Compression Question

[pioneerguy600]

I had a buddy smoke a Sachs Dolmar 115 so bad that he thought the saw had terrific compression, he stood on my doorstep and showed me how much compression the saw had. I took the saw from him and with one long slow pull I told him he had badly scored the P&C. he argued that he had mixed the fuel oil properly and swore he only used fresh gas and the best oil, but when talking later with his wife she told me he was running the leftover gas out of his oil injected outboard motor in it at the end of boating season here.

 

[stihltech]

The thing is that there is no one test that will show the condition of a saw. The starter handle test without pulling the muffler and carburetor to see the piston condition is still just a guess. With out a pressure and vacuum test, grabbing on to the crank to check bearing play, and then taking things apart (carburetor, remove cylinder, check carb and fuel system), it is still only a guess. Visual inspection of parts is when you find the issue with the mechanical parts of the unit.
Of course, I still have the magic wand.

 

[Farmer_Nate]

Like a pro

 

[Lightning Performance]

The thing is that there is no one test that will show the condition of a saw. The starter handle test without pulling the muffler and carburetor to see the piston condition is still just a guess. With out a pressure and vacuum test, grabbing on to the crank to check bearing play, and then taking things apart (carburetor, remove cylinder, check carb and fuel system), it is still only a guess. Visual inspection of parts is when you find the issue with the mechanical parts of the unit.
Of course, I still have the magic wand.

If the visual inspection shows wear I'd image it needs replaced. How much measuring do you do is the real question. Gazing at a rig gap is one thing but how to check the wear surfaces on the crank?... hum. Are you measuring in mm, thousands or ten thousands?
What kind of clearance do run on your pistons?
Wrist pins?... And how do you measure those?
Just curious

 

[lone wolf]

The thing is that there is no one test that will show the condition of a saw. The starter handle test without pulling the muffler and carburetor to see the piston condition is still just a guess. With out a pressure and vacuum test, grabbing on to the crank to check bearing play, and then taking things apart (carburetor, remove cylinder, check carb and fuel system), it is still only a guess. Visual inspection of parts is when you find the issue with the mechanical parts of the unit.
Of course, I still have the magic wand.

I agree the best way to trouble shoot a saw 100 percent is too rip it down all the way and do a vac -pres test etc.
Seems a lot of trouble can come from bad carbs because of ethanol fuel.

 

[lone wolf]

If the visual inspection shows wear I'd image it needs replaced. How much measuring do you do is the real question. Gazing at a rig gap is one thing but how to check the wear surfaces on the crank?... hum. Are you measuring in mm, thousands or ten thousands?
What kind of clearance do run on your pistons?
Wrist pins?... And how do you measure those?
Just curious

I havent seen many wrist pins wear. Pistons should be replaced along with seals when apart.

 

[Farmer_Nate]

My first saw refresh, which occurred rather recently, I re-used the OEM piston with a new ring. The skirt had a polished appearance at the bottom where it had been wiping across the intake port for 30 years, but overall works fine and original machine marks were visible over most of the rest of the piston. New piston may have tightened things up a bit more, but it is O.K. as-is so far with the new ring.

It has new crank seals.

I was advised by others on the site to re-use certain parts shown in good condition. Things were checked.

 

[Evan]

Everyone one cuts corners, I used to too and that left me chasing my ass testing this cussing that when all along it was just leaking seals leaking rings shes just flat in need of some tlc and a good rub down

Often times with chainsaws the cover reflects the insides all the Tests in the world arent going to say it doesnt need seals or new piston if thats whatvis needed.

Now for the mist part theres nobreason for me to check compression or vac test a saw as ive got a pretty good feel for whats needed because the saw talks to me.

Kinda like listening to your wifes needs, with no tlc shel seemingly be fine then one day shes gone getting what she needs somewhere else.

 

[Lightning Performance]

I agree the best way to trouble shoot a saw 100 percent is too rip it down all the way and do a vac -pres test etc.
Seems a lot of trouble can come from bad carbs because of ethanol fuel.

I find intermittent seals that test good but leak on the pto side. Sometimes I spin the crank and the pressure bleeds off. The seal is usually hard. Wrist pins have been hit and miss from several AM companies. Being oversized if you use an OEM pin in odd pistons it's loose. I've had new pins OE too tight and most I'd bet just ram the pin in. It should be clearanced 0.0010 to 0.0013 dry fit and checked with a dial indicator in one tenthousands. Normally they fit fine in sets but not always even Meteor.

If the seal comes out the case gets flushed dry and the crank end play and radial movements get check with a dial indicator. If it wiggles at all it needs bearings so no need to measure anything. I'm betting many just replace the seal and send it. Checking the wear prone areas is normally done with a straight edge and some back lighting. Polishing the drum bearing area on the metal surface that had damage usually results in loose drums that wobble but not always. Many times that area becomes covered in plastic from the drum bearing, tarps, fishing line and string melted on the crank. I find little issues with the worm drive area on most saws. Flywheel side tapers are always checked. If the flywheel doesn't press fit tight by hand so it sticks good it needs to be lapped on. Lapping in flywheels with a built in key get ground out first or replace them. Checking the connecting rod endppay while in the cases but clean and dry is always a good idea if your not pulling the crank.

Doing all seems pointless now when we can ask the saw whisperer.

 

[Farmer_Nate]

Doing all seems pointless now when we can ask the saw whisperer.

I don't get the meaning of that.

Does that mean plugging in a newer saw to electronic diagnostics?

 

[lone wolf]

I don't get the meaning of that.

Does that mean plugging in a newer saw to electronic diagnostics?

Im guessing it refers to an all knowing person on here,sarcasm no doubt though.

 

[Farmer_Nate]

Yes, I wondered that, and hoping it was not I.

I don't profess to know it all.

 

[stihltech]

I do not know it all either. Just using the last 50 years as a Stihl tech for experience. If you don't have to make the same mistakes, it will save a bunch of frustration. I guess I am like the farmers insurance commercial.

 

[Farmer_Nate]

I do not know it all either. Just using the last 50 years as a Stihl tech for experience. If you don't have to make the same mistakes, it will save a bunch of frustration. I guess I am like the farmers insurance commercial.

This help prevent problems?

 

[stihltech]

It is amazing how many saws get repaired by fixing pressure and vacuum leaks.

 

[ZeroJunk]

It is amazing how many saws get repaired by fixing pressure and vacuum leaks.

Nor, how many times it is recommended for issues that have nothing to do with it.

 

[dmb2613]

25% of saw problems are gas related, 50% are operator problems and 25% everything else. I see a lot of Stihl techs that dont know their a$$ from a hole in the ground. Some are right sharp. I often wonder when I am at Stihl school why dont some of these guys sell cars or something. The ask the same dumb a$$ questions every year. Kept the rest of use in class much longer than needed.
I have fixed many saws over the phone lol