McCulloch Chain Saws

[heimannm]

The 70 cc piston line up L-R: LRB w/2 thick rings, 85239 w/2 thin rings, 85240 w/2 thick rings, 69412 w/2 thick rings, 68421 w/2 thick rings, and 69031 w/2 thick rings (I don't have 69030 on hand, 69031 is +0.020.



69412 is equipped with a chrome ring on top



85240 has two cast iron rings



Looking through the rings, only 87166 are chrome, all the other thick rings are cast iron. If you look at the list above, the only call for the 87166 rings are for the early 7-10A with the sleeve, notice that there are two oversize pistons listed indicating the cylinder can be bored oversize.

Mark

 

[PogoInTheWoods]

What is the difference in the Pistons 85239 and 85240 in the specs page. Maybe I have it wrong, but it seam the pro 700 and the 6-10 share the same piston? If so I could buy the LBR piston and compare it to the one from Greece when it gets here. So did you use the original wrist pin?

You just had to ask. LOL For starters, they are two distinctly different pistons requiring different wrist pins, bearings, and connecting rods.

As you are discovering, the 70cc piston subject is a broad and diverse one with absolute answers depending on any number of variables.

Mark's excellent post above illustrates the commonly published piston/ring permutations. While some debate seems to revolve around the 85239 rings, another important consideration among all these pistons are the wrist pins, bearings, and connecting rods involved. The pistons will all fit any of the three different cylinder designs, but there are obviously two distinct types of pistons which correspond in one way or another to at least three types of cylinder transfer/port designs. There are also two different sized wrist pins and bearings involved which need to correspond to the correct connecting rod. The correct piston for the cylinder transfer type is a debatable subject, but should obviously be a consideration in determining how 'correct' you want your rebuild to be. The de-facto 70cc solution seems to be the thin-ringed 85239 these days, but I'm not convinced of that particular approach doing much more to a vintage 6-10 or 7-10 than just turning it into a PM700 with incorrect transfers..., if the correct connecting rod is even on the crank to begin with.

As mentioned in an earlier post on the subject, I jotted down what I could derive from both the commonly referenced tables (and associated IPLs) regarding which pistons used which rings, and which pins are used for which connecting rods..., which is obviously as important as any other consideration. Also included are some measurement differences not in the tables -- primarily side and top/down measurements depicting those differences. I'll try to dig it up and post if it's legible enough for prime time.

If Mark's photo was a direct frontal view, the wrist pin/bearings considerations I'm referencing would be obvious. He posted an earlier pic which does illustrate the differences quite clearly..

 

[PogoInTheWoods]

Better pics showing the obvious differences/considerations presented above. (Courtesy of Mark from the last extensive discussion on the subject.)

​

 

[Jethro 2t sniffer]

I love this piston yarn. I completely forgot about the rod n pin difference

Ok question....
I have a random new 70cc piston it came with a 700 I bought. From memory it's the later windowed style. Always thought it must be an LRB but its in a plain white box no branding whatsoever. I haven't got a picture and its at work half hour away in a pile of 7-10

Did the 7-10 extra balls thing ever get confirmed why? Was it the open non devided transfer? Was it port timing? was it squish? Or a combination??

All my good 7-10 cylinders are the later devided transfer type my 1 and only older 1 is a running parts saw.

I ask as I'd like to hog out the divider if that's all it is and possibly adjust the porting just a little too. I know they enjoy a little extra intake

 

[edju1958]

I'm trying to part together a muffler for a 2-10 that'll be up & coming on my list.I have the body/duct,part # 83105.I need the cap,part # 62380,baffle - part # 62379B,& the screws that hold the cover on,part #102341,lockplate - part # 69890,& small shoulder bolt - part # 110506.
I got off the phone with Bob J.& almost had a heart attack when he told me the baffle alone was $52! To hell with the baffle,I can make one for a lot less than $52

 

[PogoInTheWoods]

There is no "thick ring" 85239 today, the only 85239 you will find is a thin ring piston that uses 89732 thin rings.

And after seeing your latest lineup pic with the 69031, and reviewing my notes and a couple of IPLs, I'm going way out on a limb here and proclaiming a 69030 the piston that has been referred to and listed in the publications as a "thick ringed 85239"..., which it essentially was/is. Of all the pistons involved, they are the only ones that share the same windowed design and the larger 69020 pin and bearings and shorter 83060/85352 connecting rod. (I'm curious what pin version the LRB piston is supposed to use.) And while the tables seem confusing, they do accurately reflect what is generally in the associated IPLs. A few asterisks in the right places could have certainly gone a long way in providing some needed clarification.

Hey, Jethro. My money is on the earlier pistons/transfers as one of the distinctive differences between the 70cc saws, but a sharp chain goes a long way, too. LOL

 

[Woodslasher]

I'm trying to part together a muffler for a 2-10 that'll be up & coming on my list.I have the body/duct,part # 83105.I need the cap,part # 62380,baffle - part # 62379B,& the screws that hold the cover on,part #102341,lockplate - part # 69890,& small shoulder bolt - part # 110506.
I got off the phone with Bob J.& almost had a heart attack when he told me the baffle alone was $52! To hell with the baffle,I can make one for a lot less than $52

If it is the pancake style, www.saw salvage.co has a cap, look under new old stock parts.

 

[edju1958]

If it is the pancake style, www.saw salvage.co has a cap, look under new old stock parts.

Not the pancake style.I have a few of those floating around here,but I don't think I can swap one of those in instead of the one that came on the saw.

 

[Xpropane]

Better pics showing the obvious differences/considerations presented above. (Courtesy of Mark from the last extensive discussion on the subject.)

View attachment 956275

​

I clearly see the wrist pin diameter difference, it appears piston to pin hight looks different as well. 85240 would require a longer rod to match the transfer timing, and quench. I didn't believe I had a choice. I will go back and try to find the previous piston deep discussion. Thank both you and Mark for the pictures and rehashing the topic!

 

[PogoInTheWoods]

There is no "thick ring" 85239 today,​

There aren't many of any of them today. LOL

But there were indeed both a thick (wide) ring and a thin ring 85239 for a period of time as specifically referenced in the extended '74 91123 IPL for the 7-10A.
(I knew I had seen this somewhere.)

Clearly a numbering transition away from the 69030 thick ring piston to what was to be the thin ring 85239 replacement for the future, but a thick ring 85239 existed nonetheless and certainly seems to have been accurately reflected in the various tables and IPLs as was appropriate for the listed applications.

​

 

[Jethro 2t sniffer]

Hey, Jethro. My money is on the earlier pistons/transfers as one of the distinctive differences between the 70cc saws, but a sharp chain goes a long way, too. LOL

Might be worth having a go then when I put a 70 back together. I have a 700 or a 7-10 to choose from. Couldn't agree more about chain though really tuning up the rakers to suit the power and power curve available seems to make the difference once a sharp tooth is reliably achieved.

I still wonder about that transfer as the 82cc seems to be the opposite with the 80 and older 81s.

Would need to time up all the different cylinders and thats above me

 

[rwoods]

I love this piston yarn. I completely forgot about the rod n pin difference

Ok question....
I have a random new 70cc piston it came with a 700 I bought. From memory it's the later windowed style. Always thought it must be an LRB but its in a plain white box no branding whatsoever. I haven't got a picture and its at work half hour away in a pile of 7-10

Did the 7-10 extra balls thing ever get confirmed why? Was it the open non devided transfer? Was it port timing? was it squish? Or a combination??

All my good 7-10 cylinders are the later devided transfer type my 1 and only older 1 is a running parts saw.

I ask as I'd like to hog out the divider if that's all it is and possibly adjust the porting just a little too. I know they enjoy a little extra intake

I don’t know anything about the 7-10 except what I have read here. However, I believe there is some MAC literature that says the divided transfer improved performance with the 82cc MACs. That said I would hesitate modifying your cylinder. I have another reason as well but it is too long for my tired finger to type on this phone.

Ron

 

[rwoods]

Might be worth having a go then when I put a 70 back together. I have a 700 or a 7-10 to choose from. Couldn't agree more about chain though really tuning up the rakers to suit the power and power curve available seems to make the difference once a sharp tooth is reliably achieved.

I still wonder about that transfer as the 82cc seems to be the opposite with the 80 and older 81s.

Would need to time up all the different cylinders and thats above me

See that you were already thinking about the 82cc.

Ron

 

[PogoInTheWoods]

Lots of variables involved with the 70cc saws -- from port timing/ignition timing to the different transfer styles to the physical differences between intake and exhaust ports on the different cylinders, carbs..... Some guys seem to get the perfect combination and others not so much.

 

[bob kern]

The
View attachment IMG_2969.MOV
850 lives to eat more oak and hickory

 

[Jethro 2t sniffer]

I don’t know anything about the 7-10 except what I have read here. However, I believe there is some MAC literature that says the divided transfer improved performance with the 82cc MACs. That said I would hesitate modifying your cylinder. I have another reason as well but it is too long for my tired finger to type on this phone.

Ron

See that's what makes me wonder if it really is the transfer at all and instead its elsewhere. Maybe it was a longevity thing Maybe the later cylinder style saws last longer.

Lots of variables involved with the 70cc saws -- from port timing/ignition timing to the different transfer styles to the physical differences between intake and exhaust ports on the different cylinders, carbs..... Some guys seem to get the perfect combination and others not so much.

Exactly. What is that combination

 

[super44]

You just had to ask. LOL For starters, they are two distinctly different pistons requiring different wrist pins, bearings, and connecting rods.

As you are discovering, the 70cc piston subject is a broad and diverse one with absolute answers depending on any number of variables.

Mark's excellent post above illustrates the commonly published piston/ring permutations. While some debate seems to revolve around the 85239 rings, another important consideration among all these pistons are the wrist pins, bearings, and connecting rods involved. The pistons will all fit any of the three different cylinder designs, but there are obviously two distinct types of pistons which correspond in one way or another to at least three types of cylinder transfer/port designs. There are also two different sized wrist pins and bearings involved which need to correspond to the correct connecting rod. The correct piston for the cylinder transfer type is a debatable subject, but should obviously be a consideration in determining how 'correct' you want your rebuild to be. The de-facto 70cc solution seems to be the thin-ringed 85239 these days, but I'm not convinced of that particular approach doing much more to a vintage 6-10 or 7-10 than just turning it into a PM700 with incorrect transfers..., if the correct connecting rod is even on the crank to begin with.

As mentioned in an earlier post on the subject, I jotted down what I could derive from both the commonly referenced tables (and associated IPLs) regarding which pistons used which rings, and which pins are used for which connecting rods..., which is obviously as important as any other consideration. Also included are some measurement differences not in the tables -- primarily side and top/down measurements depicting those differences. I'll try to dig it up and post if it's legible enough for prime time.

If Mark's photo was a direct frontal view, the wrist pin/bearings considerations I'm referencing would be obvious. He posted an earlier pic which does illustrate the differences quite clearly..

My head hurts.

 

[Xpropane]

My head hurts.

Lots of overtime the last few months, and any free time spent dealing with firewood and saws+ boiler. My head is spinning a bit also. I need to clear off a bench, get it tore down and figure out just what I have in the saw. Hope to get this accomplished tomorrow.

 

[bob kern]

Taking both 700’s and the 850 to clean up a maple. Tree company did a drop and run so I’m helping a young man who only has a little troybilt. Taking an 051 too just to get new gas in it. Taking the 850 for a final tune in the wood while I’ve got a decent log to cut. It hardly notices anything under 16” lol

 

[edju1958]

Taking both 700’s and the 850 to clean up a maple. Tree company did a drop and run so I’m helping a young man who only has a little troybilt. Taking an 051 too just to get new gas in it. Taking the 850 for a final tune in the wood while I’ve got a decent log to cut. It hardly notices anything under 16” lol

I might've missed it,but what size bar are you running on the 850?