Looking for Ideas, M7 Burndown

Arctic Thunder · Dec 15, 2013

First ride of the year. 05 M7, new pistons last year.

Notices when we started if for the first time this year it tried to back fire a couple times. I was thinking reeds. But it fired up and ran fine, tank was completely empty, I filled it with 91oct unleaded. I also filled two other sleds from the same pump on the same day.

On this day, the sled again started fine, little backfire again, nothing big. Started and was fine, the kid rode it for about 5 miles, and it died. We had lots of snow so the coolent temp was good. So I tour it down today and it looks like something caught the PTO side intake port, chipped the top of the piston, and it bounce around in the head, and worked it's way over the MAG side and damaged that piston also. The Mag cylinder is good, PTO is junk, head is in tough shape and pistons are shot of course.

I pulled the reed cages thinking I lost a peddle or maybe even the screws in the cage and it went through. Nope they look like new.

I would at first glance say detonation, but this sled is bone stock and running 91 grade fuel. Sled is using oil, oiler is set correctly.

My thought is this. Last ride of the year last year or starting this season, the ring caught the intake port. So starting this year this blow by on the ring was causing the backfire.

Anyway I am looking for parts if anyone has cylinders or a head laying around, going back together with stock cat pistons, wrist pins and bearings.

Thanks Thunder

CB.8 · Dec 15, 2013

Carbed or EFI?? If it is carbed I'd say you didn't clean them.

Arctic Thunder · Dec 15, 2013

CB.8 said:
Carbed or EFI?? If it is carbed I'd say you didn't clean them.

EFI

sledtahoe · Dec 16, 2013

parts

Looks as if something came apart or was not put together properly. Besides that why run 91 when cat timed it to run 87 which it runs better on anyway...

clutch · Dec 16, 2013

Is the ring locator pin in place still? If so I would check to see if the rod bearing is coming apart.

mountaincat 800 · Dec 16, 2013

I have a stock head that is new if interested. PM me.

Arctic Thunder · Dec 16, 2013

mountaincat 800 said:
I have a stock head that is new if interested. PM me.

Thanks mountaincat. I found a head last night, it's on the way.

I also got the new cylinder and pistons, rings, etc from Eric at racinstation. Super service from this guy.

Thunder

Arctic Thunder · Dec 16, 2013

sledtahoe said:
Looks as if something came apart or was not put together properly. Besides that why run 91 when cat timed it to run 87 which it runs better on anyway...

I am running 91 just because I was filling up an HCR and it requires 91 and had the hose running. Plus I am never super confident in fuels anyway. So if I tried to cheep out and run 87 I would probable be getting something less then run into other issues. So like I said I don't think I had any detonation with the 91 fuel.

Good call though, no reason really to run premium.

Thunder

boondocker97 · Dec 16, 2013

Was the fuel blended with ethanol?

Arctic Thunder · Dec 16, 2013

boondocker97 said:
Was the fuel blended with ethanol?

Yep, same fuel I have been running for the last couple years. I haven't had issues with ethanol as long as I run it out and keep it fresh. Just because I don't know the issues with ethanol, how would this failure possible be caused by ethanol? Just asking.

Thunder

Arctic Thunder · Dec 16, 2013

I think I have found my problem.

Ring Gap.

Take a look at how tight the gap is on the ring that caught the port. I can tell you as it sits here now it has no gap at all. I am sure things can move around after running etc.

All the locating pins are in place, and no other obvious signs of anything coming loose. Wrist pin bearings look very good also.

Thunder

madsledder · Dec 17, 2013

Did you put the piston in backwards?They have to go in a specific way or the ring will catch the ports. I also seen something like that on my m after a rebuild from running it to hard to quick after rebuild.

boondocker97 · Dec 17, 2013

Arctic Thunder said:
Yep, same fuel I have been running for the last couple years. I haven't had issues with ethanol as long as I run it out and keep it fresh. Just because I don't know the issues with ethanol, how would this failure possible be caused by ethanol? Just asking.

Thunder

Not saying it did or didn't cause the problem. If you were getting by running that fuel for a couple seasons before then that probably isn't the culpret unless it had more than 10% blended in it by accident. My sister filled her truck at a pump last year that was labeled 10% but they must have filled the ground tank with E85. Truck wouldn't even run and had to get it towed to a mechanic shop so it does happen.

For some reason E10 (10%) seems to be approved for use in small engines, but once it is bumped up to E15 it starts to raise havoc. Other than collecting water, it burns hotter and I don't believe it provides the same cylinder lubrication characteristics. A year or two ago a study was done with 4 outboard boat motors. If I recall two were identical Evenrudes and two were Mercurys. One of each was run on E15 and one was run without ethanol. They were going to run them for XXX hours and inspect afterward. They had to stop part way because one the motors was running rough on E15. It was torn down and inspected and deemed not fit to continue. The other three finished. When the other one running on E15 was torn down it showed damage as well. They didn't specify what kind of damage exactly. The AMA is also fighting implementation of E15 at gas pumps because it can damage motorcyle engines.

Cat has a wire in the harness that you are supposed to unplug that richens the mixture to run ethanol blended fuel. Not exactly sure where it is, you would have to look in your manual. Lots of people seem to run it without issues but I will not put it in my sleds, quads, bikes, etc. because I don't feel it is good for them. Just my 0.02

Arctic Thunder · Dec 17, 2013

madsledder said:
Did you put the piston in backwards?They have to go in a specific way or the ring will catch the ports. I also seen something like that on my m after a rebuild from running it to hard to quick after rebuild.

If you look real close at the pictures you can see the factory dimple in the top of the pistons. And it caught on the intake port, that is close to the ring gap. So I did make sure they were in right. And they were. Good suggestion to check that's for sure. Thanks

Thunder

Arctic Thunder · Dec 17, 2013

Any chance, this all started with detonation? I know it could have I suppose. But do you think this amount of piston/head damage could have all come from the piece of piston that busted off? And what is the likely hood of the piece from the PTO side getting into the pipe and sucked into the MAG side and doing more damage. I have a chip in the MAG piston also, but I think it was caused by the loose piece form the PTO getting into the port on the MAG. Thoughts?

Secondly, if I was running low on fuel pressure I would have expected to have a melted piston, not the damage that I have. I would expect a standard lean burn down with low fuel pressure or a faulty injector. Right?

Thanks again, it's going back together in a couple days.

Thunder

Thunder101 · Dec 17, 2013

have you checked the bottom end ?

Rixster · Dec 17, 2013

That is 100% from detonation, bad fuel. I bet that thing was making some bad noises before she stopped.

Snowmow · Dec 17, 2013

Thunder.... I would siphon every drop of fuel out and put the last bit in the tank in a smaller clear container. Perhaps you have some water on the bottom of the tank. If the failure was caused by det and the other sleds were running same fuel same day. Could have some water on bottom.

Arctic Thunder · Dec 17, 2013

Snowmow said:
Thunder.... I would siphon every drop of fuel out and put the last bit in the tank in a smaller clear container. Perhaps you have some water on the bottom of the tank. If the failure was caused by det and the other sleds were running same fuel same day. Could have some water on bottom.

This is possible. I stored this sled BONE dry. And added fuel to it. It could have drawn condensate as it heated and cooled every day that's for sure.

I will suck it all out, then see what I find.

I think I will also add some isoheat (red) to move any remaining water through and get it cleaned up. (might even dump in a gal or two of av gas, just because it works really well to clean up the moisture and is higher oct also)

But I suppose I better check my other two sleds also.

Thunder

sledtahoe · Dec 17, 2013

87

Arctic Thunder said:
I am running 91 just because I was filling up an HCR and it requires 91 and had the hose running. Plus I am never super confident in fuels anyway. So if I tried to cheep out and run 87 I would probable be getting something less then run into other issues. So like I said I don't think I had any detonation with the 91 fuel.

Good call though, no reason really to run premium.

Thunder

The main reason I run 87 is because around here they go through it more so it is the freshest fuel...ethnol gas sitting is no good collects water.

Looking for Ideas, M7 Burndown

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