Stihl MS 290 Engine Failure

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This one is interesting, so I decided to post it for feedback. A fellow brought in a Stihl MS 290 that had been running fine but he said it stopped and could not be restarted. Seemed like no compression, so I decided to tear it down and rebuild it. I measured compression at 70 psi, so the top end was a gone goose. First find was a ruptured intake manifold boot. The second find was a missing piston snap ring that had come loose and wrecked the piston and rings. Here's the proof:
View attachment 756619 I inserted the scrap paper to better show the two tears in the intake boot. What I would like to know is which one failed first? The intake boot or the piston's snap ring that came loose and bounced around inside the combustion chamber until it tore up the piston, the rings, and damaged the cylinder?

BTW, the spark plug was dry as a bone as if it had been heated with a torch. And, the piston, rings, and cylinder are undamaged and clean on the exhaust side. WDYT?
I like these kind of posts I learn a lot reading reading them Thanks Doc
 
Obviously the boot was tore from flexing where it was clamped down and couldn't move. I don't see how the clip coming off could had any thing to do with that, but the boot being tore causing the lean condition, over revving and or heat likely would cause the clip to fail. OEM clip may of stayed put a bit longer then aftermarket but I don't think the final outcome would be much if any better.
 
Bull, torn boots don't cause the clips to fail.

Just because one finds a problem when going through a saw that died, doesn't mean that it killed it, or had anything at all to do with anything at all.

Kind of like blaming everything and anything on global warming.
 
Torn boots allow excessive air intake causing the engine to over rev and burn hotter like a torch when you increase oxygen to get that small blue flame to cut iron. The clip failed because of the heat and rpm,s and it happened to be the weakest link to those conditions. Clip finished off the engine before the other engine parts succumbed to heat or rpm. The boot being torn led to the effects of the major damage.
 
Torn boots allow excessive air intake causing the engine to over rev and burn hotter like a torch when you increase oxygen to get that small blue flame to cut iron. The clip failed because of the heat and rpm,s and it happened to be the weakest link to those conditions. Clip finished off the engine before the other engine parts succumbed to heat or rpm. The boot being torn led to the effects of the major damage.

If it failed under warranty, your description would be exactly what I'd write on the claim.
And nobody in the Stihl pipeline could argue the point.
Those saws running 14,000 ~ 14,500, no load isn't uncommon.
A good saw, but not designed for much over that.
Most leave the shop running very rich to slow them down.
 
I think "huztl/farmertec strikes again" is the best summation. Someone should start compiling these threads to paste on every "I wanna build a chicom 660" post.
 
Yeah, we can only assume. I would also like to see the other side of that piston. It is too shiny to be a 8 year old piston that suddenly lost it's clip. I have seen guys distort the hell out of them trying to install them, then try to rebend them back to original "shape".

It is very safe to assume that the parts are not oem. Or the work was done by a Stihl dealer, as the cost would be over $450 at the least.
 
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