MCCULLOCH The official McCulloch thread

[Steve]

So I know there may be more than one right answer, but would I be able to use a set of thin rings for a PM700 in a 7-10 if it had the thin ring piston, or would I be able to swap in a 700 piston?
Steve was nice enough to send me a set of NOS rings for a 700, as I was thinking of putting together another one.
My 7-10 is a little tired though(140 psi), and I thought maybe that one needed freshening up first, since I really enjoy running it more than my 700.

Yes. The thin rings are the same. And I'd rather have a fresh 7-10 over a 700 any day of the week!

 

[Al Smith]

I've only owned one 7-10 for a short period of time which was the one I bought for my wife's nephew .Seems to me that's the one I had to land a complete ignition system for which came from a 10-10 in Ont.
At any rate looking at the IPL's from 1970 and 1976 the later shows the thin ring piston .I personally think perhaps the 7-10 in relation to the 700 is the fact the 7-10 is a points ignition which you could advance the timing a tad bit with the breaker points setting .What I do know is a few degrees advance on a 6-10 makes a world of difference on how it ran .Now that's an earlier right hand start version of the 70 cc saws not the cinder block PM 610 .
If that 7-10 has 140 PSI static compression I wouldn't worry about it .At speed it will be higher than that .

 

[Steve]

I've only owned one 7-10 for a short period of time which was the one I bought for my wife's nephew .Seems to me that's the one I had to land a complete ignition system for which came from a 10-10 in Ont.
At any rate looking at the IPL's from 1970 and 1976 the later shows the thin ring piston .I personally think perhaps the 7-10 in relation to the 700 is the fact the 7-10 is a points ignition which you could advance the timing a tad bit with the breaker points setting .What I do know is a few degrees advance on a 6-10 makes a world of difference on how it ran .Now that's an earlier right hand start version of the 70 cc saws not the cinder block PM 610 .
If that 7-10 has 140 PSI static compression I wouldn't worry about it .At speed it will be higher than that .

7-10 has different cylinder porting and muffler than a 700. The points ignition does help too.

 

[Al Smith]

If I recall the 7-10 had the bottom curve muffler which is probably the best option on any of the 10 series if you can find one .Of any of the 70's I own or once did the 6-10 ran the best but I reworked a lot of it to get it that way .They are a firewood size and weather a few seconds here or there would make difference in a days work would be speculation at best .

 

[Jethro 2t sniffer]

The 700s have divided transfer ports and the early 7-10s have an open transfer. I have two of the later 7-10s with the divided transfer ports but they still outrun my 700 so I could be some port timing in it also. Would be interesting to time them up n see. And the SP70 also.

Tinman on YouTube is rebuilding a SP70 at the moment and timed it up. He will be porting it after running it stock. He built billy a stonking little homelite

 

[Maintenance Chief]

I watched buckin run that homelite and it seemed boggy? I think alot of the porting that gets done on the YouTube channels steals from Peter to pay Paul, as in they loose the low end torque for rpms.

 

[Jethro 2t sniffer]

I watched buckin run that homelite and it seemed boggy? I think alot of the porting that gets done on the YouTube channels steals from Peter to pay Paul, as in they loose the low end torque for rpms.

Absolutely boggy. Think it took him 3 saws to get that 1 running as well as it does.

Be interesting to see if the SP70 winds up too boggy or not.

Me personally I enjoy a nice bottom end and to take that away from a mac seems silly and alot of port jobs on macs seem to wind up that way

 

[Steve]

Absolutely boggy. Think it took him 3 saws to get that 1 running as well as it does.

Be interesting to see if the SP70 winds up too boggy or not.

Me personally I enjoy a nice bottom end and to take that away from a mac seems silly and alot of port jobs on macs seem to wind up that way

Most of the 10 series are pretty much maxed out from the factory. If you could easily get more compression they would really turn on. Welding pop up pistons works well in a cant racer but not a good idea for a work saw. The best mod for a 10 series is remove some material from the bottom of the piston skirt on the intake side. That will increase intake duration without affecting anything else. A few degrees of ignition timing never hurt either.

 

[Maintenance Chief]

I

Most of the 10 series are pretty much maxed out from the factory. If you could easily get more compression they would really turn on. Welding pop up pistons works well in a cant racer but not a good idea for a work saw. The best mod for a 10 series is remove some material from the bottom of the piston skirt on the intake side. That will increase intake duration without affecting anything else. A few degrees of ignition timing never hurt either.

I haven't heard about the skirt modification, thanks.

 

[Jethro 2t sniffer]

I

I haven't heard about the skirt modification, thanks.

Yeah I think Roland did a post on other forum about on a 10-10S was only a mm or 2 from memory but big difference and didn't kill the bottom end

 

[Jethro 2t sniffer]

I've been wondering about machining the base and bearing recesses to close up the squish but would require some port correction also

 

[Dream]

Absolutely boggy. Think it took him 3 saws to get that 1 running as well as it does.

Be interesting to see if the SP70 winds up too boggy or not.

Me personally I enjoy a nice bottom end and to take that away from a mac seems silly and alot of port jobs on macs seem to wind up that way

I dont care how many rpms it turns, if you bog to 5k when you dog in or get into hard or sappy, how have you improved it? I dont ever want to lose the torque that my 10 series have at any cost.

 

[Dream]

Most of the 10 series are pretty much maxed out from the factory. If you could easily get more compression they would really turn on. Welding pop up pistons works well in a cant racer but not a good idea for a work saw. The best mod for a 10 series is remove some material from the bottom of the piston skirt on the intake side. That will increase intake duration without affecting anything else. A few degrees of ignition timing never hurt either.

Answered my question. I was wondering about a popup.
Like the skirt idea and bump the timing a little.

 

[PogoInTheWoods]

I continue to be fascinated by the PM700 vs. 7-10 comparison and how much stronger the 7-10 is supposed to be. I think it's been fairly well established that both types of cylinders can be found on either saw (at least on the PM700).., which may or may not be of any consequence. I've yet to see it be conclusively determined as a significant factor by any measurable means other than owner opinion and general comparison.

Then there are the carbs as other potential contributors to the difference. More easily swapped and compared than cylinders, but still not conclusively A-B-C tested/compared to my knowledge.

That pretty much leaves the ignition design as the only fixed difference between the two saws which could account for any performance enhancement of the 7-10 over the PM700 (with all other elements being equal, of course).

It would be interesting to set up a timing comparison between the two ignitions (obviously by someone with plenty of spare time on their hands) using baseline hi and low tuning of each saw with a tach. Then using the same flywheel for each saw with timing marks on both the flywheel and cases at 26° BTDC, observe and record the timing curves of each system for comparison using a timing light. All other things being equal, one would think the points ignition would exhibit less advance overall -- especially in the power band (if any at all) -- if the ignition system is indeed the main factor in the 7-10's perceived power superiority over the PM700. I seem to recall Mark H. doing a comparison between the two-piece and single modules on and 81E, but haven't researched the subject otherwise. Maybe someone has already done this?

Until then, there are still too many known variables involved for me to readily accept the general proclamation that a 7-10 is that much more saw than a PM700. I have each, but both need work to even get to square one for any type of honest comparisons.

At present, I'm still inclined to grab my 371xp or 044 when I need a 70cc saw.

 

[Jethro 2t sniffer]

I continue to be fascinated by the PM700 vs. 7-10 comparison and how much stronger the 7-10 is supposed to be. I think it's been fairly well established that both types of cylinders can be found on either saw (at least on the PM700).., which may or may not be of any consequence. I've yet to see it be conclusively determined as a significant factor by any measurable means other than owner opinion and general comparison.

Then there are the carbs as other potential contributors to the difference. More easily swapped and compared than cylinders, but still not conclusively A-B-C tested/compared to my knowledge.

That pretty much leaves the ignition design as the only fixed difference between the two saws which could account for any performance enhancement of the 7-10 over the PM700 (with all other elements being equal, of course).

It would be interesting to set up a timing comparison between the two ignitions (obviously by someone with plenty of spare time on their hands) using baseline hi and low tuning of each saw with a tach. Then using the same flywheel for each saw with timing marks on both the flywheel and cases at 26° BTDC, observe and record the timing curves of each system for comparison using a timing light. All other things being equal, one would think the points ignition would exhibit less advance overall -- especially in the power band (if any at all) -- if the ignition system is indeed the main factor in the 7-10's perceived power superiority over the PM700. I seem to recall Mark H. doing a comparison between the two-piece and single modules on and 81E, but haven't researched the subject otherwise. Maybe someone has already done this?

Until then, there are still too many known variables involved for me to readily accept the general proclamation that a 7-10 is that much more saw than a PM700. I have each, but both need work to even get to square one for any type of honest comparisons.

At present, I'm still inclined to grab my 371xp or 044 when I need a 70cc saw.

That was a nice read Poge.

Interesting thoughts about the ignition all my points Mac's seem to have a little something about them. The 81 is not as fresh as the 850 or 800 yet is every bit the saw of the other two. Not to mention lighter also.

Hard to not grab a 371

 

[Steve]

I continue to be fascinated by the PM700 vs. 7-10 comparison and how much stronger the 7-10 is supposed to be. I think it's been fairly well established that both types of cylinders can be found on either saw (at least on the PM700).., which may or may not be of any consequence. I've yet to see it be conclusively determined as a significant factor by any measurable means other than owner opinion and general comparison.

Then there are the carbs as other potential contributors to the difference. More easily swapped and compared than cylinders, but still not conclusively A-B-C tested/compared to my knowledge.

That pretty much leaves the ignition design as the only fixed difference between the two saws which could account for any performance enhancement of the 7-10 over the PM700 (with all other elements being equal, of course).

It would be interesting to set up a timing comparison between the two ignitions (obviously by someone with plenty of spare time on their hands) using baseline hi and low tuning of each saw with a tach. Then using the same flywheel for each saw with timing marks on both the flywheel and cases at 26° BTDC, observe and record the timing curves of each system for comparison using a timing light. All other things being equal, one would think the points ignition would exhibit less advance overall -- especially in the power band (if any at all) -- if the ignition system is indeed the main factor in the 7-10's perceived power superiority over the PM700. I seem to recall Mark H. doing a comparison between the two-piece and single modules on and 81E, but haven't researched the subject otherwise. Maybe someone has already done this?

Until then, there are still too many known variables involved for me to readily accept the general proclamation that a 7-10 is that much more saw than a PM700. I have each, but both need work to even get to square one for any type of honest comparisons.

At present, I'm still inclined to grab my 371xp or 044 when I need a 70cc saw.

I don't use science. It's a damn chainsaw after all.

I have built a fresh 7-10 and 700 at the same time. Both used the same piston and rings. Each had a different transfer porting. The mufflers where different and of course, the ignitions where different animals. The carbs where different. The 7-10 has a tillotson HS. The 700 a walbro SDC.

The 7-10 just had better throttle response. Period. Why? Just did.

The 7-10 is substantially lighter than a 700 too.

My unscientific opinion is if you have a choice, get the 7-10.

 

[PogoInTheWoods]

I forgot about the mufflers. Oops.

 

[Jethro 2t sniffer]

I don't use science. It's a damn chainsaw after all.

I have built a fresh 7-10 and 700 at the same time. Both used the same piston and rings. Each had a different transfer porting. The mufflers where different and of course, the ignitions where different animals. The carbs where different. The 7-10 has a tillotson HS. The 700 a walbro SDC.

The 7-10 just had better throttle response. Period. Why? Just did.

The 7-10 is substantially lighter than a 700 too.

My unscientific opinion is if you have a choice, get the 7-10.

Ya didn't happen to port time it did ya?

I've had a similar experience with the tilly vs sdc on the same saw it was a sdc65 not the 37 or 44.
The 81 also on a tilly so it could be why its snappy as. Ghe other 82s are on a 44 and zama.

The muffler really is only the cover. Might try a modded 1 on the 700 and see. Its hard to pick the 700 over the 7-10s just for the weight alone

 

[Dream]

So I'm currently running an SDC on my 7-10. The Tilly had some wear in the throttle shaft, and wouldnt tune right.
Was concerned about getting enough fuel, as the SDC is from a 1010A, but it tuned right in. 4 strokes out of the cut as it should. Idles fine. Throttle response seems good, so I'm assuming its not hurting the saw. No noticeable difference in performance from the Tilly to the Walbro, but the old one did have issues.
I'll have to see which SDC it is.
Have to clean the carb anyway. Fuel filter is coming apart and going into the carb.
Maybe someone more experienced can tell me if I'm going the right or wrong way?

 

[Steve]

Ya didn't happen to port time it did ya?

I've had a similar experience with the tilly vs sdc on the same saw it was a sdc65 not the 37 or 44.
The 81 also on a tilly so it could be why its snappy as. Ghe other 82s are on a 44 and zama.

The muffler really is only the cover. Might try a modded 1 on the 700 and see. Its hard to pick the 700 over the 7-10s just for the weight alone

No, I'm not that into figuring out why one has a slight edge over the other.

I do not care for walbro carbs. I prefer tillotson any day of the week but they are hard to find set up for a 10 series mac. You can't hardly go for a walk without tripping on an SDC though! The biggest variable in this debate is saw condition. You can't just get parts for vintage saws like it's a late model saw. So if you have a 700 in better shape than a 7-10 and it beats it's azz, you could argue the 700 is king.

I ran a well used super 250 against my fresh rebuild regular 250. The fresh 250 spanked the super even with a smaller carb and less cubes.