McCulloch Super Pro 125c build thread

[jacob j.]

A little more work on this bidness...Today I'm building two more short blocks, one with a NOS SP-125c cylinder. I have an older iron-liner cylinder
I'm also building a runner out of. Here, I'm re-ringing the piston with some vintage Wiseco chrome-lined rings. You can use these in the iron-liner
saws but of course not in the chrome-lined 125c jugs.

 

[jacob j.]

On the large-frame Mac saws, you want to install the bearings on the crank first. If you try to install the PTO bearing in the crankcase first, you
won't be able to get the piston and rings in the bore. I put the bearings in the oven for about ten minutes at 200-225° f and the crank in the freezer
for a half hour, and the bearings usually slide right on. Then I put the bearing/crank assembly in the freezer for another half hour before installing
the assembly in the crankcase.

 

[jacob j.]

Here, I'm installing the reciprocating assembly in the block, and I've already installed the new PTO seal.

 

[jacob j.]

I take off the cap and rod bolts prior to installation. The bottom of the bore in the large-frame blocks has a taper or recess which helps with working the
piston and rings in. You just need to make sure the rings are lined up on the ring locating pins and then lube the ring area real good with assembly lube,
and carefully work the mess in.

 

[jacob j.]

Now the fun part - getting the big end needles in. 85420 is the latest part number I have for the SP-125 needles, but there are other part numbers that work
fine, including the needles from the CP-125 which have the 69891 part number. Usually in a new package, you get 25 needles, even though the engine only
takes 24 max. I guess the one extra needle is in case you lose one. I use the proven method of sticking the needles on with grease - I do 12 on the upper side
of the rod journal, and 12 on the cap. Then I rotate the crank over, and line up the upper end of the rod which sticks out of the bore. When I get the rod journal
and rod lined up, then I carefully set the cap in place. Then I stick the rod bolts in and pull everything together with the rod bolts.

 

[jacob j.]

Once you get the cap snugged down, you'll need to make sure you've lined up the strike-off areas correctly (where the cap was broken off of the rod at the factory). There'll
be a very faint line where the cap and rod mate if you're lined up correctly. I don't torque the rod bolts at this point - I wait until I get the backing plate installed. With only
the PTO side bearing seated at this point, everything is still too unstable to get an accurate torque reading. Once you have the backing plate on and everything bolted together,
it will be a lot more stable and you can get a better torque figure.

 

[jacob j.]

This here is my secret weapon for torquing the rod bolts - it's a quality tool. I actually have an extra new 1/4" drive torque wrench if anyone needs one.

 

[Nutball]

Very unique and unusual engine by today's standards. Looks like quite a puzzle if you don't already know all the tips and tricks.

 

[Frank bierce]

I take off the cap and rod bolts prior to installation. The bottom of the bore in the large-frame blocks has a taper or recess which helps with working the
piston and rings in. You just need to make sure the rings are lined up on the ring locating pins and then lube the ring area real good with assembly lube,
and carefully work the mess in.

Some more great information Jacob!!

 

[p61 western]

Once you get the cap snugged down, you'll need to make sure you've lined up the strike-off areas correctly (where the cap was broken off of the rod at the factory). There'll
be a very faint line where the cap and rod mate if you're lined up correctly. I don't torque the rod bolts at this point - I wait until I get the backing plate installed. With only
the PTO side bearing seated at this point, everything is still too unstable to get an accurate torque reading. Once you have the backing plate on and everything bolted together,
it will be a lot more stable and you can get a better torque figure.

That's a funny looking 346 boss.

 

[jacob j.]

That's a funny looking 346 boss.

Speaking of which, mister...

 

[p61 western]

Speaking of which, mister...

Lmao

 

[Lee H]

Yup, These old Mac's are very unique in there own design but once you have had one apart
and reassembled they are pretty basic and easy. I really enjoy doing the 101's, 797,s and 125's.
Fun saws to work on and when you first fire it off it's like heaven to bring the ole girl back
to life.

Nice job Jacob.

 

[Al Smith]

Just as a tid bit of info and little known fact the pressure cracked connecting rod was a McCulloch innovation and is now used by a majority of manufactures in the automotive industry .To further add to that Ford had a new engine ,before I retired that had pressure cracked main bearings . These things just evolve as time marches on .

 

[exSW]

This here is my secret weapon for torquing the rod bolts - it's a quality tool. I actually have an extra new 1/4" drive torque wrench if anyone needs one.

Check your inbox

 

[Al Smith]

There isn't anything actually secret about these . top break over torque wrench made for production .has to be preset .I have about 8 0r ten of these. Center Snap On dial,metric and standard .Bottom precision Facom beam metric .Set tool for a precision gauge .All freebies .find dumpster will dive .

 

[Lee H]

There isn't anything actually secret about these . top break over torque wrench made for production .has to be preset .I have about 8 0r ten of these. Center Snap On dial,metric and standard .Bottom precision Facom beam metric .Set tool for a precision gauge .All freebies .find dumpster will dive .

Those are the best torque wrench's out there. Accurate to 2 %, That's what I
use on all my low torque spec bolts.

 

[jacob j.]

There isn't anything actually secret about these . top break over torque wrench made for production .has to be preset .I have about 8 0r ten of these. Center Snap On dial,metric and standard .Bottom precision Facom beam metric .Set tool for a precision gauge .All freebies .find dumpster will dive .

Very cool Al - I saw some of dial gauge type Snap-Ons on ebay and thought about trying one of those. A buddy got me the Teng wrench after I did some freebie repairs for him.

 

[jacob j.]

Well, I got two more short blocks done today - ready to build saws with:

 

[jacob j.]

That's a funny looking 346 boss.

Did you get your 346 done Mike? I got mine done today: