melted 670 piston. now need specs - Snowmobile Forum: Your #1 Snowmobile Forum

eddie · 01-08-2005, 10:14 AM

Hey guys!

I have a 1998 MXZ 670 that just started melting the PTO piston, near the intake ports. It crapped out after about 20 seconds of a high speed blast at WOT. I believe it was because I pulled the airbox off and was just using foam cone air filters. I didn't rejet richer and I bet that was the issue. At least that's what I've been learning online.

I towed it home and did a compression test to find one side was 135 and the other was barely 90. I pulled the heads to find the piston crown started to melt right where the top ring meets with that little index pin in the ring groove (ya know what I mean?). The cylinder wall is scored but isn't horrible... I've seen worse! So I know I gotta take it in for a bore. My issue is I don't have a manual and I need the patterns and torques for the 12 head bolts and the 8 clyinder bolts. I'd really appreciate it if someone could share that with me.

Thanks in advance!

Ed in St. Charles, IL

eddie · 01-08-2005, 01:45 PM

I found it!
They are both 21 ft lbs. Thought I'd post it here for future searches.

Ed

**smallengineguy** · 01-08-2005, 05:29 PM

Start from the middle and work your way out when torquing.

eddie · 01-09-2005, 05:33 AM

Thanks for that, SmallEngineGuy.

Would you happen to know what I can use instead of molylube? I read that I need to use a few drops of molylube on the wrist pin bearings during installation. In the past I'd usually just lube it with premix oil but I wonder why they'd call for molylube.

Thanks,
Ed

**smallengineguy** · 01-09-2005, 08:26 AM

I've used plain 2 stroke oil for years, works fine!