Help on a Husky 262XP

[purdyite]

I'm at a loss. Saw won't fire AT ALL. Here's the rundown:
cleaned the carburetor, set to factory one turn on hi and lo.
New fuel line.
Checked flywheel key alignment.
New spark plug.
Disconnected the coil kill wire to test for a grounded coil.
Tested for spark--ok. Tested plug--ok.
added fuel mix to the carb throat.

In every case, absolutely no response. Then I checked compression. Now I don't have a tester that is specifically for small engines, but without pressing the decompression valve, I never got above 80 pounds. Never seen one this low before. With compression that low, will it not even pop to ignite the fuel? I looked into the intake and the piston/cylinder wall look ok. Looking at the exhaust side the piston looks pretty bad. I first thought I had an electrical issue, but coil/wire/plug seems fine. I need to know if I'm on the right track thinking that a new piston/cylinder is in order. Thanks for any insights on this. Doing this for a friend.

 

[Tobystihl]

Pot and piston is the order of the day

 

[Chevboy0167]

Can you post a clear pic of the exhaust side piston here for us?

 

[holeycow]

My 90 is quite a hard pull. And hangs by the pull rope and very, very slowly goes down. At 80 lbs it most certainly will not be like that.

Coil gap? Flooded?

 

[Bob Hedgecutter]

All you need is, fuel/air in combustible levels entering the compression area- spark- timing of said spark and compression.
So guess which one you are missing?

If the piston is toasted- its toasted- but if you were to remove the plug and chuck a teaspoon full of oil down the plug hole, swill it about a bit, put the plug back in, lead back on and try to fire it up then........?

 

[purdyite]

Photos from the exhaust--first image you can see the ring; second is the piston wall, third is the back of the cylinder

 

[Gord404]

yup toast- might be mistaken for compresion for a half stuck piston- pres-vac test before you pull it down to see what caused that- pistons don't normally wake up in the morning and plan to die that day

 

[irhunter]

pres-vac test before you pull it

+1 for pressure and vac test before unbolting cylinder.

Also...do not order any parts right now.

Roy

 

[Bob Hedgecutter]

Piston being in backwards didn't help your cause.

 

[eb20]

.

good eye Bob !

 

[purdyite]

Got a little more info from the owner's son...Dad is a wood cutter, worked for a ROW clearing company. He said he "thought it was losing compression". When I got it the tank was dry, clearly hadn't been used for some time. The backward piston came to me that way. I will pressure/vac test when I break into it.

 

[cscltd]

Maybe the clearing company rotated the piston when the original exhaust side was scored to get even wear on piston??-lol

 

[steele_109]

I just rebuilt a husky 353 for a tree service.When i opened it up it wasn't scored but the piston was backwards.The pin had wore a channel below the exhaust through the plating and into the aluminum and above the port was another channel just not through the plating.The guy who brought it to me claimed it had never been opened up.

 

[purdyite]

Well, the piston and ring was TOAST. New piston/cylinder, compression went from 80 to 140. Did a pressure/vacuum test on the old cylinder/piston; wouldn't hold any at all. Runs very well now.

 

[purdyite]

Well, the piston and ring was TOAST. New piston/cylinder, compression went from 80 to 140. Did a pressure/vacuum test on the old cylinder/piston; wouldn't hold any at all. Runs very well now.

 

[Bob Hedgecutter]

Yeah now hang on just a bit- 140 is okay, but not great yet- hopefully the ring will bed in and it comes up a bit.

But, the second bit? A worn piston rings/cylinder scenario does NOT effect a pressure and vacuum test. This tests the combustion chamber and crankcase areas for air leaks- putting a "new" top end on a leaky case (main oil seals etc) will boost compression and get the saw running for a short time- but if the air leak is still there- well then it becomes "we do it nice, coz we do it twice."

 

[purdyite]

I DID check the crankcase, no leaks--crank seals good.

 

[Bob Hedgecutter]

I DID check the crankcase, no leaks--crank seals good.

Then how, pray tell- did the old top end not hold pressure- yet did after fitting the new one?
That statement does not compute.

From post #14 Did a pressure/vacuum test on the old cylinder/piston; wouldn't hold any at all.

 

[purdyite]

I also pressure tested the cylinder at TDC without the intake/exhaust blocked off, just to see if there was any resistance at all. Could send a pic, but the ring was bound up with aluminum transfer and wasn't sealing at all.

 

[Bob Hedgecutter]

I also pressure tested the cylinder at TDC without the intake/exhaust blocked off, just to see if there was any resistance at all. Could send a pic, but the ring was bound up with aluminum transfer and wasn't sealing at all.

Okay, that is not how a pressure test works.
Trying to pressure test the combustion chamber alone will get leak down past the ring- more so with a damaged/worn out ring- but also with a brand new one.
Only way you can possibly test this region alone is through the spark plug hole and if with a new top end and assembly oil to help seal the piston to the bore- if the crank is not rotated to allow the below transfer area to pressurise, the test proves nothing about the ability of the saw to hold pressure and be airtight.