2nd ? of the day -

Does anyone know what kind of compression reading I should expect from an '01 txt 321?

When looking through the exhaust port, I can see a couple of lines or vertical scores on the piston. I know I got some sawdust particles into the engine a while back. Wonder if that has affected things, and whether it's time for a new top-end...thus the question about the correct compression reading.

Thanks,

Jeff

Hi Farmer Jeff,

I can't help a specific compression reading but a few fine scratches on the piston is normal. Usually the rings wear to the point that the end gap becomes excessive. However, if you are considering pulling the cylinder I suggest you check if you can still purchase the original type piston.

I decided that after 10 years that I would treat my 321 to a new piston and rings. The dealer couldn't supply the original Mahle piston because they are no longer made and sent the S3 replacement. Unfortunately, the S3 piston is 60 grams heavier the the Mahle piston (40gms in the piston and 20gms heavier in the pin). When I questioned this issue I was assured there would be no problem and copped a lecture about how I should appreciate the fact that S3 went to the trouble to make suitable pistons.

So I used the S3 piston and it's ok at low revs. However, when blasting up hill climbs at higher revs, the vibration is really quite bad. Clearly 60 grams is a huge difference on a piston the only weighs around a couple of hundred and the crank is not balanced for that. I regretted ever changing it because it ruined a great bike.

I would suggest that if you can't get the Mahle piston then just replace the rings and give the piston a bit of a clean up. The original rings are probably still available.

Chris.

Edited September 7, 201213 yr by aussiechris