SP81 Cylinder and Piston. Smoked?

[Chainsaw Jim]

I knew I heard that cannabis was in wide use in Oregon.

What does your interest in cannabis have to do with the value of the sp81?

 

[davidtown]

Thanks for all the participation.

I am working on cleaning up the cylinder and piston...pictures attached. Also found the rings to have a pretty significant gap. At least 1/16 to 1/8 gap. Pretty surprised it ran. Now I'm on the look for a piston and or rings to give it a shot at life again.

Finding it difficult finding out what cylinder I have. A, B or C. On the top of the cylinder the is an extremely small marking (accidental or intentional I can't tell) that could be the letter C. I believe I have found an A piston/ring kit ($20) and a C piston/ring kit ($50).

Also, rings that I have found are about $30 but the issue with that is I am not able to tell if they are the thick or thin rings. My rings measure 1/64'' and I believe they are the thin ones.

Last bit of info for now...The inside of the piston has the markings ART 2 and EX on the side. Nothing on top.

In short...what is the consensus of the cylinder? A, B or C??? Is the piston OEM?

 

[rwoods]

Unmarked cylinders are “B”s. Your piston is thin ring. Looks to be an OEM piston to me. I would buy some OEM rings and reuse the piston. Ron

 

[davidtown]

Perfect. Thank you. I am able to find PN: 92519 which is the piston and rings for the "B" piston. Not adverse to this option.

If you have a PN for rings only...I'd be all interested. PN: 87854 is for a set of rings but that is the only PN listed in the IPL. Called Randy's Something Or Other...and they had the rings but the gentleman believed they were the thicker set of rings.

Thank you.

 

[davidtown]

I purchased a piston/rings set from Little Red Barn and put everything back together. Also installed new crank seals and an oil tank gasket. $80 in parts.

Anyways, she starts, runs, oils and annoys the neighbors. Thanks to all who helped. I'm pretty happy with where the saw sits right now.

Be well,
Dave

 

[rwoods]

Throw that old piston in a box and save it. You may need it one day. Glad you got it going. Ron

 

[davidtown]

On a side note...what should the max WOT rpm be set to? Not finding a specific number for the SP81 but something around 10,000 in old Mac saws. I have a tach to get it accurate.

The piston is shot. I damaged it several times. First time happened when I was trying to get the bearings out, the HF C clamp broke and the piston shot across the shop floor bouncing on the edges and damaging it. Next happened at my home press breaking it for good by pressing out the bearings. I'll keep it for a while till it is time to clean the shop again and I forget what it is off of and in the garbage it goes.

 

[rwoods]

I have broken a few trying to get the bearings; at least they were too damaged already.

Standard practice is to tune the saw under load. Your carb may have a fixed jet on the high side. If not, 11,000 or so should be fine after break-in.

Without a chain low 12,000 should be fine.

Ron

 

[davidtown]

Ran the saw today. Went out to help a buddy buck up a bunch of dry Pondo for his father-in-law. Definitely paid more attention to the bar since there is not a chain brake.

Things were chugging right along and I was pretty happy. Then...out of nowhere she came to a screaming halt, locked up and now leaks bar oil out of the exhaust. Can't pull the starter cord. The chain spins freely by hand. I knew something wasn't right...you know the whole not starting thing was my first clue. So, I put the saw in time-out and used a different one to finish the days work. Gonna start pulling things apart till I find the issue. Man this saw was awesome while she lasted.

 

[davidtown]

Well, this took all of 5 minutes to solve.

Complete blowout in the crank case. Pictures attached.

So, what do I do now? Sell for parts? Find replacement parts? I'm happy to keep dumping good money into this thing cause i believe it needs to continue to live. What do you people thing?

 

[rwoods]

Is that the original crankcase? Original rod bolts? Looks like impact damage to me. I guess if you got clearance now, all the pieces are out, and no internal damage then plug the hole and run it. Ron

 

[davidtown]

Ron, thanks for the encouragement and good idea. I believe all parts are original to the saw.

Looking at the case it appears to be aluminum and not magnesium. Is this correct?

Be well,
Dave

 

[rwoods]

I don't know. You have me wondering if it didn't hit before why did it hit this time. Did you put a washer on the rod bolt by mistake? I don't see one. Ron

 

[rwoods]

I am going to post your picture in the MAC sticky thread. Maybe someone there can help. Ron

 

[davidtown]

Ron,

I don't think i messed with the crank bolts. At least i hope i didn't start to pull it apart, realize there were 22 tiny roller bearings waiting to run free all over the floor and forget to tighten it back up. I'll know more in a few days.

 

[davidtown]

Ended up not being an issue with the crank. The piston broke and then the crank was able to blow through the bottom case.

The piston spins but is ultimately stuck and won't come out.

Anyone want to buy a parts saw?

 

[smokey7]

Is the crown of the piston in tact? You can assemble some fittings and use a grease gun to push the piston out until a port is open. Usually once you get it moving you can get it out the rest of the way after that.

 

[rwoods]

Stick a rod, dowel or screwdriver down the spark plug hole and tap that baby out if it isn’t hung in a port. If you get it out maybe someone here can help you find a oem piston. Ron

 

[davidtown]

Thanks for the tip. Pulled the plug and banged out the piston. Cylinder has real issues now too.

 

[davidtown]