97 Vmax 500 Twin using lots of gas then blew

musselman

musselman

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My 500 twin started using tonnes of gas and oil and then halfway through our RAP trip (Round Algonquin Park) it lost compression in the mag cylinder. Took the engine apart today and it looks like the pin that holds the rings in place came out and the ring caught the exhaust port. What would have caused it to use so much gas? Was it due to the failure in progress? I will post up some pictures of the damages later. Thanks
 
musselman said:
it looks like the pin that holds the rings in place came out and the ring caught the exhaust port.
Click to expand...
the two have no relation at all to your problem,it was a problem Yamaha had back in '97,the fix was a updated piston.

also some '97 pumps when fail go to full flow out put,you just happen to have these issues at the same time.

fix is first try to readjust oil pump if still to ritch then a new/used pump is in order.

500 were always hard on fuel if not re jetted some.
 
Well it was always hard on gas but just one weekend before this happened it started using a lot more. Like it would get about 100 km to a tank. Not sure what would be causing that to happen.
 
thats right too much in the gas to keep up, like sucking the gas right thru the motor, no power coming from the bad side, my twin will do that too when the plugs are starting to foul up....usually happens when a guest is riding the sled and don't realize the bog from the misfiring...CP
 
Well it was driven the same as always when it started using twice as much gas. Would the oil pump failing open cause it to use more gas as well?
 
Anyone have any thoughts on the excessive fuel and oil consumption? I'm just trying to find out what went wrong so the new motor is not damaged as well.
 
Hard to say maybe it wasn't running on both cyls sucking down more gas.

go over everything twice checking it out.
 
Yes I believe so, it looks like a 0.04" or deeper gouge. Do you think the 2 separate hits happened at the same time, or do you think the hit on the side may have been causing the fuel usage?
 
Hard to say,probably soon after each other,then when that cyl went down it required more throttle to keep her going.

how many miles on this engine? how was jetting? don't see allot of wash going on.
 
Strange usually factory jetting on the twins back then yield rich jetting
but from what i see or don't see there lack of was is wash(fuel washing the piston dome clean) the tell tail signs of the wash trails on the intake side of the piston are not there lots of just carbon telling me lean,can you post pics of the plugs???
 
Well I can't seem to find the plugs that were in it. I changed them out at the time thinking it may have fouled a plug. From what I remember they were a dark brown to black colour.
 
Well about all you can do is check things over wile reassembling take your time, thats allot miles,Kilometers don't know if you plan on keeping the sled but you may also want to do the crank seals wile you have it down that far.

actually you did good getting all them Kilometers on with out this happening sooner, some went at like 4-5,000 Kilometers.

i have a set of rings if you need them.
 
Well I'm having thoughts about scrapping this engine, I have never liked it (poor response and poor fuel mileage). I have a lead on a crashed 700 sxr and i'm thinking of putting the engine in the 500 chassis.
 
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