RMK 700 burn down ??'s

[rmkrazi]

I recently burnt a hole in the mag piston of my '01 rmk 700. The hole is on the front left of the piston and it burned all the way down to the ring land. The head has been blasted with the shrapnel from the burn down and small pieces of aluminum are embedded in the dome of the head. Can I clean this up and re-use it or do I need a new head? I haven't determined the cause of the burn down yet but I was wondering if the location of the hole in the piston is any indication of where the the lean condition originated...assuming this wasn't due to incorrect jetting...
Thanks for any input

 

[JROD]

Could be jetting or needle position. Could be bad fuel and detonation problems. Could be a lean condition that caused deto. Do you have any pictures of the piston?

For the what the cost of a head is, I would recommend doing that and not taking your chances. You don't want any unneeded turbulence in your combustion chamber that wasn't already designed into it, no matter how little it may seem. It may seem minor but if reused, could create more deto issues down the road.

J

 

[clutch man]

I recently burnt a hole in the mag piston of my '01 rmk 700. The hole is on the front left of the piston and it burned all the way down to the ring land. The head has been blasted with the shrapnel from the burn down and small pieces of aluminum are embedded in the dome of the head. Can I clean this up and re-use it or do I need a new head? I haven't determined the cause of the burn down yet but I was wondering if the location of the hole in the piston is any indication of where the the lean condition originated...assuming this wasn't due to incorrect jetting...
Thanks for any input

how many miles on your sled, were you running ethanal gas, have you changed jetting, or pipe, is there a hole in your pipe or can?
Is there a hole in the carb boot, or did the air box come off?
Check that stuff out and if you have high mile it may be a bad seal.

 

[rmkrazi]

how many miles on your sled, were you running ethanal gas, have you changed jetting, or pipe, is there a hole in your pipe or can?
Is there a hole in the carb boot, or did the air box come off?
Check that stuff out and if you have high mile it may be a bad seal.

When I bought the sled it had around 4,500 miles, but the crank had just been re-done and pistons 1,000 miles before that. I'm assuming that the pto crank seal was done at the time and i just changed the mag seal at the beginning of the season. I fill up with exxon and thought that they were ethanol free, but maybe not. Been running with the same setup from the end of last season up till the burn down, so probably 500 miles as it is.
I'm just gonna have to do some investigating to really find the true cause of this... Thanks

 

[clutch man]

When I bought the sled it had around 4,500 miles, but the crank had just been re-done and pistons 1,000 miles before that. I'm assuming that the pto crank seal was done at the time and i just changed the mag seal at the beginning of the season. I fill up with exxon and thought that they were ethanol free, but maybe not. Been running with the same setup from the end of last season up till the burn down, so probably 500 miles as it is.
I'm just gonna have to do some investigating to really find the true cause of this... Thanks

when you changed the mag seal what did you use on the crankcase for sealent?
did you put grease in the seal?

 

[rmkrazi]

when you changed the mag seal what did you use on the crankcase for sealent?
did you put grease in the seal?

Are you talking about sealing between the mag housing and the crankcase... If so I used some high temp rtv silicone. You don't have to split the cases to replace the mag seal on these particular domestic twins mind you. There was already some grease on the seal when it came out of the packaging. I dabbed a little more on upon re-assembly. Thanks again.

 

[clutch man]

Are you talking about sealing between the mag housing and the crankcase... If so I used some high temp rtv silicone. You don't have to split the cases to replace the mag seal on these particular domestic twins mind you. There was already some grease on the seal when it came out of the packaging. I dabbed a little more on upon re-assembly. Thanks again.

Yep i build them all the time but you should use 1194 3 bond or Polaris crank case sealent. if you used any thing but that, it could leak. that sealent has to be on the crank case and the water pump housing.

 

[rmkrazi]

Yep i build them all the time but you should use 1194 3 bond or Polaris crank case sealent. if you used any thing but that, it could leak. that sealent has to be on the crank case and the water pump housing.

Isn't that why the seal is there? I don't see how having that area sealed up is gonna make any difference. The seal is whats suppose to prevent air from being sucked in right? So as along as the crank case halves are sealed up, it shouldn't be to critical. Or am I wrong? Thanks

 

[sledmasterr]

The mating surface of the pump housing and case is inboard of the mag side seal, without the proper sealant air could enter in this area and cause a lean condition. Good luck to you, hope you get her squared away....

 

[clutch man]

The mating surface of the pump housing and case is inboard of the mag side seal, without the proper sealant air could enter in this area and cause a lean condition. Good luck to you, hope you get her squared away....

Amen that is right on

 

[polarblu]

Amen that is right on

When a builder puts an engine together they put on whatever sealant they use on all mating surfaces. All those surfaces are cleaned and resealed. Seal gone then oil is all over the magneto, you will see it. As for sealants there are many, not just polaris, or loctite. If the surface is clean and flat then any good qaulity RTV or gasket maker works, i personally like the grey stuff from International used on Ford trucks. Apply and assemble in one try, if you let it dry even a few minutes your case half wont torque right. You will feel it, its like you are turning and turning and no click or beep from your wrench. STOP and start again.

 

[FEZ]

All things being the same as last season this is what I would look at

1) did I clean the carbs?
2) water in the fuel/bad fuel
3) do I use Isopropyl? If not, then refer to #2


Sometimes we don't find the answer. Rebuild it, make sure them carbs are clean and drain the fuel and refill. Don't forget a couple ounces of Iso.


And for the record, I have been running 87 Ethanol in my 00' 700 RMK for 10 years/5K miles without a single burndown. Mostly stock motor/pipe/carbs with 175-178 mains safely to -5 in MN.

 

[polarblu]

All things being the same as last season this is what I would look at

1) did I clean the carbs?
2) water in the fuel/bad fuel
3) do I use Isopropyl? If not, then refer to #2


Sometimes we don't find the answer. Rebuild it, make sure them carbs are clean and drain the fuel and refill. Don't forget a couple ounces of Iso.


And for the record, I have been running 87 Ethanol in my 00' 700 RMK for 10 years/5K miles without a single burndown. Mostly stock motor/pipe/carbs with 175-178 mains safely to -5 in MN.

Quickest way to see if you water in your gas is look!!!! It looks like a blob floating around at the bottom of your tank, it isn't easily disturbed so you can tilt the sled a bit and watch. A little bit of vibs from your engine will break it up but you will see what looks like bubbles in your gas. There should not be allot of bubbles in your gas (most sleds do not have a return line) especially large bubbles. Clean your tank and run clean gas and leave the rubbing alcohol in your first aid kit.
I have not seen water burn a piston.
Diesel is an easy way to see this Amoeba looking mass of water, water is heavier and sinks to the bottom, it also sticks to itself hence the blob.

 

[Givemeaboost]

I would check your waterpump and make sure the impeller is good or the belt is tight. I've seen two of the 700's burn down because of this and I have a 700 Yamaha that seized two pistons because the nut that holds the impeller on fell off. Ken...

 

[FEZ]

I have not seen water burn a piston

Funny you say this. I remember back in the 70's and early 80's we used to burn stuff down quite often between my family and one of my Dads friends. Between us there are 9 boys and lots of different manufacturers. Well after we started using the ISO the burn downs dropped dramatically.

Even as recently as 2003, I think, we were out west a Doo 925 was down a cylinder. Well after an hour of f'ng around I recommended he pour a cup of hot water on the carb of the dead cylinder. GUESS WHAT? It fixed it, YUP, ice in the carb. How did it get there? YUP! From the tank. What stopped it? ISO.

I have seen my share of iced up carbs and there ain't much besides water that turns to ice, at least where I come from Not too many ways for it to get inside a carb either last time I checked.

Now this may not be his issue, but all things being the same as last season, poor fuel would be high on my list of culprits. A little ISO will not hurt anything and if there is any water, it WILL take care of it.

Again, I could be wrong, just ask my wife! But to tell someone to leave it in their first aid kit is just not a very educated or informative response.

 

[polarblu]

Well thats your opinion! I prefer to give advice on how to fix a problem, not mask it.

 

[FEZ]

I have not seen water burn a piston.


And is this not your opinion?

Again, my advice was to clean the carbs, drain the fuel, add a couple ounces of ISO because 1, it does work and 2 it does no harm.

Why are you so against ISO? If after he drains all that he can out of the tank and some fuel is remaining, wouldn't the couple ounces of ISO take care of what water, if any, is left?

And my opinionis I think you need to get out more often if you think water does not burn down snowmobile engines sometimes.

 

[clutch man]

I recently burnt a hole in the mag piston of my '01 rmk 700. The hole is on the front left of the piston and it burned all the way down to the ring land. The head has been blasted with the shrapnel from the burn down and small pieces of aluminum are embedded in the dome of the head. Can I clean this up and re-use it or do I need a new head? I haven't determined the cause of the burn down yet but I was wondering if the location of the hole in the piston is any indication of where the the lean condition originated...assuming this wasn't due to incorrect jetting...
Thanks for any input

You burned the meg cyl, you dont have the proper sealent on the water pump housing. do the math it was a lean burn down. remove the water pump housing install a new seal and the proper sealent. install new polaris pistons.
Clean your carbs, have your heaqd cleand up at a mechine shop and you our good to go. ps with a small leak you will not get oil in there but at high rpm you will get air (a lean burn ). do not use an rv sealent.
I run a snowmobile repair shop and have seen this hapen, and had to fix them.

 

[rmkrazi]

You burned the meg cyl, you dont have the proper sealent on the water pump housing. do the math it was a lean burn down. remove the water pump housing install a new seal and the proper sealent. install new polaris pistons.
Clean your carbs, have your heaqd cleand up at a mechine shop and you our good to go. ps with a small leak you will not get oil in there but at high rpm you will get air (a lean burn ). do not use an rv sealent.
I run a snowmobile repair shop and have seen this hapen, and had to fix them.

Well it gives me peace of mind to know that. As for the bonding agent, how much should I apply to the housing and where at? I would assume just a small bead around that machined surface of the housing should be sufficient unless you say otherwise.
Thanks again all for the input