Another wiseco bites the dust...

Y

Yamablue

Member
Joined
Mar 7, 2004
Messages
221
Location
Ham Lake, Mn
Well I figured I'd check the piston wash before I headed out to the lake to play with the clutching, and low and behold there was an anomoly on my piston. Further study led me to the conclusion I had a broken ring (guess that's why compression is around 100 vs 120 in that cylinder). Well I just had to know now, so I yanked the head to get a better look. The ring rubbed into the cylinder at the corner of the exhaust port on top and bottom, still looking like a broken ring. Yanked the cylinder expecting a piece of ring to fall off and no go. Turns out the pin that sits in the gap came out and the ring worked its way around the cylinder till it got to the exhaust port and made a home. I ran about 1500 miles on the pistons and rings, so I guess its time to change rings anyways.

I sure hope millenium can build up the cylinder right there or maybe someone else per recommendation. I will post some pictures of the cylinder later, maybe I can get away with just putting a new piston and ring set in there till the next time I burn my motor down.

 

They can fix gouges in cylinder walls. And they have cylinders for exchange if you would like to ride again as soon as possible.
 
Wiseco has had problems with pins coming out.. Get this one: we got new Wisecos for our Pro Stock and one piston didn't even have the pin in it. Go figure.
 
Well Sh!t, I sure hope it can be fixed. They are different numbers because they are not a matched set. I had melted the Mag and PTO last and just replaced those two.
 
That cylinder can be easily fixed at Milenium. Wiseco just made a run of 72.9mm pistons as I just bought 3 sets, they have to have a order of at least 9 sets before making a run. What head are you using on this motor?
 
I've got a Peak head with 20cc inserts with the piston clearance cut into the head, angle changed to 15* from 9*. The squish clearance is 0.047" with the squish band about .480" wide. Lake race ported cylinders, CPR pipes, 38mm XCR 800 carbs w/tps vested to belly pan, VF2 reeds, cut up airbox.
 
tell me about the settings in your carbs.

Also what part of the rpm range does it seem to munch the pistons?

this isnt really pertaining to the latest damage, thats a fluke or bad luck with a ring pin coming out, but I am referring to you saying its eaten alot of pistons before this problem happened.
 
Heat problems

I would bet that this motor is running hot. Any snowmobile engine that is consistently run at temperatures over 150 + will experience shorter engine life! This means premature piston failure such as piston skirt collapse and the anti-rotation pins falling out of the pistons. Most racing engines that produce 30% or more horsepower than stock engines produce a bi-product of both power and heat. Most heat exchanger's are inadequate to handle the increased heat that is produced by the larger and more powerful engine. Then the pistons begins to shrink and slowly fail. This happens slowly with a slow death to the engine. The skirts collapse and the pin falls out. This is common. Get yourself a temp guage and install a tee in-line just after the head to measure the temp. Control the temp and a lot of temp related problems will go away.
 
I'm not really having any problems with the motor as far as melting pistons anymore. You have helped me work this out from burn down to burn down. I think I bought a Simon CDI from you as I run the motor aroun 9300rpm. I currently have 390 mains, hooded needle jets with the stock 2001 XCR800 jet needle with the clip at p4 with 1 washer under it I believe. Pilots are 50 with screws 2.25 out. I put the airbox back as per your recommendation I believe. I have it set rich intentionally for use with my variflow. I just haven't put it on yet. The munching piston issue went away when I redesigned the chamber that MPI gave me with the head.
 
Ok, good no more piston problems,was just wondering about it when I read that in your post., Sorry you just got a case of bad luck on the pin coming out.
 
I see that wiseco has a .5mm and a 1mm oversize piston. Would it be ok to have the plater open it up a little if that will clean up the gouge, or just have them fix it and keep the same bore?
 
what they will do is strip the cylinder, weld the gouge and rebore the cylinder to spec, renic it and your ready to go, not hard for them to do. Just send them a new piston with the cylinder and what skirt to wall clearance you want in it. I would keep all the pistons the same size, that way all the weight is even on the crankshaft.
 
Yeah good point. With a wiseco piston, should I stay with the sheet recommendation for p-cw clearance or what? I can't remember what I set it to before, but I did have them open a little from stock since they are forgings instead of cast.
 
140-145 degrees should be max on coolant temp. Anything hotter will relax rings and they will break.
 
Heat related failure

Yamablue - I wish I could run 134 degrees. I was 155 most of yesterday when testing. Anyone with ideas for better cooling? Seems most big bores that have posted with problems over the last several years leave the board. Most probably give up after several failures. My pistons are trashed every 2k miles. I think its all attributed to HEAT.
 
Coolers

I made heat exchangers for the tunnel in my 780. I bought the material fromMountain Performance and welded them up. Significantly improved cooling. Sled usually ran about 125-130 degrees. When I was running an SRX cooler in the back it ran about 155 degrees. The sled holds almost a gallon more antifreeze than a stocker. The lower temps were probably attributed to the better coolers and the higher capacity.......and MRVIPER700's head modifications.

Madmatt
 
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