06 700 rmk rebuild question

ak2co · Oct 26, 2009

rebuilding my 06 700 rmk cfi(755)
I am trying to figure out the cause of the piston damage so after the rebuild it doesnt happen again
question 1) did the ring just break and casue all the scuffing and dome damage
question 2) lack of oil cause rings to break and damage (blew out oil lines and appeared clear)
question 3) detonation lead to damage (cfi sled and other cylinder good)

and lastly took it apart and the damaged cylinder had just oil in the crankcase and the good cylinder had coolant. is there suppose to be coolant in there?
any help would be a appriciated
this is my firsrt top end rebuild of a two stroke

guidoxpress · Oct 27, 2009

OMFG!!

thats by far the worst piston i have ever seen..lol..

where you riding it when it blew?

i am no motor exspert, so i will keep an eye on this thread

ak2co · Oct 27, 2009

never really "blew" just started backfiing at anything above idle, it was a slow deterioration. started low idleing and then reverse barely worked. changed plugs and stopped backfiring. rode for another hour same thing, pulled the the wire and limped it back on the pto

BIGGDAWG · Oct 27, 2009

Well to me that looks like detonation/burned piston that caused the ring to break.

possible causes: plugged injector, clogged fuel filter, air leak from torn intake boots or leaking base gasket

as far as coolant in the case that probably got there when you pulled the jug. no it shouldn't be in there with everything sealed but i have yet to pull a top end and not get coolant in the case.

just make sure you clean the case and crank good getting all the metal and stuff out. run a quart of oil in your first tank of gas, and i like to prime the oil system with a drill before i run them. i take my drill and chuck the oil pump in it and then fill the oil reservoir now run the pump and hold the lever in the full open posistion. watch the oil in the lines and run till you don't see air bubbles.

any more questions feel free to ask.

good luck

ak2co · Oct 29, 2009

thanks big d
all the marks on the top look square like the end of a ring, but i thought it was wierd about the pattern(just around the edges). the top middle of the piston is actually in good condition, which is why i thought ring breaking, or oil,
can a poo dealer check injectors?
i do have some minor cracks in the boots which i will get new ones but they both have the same crackage(word?) base gaskets were good
i will do what you recommended and clean the s out of it slap it a coulpe times prime and play
thanks again

BIGGDAWG · Oct 29, 2009

check here for your intake boots. a lot cheaper that the polaris ones. i just put new polaris ones on mine before i found these. i will be picking up a pair to have on hand.

intake boots

suitcase · Oct 29, 2009

"air leak from torn intake boots or leaking base gasket"
That would be what I would put my money on. Have had that happen, from an air leak in base gasket. Mine was not that bad not even close, it was 98 700 that I had put to many miles on with out puting any motor work in to it. I know better now.

XC700116 · Oct 29, 2009

Out of curiosity what did the head O-rings look like? Ever seen what happens when you put a bunch of water on a piece of aluminum that is just a few degrees below melting? I only say this because of the big azz hunk of material missing from the Exhaust side of that piston. Another thing to consider is to check if there is any damage to the exhaust valve on that side.

Besides the water my first guess would be a lean burn down (edges of piston and then ring break) probably due to a gasket or boot leak or foreign object causing a score and then a ring break. I recently had a 900 apart that had a piston/cylinder score and it didn't show any signs of lean or lack of oil. However, I have never seen a stock intake system have that kind of grime and gunk stuck on the reeds. I mean this thing is astoundingly dirty for a system that has no fuel going through the reeds. but then again that may be part of why it all sticks there too since there isn't anything to wash it off. needless to say I am not at all impressed with the stock intake on those sleds and how much junk gets to the motor.

ak2co · Oct 29, 2009

head o rings looked good for a quick inspection , but i knew i was getting new ones so i threw them away. i see what you mean about the water ...bomb on top of the piston.
i was curious about the boots though. i understand that with carbs (main jets) the fuel is metered before the boots and any air leak makes it lean but with injection it not that way right ?? so cracks shouldn't affect it ?? hell i dont know but the base gaskets were good
the reeds are ditry though and it has been rolled many times, (if anyting got in there, it must have been like a damn puzzle getting it into the cylinder,,, roll left 3 over 1 right 2 and INNNNNNN)

BIGGDAWG · Oct 29, 2009

well on a sled the injection system runs in an open loop all the time calculating fuel from tables comparing throttle position,rpm,temp and altitude and a more but it is calculating this on the known amount of air that can pass through the throttle bodies at x opening, if the boots are cracked and leaking, more air is entering the engine than is programmed in the tables causing the lean condition and burning the engine down.

does that make more sense? hope it helps to understand how it works.

ak2co · Oct 30, 2009

oh ya forgot about the tps, i was just thinking exhaust temp,rpm,,,,,,,...the other cylinder looked good though. i probably missed something on the take down. ill get ib together and be riding shortly.. just got 8 inches in denver

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06 700 rmk rebuild question

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