New saw builder needing advice.

[Tinman204]

Hey everyone. I'll try and keep this brief.

After doing the top end/carb on my last pick up a late model stihl ms260 I got the CAD bug.

Picked up another ms260 pro from kijiji for $40 CAD.

Soon as I pulled it over i knew the engine didn't feel right. Piston rings are stuck, piston is scored, exhaust side of cylinder has some aluminum transfer. Cylinder looks salvageable.

I cleaned up the saw , made block off plates for the exhaust and intake.

I did a vac and pressure test . First 2 pressure tests failed. Found a huge leak at the compression release, it had carbon built up on it, I cleaned it good put it back in and did another test.

It passed the test. Did soap and water in the pressure test just to be sure and no bubbles anywhere.

So I pulled the top end. And starter looking at the bottom end.

The wrist pin and connecting rod move freely and look good.

The crank is tight, it spins but the bearings feel like they are on their way out. Defiantly seized bearings in the saws future of someone tried to run it.

So my question is if the saw passed a vac and pressure test what would cause the bearings to fail?

I guess having a leaking comp release is the best thing for a saw. The leak was slight but it was there for sure.

From the plug, muffler and top of the cylinder I'd say this saw was pretty rich most of its life.

Any thoughts?

 

[Ozhoo]

You mentioned pressure but did you conduct a vacuum check? Crank seals fail under vacuum long before they fail under pressure.

 

[Tinman204]

Yes I did a vac test @7.5lbs . It passed.

I expected the crank seals to be bad just by the way the saw is burnt up. It's also an ms260 and I've heard those are prone the failures on the clutch side.

Maybe my test results are wrong.

 

[Tinman204]

I'll add that my last ms260 that I rebuilt had a top end that looked identicle fo this one. That one also passed a vac and pressure test.

Chocked that one up to bad tuning.

 

[Hdtoolmkr765]

I've had a lot more saws with scored pistons and good crank seals than ones with scored pistons and bad crank seals. Lots of reasons for this, bad fuel mixture, leaking intake boot, leaking decomp valve, someone that didn't know how to tune a saw and just thought their saw ran a lot better with the H screw closed, it's not always a bad crank seal that scores a piston and cylinder.

As far as bearings failing, that can happen for reasons such as normal wear, bad fuel mixture, cheap oil over long period of time, running chain too tight etc.

 

[Tinman204]

I've had a lot more saws with scored pistons and good crank seals than ones with scored pistons and bad crank seals. Lots of reasons for this, bad fuel mixture, leaking intake boot, leaking decomp valve, someone that didn't know how to tune a saw and just thought their saw ran a lot better with the H screw closed, it's not always a bad crank seal that scores a piston and cylinder.

As far as bearings failing, that can happen for reasons such as normal wear, bad fuel mixture, cheap oil over long period of time, running chain too tight etc.

Thankyou

This is the kind of experience that I lack.

I had a better look at the bottom end and it's very clean. Too clean for a 2 stroke, there should be way more oil residue in there.

Also the comp release was sticking open slightly. I'm guessing that would make the saw race.

Oh well I'll split the case this week and start there with new bearings and seals. Then I'll do the top end and finish up with a carb rebuild.

Was going to port it but I think I'll get it running before I do any porting.

Thanks for the help.

Have a guy wanting to sell me an 084 that needs some work so this whole CAD thing is going to get out of hand.

Be nice to have a milling saw................

 

[Hdtoolmkr765]

Just make sure the 084 muffler is in decent shape, those are getting tough to find and are somewhat expensive when you do find them. There are a couple on feepay lately, but normally there are not many. In fact a lot of 084 parts are getting tougher to find and more expensive.

 

[Tinman204]

Yeah I did some reading on the 084 on here and read about the mufflers as well as how a lot of parts are no longer available.

I'll probably only pick up that 084 if it's in decent shape. May be a neat saw to put on the shelf and look at.

My 038 mag is enough "big saw" for me.

 

[Hdtoolmkr765]

Absolutely, if it's in decent shape, I'd buy it, I have 3 runners and another one in a box, I'd still buy another one if I ran across a decent one and the price was right. I like 084s.

 

[Tinman204]

To be honest I thought the guy meant an 088 as I'd never heard of an 084.

Have to wait and see if he ends up selling it.

 

[Hdtoolmkr765]

CAD is a wonderful thing, you're in the worst place for therapy...

 

[Tinman204]

Ha ha,

I'm a collector at heart, I'm in treatment for what we call GAS (Gun Acquisition Syndrome) on other forums so chainsaw collecting will come natural to me.

 

[Hdtoolmkr765]

They somehow go hand in hand for me as well, I've been collecting 1911s and Belgium made Brownings a lot longer than I have been collecting saws.

 

[Tinman204]

I like bolt action military rifles, mostly from ww1.

Just got my RPAL so the canadian gov says I can now own pistols. A high power and 1911 are top of the list.

 

[Tinman204]

Had some time after work this afternoon so I went into my basement shop and pulled down the powerhead right to the bare cases.

Pressed out both bearings and the big bearing was very close to being piled up. The small end had a small piece of metal in it, looks like a piece of the race broke.

Gave the whole saw a bath and it actually cleaned up pretty well.

Told my wife I was going to sell it but I may keep this one. Its mechanically very good and it's in a more used condition. My current 260 is minty minty and it would be a shame it beat it up. May keep this one as a daily driver.

Should I use factory stihl crank bearings and seals or are aftermarket ok?

I've been happy so far with the aftermarket farmertech piston in my other 260. 30 tanks or so later and the piston still looks new. Makes me wonder about seals and bearings?

 

[bulletpruf]

Had some time after work this afternoon so I went into my basement shop and pulled down the powerhead right to the bare cases.

Pressed out both bearings and the big bearing was very close to being piled up. The small end had a small piece of metal in it, looks like a piece of the race broke.

Gave the whole saw a bath and it actually cleaned up pretty well.

Told my wife I was going to sell it but I may keep this one. Its mechanically very good and it's in a more used condition. My current 260 is minty minty and it would be a shame it beat it up. May keep this one as a daily driver.

Should I use factory stihl crank bearings and seals or are aftermarket ok?

I've been happy so far with the aftermarket farmertech piston in my other 260. 30 tanks or so later and the piston still looks new. Makes me wonder about seals and bearings?

If you're going to keep the saw, I wouldn't shy away from aftermarket bits. But if you're going to sell it, go with OEM; aftermarket parts hurt resale value.

 

[b fish]

Stihl parts in the Heart of that Sweet Saw!

 

[Little Al]

Stihl parts in the Heart of that Sweet Saw!

Could I ask why? in terms of bearings there are several company's that produce bearings superior to OEM

 

[cuinrearview]

Could I ask why? in terms of bearings there are several company's that produce bearings superior to OEM

Do you have a source for a Nachi, SKF, Koyo, or the like for the PTO side of this saw? If so, please share...

 

[Little Al]

Do you have a source for a Nachi, SKF, Koyo, or the like for the PTO side of this saw? If so, please share...

We used to obtain SKF through Bearing Boys may be a No No for you as its a UK company I'm most surprised there is no up market bearing outlets in the US