Installing a CROSS PERFORMANCE cylinder Kit for my Stihl 084.

[sefh3]

Looks like it's scored from the carbon. Low quality of gas.

 

[Onan18]

Looks like a bit of scoring on that piston. A leak down test is pretty much mandatory before you tear it down.

What he said.

 

[quietfly]

I've only had the saw for about a month now and have only run maybe 2 tanks of gas through it. I use non ethanol 91 mixed up with stihl oil at 32:1

 

[quietfly]

So What would you guys all suggest I do before the tear down, and why? I know i should take it to have the compression tested. I've seen the leak down test suggested

 

[decableguy2000]

Please pressure and vacuum test before you disassemble, it will save you time down the road. As far as the small parts, I like use a plastic divided box, and take some pictures as you go. Also try to get a work shop/ service manual for the saw, the Stihl manuals are nicely written IMHO. You want to do these test before you tear it down so you know why it scored the piston. Several good videos to watch on it.

Jeremy

 

[beaglebriar]

The scoring on the piston makes me think it has been run lean at some point. Leak down testing will help you find the leak if there is one. Since you bought the saw second hand you really don't know the history and it could very well have been rebuilt at some point. Basically the scoring could be new or it could be from a previous break down. You need to figure it out before going further. I wouldn't be concerned with compression much.

 

[riverrat2]

I've only had the saw for about a month now and have only run maybe 2 tanks of gas through it. I use non ethanol 91 mixed up with stihl oil at 32:1

I'm inclined to believe it was that way when u got it,,, I agree it is carbon scoring from years of cheap fuel/mix, your two tanks through it didn't do that.....you would be surprised how well that piston will clean up!!! I need a decent used P/C if you decide to part with the old one!!!

"This is a straight swap, the saw is running pretty well right now " (Quote from OP)

if the saw runs good, sits and idles well, restarts well,,, why/how does it have an air leak??? it looks slobberingly fat to me not lean by any means

 

[quietfly]

I'm looking into doing a Leak down / vacuum check, although i might give in and take it to the dealer for that. So far the saw has been running well, so the question is is it possible the scoring is old?
I have the service manual and have been going over section 3 which explains how to disassemble the cylinder and piston. i've also found a few videos, although none in English on the 084.
This video was well made and although the pieces are different, the process is pretty much the same as whats described in the service manual

 

[jakethesnake]

Probably is old

 

[riverrat2]

please read post 27

 

[beaglebriar]

I'd agree that since the saw has been running well it's probably fine. For peace of mind personally I'd give it a thorough check up. Especially since the OP intends to use it for milling.

Here's a pic of saw I just rebuilt. That piston is still in the saw and runs beautifully. It's my personal saw. I probably would've replaced it if it were for someone else. This is just to give you an idea how bad they can look and still be OK.

 

[quietfly]

@riverrat2 we must have cross posted, i didn't see your post when i wrote my last. Yes she idles well will sit there and just idle away. The last owner told me he had her tuned fat for milling so i just left her there. At some point I should probably tinker a bit with the tune.

 

[quietfly]

@beaglebriar thanks for sharing that i feel alot better now, parts for this saw are hard to find and i was just thinking how screwed id be if the crankcase was damaged etc....

 

[riverrat2]

If it was mine, I would snatch the jug, and clean it up decarbonize it well, pull the piston rings and clean the ring grooves and clean the carbon off the top, that piston still has much life in it by what I see is left of the Machine grooves and really evaluate it... What you posted about the milling from previous owner fits perfectly from what I see in your pix'

I wouldn't be afraid to clean her up if it all looks good put a fresh set of OEM rings in it and run the heck out of it!!! post up some pics of the entire piston skirts when you get it apart

 

[riverrat2]

@riverrat2 we must have cross posted, i didn't see your post when i wrote my last. Yes she idles well will sit there and just idle away. The last owner told me he had her tuned fat for milling so i just left her there. At some point I should probably tinker a bit with the tune.

I tune all of my saws to where they just start to 4 stroke and then they clean up in the cut

 

[quietfly]

Since pictures are worth a 1000 words, i figured these moving pictures should tell a whole bunch.....

The wood is some hemlock from my mushrooming pile.
So, how does she sound to you guys, let me know.

 

[Redfin]

Really fat.

 

[beaglebriar]

Really fat.

Uh huh.

 

[riverrat2]

Lol is the chain on backwards???? as I thought Slobberingly fat

yes it is way rich, it does idle nice, take another video with it idling and rotate the saw like you would be falling a tree, from both sides and return to upright. if it continues to idle smoothly the whole time you don't have an air leak, after you shut it off check both ends of the crankshaft for radial end play

 

[angelo c]

Chris,
Get us a close up of the chain too.
And yes, it's wayyyyyyyyyyyyyy rich.