Stihl 084 Project

[Sawcanuck]

Hello!

Just got my recently acquired Stihl 084 in the mail the other day and had a little time to look at it today. I am a bit of a rookie but have learned a lot from lurking on this forum for a long time and doing a lot of reading. I was told it just lost compression and the guy figured his employee may have straight gassed it. Piston is badly scored.

I decided to do a pressure/vacuum test before opening it up to be sure there is no air leaks that could have caused the damage. Had to make a couple of block off plates to fit. I found it has a significant leak from the "port" below the decompression assembly. The little screw was there but was loose so I tightened it up and still leaking from the opening just above the screw. Now I have a couple of questions...

What is the purpose of this port?
Does a leak from this port indicate a faulty decompressor?
What is the purpose of the screw?
Should there be any sort of washer with the screw (there isn't one now)? I know this screw was loose/missing at some point while the saw was running since there is a hole burned through the plastic top cover in this location.
Could the screw being loose have contributed to the failure?



I will likely be looking for further help on this saw as I dig deeper. There are some things I already know that I will need but I am sure there will be more as I dig deeper.

Thanks for your help!

 

[alexcagle]

The screw is to gain access to the decompression port to be able to clean out any carbon buildup.
The screw doesn't use a washer, and can be sealed with loctite 266 red.
The decompression valve will leak under pressure and vacuum tests. That's normal.
A blockoff plug will seal it for testing, like this one. There is a tiny steel washer that is required to seal both the decompression valve and the blockoff plug.

 

[Sawcanuck]

Thank you for the replies. So just to make sure that I understand...

The opening on the side is where the decompressor vents to.
Air leaking here under pressure to the case has to be coming through the decompressor.
It is normal for this port to leak air while testing
The plug described above will close off the decompressor hole and the vent port.

If the decompressor is expected to leak under pressure/vac testing then would it not leak when the saw is running as well?
Would the little screw being missing or loose contribute to the failure of this saw?

Thanks!

 

[Sawcanuck]

Checked with my dealer and he said he was unable to get this plug anymore.