Bad piston??
- Thread starter rocks rev
- Start date
DETO.......looks like it was under octane to me..or to much timing....
what were the conditions when it went? super hot temps could do it as well...
It didn't blow up, I was tearing it down to part it out and found this. New top-end with about 200mi. on it. I would add 1 gallon of Av-gas with each fill-up so octane should have been fine. Have never messed with timing and had RKT's MPEM reprogram.
At any point in recent rides where it felt like it powered out? It definetly hit deto..thats why the piston dome is melted..looks like it was riich enough which then points to octane, timing or heat....
M
mike_s
Well-known member
Timing, while possible, is doubtfull in this instance. Usually when the timing is too far advanced, or too high of heat range plug is used, there will be a crater directly under the spark plug. I dont see that here. I am guessing a combination of low octane/ bad fuel combined with high engine temperatures caused this near failure. the piston wash looks alright signifying the mixture was not overly lean, which leads me to say poor fuel quality or low octane/engine overheat.
With the RKT kit were you running his higher compression head? 14.1-6-or 8? What elevation?
With the increased compression comes increased need for octane. Maybe one gallon of Avgas (100LL) in a 12 gallon tank was not enough.
Maybe needed a gallon or gallon and a half of full 110 or 3 gals. of 100LL.
Just some thoughts.
With the increased compression comes increased need for octane. Maybe one gallon of Avgas (100LL) in a 12 gallon tank was not enough.
Maybe needed a gallon or gallon and a half of full 110 or 3 gals. of 100LL.
Just some thoughts.
S
sledsrock
Well-known member
Remember 'wash' is an average at best, unless you're borescoping on the mountain - even then it takes time to change. Them pistons were extremely hot at the exhaust port, hot enough to distort the forged alum. Could be rich as crap in the middle and scary lean up top. When you did plug checks what did the top and mids look like?
At start of season (new pistons) I started with 2 gallons of AV and top off with 91(supposably) then after each ride add a gallon of AV and top off(usually 6-7 gal.) I switched sleds from my 04 to my 05 and all I did was put in 370 main jets. The 05 was orignally set up for a SLP pipe/can and 14.6 head 4 years ago so maybe it was lean up high. LIVE and LEARN I guess, atleast the 05 With an 860 im getting is set up already.
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sledsrock
Well-known member
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do tell what head are you running?
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I guess that's the risk you take when riding a doo...
WHATEVER!! It doesn't matter what you ride, all I know is "STOCK" SucksI guess that's the risk you take when riding a doo...
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The head with my bad pistons? or on the 860?
WHATEVER!! It doesn't matter what you ride, all I know is "STOCK" Sucks
haha true that! I can't wait till I'm outta college and I have the time to learn and tinker with sleds more!
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sledsrock
Well-known member
The head on the 860.
I'm sure you seen it by now RKT
That damage was caused by bad gas paired with high compression. I also think 370 at our elevation is a tad lean. You may also want to raise or shim the needle up 0.5 or 1 position also.
IMO, most deto and burn downs happen at the mid range and the bottom of the main jet cycle.
IMO, most deto and burn downs happen at the mid range and the bottom of the main jet cycle.
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