Piston Failure??? Stihl MS362s

[CR888]

I wonder if you have a defective coil that advanced the timing. The flywheel could have slipped as well. Has it been off.

I was going to post the exact same thing but I believe these failure are from more than 1 saw so kinda ruled that out. If it all happened on the one saw I'd toss that ignition coil as far as I could. Rarely ignitions are defective new, it can happen. Even rarer do new ignition modules work & be defective at the same time but its entirely possible especially in an odd case like this.

 

[CR888]

If they straight gassed one saw, it may be called operator error. If they straight gass the number involved, it is called "deliberately destroying" them.

a whole different story then.

Sure but these pistons look far worse than the average 'straight gas seizure'. All pistons are destroyed as bad as it can get.

 

[MrWizard]

Sure but these pistons look far worse than the average 'straight gas seizure'. All pistons are destroyed as bad as it can get.

All of my research and knowledgeable folk I've spoke with is that this breakdown of lubrication is almost the reverse of straight gas. Failing due to lack of oil, instead oil breaks down and fails at high heat. Not simple ring break down and metal to metal transfer, but instead an explosion of the piston creating the transfer of metal on all sides of the cylinder walls to the piston.

 

[tomdcoker]

Yup the underside of the pistons have the dreaded death ash.....not enough oil in mix. Well what do you think is going on?

What amount of fuel are they mixing at a time? Also if they are mixing a large container ( 5 Gallon ) are they mixing it good. It is hard to shake a 5 gallon container. I had a customer a couple years back that told me had had burnt up 6 or 7 saws up in a year. Questioned him about it and the only reason we could think off was gas and oil not mixed properly. Tom

 

[X 66 Stang347 X]

running any E85?

 

[SteveSr]

I for one appreciate honesty and transparency. The reason I've put so much effort into this issue is I have 10 years experience and our Silver Tech has almost 3 years experience working on chainsaws. Reputation is a big thing in this industry.

Looks like someone needs to go work with these guys for a day.

One other thought... Are these saws put thorough any kind of break-in after they are rebuilt or just handed over to a saw jockey to run balls-to-the-wall. This might help explain your immediate rebuild failures. Adding more heat since they are not broken in might push them over the edge. I have broken several 260s and have definitely noticed a decrease in friction / increase in idle as the saw breaks-in. Older saws that run richer might be able to handle more break-in heat / abuse than these newer ultra-lean saws.

One more thought... Pre-ignition is caused by too much heat, too low octane fuel, or ignition timing too far advanced. Have you checked timing advance on a rebuild and compared it with another no-issues 362? Other way would be to swap out a coil just to rule out coil going wonky advance when it gets hot. These ignition modules have CPU processors in them which may not like the high temperatures that they are exposed to and go wonky when overheated.

One more thought... How are these carbs being setup? Are you tuning them for max RPM at shop temperatures (70F)? If so they will get considerably leaner at colder temperatures as the cold air is more dense. If I am tuning a saw at higher than the lowest likely operating temperature I usually leave it a little rich to account for this effect.

My $.03,
Steve

 

[SteveSr]

running any E85?

Will a saw even run at all on E85? That E85 is 15% gas and 85% ethanol.

 

[HarleyT]

Will a saw even run at all on E85? That E85 is 15% gas and 85% ethanol.

I have been running on ethanol for years!!

 

[X 66 Stang347 X]

Will a saw even run at all on E85? That E85 is 15% gas and 85% ethanol.

Yes it’ll run. It’ll run way lean and it burns real dry.
Joel at Stihl claims the TS500i will run and compensate for the extra fuel needed with e-85. He said it wasn’t advised and didn’t say how long it would do it but it did.

 

[SteveSr]

Yes it’ll run. It’ll run way lean and it burns real dry.
Joel at Stihl claims the TS500i will run and compensate for the extra fuel needed with e-85. He said it wasn’t advised and didn’t say how long it would do it but it did.

There is a BIG difference between a carbureted and fuel injected engine like the TS500i.

 

[MrWizard]

What amount of fuel are they mixing at a time? Also if they are mixing a large container ( 5 Gallon ) are they mixing it good. It is hard to shake a 5 gallon container. I had a customer a couple years back that told me had had burnt up 6 or 7 saws up in a year. Questioned him about it and the only reason we could think off was gas and oil not mixed properly. Tom

so this was one of our first questions. they have mix if I remember correctly 50 gallons at a time, then fill up their gas jugs from that container each day. I was still on the gas thing until our last rebuild we sent out which was destroyed with the motomix still inside the tank. said that it failed within that one tank full of motomix. which through me off completely on the gasoline issue, I did however find out the grade they're running is 87 Octane 100% gas.

 

[MrWizard]

Looks like someone needs to go work with these guys for a day.

One other thought... Are these saws put thorough any kind of break-in after they are rebuilt or just handed over to a saw jockey to run balls-to-the-wall. This might help explain your immediate rebuild failures. Adding more heat since they are not broken in might push them over the edge. I have broken several 260s and have definitely noticed a decrease in friction / increase in idle as the saw breaks-in. Older saws that run richer might be able to handle more break-in heat / abuse than these newer ultra-lean saws.

One more thought... Pre-ignition is caused by too much heat, too low octane fuel, or ignition timing too far advanced. Have you checked timing advance on a rebuild and compared it with another no-issues 362? Other way would be to swap out a coil just to rule out coil going wonky advance when it gets hot. These ignition modules have CPU processors in them which may not like the high temperatures that they are exposed to and go wonky when overheated.

One more thought... How are these carbs being setup? Are you tuning them for max RPM at shop temperatures (70F)? If so they will get considerably leaner at colder temperatures as the cold air is more dense. If I am tuning a saw at higher than the lowest likely operating temperature I usually leave it a little rich to account for this effect.

My $.03,
Steve

my silver tech built these and set them imo a little too lean, after his break in he set them at 13,3. the next one which I will have control of will be broken in and ran about 12,5 to 12,8. I tend to break mine in a little longer than our silver tech. I will actually check timing, stihl tech didn't mention the timing being a possibility his conclusion was simply user error. I understand you have broken those 260s, but did you ever see failures of this level?

 

[MrWizard]

Yes it’ll run. It’ll run way lean and it burns real dry.
Joel at Stihl claims the TS500i will run and compensate for the extra fuel needed with e-85. He said it wasn’t advised and didn’t say how long it would do it but it did.

pretty excited about the 462 as well as the 500i

 

[ericm979]

Stihl calls for 89 octane in the manual. I've used 87 without issue in some of my saws but that doesn't mean that all saws can. Tuning a little lean or ignition a little advanced combined with low octane could cause detonation like what damaged that first set of pistons.

 

[cedar rat]

I looked at the pics several times yesterday and read this thread a couple times. I just don't see how someone could do that kind of damage cutting wood.

I wonder if the saw was left idling with the chainbrake on for a very long time, say 45 minutes if that would cause this destructive over heating?

Like OP said, how could a saw get that hot without the operator knowing there was something wrong?

You have me intrigued, I hope to see an update as to the cause!

 

[t0mm96]

Might be bleach in the fuel.
Some angry employee, or bad competition?

 

[Mauser]

I wonder if the saw was left idling with the chainbrake on for a very long time, say 45 minutes if that would cause this destructive over heating?

Idling with the chain brake on is never going to hurt anything - at idle, the clutch should never engage the chain sprocket, so the brake makes no difference at all.