Burnt up another piston and cylinder
- Thread starter DRoZ
- Start date
In my experience this type of failure is caused by detonation. I would definately check the ignition timing. Run a lower heat range plug. What fuel are you running?
I live her in Oregon as well (and only ride the dunes) and that picture is identical to my daughters motor last year. That is caused from a lean/detonation condition. Im sure just before she popped it was pingin to beat the band.
I did nothing more then re-bore, stepped up from 310 to a 350 main and raised the needle 1 clip position. I used OEM gaskets. Problem fixed.
She smoked like a pig at first, so I advanced the timing 2-3 degrees and she runs like a rapped ape now. Still has a lil oil at the exhaust flange and it's wet at the tail pipe. Plug is a dark milk chocolate.
I did nothing more then re-bore, stepped up from 310 to a 350 main and raised the needle 1 clip position. I used OEM gaskets. Problem fixed.
She smoked like a pig at first, so I advanced the timing 2-3 degrees and she runs like a rapped ape now. Still has a lil oil at the exhaust flange and it's wet at the tail pipe. Plug is a dark milk chocolate.
Wow I have never heard of this. I would have bet money that the timing was too far advanced. Can you explain how lean jetting can cause detonation? I would assume the piston would sieze before the engine got hot enough to detonate.
if youre lean or have an air leak, it can cause the top end to seize. the best way i could tell you is lean=not enough fuel and oil getting into the top end thus causing the piston to not have enough oil and get hot. when it gets too hot, it can detonate. i think. someone else will chime in though
at the dunes i always ran 32:1 fuel to oil ratio and out side the dunes i ran 40:1..so you always wanna thicken up with extra oil, and oil ur air filter very well, almost excessive to catch all the silica particles in the air
you are correct. the piston gets so hot from the lean condition that it ignites the fuel before top dead center and then the reaction from when the spark plug does fire it pre-ignites in the same place over and over. eating away at the piston just as you see in the pic.
Now, the other poster is right too. You can have your ignition too far advanced and have a similar situation, but the motor does get hot, in fact it stay cool.
Take a look at the original pic. See how the paint is baked off the cylinder ? that was very hot.
i'd like to add, just for reference
that my exact same fry job was at around 40 degrees that day, and i doubt heat was an issue ?? just cruising in 6th gear, if anything i was lugging it slightly at around 35/40 mph for about a mile up the hardroad, i was also fluctuating the throttle, so it wasnt at any specific rpm range for too long,
as this was only my 3rd ride on a fresh top end, and i was treating it as still under the breakin period
i was also running a hotshot cdi, which prolly advanced the timing too far ????, coupled with a green base gasket leak, but i heard no pinging ?????
my jetting has stayed the same for all of last season and this so far, it was not my jetting but the airleak/timing combo
that my exact same fry job was at around 40 degrees that day, and i doubt heat was an issue ?? just cruising in 6th gear, if anything i was lugging it slightly at around 35/40 mph for about a mile up the hardroad, i was also fluctuating the throttle, so it wasnt at any specific rpm range for too long,
as this was only my 3rd ride on a fresh top end, and i was treating it as still under the breakin period
i was also running a hotshot cdi, which prolly advanced the timing too far ????, coupled with a green base gasket leak, but i heard no pinging ?????
my jetting has stayed the same for all of last season and this so far, it was not my jetting but the airleak/timing combo
Yulp. The cylinder area can actually get so hot that the ground strap on the spark plug begins to glow red, and ignites the mixture even before a spark is initiated as well.
aaaahhhhhh, good explanation as to why they wont shut off sometimes too........... glowing ground strap !!!!!!
It's tough sometimes on dunes. I've seen quite a few perfectly fine bikes and quads hit the smoke signals. It's even harder being an air cooled engine on hot dunes and runny WOT a lot with a heavy load from the sand being on the engine. I like to think of it as thinking of yourself trying to run through shaded woods......now think of yourself trying to run just as fast on hot sandy dunes.....it's tough. I:I
wait til you have a 10 year riding one, having the time their life and them thinking that "extra" ting ting ting sound is a BAD noise until it's too late.
the worse problem with younger kids riding a bike that is out of tune like we speak of is knowing and recognizing the signs of trouble brewing. the other problem (at least with my kid) is that she like to get into 3rd gear (her favorite) and ride it like a sewing machine from BOG to WOT and back again, then cruising across the dunes at 1/3 throttle near max revs. The air velocity across the emulsion tube is cut in half and the carb slows its fuel delivery (but not air volume) and it leans out, start to ping and then BAM !!!! she dies.
that video was hard to watch, i bet that motor didnt last the rest of the season. but man these motors sure can revvvvvvvv
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