MCCULLOCH The official McCulloch thread

[legdelimber]

Maybe try putting a sheet or strip or 2 of paper inside the cylinder and see how the piston fits in then?
Try different areas and see if you notice any difference between them?
Either by how deep into the cylinder and also around different sides of the cylinder.

 

[heimannm]

Today I measured the bore of the cylinder I took off, seems pretty well round and pretty straight top to bottom. My measurements were .001-.002" over what the chart lists for the "C" bore size. I will try measuring a "C" piston tomorrow and see how my measurements compare with the chart.

I did finish putting the saw together today with bit and pieces I could find around. Started and ran well, I was only able to run it for 2-3 minutes and no heavy load yet, but when I shut it down the compression was very good. If I have a chance I will run it longer under load tomorrow and see what develops. The clutch cover and bar & chain are parts I keep on the back of the work bench for testing saws.





For now I have and SDC51A fixed H carburetor on the saw with the 32 jet.





The carburetor supplies plenty of fuel.

Mark

 

[jacktheripper]

I’ll take that problem saw off of your hands if it’s bothering you too much!

 

[heimannm]

If you don't know the background...I had 4 cylinders sleeved some while back, SP80, SP81, PM850, and PM800. The first one I tried (SP81) would run for about 90 seconds in a hard cut then die for lack of compression. Went from around 140 to less than 90 PSI...let it cool down and the compression would come right back up again. For the sake of science, I decided I would try another cylinder to see if it was peculiar to that one cylinder, or if they all would experience the same results. For this saw (above) I used the same crankcase bottom/oil tank, crankshaft, connecting rod, and piston as the previous saw.

I still have two untested sleeved cylinders on hand, the SP80 and the PM800. I think the only course of action moving forward will be to build saws around them as well and see how they behave.

Mark

 

[jacktheripper]

If you don't know the background...I had 4 cylinders sleeved some while back, SP80, SP81, PM850, and PM800. The first one I tried (SP81) would run for about 90 seconds in a hard cut then die for lack of compression. Went from around 140 to less than 90 PSI...let it cool down and the compression would come right back up again. For the sake of science, I decided I would try another cylinder to see if it was peculiar to that one cylinder, or if they all would experience the same results. For this saw (above) I used the same crankcase bottom/oil tank, crankshaft, connecting rod, and piston as the previous saw.

I still have two untested sleeved cylinders on hand, the SP80 and the PM800. I think the only course of action moving forward will be to build saws around them as well and see how they behave.

Mark

Yep, that makes sense. Your issue could be in the ring material. I wonder if the ring is not breaking in right on the sleeve. If it didn’t break in well, it could have gone limp and lost its spring, or may get hot and limp when running.

 

[heimannm]

The piston used was a NOS McCulloch 92520 piston assembly which included the rings and bearings. I did some checking back when and it seemed at the time that McCulloch used the same thin rings (on earlier models) on either chrome plated or iron bore models so I figured the rings should be good. Some of the earlier thick ring pistons had chrome plated rings, some were even specific with a chrome top ring, but the thin rings all seemed to be the same.

Mark

 

[heimannm]

I did not get to cut wood today due to cold temperatures and wind, but the saw was started and run several times and we checked compression cold and hot and it was always 140+ which in my estimation is pretty good.

After running a bit I noticed the fuel tank is leaking so I will have to find another one in the attic and swap them out.

I am encouraged at this point that this sleeved cylinder may work O.K. I did mic the cylinder that came out of the saw as well as a new "C" piston and while my numbers were actually a bit over what the chart says, the piston and cylinder match the clearances calculated from the chart very nicely.

Mark

 

[Maintenance Chief]

The piston used was a NOS McCulloch 92520 piston assembly which included the rings and bearings. I did some checking back when and it seemed at the time that McCulloch used the same thin rings (on earlier models) on either chrome plated or iron bore models so I figured the rings should be good. Some of the earlier thick ring pistons had chrome plated rings, some were even specific with a chrome top ring, but the thin rings all seemed to be the same.

Mark

I was gonna actually suggest using the LRB piston with Mac bearings as a thick ring alternative.
Rings transfer alot of heat from the cylinder.

 

[heimannm]

I have two more sleeved cylinders that I haven't done anything with, several possibilities moving forward. The thing that concerns me about the LRB pistons is they are "one size fits all" and the cylinders were all finished to accommodate the "C" pistons since I had them and they seem to be less demand for those than "B"'s and "A"'s.

Mark

 

[Gary Courtney]

oppurtunity locally one owner saw what is a good price. he just had fuel lines replaced and plug. tune-up