Sled is a 2007 mxz xrs 800. First motor blew mag side piston deto, new crate engine with new carb boots blew mag side piston after 1 season. There is a split in the y pipe could this be causing this condition?
What could of caused this?
- Thread starter 2010rmk800
- Start date
what head? Typically a split in the Y is good, But not in a Motor! very Bad
Last edited:
There is a crack in they pipe in the center on both top and bottom I took a pic with light in manifold to see it better
Another
M
From what i can see in that picture, it looks like severe detonation. Had to be goin on for a while to errode that much of the piston crown. Could it be the y pipe? Possibly, but i wouldnt thinkma crack that small would cause it unless youre running on the ragged edge already.
unless that crack opens up more with heat it does seem small and being in the center shouldn't your other side show some symptoms as well..??
no modifications..head shave etc..??
no modifications..head shave etc..??
anyone else notice how clean the top of the piston is? only 2 things I know could cause that to a year old piston.
Last edited:
I bought the sled like this so I don't know a lot of history but I know he had a can from a 600 put on it and the only thing I can find is the split in the manifold both top and bottom. I was thinking the same thing that both pistons should have looked close to the same but they dont.
89sandman care to share?
well its totally washed so unless there's been a major water leak in that cylinder its running massively rich on at least that side. what does the other piston look like? does it look like its been burning right. is it carbed or efi?
M
Those arent the only things that will wash the piston crown of carbon. Detonation or preignition can also leave the piston crown nice and clean as the shockwave the they create knocks it loose and removes it as well. Had it happen to me many many times, only thing that gave the hint of what was goin on were the holes in the piston exactly in the center of the crown, or the major errosion around the exhaust port.
On edit, do i see the beginnings of a crater on that crown, or is that a drop of oil?
B
It could be the can. I rebuilt an 800 once that had a 600 can on it. I don't remember the brand but it was chrome. The inlet pipe to the can was 1/4" smaller diameter than the stock 800 can. The inlet pipe to the can was also blued pretty bad. Replaced pistons & can & never had another issue. I'm convinced the 600 can caused the burn down in that case.
I don't think its the can...
you say it blew the same side after one season on the new crate engine , so what kind of season,how many miles did you get on it...a hundred,1500 hundred..??
It will give an idea of the extremity of the issue if it can be related to the duration..
you say it blew the same side after one season on the new crate engine , so what kind of season,how many miles did you get on it...a hundred,1500 hundred..??
It will give an idea of the extremity of the issue if it can be related to the duration..
Sorry guys for taking so long to get back been crazy busy. I bought the sled like this and all he told me was there was a new crate motor in it the beginning of the year and it blew in the spring maybe 4000kms. He said the old engine blew due to carb boots which were replaced I took better pics of both pistons side by side to compare it don't look washed like the previous pic did
Pistons
Exhaust side
you actually melted the piston...
the cracked ypipe will ADD un metered air (lean out)...add possible tight squish (I run the 8 hole gasket in ALL 800HO ptek) and possible low octane pump fuel...bingo
top of piston is just aluminum from the melted side...
rebuild...add 8 hole...add .010" shim to needle...drop mains to 430..weld y pipe...put in fresh gas...ride...BJ
the cracked ypipe will ADD un metered air (lean out)...add possible tight squish (I run the 8 hole gasket in ALL 800HO ptek) and possible low octane pump fuel...bingo
top of piston is just aluminum from the melted side...
rebuild...add 8 hole...add .010" shim to needle...drop mains to 430..weld y pipe...put in fresh gas...ride...BJ
That sounds like he done this a few times,,,
M
One flaw in this theory, the crack is directly in the center of the cylinders. It would add equally to each. Only the one had a problem. Look at the crank seal on that side, also check that the pulse line isn't leaking. You have an air leak on that cylinder someplace. My bet is it went down, previous owner threw a new piston and cylinder at it and never bothered to find the cause of the failure.
Last edited:
looks to me that the other piston wasn't going to be far behind the damaged one so I think in reality both cylinders were being affected by same issue which I reckon BJ is indicating..
