M7 melt down analysis

[sra1218]

The mapping he chose may have been too lean for the conditions.

 

[sra1218]

hmmmm

well i started pulling things off today to get the motor out for rebuild. i was removing the throttle bodies when i heard something hit the belly pan. It was a torn up white piece of plastic. so i decided to pull the recoil Assembly. the photos show what i found.


could the rope getting wedged somewhere, leaving the pal engaged on the flywheel, thus destroying the pull start cause the motor to pop? I know someone mentioned it earlier.

 

[Blk88GT]

I've had my recoil come apart, but it never burned down. I'm not sure if it's possible or not? Interesting thread!

 

[sledtahoe]

stator

I would be worried about the stator getting damaged, better look that over..

 

[vinpie1]

We are going to rebuild his motor in the next few days. I will look the stator over for sure. I still feel that its the PTO crank seal letting a little air in. I have only seen the detonation dimple on pistons that suffered air leaks.Thanks to all that have helped. This is why Snowest is the best!

 

[sra1218]

Tore her apart

Well, over the weekend vinnpie and i tore into the motor.

The damage is as follows:
Toasted cylinder (small chunk taken out, hangs fingernail easily)
Stator has chunks out of it
Ignition timing pickup has chunks out of it
flywheel scratched
the photo of the top of the piston shows the light dimple

Now thinking that when the ignition timing sensor went out it threw the timing of the motor off causing detonation. Still haven't ruled out a crank seal, due to the fact that it is on the pto side, and i am going to replace them anyway.

crank feels buttery smooth.

Hopefully the ecu is okay.......

If all of this was caused by a broken pull rope, everyone should take this as a valuable lesson. If your pull rope breaks, pull it off with a 10mm socket and ride it out.

here's to hoping ill be chirping broadies by next weekend!

 

[Thunder101]

Good job on the update.
Sure is a interesting mess you have there .

 

[arctic2009]

Well, over the weekend vinnpie and i tore into the motor.

The damage is as follows:
Toasted cylinder (small chunk taken out, hangs fingernail easily)
Stator has chunks out of it
Ignition timing pickup has chunks out of it
flywheel scratched
the photo of the top of the piston shows the light dimple

Now thinking that when the ignition timing sensor went out it threw the timing of the motor off causing detonation. Still haven't ruled out a crank seal, due to the fact that it is on the pto side, and i am going to replace them anyway.

crank feels buttery smooth.

Hopefully the ecu is okay.......

If all of this was caused by a broken pull rope, everyone should take this as a valuable lesson. If your pull rope breaks, pull it off with a 10mm socket and ride it out.

here's to hoping ill be chirping broadies by next weekend!

I could be wrong.. but that dimple is the mark to show whether or not the piston is in the correct way.

 

[sra1218]

I could be wrong.. but that dimple is the mark to show whether or not the piston is in the correct way.

the little mark is what tells you its in the right way, but the piston has a light dimple about the size of a dime. the other piston does not have it.