Nytro 240MCX ENGINE Blown

[SquamishPaul]

2 litres of coolant gone and Medium rare pistons, 25lbs on compression test.The sled sputtered and died last saturday, doing powder turns after a long pull into a bowl. The sledhad been running superb, with recent new primary and secondary clutches and lighter weights to bring the rpm to 8900. No poor running, stalling or backfiring prior to failure, no over boost, no hitting the rev limiter, same gas as always chevron 94, same station. The one piston shows roasting on onw edge and the other 2 show no visible damage. The top end was fine. The aluminum shim on the head from the turbo kit has failed on some installs, but mine had built up yamaha shims and was sound. The temperature was fine, I have a gauge, the snow was super deep.
I had problems with the Nytro just cutting out and stopping dead like the kill switch went on the previous weekends, but it would start up right away again 3out of 4 times. The instrument pod would be dead too for a while. Someone suggested ugrading to 2010 relays to cure this problem. The sled is stored outdoors under cover, so moisture is always suspect. The connectors have been all filled with dielectric grease. Last year the 10 pin connector for the turbo gave me trouble with connectivity,and it would run rough and puff black smoke until it was repaired.
The engine has 9300 km, 8000 km with the turbo on. The boost was set lower for a 3 seasons and late last yeay was dyno'ed up to the full 240 by the local shop Diamond Head Motors.
The Yamaha ECU has failed before due to moisture and its location was updated. The MCX chip has been sent to Prince George for testing.
Any riders out there had an engine failure yet??? This failure is stumping me and the dealer can't say definitively why it reads 25 psi on all 3 cylinders.
Thanks in advance, and thanks to the '11 Polaris 163 and the '11 XP boarders who pulled me out of Brandywine.

 

[yukon yamaha]

Have them do a leak down test!! it will tell you what is wrong, if it overheated it may have ovaled the top 3/4" of the cylinder(sorry for the spelling) and you are having lots of blow by.... I have seen this happen on one of the apexs that we have worked on in the past, but his was all due to heat... you will have to get them to take the head off to measure the walls..... but it would be worth doing! Sorry for the bad luck , i hope it is a simple fix!

 

[SEVS11]

Wow!!! This almost unheard of with a mcx kit? Do you have a MCX display and if so was their a possible lean condition? Did you have any blow-by coming out the catch can outlet at anytime? Makes you wonder how it could run perfect then all of a sudden die and all three cyl have the same amount of compression weird....

Please keep us posted since I will be keeping an extra close eye on mine lol. Sorry to hear about your engine failure,good luck!

 

[rxrider]

It's detonation I'm pretty sure of. Deto kill the rings and not more compression. Check cylinders for out of round, also a sympthom when deto happens.
Take the engine apart and rebuild, throw in a set of Carillos while at it, new low compression pistons 9:1 (rings comes with the set), get rid of the head shim.

What fuel did you run? MCX hardly ever detonate on proper fuel and correct tune.

 

[SquamishPaul]

It's detonation I'm pretty sure of. Deto kill the rings and not more compression. Check cylinders for out of round, also a sympthom when deto happens.
Take the engine apart and rebuild, throw in a set of Carillos while at it, new low compression pistons 9:1 (rings comes with the set), get rid of the head shim.

What fuel did you run? MCX hardly ever detonate on proper fuel and correct tune.

I ran Chevron 94 all the time and used stabilizer in the summer as well as starting every month or less.

With 2 litres of coolant gone, and cracks in the engine coolant cavity, as wellas in the lower block, it is still weird how only one area of the piston wall and ring melted on each cylinder. Other mystery ideas are secondary injectors creating lean condition, coolant steam in the crankcasewall at the cylinder bore, coolant freezeup in the oil vent to the Jacob valve[have had the switch ice,freeze and fail rolling over, tether pulled]
This engine was dynoed at an honest 240 and ran great dispite relay issues, the only recent change was a new primary and secondary clutch with new weights that let it rev to 8900 instead of 8200 max.

 

[rxrider]

Was it damaged on the intake side of the piston? It's usually where the detonation shows.

 

[SquamishPaul]

Was it damaged on the intake side of the piston? It's usually where the detonation shows.

There was no damage on the intake side at all.
One piston had an additional damage on top like a woodpecker pecked a 3/4 outside piece. Yamaha says likely the gas too. Will post a new thread on 94 gas and update when I hear from the boys at Yamaha.

 

[rxrider]

Detonation can act like a Woodpecker.