McCulloch Super Pro 125c build thread

[jacob j.]

I've spent the day pulling down my dad's old saws and wanted to show you guys some detail.

First up are the differences between the SP and CP blocks. I tried to show the difference in the combustion chambers - it's fairly substantial.
The SP chamber is smaller, has a much wider squish band, and is taller than the CP chamber. The CP chamber has a very narrow squish band
and has more a hemispherical shape. This was about the era when Dodge was coming out with the hemi heads on their V-8s so maybe they
influenced Bob McCulloch. The CP block is on the right.

 

[jacob j.]

Exhaust port differences - SP blocks have the large, oval opening and the three mounts for the SP style muffler. CP blocks have a bridged exhaust and a recess for the
rectangular exhaust gasket.

 

[jacob j.]

Ignition mount differences - diagonal mounts on the SP block (left), and horizontal mounts on the CP block (right).

 

[jacob j.]

101b block detail - long, ovalized exhaust port with recessed exhaust gasket, head with tiny combustion chamber, third exhaust mount is in the head.

 

[jacob j.]

I hot-tanked this block this morning - surprisingly it turned out quite well. After hot-tanking these steel sleeve blocks (like an automotive engine),
you want to get some oil on the bore right away or it'll start rusting immediately. If it's been in service a long time already then it may have congealed
oil in the pores and won't rust too bad.

 

[jacob j.]

More detail on the 101 head that Saw-King welded the mounts for.

 

[jacob j.]

Piston and rod differences - SP slug and rod on the left with the 9/16" wrist pin and needle rollers in the small end of the rod;
CP slug and rod on the right with 1/2" wrist pin and needle rollers caged in the piston.

 

[jacob j.]

Back side of the pistons - SP has an open wrist pin galley, CP is a "blind" piston so that the wrist pin galley is not open to the exhaust side of the piston.

 

[jacob j.]

Coils - on the left, a "Super Series" Mac coil with the horizontal mounts. On the right is a Pro Mac 610/650 coil that my dad modified to fit an SP-125 block.

 

[jacob j.]

As per Nathan and Mike's advice, I'm saving all my lower end rollers and marking which block they came out of.

 

[jacob j.]

Last shot - an SP crank with the bolt-on weights, and a 101 crank with the weld-on weights. McBob always indicated that the SP cranks made a smoother running saw.

 

[Steve]

Thanks for the great write up JJ!

 

[Bigmac]

Ignition mount differences - diagonal mounts on the SP block (left), and horizontal mounts on the CP block (right).

Great write up JJ! Dose that cp block have any number on it? Been curious about that! What muffler did your dad like on the 101?

I am running the 125 crank in my sdc saw, because of mcbob! I have two welded style cranks, one was a cp crank and the other was a 101aa, after seeing so may counter weight issues, I think I will have a buddy fussion Tig the counterweights to have some more insurance!

 

[sawfun]

More detail on the 101 head that Saw-King welded the mounts for.

I believe Lee has done that as well.

 

[p61 western]

Ignition mount differences - diagonal mounts on the SP block (left), and horizontal mounts on the CP block (right).

Looks like maybe a early boost port CP block Jacob? Thanks for sharing this stuff on your dads saw. This is pretty much how my build is going to be.

 

[Bigmac]

Looks like maybe a early boost port CP block Jacob? Thanks for sharing this stuff on your dads saw. This is pretty much how my build is going to be.

I think it’s the late style, replacement block, That’s why I’m curious about the numbers

 

[Frank bierce]

Some great technical info added there Jacob!!

 

[Bigmac]

101b block detail - long, ovalized exhaust port with recessed exhaust gasket, head with tiny combustion chamber, third exhaust mount is in the head.

Just as a note, it looks like a 3/8 reach plug was ran in that head for a while? Some kart head were made for 3/8 reach plug and some 1/2. I have both styles the 1/2 reach plug only comes in a longer body, the karts recoil cove is cut different and has a different boot, you can modify the saw cover if desired

 

[NPKenny]

Dang good thread!!!

 

[p61 western]

Just as a note, it looks like a 3/8 reach plug was ran in that head for a while? Some kart head were made for 3/8 reach plug and some 1/2. I have both styles the 1/2 reach plug only comes in a longer body, the karts recoil cove is cut different and has a different boot, you can modify the saw cover if desired View attachment 201997View attachment 201998

Very interesting stuff there.