M7 Burn Down Cause?

GBrown · Mar 15, 2011

2006 M7 with Speedwerx 800BB, speedwerx single pipe and can, sno-pro intake, oil delete, Digitron EGTs and speedwerx reprogrammed ecu. PTO piston burned down in about 200 miles after build. I had checked wash (through the exhaust valve slot, maybe misleading view angle?) and plugs the first couple rides out and wash and plugs looked good (I am new at this so maybe I was misreading) with a max EGT of about 1150 (probe is 4" from piston skirt).

Sled ran great, which is what I understand they often do before burning down from too lean. EGTs the day it burned down were actually reading cooler on the PTO side so I suspected something was wrong but didn't think I was in danger of a burn down because it was running cooler, obviously I was wrong.

Can someone tell me by looking at the pictures was this burn down from too lean, detonation (bad gas?), or something else I'm not seeing.

Thanks,

Garrett

catunder · Mar 15, 2011

Too Lean

The simple answer is that it was SIMPLY LEAN. The difficult answer is what caused it. Fuel program, plugged baro tube, highly oxygenated fuel??? Sorry for your bad luck.

007 · Mar 15, 2011

Is that the end of the ring or did it break there? Piston in backwards? Couldn't see the marks?

KJP

907to406 · Mar 15, 2011

What kind of oil delete, and did you do the oil delete at the same time as the rebuild? That would be the first thing I looked into.

GBrown · Mar 15, 2011

Piston is installed in the correct direction. Not sure if that's the end of the ring or it broke, haven't pulled the jugs off yet.

Not sure what type of oil delete is installed as I bought the motor used prior to the rebuild. It was supposedly a speedwerx built hillclimb race motor so I suspect its whatever type they use but can't be sure. I premixed at 40:1.

GBrown · Mar 15, 2011

From what I have tried to research it looks like the wash on the Mag side is OK and the wash on the PTO is almost non-existent. What would cause them to be different?

tundramonkey · Mar 15, 2011

Looks like the ring caught on something.

How'd the power valve look on the PTO side? Any chunks taken out of it? Did you check the ring gap when you did the BB kit?

As far as a lean condition, could be bad crank seal.

4Z · Mar 15, 2011

catunder said:
The simple answer is that it was SIMPLY LEAN. The difficult answer is what caused it. Fuel program, plugged baro tube, highly oxygenated fuel??? Sorry for your bad luck.

Ditto

GBrown · Mar 15, 2011

tundramonkey said:
Looks like the ring caught on something.

How'd the power valve look on the PTO side? Any chunks taken out of it? Did you check the ring gap when you did the BB kit?

As far as a lean condition, could be bad crank seal.

Power valve on the PTO side did have a few chunks missing.

Thunder101 · Mar 15, 2011

looks like light deto to me, raddled out a loc pin. if your temps were 1150 at the highest then they may not be reading correctly ? . But im going to stick with light deto, maybe fuel quallity for comp. find a part # or ratio # on head and call SW for info.

cooldown · Mar 15, 2011

I think thunder 101 is right if you are getting detonation your egt temps will drop.Bad fuel?

Rixster · Mar 15, 2011

I am not sure what pistons that kit uses but I will tell you what I was told many times when mine looked like that. A little lean but, thats just a good old weisco piston failure. A mechanic a cutlers told me that as well as a mechanic at a different shop. Apparently weiscos have weak ring lands ? Maybe not if you over fuel it, but when running on the edge it magnifies everything.

007 · Mar 16, 2011

Thunder101 said:
looks like light deto to me, raddled out a loc pin. if your temps were 1150 at the highest then they may not be reading correctly ? . But im going to stick with light deto, maybe fuel quallity for comp. find a part # or ratio # on head and call SW for info.

That what I was thinking if the piston was installed right. Had a friend do that same thing on a 800 kit with a wiesco piston.

KJP

GBrown · Mar 16, 2011

Rixster said:
I am not sure what pistons that kit uses but I will tell you what I was told many times when mine looked like that. A little lean but, thats just a good old weisco piston failure. A mechanic a cutlers told me that as well as a mechanic at a different shop. Apparently weiscos have weak ring lands ? Maybe not if you over fuel it, but when running on the edge it magnifies everything.

I was told by speedwerx the kit uses the stock Arctic Cat 800 pistons.

So it sounds like detonation caused this, I'm guessing bad gas or something else? Does the Mag side piston look too lean to you guys or does it look like my A/F ratio is ok?

Thanks for all the help.

Thunder101 · Mar 16, 2011

Mag side has light deto and it was the deto that took down the pto most likey raddled the location pin out , ring turns and then it snags or the deto causes the ring land to brake.
Tell us more about what you think ? and what comp you have, what alt you were riding, timing key, what fuel did you have in it ? what pipe ? Did you talk to SW

GBrown · Mar 17, 2011

Sled has the speedwerx pipe made for their 800BB kit, when I ordered the kit last year I got it as a complete package with the cylinders, pistons, domes, y-pipe, pipe, and can together.

When I ordered the kit I spoke to them about riding elevation and told them I would be unloading around 3500' and most of my riding would be done between 5000'-9000' which is exactly where I was riding the day it died.

Fuel used was always 91 octane premium from a brand name source such as Chevron or Shell.

I haven't talk to speedwerx yet but my guess is I got unlucky with some bad fuel.

One more question for you guys, is there a certain sound you can hear with these engines when detonation is occurring? Would like to be able to tell when this is happening in the future.

CATSLEDMAN1 · Mar 17, 2011

burning questions

likely not "bad fuel " related or you would see about same effect on both sides of the twin.

the piston with the white / bare aluminum ring around the outside has been detonating a lot...........and no you cannot hear that riding your water cooled sled. Good dyno shops go to great pains to be able to hear with correct equipment and have often one shut down guy listening........any deto they pull plug on that dyno run.

So at some fuel delivery area you have a lean conditon on the cyl that went down. Often thats just because side to side on any twin you have different fuel requirements,.......one side always needs more fuel. So if the good side that didn't burn doesn't have some 1/2 dime size wash marks, your overall setting is likely too lean.

ALSO.......M7 marginal on cooling anyway, you might simply have had overheating and your fuel is ok, so what conditons were you .....?

Probe temps like 1150 are for mashed on the bar long hot runs. If you can see 1150 temps in short stabs of the throttle, you have a lean condition. 3/4 throttle good running engine you should never see 1100 temps if you want a nice full power.

Anyway.........lots to ask yourself. Remember, sleds always ok, tuner default.

tundramonkey · Mar 17, 2011

What domes do you have 12.7:1 or 14:1? Do you know which pipe, the AC700S-3 (above 5000 ft) or the AC925S-M (good at all elevations)?

Did the burn down happen below 5000 ft?

mbcat · Mar 23, 2011

Did you say it was a speedwerx hillclimb race engine, if so did it blow low to mid throttle. If so the cdi and fuel map are probably set up for only wide open operation. Friend of mine bought a cat salvage 600 hillclimb race engine and a 20 liter pail of pistons before he figured it out!

Thunder101 · Mar 23, 2011

20 liter pail of pistons before he figured it out!

lmao

M7 Burn Down Cause?

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