here are some pictures of the latest burndown ....not sure exactly what caused it ...since it is not my sled ...its a 14 year old kids sled.....i think it was a combination of bad gas ,low snow conditions ,and running it too hard ....the carbs were cleaned 2 days before this happened ,,,sled went 65 miles before this happened ,,,,,,,,after tearing it apart it looks to be ported looks good but a little thin in spots .....heres the pics let me know what you think ....i am looking to get a cylinder and have it ported to match any idea whos work this is ?
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daman
New member
Is there any melting of the piston edge,exh side?
no1chevyboy
New member
did ring locating pin let loose?
How does the crankshaft rod bearing look? It almost looks like it came apart, either way, I wouldn't assemble/run this engine without getting the crank rebuilt ect...
no1chevyboy
New member
how many miles on sled ?
yes the edge of piston is burned off on the exhaust side ...burned so much i think thats why the ring let go ....sled has 2500 or so on it .....was told sled started missing not sure how far it was drove this way ....so they shut it down and went for the truck and trailer ...drove sled on trailer and come home and drove it off trailer and on to another trailer and thats when it started making alot of noise ...so it was shut off ...when i got there the motor olny turned half way and stopped ....the bottom end looks and feels good .....wasnt 99 under crank recall ? dealer says no ??
The 99 crank is not good either. The pins are just glued, not welded. Get them welded while you have the crank out.
daman
New member
i would say thats why too,bad gas and bad jetting is prabably why sheYA*AM*A*HEAD said:
went down,a 14 year old wouldn't have used priemum fuel.Some studded 700's in '99 had crank problems yes.
I suspect a leak at the carb boots or some other condition causing it to be lean and burning the piston top at the exhaust port. Very possible that this condition was created during the carb cleaning. It is just to close after the carbs were removed and reinstalled. Now if symptoms were already occurring before the carb cleaning (low power, etc.). Then the damage likely started before then and may be caused by something else. I cannot blame the gas unless I know it was poor. It is just too easy of a knee jerk reaction to blame the gas. Unfortunately many a mechanic takes this easy road out. Instead, I like to find definite proof before simply rebuilding the engine. I have had far too many simply repeat the process again sometime after the rebuild. (got one in the garage right now) Some happen right away, and some down the road.
This is why I like the concept of a low pressure crankcase leakdown test like the one used by Skidoo on the rotax engines. (not the common cylinder-only leakdown test) I think that this might find contributing factors that would otherwise be overlooked.
As eluded to by others, crank phasing and the bottom end should definitely be checked.
This is why I like the concept of a low pressure crankcase leakdown test like the one used by Skidoo on the rotax engines. (not the common cylinder-only leakdown test) I think that this might find contributing factors that would otherwise be overlooked.
As eluded to by others, crank phasing and the bottom end should definitely be checked.
daman
New member
it's not a knee jerk ding it's a fact,,the gas of today just sucks,,not like back when that sled rolled off the assembly line. that was one nail in the box IMO.Ding said:
staggs65
Moderator
doesn't appear to be any piston wash either, plenty of crud though
sounds like you have had a 14 year old kid 
.... i have got several versions of what happened ....i cleaned the carbs and if i remember correct it is stock jetting ....and when i pulled the plugs they were black ....sounds like i need to split the case and investigate deeper ? ....or just throw in a spare motor i have on the shelf ...and save some time and money ...and sell whats left of the old motor .....to help the kid get some money back since he has almost twice what the sled is worth in it ....
.... i have got several versions of what happened ....i cleaned the carbs and if i remember correct it is stock jetting ....and when i pulled the plugs they were black ....sounds like i need to split the case and investigate deeper ? ....or just throw in a spare motor i have on the shelf ...and save some time and money ...and sell whats left of the old motor .....to help the kid get some money back since he has almost twice what the sled is worth in it ....
daman
New member
Black as in rich??
here is a pic how do they look to you ,,,cause i know you have seen more than i have ....the 2 good cylinders the plug looks good on one side and if you flip it over the other side looks new ...and the bad cylinder is black all the way threw ...dry black carbon ....also here is the pics of the other pistons what do you think of the wash ?
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mopar1rules
Active member
she was lean for sure. no piston wash and the oil was burning to the head domes from all the heat.
all 3 lean ...guess its time to find out why lean on all 3 .....makes me wonder about the jetting now ,carb boots leaking , would crank seals do that ? someone point me in the right direction to look cause i am not gonna rebuild this til i know for sure what caused this ...thank you to all you guys for helping me out on this one ...as i am doing all this work for free since it is owned by a 14 year old kid and his dad has passed on .......
Lean...no wash, also looks like "Grey Death" on the one shot of the plugs. Black can really fool you some times. Is it possible he ran low, and out, of fuel while on a wide open run?
you think the floats set wrong ? ill add that to the list to look at ...800vmax4 said:
I definately would check the floats,as well as everything else to do with the carbs... it is quite possible and likely something occurred during the carb cleaning. I would make sure all the carb settings are stock, needle clips ect. Also check the fuel tank filter/pickup and the little fuel screens under the float needle seat. Check reed cage gaskets/installation...I have heard of gaps occuring when installing reed spacers as well.
My .02
My .02