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Discussion Starter · #1 ·
I rebuilt a 700 motor and put the original cylinder head back on for the purpose of getting it running (fired in three pulls :div20: ). It was pitted on the PTO side. How badly will this affect performance?
 

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in my opinion one of 2 things caused this..... DET or water getting in the combustion chamber.... did you find any problem that would have answered why it happend? did you check the crank to see if it was in phase? blown head gaskets? the head should be replaced befor its riden , just starting it up for a min will not hurt it. If left like that it may put a strain on the crank due to differance in compression ?
 

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Discussion Starter · #4 ·
Originally posted by xc-mark@Sep 10 2005, 08:18 PM
in my opinion one of 2 things caused this..... DET or water getting in the combustion chamber.... did you find any problem that would have answered why it happend? did you check the crank to see if it was in phase?  blown head gaskets?  the head should be replaced befor its riden , just starting it up for a min will not hurt it. If left like that it may put a strain on the crank due to differance in compression ?
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I bought a 1999 700 XC SP over the summer. The motor came all disassembled in boxes. The PTO piston suffered a meltdown and the PTO cylinder was also gouged.
The PTO side bearings also failed and spun in the case. I figured the pitting was from the heat of the burn down. I don't think the head is warped since I have no coolant leaks or a sweet exaust smell.

Will the pitting cause a loss of power or premature engine failure?
 

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on my 99 xc 7 mod i detonated a piston and junked the cylinder and the head got beat up from the ring floating around in there. and when wee put the big bore cylinders fack on we just smoothed it out alittle. the comp was within 3 pound of the other one an ran just fine after tat for 2800 miles i had the sled.
 

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probably could just have some one recut the head and redo the squish band. als here is a pick of my melted pistion.
 

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If there is any differance in the cc of each chamber ,this will cause a in ballance in the comperssion ration ... this could cause problems down the road. It is possibe to recut heads , I am only guessing but I think your pits maybe to deep? did you find the problem why it burnt down? was there water in the fuel? dirt in the carbs? is the oil pump OK? One hole doesnt just fail just because..... I hate to sound like a broken record but every year there is some poor owner that rebuilds a topend and ends up redoing it the next winter because they didnt find what casued the failer. is the head full of dings or does it look like its melted away? just looking for clues at the seen of the crime!
 

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Discussion Starter · #8 ·
Originally posted by xc-mark@Sep 11 2005, 08:55 PM
If there is any differance in the cc of each chamber ,this will cause a in ballance in the comperssion ration ... this could cause problems down the road. It is possibe to recut heads , I am only guessing but I think your pits maybe to deep?  did you find the problem why it burnt down? was there water in the fuel?  dirt in the carbs? is the oil pump OK? One hole doesnt just fail just because..... I hate to sound like a broken record but every year there is some poor owner that rebuilds a topend and ends up redoing it the next winter because they didnt find what casued the failer. is the head full of dings or does it look like its melted away?  just looking for clues at the seen of the crime!
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I think the pitting may be too deep. It looks like it has melted away from severe heat rather then chipped. The engine came in pieces, I have had the carbs apart and they were clean. How would you check an oil pump to see if it is working correctly? The first thing I did when the engine fired was hold the oil pump wide open. It was getting lots of oil.

Would a crank seal seem like a probable cause of this failure? Could that cause a lean condition that generated enough heat to take out the crank bearings as well? Whatever it was took out the whole PTO side of the engine.
 

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Sharp edges in the combustion chamber will cause detonation. Try smoothing with a die grinder. Install the head and see how close the cranking compression is cyl to cyl. If it is within 5 lbs., it will be fine for trail riding.
 

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I agree with Pockets. Maybe sand any high spots down. Yes, the crank seal on the PTO side could have easily caused the melt down. The spun bearings could have caused the seal to go, or certainly made it near impossible to seal properly? Next question would be what caused the bearings to spin? Oil starvation? Rust due to improper storage/junk oil? Just wondering if the other bearings have been carefully checked, and wondering if it may be smart to replace them "just cuz" ?
 

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Originally posted by michahicks@Sep 12 2005, 06:58 AM
I agree with Pockets. Maybe sand any high spots down. Yes, the crank seal on the PTO side could have easily caused the melt down. The spun bearings could have caused the seal to go, or certainly made it near impossible to seal properly? Next question would be what caused the bearings to spin? Oil starvation? Rust due to improper storage/junk oil? Just wondering if the other bearings have been carefully checked, and wondering if it may be smart to replace them "just cuz" ?
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You realy dont wanna sand the high spots unless no other way , have you tryed to acid wash it?
 

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Discussion Starter · #12 ·
Haven't tries any acid wash. I did gently go over the pitting with fine sand paper but it didn't make much of a difference.

How could I check to insure the oiling system is working properly?
 

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premix in the gas tank,and monitor your oil usage in the resevoir
 

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Discussion Starter · #14 ·
I do have premix in the gas tank. 50:1, actually probably a little richer. I will keep an eye on the resevoir. I haven't run the engine too much because I don't want to overheat it idling in this warm weather.

So I guess the best thing to do at this point is search for a new cylinder head. Any suggestions? Should I stick with stock or are aftermarket heads worthwhile?

Also if I did purchase an aftermarket head how much would the jetting change? I have a very good setup from some members on the forum that I was going to be using this season.

Recommended jetting was 185/180.
 

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when you run oil in gas(in oil injected sled that mixes
the oil in the fuel pump) it makes the sled run lean
and you could melt it down.
 

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Originally posted by Seguin Interceptor@Sep 12 2005, 10:43 AM
I do have premix in the gas tank. 50:1, actually probably a little richer. I will keep an eye on the resevoir. I haven't run the engine too much because I don't want to overheat it idling in this warm weather.

So I guess the best thing to do at this point is search for a new cylinder head. Any suggestions? Should I stick with stock or are aftermarket heads worthwhile?

Also if I did purchase an aftermarket head how much would the jetting change? I have a very good setup from some members on the forum that I was going to be using this season.

Recommended jetting was 185/180.
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you shouldnt have to jet up much or any at all for aft head. i ran my 98 xc 7 with 12:5 to 1 head we jetted up one size no probs
 

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Originally posted by slo xc 7@Sep 12 2005, 02:31 PM
when you run oil in gas(in oil injected sled that mixes
the oil in the fuel pump) it makes the sled run lean
and you could melt it down.
YA YA,,I know,but when did you ever here of it happening to someone??
 

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One option would be to send the head out to Indyhead on this site , to get the head cleared up and recut to his specs.
 

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Originally posted by ivar@Sep 13 2005, 09:50 AM
One option would be to send the head out to Indyhead on this site , to get the head cleared up and recut to his specs.
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samy guy did my motors and heads. but he has a real problem getting things done in a timely matter
 
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