compression numbers on my mm

ebayfreak

ebayfreak

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Joined
Feb 17, 2007
Messages
195
Age
54
Location
newfoundland, Canada
i got a 2001 mountain max and it's been working like crap back firing and killing plugs. cleaned carbs and checked spark. Still the same. Anyway decided to get my compression tester out and i have 125 psi on both mag and middle and 50 psi on the clutch side. haven't tore it apart yet but will i need to re ring all pistons or can i just fix the bad side. did Anybody ever have this happen and what's the best option. just rebuilt my srx and it cost me a fortune and was hoping to spend money in gas and not engine parts. Any info would be greatly appreciated.thanks!
 
ebayfreak said:
not sure but my srx had 150 psi with 8000 km it was a couple of years old then.
I always heard anything above 120 is good.
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im pushing 19000km on unopened engine and yeah. my coils give out last week so shes coming to her end unfortunately. My dad bought off the showroom floor in 97 and its been mine for 3 years now so Its got more then its money worth. I will check compression tomorrow because im very curious.
 
You could fix just the one hole but depending on your miles, might be a good idea to at least put rings in the other 2. I'm betting you need a piston on the bad hole.
 
Just change that piston and rings on that one and hone the cylinder if still good, and you can even reuse your gaskets if you clean them good and spray 2 coats on both sides of copper gasket spray and put together tackey I know a few of them sleds running around just like that (one has 25000 miles on it to) pull the carbs and find out why she poofed that hole.
 
I would bet that the crank seal went bad and that jug was running lean. My last sled was an 86 Indy that came to the same end. I would plan on doing both
Crankshaft seals while it's apart for the jug. I'm not sure about compression as I
Haven't pop tested mine yet since I bought it, should have by now. I'd say in the 140-150 range and up is healthy. I have a 20 year old husky chain saw that pops 170. Depending on miles you might want to do a complete rebuild while it's torn down since the other 2 cylinders might have out of spec leak down.
 
To check the crank seal for a leak, with the sled idleing spray some carb cleaner around the seal the mag side seal is really buried if the motor revs up you got a leak.
Dont reuse just any gaskets but them gaskets you can reuse.
 
meltdown woes

well guys it's a meltdown of clutch side piston , definitely a lean issue, so much for a cheap fix. looks like cylinder is cooked and had some bits of ring embedded in the cylinder head . I maybe looking for some parts soon, anybody that could sell me some parts at a decent price their help would be greatly appreciated!thanks!
 
i haven't pulled the crank yet, waiting to get a clutch puller from a buddy. but Looking at the crank through the case looks like some heavy heat went through the journal it's a bluish tinge. rod bearing is surely cooked.Did you lose your crank as well. or just the cylinder and piston?



Backwoods M Max said:
I would guess with 90% certainty that it was because of a bad pto side crank seal, it happened to me.
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The cranks do have a bluish tinge to them from heating during factory assembly. I would measure run out and rod play. That should give you a good indication of the condition.
 
It wasn't my mm that melted down from a crank seal but my prior sled. It was an 86 Indy and had a very erratic idle which should have been a dead give away but it was my first sled and I didn't know any better. I'm going to carb spray test my mm before I ride it the next time just to make sure nothing dried out in storage this fall. It's almost one of those yearly things to do after pulling a sled from storage, check crank seals for leaks.
 
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