Husqvarna 562XP 50PSI Compression

[bnscherm]

Hello,

I’m new to the site, and inexperienced with working on saws. I recently started looking into Alaskan milling some trees on my property into live edge slabs for home projects.

To get things started I found a used Husqvarna 562XP. Saw had some trouble starting and idling but ran well at higher RPM. Ran it this way for a few cuts and killed the piston/rings and effectively lost all compression

Ordered and installed replacement Warhawk cylinder/piston kit, but foolishly didn’t check compression before test cutting some logs. Same hard starting and idling lead me to recheck compression which is measuring 50PSI. I compared this to a smaller working saw I have that measures 100PSI. I don’t trust the numbers on the cheap compression tester, but I know it’s comparatively lower than it should be. Suspected the decompression valve which I’ve confirmed is leaking some a amount using soapy water. New valve is on order. When pulling the saw over I get one pop with each pull, but very difficult to get it to fire back to back even with starting fluid. I took off the carb and inspected the parts didn’t see any visual signs of buildup, so I put it back together without modifications.
Questions:
Could I be loosing half my compression from leaking decomp valve?
The original cylinder gasket was in like new condition, so I did not replace it, or add any additional sealant, should I take top end apart again to reinspect if the new decomp valve doesn’t help? Other recommendations?

 

[Backstage]

Probably not. I had a 55cc that pulled 90psi with the decomp button PRESSED.

You put on a completely new cylinder/piston kit and didn’t put sealant on the gasket. Very possible that’s where your leak is. Pull that cylinder and make 110% sure the surface is clean, use motoseal or similar, reinstall with bolts torqued to spec (IIRC 9nm on those, but check the 562 workshop manual).

You can also try a decomp plug.

 

[bnscherm]

Update: Installed a new decomp valve. Pressure in closed position went from 50 to 75psi. Next step is to reinstall cylinder with motoseal as recommended.

 

[bnscherm]

Removed the cylinder today to add the sealant. Found some scoring on the piston on both sides above the pin. The input and exhaust piston surfaces are clean, but the scoring is on both sides above the pin. Seems I should replace the piston again, but need to know what is causing this issue. All piston scoring failure modes I’ve read about are on the other input and exhaust quadrants of the piston.

 

[Wood Doctor]

Looks like you are running the carb lean or the fuel mix needs more oil. Or, air is leakng in somewhere, posssibly the crank shaft seals.

 

[Maintenance supervisor]

Are the rings setting in with the grove correctly? Did you clean up the cylinder (sand it) after the first piston went caput?

 

[bnscherm]

Here are some pictures. I replaced both cylinder and piston originally, and now the new piston is also scored. New cylinder seems fine still. Starting to think there must have been metal shavings left over in the crank case, that damaged the second piston as shown. First picture shows original piston on left, all the others are of the new one that was run in the saw for at most 15 minutes

 

[Backstage]

All bearings in the crankcase should also be detail inspected or outright replaced. If you've got a bearing that's fragmenting…

 

[Big_Eddy]

What oil and mix ratio are you using?


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[Big_Eddy]

Is it just me, or is the case missing a chunk on the flywheel side?


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[Chevboy0167]

Crank seals.....

 

[thenne1713]

(My Impression) is 1) that your problem is DEBRIS; On piston pics, I cannot tell if damage on Intake side or EXH side? Also cannot tell newer vs older piston, but noted that damage is very similar on both pistons (??) (but) LOOKING AT OTHER PICS, and seeing debris inside crankcase that appears to be sawdust FINES (esp. right side in pic of crankshaft/rod?), much of problem may have started w/ AIR FILTER? Fur, think about fact that fuel mix (does not go directly from carb to cylinder, like it does 4-cycle); it goes from CARB, to CRANKCASE/ rod/ piston pin, THEN TO CYLINDER/COMPRESSION. Any debris that went to piston went thru crankcase first, or came from crankcase. :-( Is CARB venturi contaminated w/ oil-soaked sawdust fines?

Is it just me, or is the case missing a chunk on the flywheel side?


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YES, CHUNK is missing in FW housing, but (even if), and debris shudda never made it around/ thru the air filter/carb ventur? MY guess is some owner/tech using screwdriver to hold flywheel while loosening?

 

[thenne1713]

Update: Installed a new decomp valve. Pressure in closed position went from 50 to 75psi. Next step is to reinstall cylinder with motoseal as recommended.

FYI, re: Compression, Husqvarna says MIN= 120-PSI to start/run, image STIHL & others say similar

 

[redunshee]

Removed the cylinder today to add the sealant. Found some scoring on the piston on both sides above the pin. The input and exhaust piston surfaces are clean, but the scoring is on both sides above the pin. Seems I should replace the piston again, but need to know what is causing this issue. All piston scoring failure modes I’ve read about are on the other input and exhaust quadrants of the piston.

If you use a new gasket, there is no need to use sealant. Your only lowering compression

 

[Automender]

I recently used a aftermarket cylinder kit and measures the squish ring to gasket surface and it was .020 inches more than the OEM. Add the original gasket and that makes a squish of nearly .070 inches. You could be losing compression also due to aftermarket machining tolerances. Original squish was .038 inches. I needed to delete the gasket to get back to original specs and compression. You should split the crankcase, inspect bearings and pressure/vac test after assembly. I had a bearing cage come apart on a saw.

 

[TRTermite]

I read 15 posts and nothing mentioned about you using starting fluid.. NOT A GOOD IDEA. Use your saw gas/oil mix Starting fluid will dry the rings and cylinder and scoring "WILL" occur I also believe it can bend a rod and a lot of other surprises But that is not what you are asking about,, carry on

 

[Huntaholic]

Is it just me, or is the case missing a chunk on the flywheel side?


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Youre right, it IS broken! I don't think that would cause his issues though, that would have more effect on the air intake side of things. Using ETHER in a chainsaw is REDICULOUS though!

 

[Woodslasher]

562 long blocks are cheap from what I've heard, maybe just buy a whole new bottom end?

 

[farmhard]

You need to split the case and install new seals at the very least. Debris gets between the bearings and seals. That takes care of 1 vacuum leak. Secondly, new fuel hose and impulse if used. Kit the carb.
The cause of the first failure was likely the cause of the 2nd.

 

[farmhard]

Probably not. I had a 55cc that pulled 90psi with the decomp button PRESSED.

You put on a completely new cylinder/piston kit and didn’t put sealant on the gasket. Very possible that’s where your leak is. Pull that cylinder and make 110% sure the surface is clean, use motoseal or similar, reinstall with bolts torqued to spec (IIRC 9nm on those, but check the 562 workshop manual).

You can also try a decomp plug.

Granted the saw doesn't run but I am trying to understand why using sealant on a gasket BELOW the piston rings would solve the issue of 50 PSI compression?????