McCulloch Super Pro 125c build thread

[jacob j.]

This old 795 piston had seen better days. I was from a rebuild I did for a local guy years ago. Sometimes the blind bore needle cage
comes out smoothly and sometimes the end cap just breaks off. Either way, then you can pull the pin. When they have this much
wear and tear, you don't want to try to save the needle bearings and cages anyway.

Extraction complete. In this picture, I'm showing the difference between the 795 and 797 wrist pins and connecting rods. The 797
rod is about a 1/4" longer than the 795, but the 795 wrist pin is longer. The 795 wrist pin is also a lot thicker and heavier.

 

[jacob j.]

How I like to set the 1/2" wrist pin assemblies - just to the point where you can start to see the ends of the needle rollers on the open side.

This means fresh mix will readily get in there and flush out contaminants and keep everything in good shape.

 

[jacob j.]

Here's some experimentation - two .030" over pistons; one is a new 101A style and the other is a used SP style. Years ago, I sent the SP piston to a former AS member and had him weld up
the crown a bit and shape out a substantial pop-up. The piston crown was damaged and I have a .030" over block that has damage to the squish band that I'm going to use it in. The new
.030" piston is for a customer saw.

 

[jacob j.]

Cleaning up the ports on a .030" over block - It had been lightly "needled" and the tops of the four of the six transfer nozzles had some issues. It's kind of hard
to see in these photos but they cleaned up well. This was another block Terry Ives bored for me years ago. I'll block sand the intake manifold mounting area.

 

[Bigmac]

Nice job! That pop up will be interesting’

 

[PogoInTheWoods]

Excellent info as usual. Even though I'll likely never have any version of one of these saws, I truly appreciate the effort to educate me about them..., just in case! LOL

 

[jacob j.]

Excellent info as usual. Even though I'll likely never have any version of one of these saws, I truly appreciate the effort to educate me about them..., just in case! LOL

Never say never - there are still a lot of these saws out there, in barns, sheds, and garages - just waiting to be rescued. The deal in 1999 where I got most of the stuff I have now was purely by accident, and I didn't
even want all of the stuff at the time simply because I had no where to put it all. The guy I was trading with though really needed the new 066 I had and he was in rough, rough shape - so I made the trade.

McCulloch saws have been ruining my life ever since...

 

[sawfun]

This old 795 piston had seen better days. I was from a rebuild I did for a local guy years ago. Sometimes the blind bore needle cage
comes out smoothly and sometimes the end cap just breaks off. Either way, then you can pull the pin. When they have this much
wear and tear, you don't want to try to save the needle bearings and cages anyway.

Extraction complete. In this picture, I'm showing the difference between the 795 and 797 wrist pins and connecting rods. The 797
rod is about a 1/4" longer than the 795, but the 795 wrist pin is longer. The 795 wrist pin is also a lot thicker and heavier.

Me sure likes long rod lower wrist pin weight.

 

[jacob j.]

Another .030" over SP saw - this one is headed to a local customer. The piston is a new 101AA style .030" oversize with a refurb 1/2" wrist pin rod and new main bearings and seals.

 

[Lee H]

Gotta love that sound.

 

[jacob j.]

I have to annoy you guys with even more 125 build minutiae - This weekend I'm putting together a .010" over saw for customer, a long-time retired
logger who started his career with big McCulloch saws. The block was previously bored by Saw-King many years ago and I picked up a new 101AA
style .010" over piston with a new 1/2" wrist pin and CP style rod.

 

[jacob j.]

I'm using the "Snake Skin" reeds in this build - I've used them in my last two builds and I really like how they run. The seller for these told me that they'll stand-up to
ethanol-containing fuels a lot better over time.



Here's an Ebay link for the snake skin reeds:

https://www.ebay.com/itm/VINTAGE-RA...KE-SKIN-REED-VALVE-McCULLOCH-SAW/382869459687

Here's the regular reeds:

https://www.ebay.com/itm/Vintage-Mc...c-49E-49-Mc49-Mc49E-Chainsaw-NOS/123817500825

 

[jacob j.]

I'm also out of new OEM big end rod needles, so I'm trying these aftermarket jobbers:




Here's an Ebay link:

https://www.ebay.com/itm/McCulloch-...-replaces-69891-fits-all-MC-Kart/174195350229

 

[jacob j.]

I didn't have new .010" over rings, but Terry Ives previously hooked me up with some Burris .012" over rings, so I had to size these to fit. When I'm sizing oversize thin rings, I use a cut-off
wheel in my Dremel and I make a Sharpie mark on the ring ends to represent approximately how much to take off after I've mic'ed the rings in the bore. In this case, I knew the ring locating
pins are approximately 1mm (.040") thick, and the minimum ring end gap according to the Wiseco ring sizing chart for thin rings is .010", so I would need at least .050" gross ring end gap if
the bore is sized correctly. So I started out slow, trimming a bit off of each ring end, carefully keeping the ring end perpendicular to the outer edge of the ring. I check the ring after trimming each
end by pushing the ring up in the bore with the piston and plotting the gap with a feeler gauge. It took a few tries but I ended up at just over .010" for each ring.



It's hard to see in this shot, but I check the rings on the piston prior to installing the crank. I rotate the piston around so I can see each ring gap.

 

[heimannm]

Just FYI for you PNW fellows, the PNW GTG is on for 11-14 June. The gathering is a few miles east of Springfield, OR off 126, follow the river south at Hendricks Bridge Park.

Mark

 

[srcarr52]

Another .030" over SP saw - this one is headed to a local customer. The piston is a new 101AA style .030" oversize with a refurb 1/2" wrist pin rod and new main bearings and seals.

Is that one of the muffler covers I welded?

 

[jacob j.]

Is that one of the muffler covers I welded?

Yessir, I think it is, I sent the parts you welded off to Mike for powder and of course they turned out great. I've got some custom
125s coming up soon, including some pretty wild stuff. I'm doing a CP saw of my dad's in metallic Candy Purple.

 

[heimannm]

Can anyone tell me if the crankshaft in the CP125 and SP125 are interchangeable? I haven't had the parts on the bench at the same time to make a comparison.

Mark

 

[Bigmac]

Can anyone tell me if the crankshaft in the CP125 and SP125 are interchangeable? I haven't had the parts on the bench at the same time to make a comparison.

Mark

They are interchangeable, only difference is left hand right hand threads on the PTO side, CP has right hand threads SP has left hand threats, the CP is also a welded style crankshaft and the SP has bolt on counterweights

 

[jacob j.]

Can anyone tell me if the crankshaft in the CP125 and SP125 are interchangeable? I haven't had the parts on the bench at the same time to make a comparison.

Mark

They are interchangeable, only difference is left hand right hand threads on the PTO side, CP has right hand threads SP has left hand threats, the CP is also a welded style crankshaft and the SP has bolt on counterweights

You can use them interchangeably, as Nathan points out, there are minor differences. The bolt-on weights of the SP crank (along with the left-hand PTO threads) were an upgrade over the earlier saw cranks. The CP crank (69346) also came in 101 engines and are getting hard to find since the kart guys are poaching them to keep the kart engines running. Nowadays they're poaching the SP cranks (85746) as well and just having the bolt-on weights TIG-welded to keep them from coming off. CP crank top, SP crank bottom: