Big chainsaw troubles..... help needed

[hemlock]

Hello,
It looks like my Husky 365 just bit the dust, and I can't figure out what happened. It was cutting along just fine, then sputtered, rattled and died. Tried to pull it over, and there was nothing. The compression is completely gone (gage reads almost zero). It was not straight gassed. The only thing I can think of is an air leak some place, but it did not feel or sound lean. What else might have caused this? Any help would be great. I think I'm about to cry. Thanks

 

[arngnick]

How new is the saw? I had a buddy that the same thing happened to him during the first year of owning the new saw. The dealer blamed it on old gas with ethanol in it. I think the reluctantly covered it onder warranty.

 

[Ashful]

Rattle? No compression? sounds like a broken connecting rod.

 

[hemlock]

Rattle? No compression? sounds like a broken connecting rod.

Thats what I thought - but when I removed the plug and pulled it over, the piston was moving.

 

[Nixon]

Pull the muffler and see what the piston looks like. You may have torn an intake boot ,or lost a crankcase seal .

 

[MasterMech]

Rattle? No compression? sounds like a broken connecting rod.

+1 on pull the muffler. Broken ring? Husky is still a single ring design no?

Check the decomp valve?

 

[hemlock]

Pulled off the cylinder, and everything looks pretty good. Is it likely a crankcase seal?

 

[Ashful]

Just so we're not making any wrong assumptions, how exactly did you test compression? Be specific.

 

[MasterMech]

Check the decomp valve?​

 

[hemlock]

Just so we're not making any wrong assumptions, how exactly did you test compression? Be specific.

With a gauge. Pulled it over a few times. It hardly blew anything.
Master Mech - I'll check the decomp.

 

[HittinSteel]

Good news on the piston! Now you just have to find where its getting air.

Isn't compression made above the intake and exhaust ports? If so, what else could it be besides decomp, spark plug hole, cracked cylinder, stuck ring, ??????

I had the same situation on a saw I compression tested for a guy. Showed nothing on the gauge. Pulled the muffler and the piston and rings were in great shape. It stumped me (and he didn't leave the saw with me for further investigation).

 

[thewoodlands]

Hello,
It looks like my Husky 365 just bit the dust, and I can't figure out what happened. It was cutting along just fine, then sputtered, rattled and died. Tried to pull it over, and there was nothing. The compression is completely gone (gage reads almost zero). It was not straight gassed. The only thing I can think of is an air leak some place, but it did not feel or sound lean. What else might have caused this? Any help would be great. I think I'm about to cry. Thanks

How's your spark splug, did it blow out , might need a heli coil.

 

[Ashful]

How's your spark splug, did it blow out

That's why I asked how he's measuring compression. If it's not putting any compression on the guage, the spark plug is out of the equation.

If the decomp valve is good, then it's time to pull the jug!

 

[smokinj]

It was cutting along just fine, then sputtered, rattled and died

"The rattle" Small sound Rings broke Big sound crank?????? Either way air leak is not going to be a rattle. Iam with Joful time to pull the head and hope its rings.

 

[cnice_37]

I'd check to see if the ring moves by using a small screwdriver and pushing it through the open exhaust port (you removed muffler already.) My guess is its stuck, pretty common on these saws I believe.

 

[Fiziksgeek]

My first thought would have been a lean seizure.

 

[hemlock]

Put the cylinder back on and checked the decomp valve and it is also good. Guess I'm bringing it to the dealer. It makes no sense at all. Everthing that would cause a compression issue checks out, but it has 0 psi. I'm thinking something else is going on. This is out there, but could the flywheel be turning on the crank, and with the plug/gauge in, it creats just enough back pressure to cause the flywheel to turn on the crank, but with the plug/gauge out, it allows the piston to turn over, due to no back pressure? It's a stretch, but it all makes no sense otherwise.

 

[MasterMech]

Put the cylinder back on and checked the decomp valve and it is also good. Guess I'm bringing it to the dealer. It makes no sense at all. Everthing that would cause a compression issue checks out, but it has 0 psi. I'm thinking something else is going on. This is out there, but could the flywheel be turning on the crank, and with the plug/gauge in, it creats just enough back pressure to cause the flywheel to turn on the crank, but with the plug/gauge out, it allows the piston to turn over, due to no back pressure? It's a stretch, but it all makes no sense otherwise.

Pretty easy to yank the flywheel and look for a sheared key. Or just mark it and pull it over, recheck the marks.

 

[Nixon]

Pretty easy to yank the flywheel and look for a sheared key. Or just mark it and pull it over, recheck the marks.

Is that going to address the 0 compression ? Seems like a real mystery ..... 0 compression ,good decomp and plug , good P/C and rings .

 

[MasterMech]

0 compression ,good decomp and plug , good P/C and rings .

But Hemlock makes a good point that the flywheel could just be spinning on it's taper. If it ain't rings, piston, cyl, decomp or spark plug, I'm open to slightly more exotic theories.

 

[cnice_37]

Check the ring!!

 

[hemlock]

Pretty easy to yank the flywheel and look for a sheared key. Or just mark it and pull it over, recheck the marks.

Thats what it is. I feel like an idiot. I marked the flywheel to the nut, gave it a pull as though starting, and the flywheel is spinning on the crank. When you pull it over slowly or remove the plug, it grabs the crank and turns. Thing is, is this good or bad - and can it be fixed? Does anyone know the torque spec for the nut?

 

[basod]

Thats what it is. I feel like an idiot. I marked the flywheel to the nut, gave it a pull as though starting, and the flywheel is spinning on the crank. When you pull it over slowly or remove the plug, it grabs the crank and turns. Thing is, is this good or bad - and can it be fixed? Does anyone know the torque spec for the nut?

Is the flywheel keyed to the shaft? If not the timing mark will matter.
If you figure that out remove the plug and use a piece of clothesline stick down in the plug hole this will prevent engine turning over during tightening

What size is the nut? rather the shaft thread(it's somewhere in the 1/2,9/16,5/8,3/4- ball bark standard size. Just close doesn't matter if metric
I'd assume it's fine thread as well. could be anywhere from 90-200ft-lbs (though probably newton-meters)

Definitely use some red(higher temp) threadlocker or similar when reinstalling

 

[Ashful]

Definitely use some red(higher temp) threadlocker or similar when reinstalling

Definitely ignore anyone's home-grown ideas, and definitely follow the procedure in the shop manual.

 

[hemlock]

I put the flywheel back on (you can still see where the key was), and torqued it down, and it fired up. My question now is - is the key critical for power transmission, or is it strictly for timing? My guess would be that being a tapered shaft, that the key is primarily for timing but still am not certain. The key was cast right into the flywheel.