Scored Piston Diagnosis

[WYsteph]

Pulled my m7 apart last night, in case you missed my last thread- made it about 5 minutes out of the parking lot last week when she won't go any faster then 60 mph and the check engine light came on. Shut her off right away and pulling the plugs which were white and the normally oily y pipe was white. The current thought was that I might have lost my oil pump, since while it was idling that morning it seemed to smoke more that usual.

Here is what I found.

First, should have put lock-tight on the power valve screws when we cleaned them a few months ago. Lost both on the clutch side.

Here is the head

Y pipe

First peek at the pistons, this the clutch side.

The mag side was sticky to the touch.

Pulled the jugs off, they are good- no marks. Here is the side view of the pistons.

Closer view of the mag side, the scratches aren't bad but I think we got her shut down just in time.

Clutch side, you can just barely feel the scratches.

The crank looks ok, no bluing or anything. Forgot my clutch puller so that is as far as I got it tore apart last night.

Getting ready to go home-

Labeled and packed everything up, I really hate trying to figure out which bolt goes where.

Packed the piston rods and crank to keep water and junk out.

Well what do you guys think? The missing power valve bolts would explain the 60 mph problem but what about the pistons? Lack of lube or ?

Did a lot of searching on here and still haven't found a good way to check and see if the oil pump is working?

 

[clutch]

It was drinking coolant. Better find out if it's a head oring or base gasket. Also clean the cases and crank very good, as coolant is very hard on bearings.

 

[WYsteph]

The head o rings looked fine and I had some issues taking the jugs off so it is hard to tell if it was the damage to the base gaskets was due to that.

Would it still be coolant since both spark plugs are white? Guess the coolant could have worked down to the crank and come back up into the other cylinder?

 

[clutch]

It can't swap sides in the crankcase, but it will go out the exhaust and back in the other cylinder through the y pipe because of the way a 2 stroke pipe works.

 

[RKT]

What code was the check engine light flashing..

Very odd pistons.. The PTO piston/side, is where the issue is.. I suspect the Mag piston has looked like that for a while.. The Mag piston look slike it was getting hot via lack of coolant on the exchangers.. but since the rings are fine... this could have happened rides ago....the PTO piston is what looks bad, IMO..

I suspect that you starved the PTO for fuel.. Possible bad injector??

Also, check the crank rods for excessive play.. Grab the rod, tight, and see if there is any up and down movement of the rod on the crank.. ANY up and down play is a sign of impending disaster..

Let me know what you find..

BTW.. nice job on the tear down and the bagging of all the hardware.. great idea!!!

Kelsey

 

[hypnotoad]

Can't really add anything but would like to find out the cause as well just for the knowledge. Was the sled using alot of coolent?, you didn't say if it was in this post unless i missed it or was mentioned in another post.

 

[diggerdown]

Your cylinder studs look pretty rusty, been leaking coolant around them?

 

[WYsteph]

The check engine light would only blink when on the throttle. I did not get a count. I pulled the plugs right away and they where both white and carbony.

I have had a coolant leak for a while now. About a cup a day. Although when it started the head o-rings and base gaskets where replaced. I did just fix a coolant leak at the heat exchanger before this ride.

Could you explain why you think the pto side is the problem? I am just thinking the its the mag side with the scuffing, But I know I dont know my engines like you do. Thanks

 

[Ski-Laxn]

Steph
If you look at the top of the piston and see the white carbon build up that is a sign and also the very clean head is asign that it started in that cylinder.

 

[RKT]

The check engine light would only blink when on the throttle. I did not get a count. I pulled the plugs right away and they where both white and carbony.

I have had a coolant leak for a while now. About a cup a day. Although when it started the head o-rings and base gaskets where replaced. I did just fix a coolant leak at the heat exchanger before this ride.

Could you explain why you think the pto side is the problem? I am just thinking the its the mag side with the scuffing, But I know I dont know my engines like you do. Thanks

The Mag side is washed clean.. It shows no sign of water in the cylinder (no gray or milky matter).. The PTO piston has gotten very hot.. this is evident because of the high carbon build up (takes heat to crystalize) and the slight detonation around the edges of the piston crown

While it is hard to tell much from just those pics.. they BOTH look odd, the Mag is much too washed and clean and the PTO is not enough.. something weird is going on for sure with both sides...

Kelsey

 

[RickM]

WYsteph

Looking at your photos and reading your comments.
I think you have had a antifreeze seap on the PTO side and it has been burning the antifreeze while you ride. The top of the piston indicates heat from foreign matter being burnt. Check your rings and see if they move freely the ring lands. Antifreeze is sticky and will make your rings slugish, also you mentioned sticky piston top, and look at your squish angle of heads, shows un burnt stuff, like antifreeze, My thoughts may be totally wrong, but i sure would suspect a little seep. Also when engine smoked like you said indicates antifreeze. ( v8 engine with cracked head or head gasket will put out white smoke out tail pipe ) similar to what your talking about. When you put it back together, be sure a run a leak down test on the cooling system. RickM

 

[AKSNOWRIDER]

stephy, has this sled been ported? I have heard of others having ported cylinders crack and seep antifreeze in..the mag piston looks like the side that leaked(notice all carbon is gone which is what happens with antifreeze going into the chamber)the white on the pto piston is small amounts of antifreeze coming thru the exhaust...when you shut the sled off on the hill and restarted after 10-15 minutes did it miss for a minute or so then clear out and run good again? if your sure the gaskets and seals were sealing ..I would drop both cylinders and the head by a machine shop and have them magnafluxed for cracks..cheap easy way to make sure your problem is fixed..(the scuffing looks to me like it is from antifreeze washing away the oil..which would also point to the mag cylinder being the culprit)

 

[sidewinder]

I vote coolant leak

I lost a base gasket on my M7 earlier this year and scored the piston on the guilty side almost identically. White residue looks identical as well. Pock marks on top of piston consistent with ethylene glycol (anti freeze) explosion. When ethylene glycol is burnt under pressure it explodes causing pitting and a sandblasted look on aluminum parts. Good luck on the overhaul. And by the way, do you teach courses in clean and organized mechanical repair?

 

[WYsteph]

Did some further inspection on the jugs since it was really late last night after I got off work. It looks like the pto side had a base gasket leak. The outside of the jug has a wet spot and looked at the crank case and it has a spot where you can see something was leaking at the same spot.

No, this sled hasn't been ported (yet.)

I will check the crank out next time I can work on it, snowing hard here and can't use the shop at Brant's work tonight.

So it sounds like this was due to a coolant leak, do I need to check the injectors and oil pump? To clean the crank I would use?


I could probably give you some pointers sidewinder... What can I say, lol, I want to be able to put this back together without help from my husband.

 

[golfsnownut]

Have you gotten your big bore kit together yet and without your husband's help? I actually want to see you to get success with this project and be proud of the accomplishments

 

[m8magicandmystery]

don;t think the piston scratches are a serious issue...i think your clutch side imperfection was caused by cold snow ingestion on a hot motor..??

 

[smoothdawg]

If this were my sled I would pull the motor and split the cases to inspect everything. It is possible you are leaking coolant through your waterpump seals. I would want to inspect all of the bearings to make dang sure I don't have a problem anywhere. Might as well put it back together with an RKT big bore kit. You are not too far away $ wise by the time you replace your stock stuff. Hope you get it figured out.

 

[WYsteph]

Well, I polished the tunnel yesterday lol. Other then that haven't touched it, in no hurry since our season is about done.

Yes I'm defiantly going to do the RKT big bore smoothdawg. I'm not sure how much more I should tear into the rest of the sled, might have to go buy a manual to put it all back together. But when I get a bit closer to putting the engine back in I'm planning to throughly check the crank, oil system, etc.

Thanks for the support golfsnownut. I'm excited to do this by myself, I really like working on my sleds, which has been a good thing the way this year went.

m8magicandmystery- unless it happened on some other trip I'm going to guess it wasn't snow ingestion. No powder, was on a rock hard trail just leaving the lodge that morning.

 

[golfsnownut]

You can buy a repair service manual on DVD thru ebay which I did for a cheap dirt and it is cool to look up on the laptop computer or desktop computer whichever....

 

[FreeAgent]

Steph,
I will burn ya a manual tomorrow and stick it in the mail. Be watching for it

Shell

Well, I polished the tunnel yesterday lol. Other then that haven't touched it, in no hurry since our season is about done.

Yes I'm defiantly going to do the RKT big bore smoothdawg. I'm not sure how much more I should tear into the rest of the sled, might have to go buy a manual to put it all back together. But when I get a bit closer to putting the engine back in I'm planning to throughly check the crank, oil system, etc.

Thanks for the support golfsnownut. I'm excited to do this by myself, I really like working on my sleds, which has been a good thing the way this year went.

m8magicandmystery- unless it happened on some other trip I'm going to guess it wasn't snow ingestion. No powder, was on a rock hard trail just leaving the lodge that morning.