Mcculloch Super Pro 125c Complete rebuild.

[hkusp9]

Do you understand how the taper between the crank and flywheel works, that the key is for alignment and the taper does the actual holding?

Yeah i get it. The key basically just sets ignition timing along with and in conjunction with the points. thats why im going to use the valve lapping compound to get a good fit with one of the other flywheels that im about to "procure" from one of the other saws, so the flywheel doesnt shear another key.

Like i said, the flywheel channel was already a little ate up and the inside taper of it didnt look too perfect when i pulled it off. That why i had so much trouble getting it off in the first place.

Like some of the other people were saying earlier though, had i cleaned it up really pretty before i put it back on, i probably wouldnt have killed it when i started it for the second time....

 

[cbfarmall]

Like i said, the flywheel channel was already a little ate up and the inside taper of it didnt look too perfect when i pulled it off. That why i had so much trouble getting it off in the first place.

Like some of the other people were saying earlier though, had i cleaned it up really pretty before i put it back on, i probably wouldnt have killed it when i started it for the second time....

In my experience a flywheel will be too easy to remove with a damaged taper, especially if the flywheel spun.

Valve grinding compound on these tapers works wonder, though yours looks pretty bad.

Chris B.

 

[heimannm]

You have a few flywheels on the other big saw that will work, don't waste any more time on one that is already trashed.

As other have pointed out already, the flywheel from just about any saw from the D-44 on up will work. If you can find one from a LH starter saw you won't even have to mess with transferring the starter pawls. customchainsawparts on e-bay will have several that would work right now if you insist on buying one. I have swapped the flywheel from a 200 or 250 on one of my SP105's to eliminate issue with broken fins on the original, same exact flywheel.

Mark

 

[buzz sawyer]

Two other suggestions.
1. Don't use sandpaper on the points, it can leave rough surface impregnated with residue from the adhesive. May not be a problem at first but after they arc a few thousand times ( a couple minutes run time), it can create high resistance. Use a file (a good raker file will work, albeit slowly). The smoother the surfaces are, the longer they will last.
2. Already suggested but check the wire where it connects to the kill switch - not much clearance in that area and it caused mine to miss badly.

As already said, don't rush it. Besides being a nice classic saw, when you get it running there is a lot of weight moving and if any of it comes loose, you can't run fast enough to get away from it.

Good luck!

 

[hkusp9]

allright, so i pulled the flywheel off another saw. Blasted all the paint and cobwebs and crap off of it, lapped it to the crankshaft perfectly, and got the key that i need.

Then i noticed that it only has one starter pawl hole for some reason. I had to drill the other one the other half of the way out, and now im trying to get the starter pawls off the first flywheel to put it on the new flywheel.

I know that these things have teeth or flanges on the shaft and that they have to pull straight up and out but how do you do that?

Is there a special tool or something, some kind of prybar that slides under the pawl or something? Im going to go read up now.

 

[hkusp9]

ok, i had to drill out one of the worthless starter pawl nails from the back and pry the damn thing off. The other one was kind enough to pry off with a crowbar, and yes at that point i had stopped caring since i knew i could (and probably should have to save the hassle) buy a new flywheel and pawls online if necessary.

Anyhow, i pried off the pawls and nail and hammered the crooked nails back in the spare flywheel, which surprisingly went in straight and look factory perfect now.

Oh, also i rebuilt the carb just now as well. Here in a second after i look up the flywheel torque values, im going to crank it up first and give it a little test idel/run before break it the rest of the way down to chean and repaint it and fix the gas tank leak...

 

[Mastermind]

ok, i had to drill out one of the worthless starter pawl nails from the back and pry the damn thing off. The other one was kind enough to pry off with a crowbar, and yes at that point i had stopped caring since i knew i could (and probably should have to save the hassle) buy a new flywheel and pawls online if necessary.

Anyhow, i pried off the pawls and nail and hammered the crooked nails back in the spare flywheel, which surprisingly went in straight and look factory perfect now.

Oh, also i rebuilt the carb just now as well. Here in a second after i look up the flywheel torque values, im going to crank it up first and give it a little test idel/run before break it the rest of the way down to chean and repaint it and fix the gas tank leak...

 

[ozflea]

I would replace that flywheel, One off one of the other saws
should work. Many of the larger mac's use the same flywheel.
Is there a 250 in the batch you got? You can also lap the
flywheel to the crank with valve grinding compound. That will
make sure both surfaces are meant to be together. A flywheel
key you will have in one of your other saws as well. Also, Replace
the coil wire you cut the cover off of. Get one off one of your other
saws as well. It's great to have a few low dollar parts saws as
some parts will interchange.

I agree with Mastermind, Slow down before you ruin this classic
saw. Rome wasn't built in a day. Take it slow and pay attention.




Lee

The SP125c has an extra 5 degrees of advance over the early type flywheels

 

[hkusp9]

The SP125c has an extra 5 degrees of advance over the early type flywheels

!!!!!

this i didnt know, i grabbed a flywheel off of something that was definitely an earlier flywheel. Interesting to note however that i did get it fired up and it ran pretty well at WOT but didnt idle and seemed to be surging at mid throttle.

Im about done messing with it to see if it will run and if its worth a further time investment. It will run, and it is worth completely breaking down and rebuilding.

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[hkusp9]

Ok, so i did some more reading and from what im hearing, increasing the gap on the points will advance the ignition timing.

Assuming that my older flywheel doesnt have the 5 degree advanced timing, and since i dont have that little white plastic factory McCulloch tming tool to check it, can i adjust the points gap to make up for the difference?

Honestly, at this point i would be happy to buy a 125c specific flywheel just to try but i cant find one anywhere online and ive been searching pretty diligently. Tomorrow if i get time im in going to try to dig into the gas tank and correct the leak as well as clean up some components underneath it.

Also, assuming that i really do get in (more) over my head on this... Is there anybody on here that will rebuild this thing for a reasonable price?

 

[russhd1997]

Ok, so i did some more reading and from what im hearing, increasing the gap on the points will advance the ignition timing.

Assuming that my older flywheel doesnt have the 5 degree advanced timing, and since i dont have that little white plastic factory McCulloch tming tool to check it, can i adjust the points gap to make up for the difference?

Honestly, at this point i would be happy to buy a 125c specific flywheel just to try but i cant find one anywhere online and ive been searching pretty diligently. Tomorrow if i get time im in going to try to dig into the gas tank and correct the leak as well as clean up some components underneath it.

Also, assuming that i really do get in (more) over my head on this... Is there anybody on here that will rebuild this thing for a reasonable price?

I don't remember reading anywhere in this thread that you actually checked the compression! If the compression is good that part of it doesn't need to ###### with!

The next thing that I would do is perform a vacuum and pressure test to make sure that there are no leaks. If the seals and gaskets are not leaking I would fine tune it and run it!

 

[buzz sawyer]

ok, i had to drill out one of the worthless starter pawl nails from the back and pry the damn thing off. The other one was kind enough to pry off with a crowbar, and yes at that point i had stopped caring since i knew i could (and probably should have to save the hassle) buy a new flywheel and pawls online if necessary.

Anyhow, i pried off the pawls and nail and hammered the crooked nails back in the spare flywheel, which surprisingly went in straight and look factory perfect now.

Oh, also i rebuilt the carb just now as well. Here in a second after i look up the flywheel torque values, im going to crank it up first and give it a little test idel/run before break it the rest of the way down to chean and repaint it and fix the gas tank leak...

FWIW, on mine, the pawl pins drive out from the back with a punch. Support the flywheel at the hub, not the fins.
Make sure the pawl pins are secure - if reusing them, put a little loctite on the splines.

You can advance the timing by opening the points but keep in mind, while they are together, the coil is building up primary field which, when the points open, collapses and induces a voltage in the secondary windings. Less time together (wider gap) means lower voltage to fire the plug. I normally set them a couple thousandths above spec to compensate for wear on the cam rubbing block.

It sounds pretty good running but do check for vacuum leaks - especially around the oil tank gaskets and inner flywheel housing as well as the seals. Also be careful with the boot under the fuel tank, they're hard to find and expensive. I've heard a boot from a Stihl 880 will work but haven't tried it.

 

[leeha]

Sounds like you got an air leak some where.

I would fix it for you but the shipping would be
expensive. Probably 50 beans each way.




Lee

 

[hkusp9]

Sounds like you got an air leak some where.

I would fix it for you but the shipping would be
expensive. Probably 50 beans each way.




Lee

Air leak was my guess as well. I dont want to run it too much with a leak and cause lean sieze or something. I think im going to disassemble it down to the engine block in order to clean and repaint it and fix the gas tank leak anyhow. Then when i get it back together i will vacuum test it and if it leaks then its going to have to get sent off to somebody because i dont have a press or the confidence to mess with the pressed in bearings.

Finally, can anybody weigh in on whether this older flywheel is actually going to be problematic or not?

 

[hkusp9]

Also, somebody mentioned checking the compression...
Its hard to get a grip on it right now with the handles off of it but still, right now its a bear to start with the compression release valve activated.

I have no idea how i would pull it over without pressing that valve in first. In fact ive never heard of anybody mention pulling over one of these things by hand to get numbers off of it.

 

[rwoods]

Also, somebody mentioned checking the compression...
Its hard to get a grip on it right now with the handles off of it but still, right now its a bear to start with the compression release valve activated.

I have no idea how i would pull it over without pressing that valve in first. In fact ive never heard of anybody mention pulling over one of these things by hand to get numbers off of it.

If I can do it - you can do it. Ron

View attachment 253326

 

[hkusp9]

If I can do it - you can do it. Ron

View attachment 253326

Holy ####!

I stand corrected....and remind me to never arm wrestle you

 

[rullywowr]

ok i went and bought some hondabond 4 and a carb rebuild kit. Hopefully i wont have to tear the engine down but i do plan on resealing the leaking gas tank.

And then i started sandblasting and primering stuff.

before

after

finally, should i JB weld these cracks and grind them smooth?

Nice Glock! What model?

 

[hkusp9]

Nice Glock! What model?

:msp_w00t: sorry, didnt notice that it was visible when i took that photo, might need to review these on the computer monitor before posting them from now on. The tiny I-phone screen didnt pick that up.

I usually unholster it and keep it close when going through the local banks drive through ATM.

This is a chainsaw forum but since you asked its a G26 with trijicon night sights, 3.5# disconnector, extended slide and mag release and maritime spring cups.

 

[Eccentric]

FWIW, on mine, the pawl pins drive out from the back with a punch. Support the flywheel at the hub, not the fins.
Make sure the pawl pins are secure - if reusing them, put a little loctite on the splines.

You can advance the timing by opening the points but keep in mind, while they are together, the coil is building up primary field which, when the points open, collapses and induces a voltage in the secondary windings. Less time together (wider gap) means lower voltage to fire the plug. I normally set them a couple thousandths above spec to compensate for wear on the cam rubbing block.

It sounds pretty good running but do check for vacuum leaks - especially around the oil tank gaskets and inner flywheel housing as well as the seals. Also be careful with the boot under the fuel tank, they're hard to find and expensive. I've heard a boot from a Stihl 880 will work but haven't tried it.

It's that way on all the large frame McCullochs that I've worked on. Would've thought that it was obvious. No need to flail at the "nails" with a crowbar (even if you "don't care" at that point). If you drive the pawl pivot pins ("nails"....ugh) too far and the pawls don't pivot freely, you can give them a TAP with a hammer and punch from the backside to loosen things back up.

Also, that saw will run just fine with a 0-degree flywheel. ALL of the other large frame Macs (including the non 'C' SP-125 saw) did. A zero degree flywheel will also make the saw a tad less cranky when starting (compared to a 5 deg flywheel).....

Frustration happens. Setbacks happen. If something as simple as some stubborn pawl pivot pins throws you into a rage where you "don't care" and go at the saw with a crowbar......................well maybe you need to find another hobby and let somebody else deal with these old beasts...