The McCulloch Chainsaw Thread, continued.

PogoInTheWoods

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I don't recall the cylinder porting being different. I havent degree mapped them yet however. Probably won't get to that until after we move. The early 70cc 10-series saw definitely have different power charachterics than that of the 7-10A and PM700.
Thanks for the input, Aaron. Seems like there's gotta be more to it than just cast iron liners, thick rings, and port hole pistons. 'Course lots of folks swear by a 7-10 handing a PM700 its lunch, too. Guess that would depend on the vintage of 7-10 since later ones essentially used the same exact thin-ring piston/shortblock assembly as a PM700. Haven't gotten into splittin' the carb/ignition/muffler hairs between em yet, but still can't help thinking the transfers would be different for the earlier pistons. Pretty sure the larger venturi SDC's prevailed toward the end of production for the 70cc saws so there should be a level playing field there.

@2broke2ride is having one helluva time trying to get a 7-10 project sorted out over in the old stomping ground and I'm just trying help gather whatever info I can beyond my own stash of Mac materials to maybe help solve the mystery. 'Bout every Mac guru out there except you has weighed in on it including Mark H. tearing it down and rebuilding it twice and still ending up with a saw that simply won't idle no matter what. Literally everything has been swapped out or replaced on the damned thing except the cylinder or the windowed piston being replaced by the older port hole style.

2broke originally got the saw from Mark as a project with a funky piston -- like someone tried to use a screwdriver thru the exhaust port as a piston stop..., possibly after replacing the piston. That piston was a newer windowed version and was replaced by another new OEM piston just like it. My running theory is the saw originally had a port hole piston that was replaced by a windowed piston that became damaged and was replaced by another windowed piston just because that's what came out of it -- essentially the "wrong" piston if it originally had a port hole piston in the first place and the transfers are different in those cylinders than the ones for windowed pistons. Whether or not the idling issue would be related is another discussion, but the only thing about this saw except the starter rope that hasn't been covered are the cylinder and the crank..., and I do mean that literally.

Haven't been able to track down anything definitive on the porting so figured you might be able to shed some light. Been scrounging around for some cylinder pics to compare but haven't found squat. I do have a PM700 I could tear down to see what those ports look like but don't have anything earlier for a comparison in the 70cc series. 10-10's used the full skirt pistons if I'm not mistaken, so tearing one o' those down may or may not reveal any significant design differences in the cylinder types for the two piston styles.

TIA for any additional enlightenment.

And good luck in Wyoming. Some beautiful country.
 

Eccentric

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Jan 13, 2012
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Thanks for the input, Aaron. Seems like there's gotta be more to it than just cast iron liners, thick rings, and port hole pistons. 'Course lots of folks swear by a 7-10 handing a PM700 its lunch, too. Guess that would depend on the vintage of 7-10 since later ones essentially used the same exact thin-ring piston/shortblock assembly as a PM700. Haven't gotten into splittin' the carb/ignition/muffler hairs between em yet, but still can't help thinking the transfers would be different for the earlier pistons. Pretty sure the larger venturi SDC's prevailed toward the end of production for the 70cc saws so there should be a level playing field there.

@2broke2ride is having one helluva time trying to get a 7-10 project sorted out over in the old stomping ground and I'm just trying help gather whatever info I can beyond my own stash of Mac materials to maybe help solve the mystery. 'Bout every Mac guru out there except you has weighed in on it including Mark H. tearing it down and rebuilding it twice and still ending up with a saw that simply won't idle no matter what. Literally everything has been swapped out or replaced on the damned thing except the cylinder or the windowed piston being replaced by the older port hole style.

2broke originally got the saw from Mark as a project with a funky piston -- like someone tried to use a screwdriver thru the exhaust port as a piston stop..., possibly after replacing the piston. That piston was a newer windowed version and was replaced by another new OEM piston just like it. My running theory is the saw originally had a port hole piston that was replaced by a windowed piston that became damaged and was replaced by another windowed piston just because that's what came out of it -- essentially the "wrong" piston if it originally had a port hole piston in the first place and the transfers are different in those cylinders than the ones for windowed pistons. Whether or not the idling issue would be related is another discussion, but the only thing about this saw except the starter rope that hasn't been covered are the cylinder and the crank..., and I do mean that literally.

Haven't been able to track down anything definitive on the porting so figured you might be able to shed some light. Been scrounging around for some cylinder pics to compare but haven't found squat. I do have a PM700 I could tear down to see what those ports look like but don't have anything earlier for a comparison in the 70cc series. 10-10's used the full skirt pistons if I'm not mistaken, so tearing one o' those down may or may not reveal any significant design differences in the cylinder types for the two piston styles.

TIA for any additional enlightenment.

And good luck in Wyoming. Some beautiful country.
Could be. I have a few 70cc Macs of various vintages to compare. Honestly won't get time to dig into them until after well after we've moved (at which time I'll have the time and space to get into my projects). Most of my saw project stuff is packed up (or will be soon). Just the few saws I grab when I need one, plus a couple saws that belong to other folks will remain unpacked.


Have a thought; I know you said everything but the pull cord has been replaced................but I'm thinking the idle issue might still be something else. Thinking that it could be related to the vac/impulse driven auto oiler pump. They often leak at the pump-to-case gasket for various reasons. Also, could be something really weird like a cracked pump body or a crankcase half with a crack or a casting flaw. Leaks can be maddening.

Has the carb been replaced with a known good unit? Could be something weird like a leaking welch plug, a blown check valve, or maybe a flaw in the carb casting (or maybe a plugged passage).

Then it could be something funky with the ignition. Maybe even a weak flywheel magnet that doesn't produce enough juice at idle speed.

Quien sabe?
 

fossil

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Nov 2, 2013
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I have two 7-10's and two 700's. I can't see any wow difference in cutting speed. The thing that's very obvious is the weight difference. If I can get off my lazy butt and and do some timed cuts I would be able to quantify the speed diff.

The 7-10's are a little more that 1-1/2 pounds lighter than the 700's Some of that is the brake but not all of it.

Both pretty stout machines though.

Best wishes on your move Aaron.
 

PogoInTheWoods

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Nov 1, 2013
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Still tryin' find one, myself.

Quien sabe?
Believe it or not, all that stuff was covered. There was indeed a crack in the oil pump body causing a leak. It was replaced as were all intake components. Saw was actually pressurized and submerged looking for mystery leaks. Entire ignition including flywheel were changed. Several carbs were interchanged. Pretty much the whole nine. A definite head scratcher.

As for the 7-10 / PM700 comparisons, there's gotta be somethin' to the 7-10 aside from the weight difference that distinguishes it from the 700 performance-wise..., at least somewhere along the line. I personally don't see how it could be across the board since they're basically the same saw at the end of the 7-10 and beginning of the 700. And a PM700 is a pretty bad ass little saw, too. Gotta be an era thing with earlier 7-10's having that edge somehow. Carb, ignition..., haven't drilled down into it, but too many folks swear a 7-10 will whup up on a PM700 for there to be nothing to it. I'll find a good one on o' these days. Have four PM700's. Got the first three all at the same time from a muni auction I won a few years back. Last one was a toss-in with a PM800 deal. Just saw 2 more in my area this week. One for $150 and another for 50 bux. Neither lasted long. Just don't see many 7-10's around here. PM850's, either. I want one o' both!
 

Eccentric

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Jan 13, 2012
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I haven't stopped in that area of Ca (passed through a bunch). Yreka and surrounding does get HOT.


I was over the boarder in Phoenix, Oregon a couple weeks ago. Fucking HOT, as was the I5 corridor heading back south.