setting was out of the 2009 service manual.check for yourself,http://www.shercousa.com/pdfs/2009manual_ST-2T.pdf unless the manuals wrong which is not unknown.2011 service manual specs not given,http://www.sherco.com/tl_files/core/pdf/manuels/2011Manual_ST.pdf

Edited September 5, 2014 by bilks

[copemech]

Those are the correct new limit specs. Yes, tight!

Back to original question, I am sure there is a spec somewhere but I cannot recall where. Seems like new linit came in somewhere around .020in on the last couple of fresh tops I had done(replate and hone to match new piston at .001in).

Once again, a lot here depends upon if you are fighting a rattle or just want/ need a bit or refresh.

Edited September 6, 2014 by copemech

[b_42woody]

Thanks for all the replies!

No, the piston does not rattle. In fact, the engine is quiet.

I called Ryan Young for advice. Based on his personal experience, 0.040 inch ring end gap seems to be the limit. Mine were 0.045 and 0.047 inches.

I ordered a new ring set from Ryan and checked the end gap after a light cylinder hone. The new ring end gap is 0.012 inches for both. I called Ryan to make sure this isn't too tight. He said it's perfect.

Here's what I wonder ..... why did the rings wear so dramatically? I don't think I've ever seen this kind of wear on rings ... especially with the bore and piston looking so good. Thoughts?

Here's why I took the top end off ...

The cylinder base gasket blew out on the outside edge of the back transfer port (where the case halves meet). This, too, is strange to me. I've never had a cylinder base gasket blow out. The original base gasket was 0.2mm thick. Ryan sold me a 0.4mm base gasket and told me to not worry about squish clearance. Before I took the cylinder off, I measured the squish clearance with a dirty piston and a clean head. It was 0.9mm. Now, with the 0.4mm base gasket and a clean piston and head, the squish clearance is 1.1mm. I assume this is safe.

[copemech]

Thanks for all the replies!

No, the piston does not rattle. In fact, the engine is quiet.

I called Ryan Young for advice. Based on his personal experience, 0.040 inch ring end gap seems to be the limit. Mine were 0.045 and 0.047 inches.

I ordered a new ring set from Ryan and checked the end gap after a light cylinder hone. The new ring end gap is 0.012 inches for both. I called Ryan to make sure this isn't too tight. He said it's perfect.

Here's what I wonder ..... why did the rings wear so dramatically? I don't think I've ever seen this kind of wear on rings ... especially with the bore and piston looking so good. Thoughts?

Here's why I took the top end off ...

The cylinder base gasket blew out on the outside edge of the back transfer port (where the case halves meet). This, too, is strange to me. I've never had a cylinder base gasket blow out. The original base gasket was 0.2mm thick. Ryan sold me a 0.4mm base gasket and told me to not worry about squish clearance. Before I took the cylinder off, I measured the squish clearance with a dirty piston and a clean head. It was 0.9mm. Now, with the 0.4mm base gasket and a clean piston and head, the squish clearance is 1.1mm. I assume this is safe.

You will get a million different opinions here on those topics. Bottom line, you are fine if it don't rattle. Rings are fine, squish is fine.

The factory did/does use select fit gaskets upon assembly. Most have one standard .4-.5 or so with sealer oround the water ports, the shim gaskets do not. I would use the standard. No difference in performance really. Max is three tsandards which may take squish up near 2.0mm for those that want to smooth power.

Ring wear? Open issue, dusty/ dirty operation? Maintenance? Oil? Normal wear?

A refresh is good, if no other issues, period. Although I would not, as the things are hard enough to kick over when well seated! I do not miss any performance in a 2.9, they are plenty for me, and I have had a few.

[dadof2]

Cylinder base gasket blow out is not that uncommon, either where you describe (probably due to a step or burrs between the case half's) or round the transfer ports where the can be very little metal thickness. Another cause is over tightening the cylinder base studs causing distortion.

I always put a trace of hylomar on a least one side of a base gasket to prevent blowout.

One of the first things an engine tuner / blueprinter should do is machine the crankcase to barrel face dead flat and parallel to the crank axis.