Mcculloch sp125/101b kart saw build thread

[qurotro]

It's quite hard to get a right pic. The flash light made it look horrible, but it's not.


Piston. Some of the scraches are just oil reflecting on the light, but it's not spotless either.

 

[jacob j.]

That doesn't look too bad. I've seen high-hour 797s that looked a little worse than that but were great runners and strong in the cut.

Eventually that cylinder would probably need to go .010" over.

 

[qurotro]

Out of gas when filming.. She wants longer bar! Tune fat too.

 

[Bigmac]

It's quite hard to get a right pic. The flash light made it look horrible, but it's not.

View attachment 326869
Piston. Some of the scraches are just oil reflecting on the light, but it's not spotless either.
View attachment 326870

I bet it had a little rust in the bore at one point, like Jacob said I wouldn’t worry about it. I personally worry more about the needles in the rod and piston being worn on a high hour saw.

 

[Scott Kelsey]

Guys, what are the thrist washers that the 125's have in their pistons? An all metal washer? Also, is this a typical replacement part if you do a rebuild or can you reuse them?

 

[jacob j.]

The thrust washers are hardened tool steel. You can re-use them if they're in good shape and don't have a lot of wear, like palpable wear marks in the surface.

They're very important - you cannot build a motor using the SP style rod without the thrust washers. They keep the small end needle rollers lined up and captured.
One of the kart guys built a 125 motor for a kart and he used polished washers that were the same size from a hardware store. He said his motor lasted about a 1/2 hour.

The needle rollers chewed through the hardware store washers and wiped everything out.

 

[Scott Kelsey]

The thrust washers are hardened tool steel. You can re-use them if they're in good shape and don't have a lot of wear, like palpable wear marks in the surface.

They're very important - you cannot build a motor using the SP style rod without the thrust washers. They keep the small end needle rollers lined up and captured.
One of the kart guys built a 125 motor for a kart and he used polished washers that were the same size from a hardware store. He said his motor lasted about a 1/2 hour.

The needle rollers chewed through the hardware store washers and wiped everything out.

Good to know. Thank you.

 

[qurotro]

A bit of a long sad story. She kicked back unexpectedly and snap back so hard that crack the starter cover.
Any of you gentlemen have an extra that can let go? Looking for one with the matching patina.

 

[Bigmac]

A bit of a long sad story. She kicked back unexpectedly and snap back so hard that crack the starter cover.
Any of you gentlemen have an extra that can let go? Looking for one with the matching patina.
View attachment 328067
View attachment 328068

I don’t have one, the yellow can vary a lot so it can be difficult to get a good match. A 250 starter will fit the short cover and are usually not too expensive. I would have no problem running that even with the crack.

 

[jacob j.]

A bit of a long sad story. She kicked back unexpectedly and snap back so hard that crack the starter cover.
Any of you gentlemen have an extra that can let go? Looking for one with the matching patina.
View attachment 328067
View attachment 328068

I can probably come up with one if you want to get me your address.

 

[Scott Kelsey]

I have this 101 rod that has slight rust spots. Do you guys know of any way I could polish this up and make it useable or am I out of luck on this?

 

[heimannm]

quroto - I have a good supply of NOS starter covers in the Target baby blue color if you can't find anything else. They are plain and do not have the cast logo.



Mark

 

[Bigmac]

I have this 101 rod that has slight rust spots. Do you guys know of any way I could polish this up and make it useable or am I out of luck on this?

That is probably toast, I could be polished a little but then it’s going to make the clearance to large probably. These are loose new, and bad parts can cause a disaster. The kart guys that I listen to say to use no more than one part worn part, so that meadow if a rod is at the service limit, you need a new crank and needles, or anything in between. A rod .001 worn and crank .001 and new needles is ok, but a crank and rod .002 and rod .0o2 and used needles is a jackhammer, it’s kinda in spec but wont last

 

[qurotro]

Bearing needles are made in increment of 0.01mm I guess. Just sayin..

 

[qurotro]

quroto - I have a good supply of NOS starter covers in the Target baby blue color if you can't find anything else. They are plain and do not have the cast logo.

View attachment 328133

Mark

That is a hell of a cut off saw!
The biggest old cutoff saw I've seen is the one with homelite 925 motor.

 

[Bigmac]

Bearing needles are made in increment of 0.01mm I guess. Just sayin..

We have been struggling to find a plentiful source of big end needles, if you have a source let us know!
.0945 in x .547in or 2.40mm x 13.90mm. There was an aftermarket supply, but they seemed to have stopped, and they were also slightly undersize.
The info I got was from Steve Ohara, longtime Mac kart guys. Larger needles might work on an oversized rod, but an undersized crank might have the larger needles butt up to each other, then you might have to remove one. Just trying to pass on info that I have found. I have thought about the oversized needles for a while, and have saved some used parts just in case, undersized cranks are really common, billet rods were available, but it sounds like they may be out of production too.

 

[qurotro]

We have been struggling to find a plentiful source of big end needles, if you have a source let us know!
.0945 in x .547in or 2.40mm x 13.90mm. There was an aftermarket supply, but they seemed to have stopped, and they were also slightly undersize.
The info I got was from Steve Ohara, longtime Mac kart guys. Larger needles might work on an oversized rod, but an undersized crank might have the larger needles butt up to each other, then you might have to remove one. Just trying to pass on info that I have found. I have thought about the oversized needles for a while, and have saved some used parts just in case, undersized cranks are really common, billet rods were available, but it sounds like they may be out of production too.

Maybe focus on the od and not the length ? You can cut long ones, but I really don't know. Just an idea, I'm probably too young and dumb for those saws..

 

[Scott Kelsey]

That is probably toast, I could be polished a little but then it’s going to make the clearance to large probably. These are loose new, and bad parts can cause a disaster. The kart guys that I listen to say to use no more than one part worn part, so that meadow if a rod is at the service limit, you need a new crank and needles, or anything in between. A rod .001 worn and crank .001 and new needles is ok, but a crank and rod .002 and rod .0o2 and used needles is a jackhammer, it’s kinda in spec but wont last

Thank you for the input. Do the big end needle bearings need to be tapered? My SP125 has tapered needles where as the 101 did not? Also, are the big end needles the same as the small end or length/diameter different? I am not anywhere near to check mine at the moment and was just curious.

 

[heimannm]

Of all the part numbers I have looked at (66049, 69891, 85246, and 102742) the ends are all tapered.

Mark

 

[jacob j.]

Thank you for the input. Do the big end needle bearings need to be tapered? My SP125 has tapered needles where as the 101 did not? Also, are the big end needles the same as the small end or length/diameter different? I am not anywhere near to check mine at the moment and was just curious.

The OEM needles I've seen are all tapered but the needles I got from Quantum Racing are not tapered. I'll measure those to see if they're the same diameter as OEM or slightly oversized. Lynn Haddock ran Quantum Racing and he knows the Mac engines intimately and built some of the fastest 101s in kart racing. Sadly, he's gotten out of the parts production from what I can see, but Terry Ives has said that he still has billet rods for 101/91.