Stihl 390 chain saw decompression valve coming apart!

[shiftright]

Mr Jim,

I agree that the dealer probably could have fixed it a lot cheaper than what they quote me. Unfortunatly the saw was 2 years out of warranty so they did not have to do anything but they did choose to offer me a discount on new saw.

The cylinder on the saw has some slight damage on the head area, but the cylinder itself is still perfect. I'm going to clean up the head area a little and pop a new piston, rings & wrist pin in it. I have the OEM piston on order, but it is $80.00.

Is the piston that you spoke of an OEM part? I'm a little gun shy of off-shore parts  ;)

By the way, when I go to put this together were will I have to use that thin wall socket?

Thanks

[30dodgeboy]

Unless the knob comes off, and a bit of flattened bit of the stem wears out, the chances of the decompression valve falling into the cylinder are very rare.
You will need to open up the engine completely to do a thorough clean up.
This is because that 'rivet' like bit stuck on the piston is not the only component in the decompression valve. There is a mustard sized tiny steel ball and a tiny spring.These too must have fallen into your cylinder.
You can never know what kind of mayhem both these will create if left to roam around in the crankcase, especially within the crank bearings.

Joe

Sorry to bring up such an old thread, but...

I have a Stihl saw that grenaded the decompression valve when trying to start it.  The pin fell down into the cylinder and jammed the piston.  While the piston and cylinder appear OK, does anyone know exactly how many other parts there are to that decompression valve?  I assume the detent mechanism consists of spring loaded balls, but just how many are there?  I am planning on disassembling the engine to verify none passed through the transfer ports, but want to know how many other parts there are to that little troublemaker valve.  Thank you in advance,
Art

[joe_indi]

Art,

Three things can fall into the cylinder from the valve, the valve stem(the rivet shaped item), a small(tiny) steel ball and an equally small spring.

Joe