scored chainsaw cylinder

frank-h(4)June 21, 2011

I have a Husqvarna 272xp chainsaw. Last year I had to replace the cylinder, piston and rings. Now, again I have low compression, 65psi, and the cylinder is showing wear. If I put some light oil in the cylinder, I'll get 100 psi. I have never changed the type or mix of the oil over the past twelve years. I cannot find any crankcase leaks. Why do you think this is happening? And, do you think this cylinder can be cleaned up with a hone, or is it shot?

Thanks

Frank

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ewalk

Frank : You should be getting around 160 to 165 lbs compression with properly matched and installed piston rings and cylinder .... I assume you parallel honed the
cylinder to a proper cross hatch to assist with seating in the rings during breakin . Piston Ring End Gap measurement was also a vital issue for proper sealing . If done by a good mechanically inclined individual and you should be up and running without any issues . The 272 along with the 266 were excellent Pro Grade performers . Do you have a decompression release on your Model some 272 units did and loss of compression sometimes was due to these units becoming faulty due to carbon buildup . How did the saw run after the rebuid and how many hours of use since the rebuild ?

    Bookmark   June 21, 2011 at 2:20PM
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frank-h(4)

The decompression button is operating properly. I pulled the cylinder tonight and took a better look. I can feel the beginning of scoring on the rear right quarter of the cylinder. It seemed to run well last year, and I would estimate it has about a hundred hours on it since the repair. What do you think of honing the cylinder a bit,and putting in a new ring?

    Bookmark   June 22, 2011 at 7:00PM
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ewalk

You could but 100 hrs is not much for a new installation. What were your Piston to wall clearances and your previous ring end gap measurements with piston installed ? Who did the Cylinder Boring and Parrallel Honing you or did you outsource this work ?

    Bookmark   June 23, 2011 at 12:11PM
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frank-h(4)

I found the cause of the problem....crankcase seal leak. I honed the cylinder and ordered a new ring. I hope I'll get decent compression. We'll see. Thanks for the input.

    Bookmark   June 23, 2011 at 7:26PM
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loger_gw

Please share brief info on how the seal was the problem. Did it allow debris in the cylinder or affect the fuel mixture in the cylinder (my guess will be debris)? Teaching and Learning Is Still Fun and important to our young mechanics. Hang In There Ewalk! loger

    Bookmark   June 24, 2011 at 10:12AM
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ewalk

Frank : I assumed from your 1st post "cannot find any crankcase leaks" that you had carried out a leakdown test of the bottom end . This is most easily carried out by removing the cylinder and blanking off the cyl. with a gasket and crankcase sealing plate. You can then pressurize the crankcase and check seals and gasket sealability . Loger: As you most likely know crankcase pressure and vacuum are used to operate the fuel carburation (diaphram) to supply fuel once the engine is primed ( and or) purged with the primer and choke assembly. A bad seal or crankcase gasket will not allow fuel to be properly drawn into the carburator . Also it can directly effect base compression . Usually erratically high idle will indicate the beginning of this sealibility problem .

    Bookmark   June 29, 2011 at 11:50AM
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frank-h(4)

I initially did a smoke test with a smoke unit that I made to find vacuum leaks in my cars. I did see some smoke, but I did not have the flywheel off, and I missed it. The leak down test did the trick. I did it with the head on. I blocked off the exhaust and intake port, then hooked up my gauge,and tee to the spark plug port.

    Bookmark   June 29, 2011 at 12:30PM
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ewalk

Frank: Have used both the smoke and propane gas leak detection method for carburator gasket or intake plenum leak detection . Usually use the pressurization method for
crankcase confirmation. Hope all goes well this time around you have a proven prograde saw ..all the best Dude !

    Bookmark   June 30, 2011 at 4:30PM
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ablackwood(VA/USA Zone 6/7)

On a related matter: my low use 16-year old Stihl 044 chainsaw stopped working in mid-cut after a few minutes of heavy work. Would not restart. Next day it started normally, but again stopped in mid-cut after a few minutes work. I checked the usual things on the fuel side and that it had spark. I use fresh fuel with Stabil additive re ethanol issue.

What is the best educated guess on cause? Thanks.

    Bookmark   November 13, 2012 at 12:18PM
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loger_gw

ablackwood, Starting a new post might get you better results. Please include some specifics on the fuel side tests. Have you done more testing yet? Such as: compression, cyl/ring/piston inspection through the exhaust port, spark arrest if app, clean cooling fins and etc that might cause it to run hot.

I would like to see a before and after scored honed cylinder that was put back into service. I put a piston/ring kit in a late 70's Poulan S-25 that had a chromed cyl w/o honing and got another 10 yrs. Excuse the High-Jacking! I just had to mentione that and possibly have some pics for the new related post!!

    Bookmark   November 13, 2012 at 3:48PM
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frank-h(4)

ablackwood, I'd check the fuel tank breather. Maybe it's getting vapor locked.

    Bookmark   November 13, 2012 at 4:58PM
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ewalk

Vapour lock for a quick evalation would be sound . A quick lossening of the fuel cap will determine ,when it begins to die out . Otherwise a fuel filter check is advised. If all is within spec then you may have a ignition module / coil on the way out usually occurrs when engine is warmed up and under load. Try your saw after a 20 minute cool down if it repeats this routine then it may well be the coil . The only other situation which would show similiar symptoms would be a overly lean fuel mixture which would cause over heating and power loss and eventual partial seizure and shutdown . Your spark plug colouration would indicate such a cause.

    Bookmark   November 18, 2012 at 11:30AM
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