I have a 03 mtn cat 600 144". Just ran a compression test and its showing 90 psi per side. 2200 miles and the motor has never been opened. I need advice. New pistons?
90 psi?
- Thread starter dyrengd
- Start date
90 psi is pretty low. Pistons in those engines had a nasty habit of having the pins that keep the rings in place fall out and then the rings turn and when the ends get in the exhaust port bad things happen. Usually you lose all compression when they break and gouge the cylinder but I have also seen them just slowly wear the ring ends and the cylinder wall. I would pull the head and see what your cylinders look like at the exhaust port. You may get lucky and be able to just get by with new pistons. I would go with SPI pistons, I have never seen one of them have the pins fall out.
Ok, it could be fine. Compression gauges measure differential and are calibrated with a spring mecanism. I have a couple of gauges, one reads 120psi and the other 95psi on the same motor testing it at the same time. So 90psi isn't necessarily a bad motor. If you had access to a known good motor, say a nearly new sled, you could use your gauge to check it and that would tell you if you have one that reads low normally.
Does the machine start easy, both hot and cold? You said that its 90psi on both sides, if it weren't... if it had say 15% variance between cylinders that would also be a sign of something bad.
All of that said, 2200 miles on a 2 stroke is in my opinion a good time to start thinking about re-ringing for maximum performance. But this is an 03 600 we are talking about, not the highest HP motor on the planet. If it starts easy both hot and cold I wouldn't be concerned.
sled_guy
Does the machine start easy, both hot and cold? You said that its 90psi on both sides, if it weren't... if it had say 15% variance between cylinders that would also be a sign of something bad.
All of that said, 2200 miles on a 2 stroke is in my opinion a good time to start thinking about re-ringing for maximum performance. But this is an 03 600 we are talking about, not the highest HP motor on the planet. If it starts easy both hot and cold I wouldn't be concerned.
sled_guy
If I go with a new topend, is it necessary to have the cylinders honed? Or can i just replace the pistons an move on?
I forgot to mention the possibility that the gauge may not read right. Like Sled Guy I have two that read way different also. I also agree that it is time to put in new rings, but I would replace pistons too. A light hone helps new rings seat better. If you don't have access to a hone a little work with emery cloth by hand works too. Just go around and around not up and down. Don't get carried away just a little scuff to put some light scratches in to hold some extra oil while the rings seat.
Just by chance what altitude are you at? Were you holding the throttle wide open? Mike
M
Sorry bad post
G
Put new pistons in it. Way cheaper then waiting for the 2,500 mile mark and having the piston fail. I had the pin sink in and that caused the ring to rotate.. OUCH. New pistons and a new cylinder was needed.
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