Posts
43
Joined
3/21/2010
Location
Saint Clair Shores, MI, USA
Edited Date/Time
1/27/2012 11:04am
to start the story off i was out practicing today at Baja Acres in michigan. during the fourth practice my bike bogged down and i pulled off the track. no compression. so i torn down the bike and the result was a snapped top compression ring which gouged my cylinder. this motor was fresh and very well maintained. maybe about an hour on the top end with a week old cylinder. i ve been around the block with racing and all and my dad and i know how to work on the bikes but what has caused the piston ring to snap. this has happened to me earlier in the season too. i have a stock 2007 yz250 2 stroke running stock jetting (which looks and runs great at the elevation here), Yamaha 2r premix 32:1. now today i mixed a gallon of 110 and 3 gallons of 93 together which works out to 97.25 octane. i was told that these bikes seem to have a problem of detonation off of 93 pump gas so i gave it a shot. i have never had this problem with any other bike as far as 60s, 80s, or 125s. could it be that 110 oct. that was mixed?
any input on the cause of this happening would be much appreciated
any input on the cause of this happening would be much appreciated
I think your issue may be related to tolerances in the cylinder. You mentioned the cylinder is a week old, so I assume it has minimal wear. I know that as your cylinder wears it creates a groove at the top that could cause the ring to snap if it were to hit against it.
Does your piston and ring fit nice and snug in the cylinder? Also, what letter is stamped on the outside of the cylinder. I used to race YZ250s and they stamp the cylinder with a letter based on the bore tolerance.
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