Mac Saw

[Sterling Brundick]

First I wish to thank those of you that have replied to my postings about vintage karting. Most helpful.

This Mac chainsaw I have with the 36" bar, what possibilites does the motor offer? The saw is a CP 125, Model # 600075, Serial # 10 - 11820. It is not frozen up. I actually used it several years ago.

[david a luciani]

post a pix.
i'm almost certain you have a great candidate for a saw to kart conversion.
the mc125 was a mc101 basically with a fixed head.
hard to modify the ports and you need a blind hone to rebore but still a real strong engine.

mostly you need to remove all the chainsaw parts.
usually you'll need to get a kart stuffer and intake and motor mount.
you could use the saw exhaust but any box muffler would look better.
dave

[mcbob]

The crank stuffer well be careful i dont think the kart stuffers fit they interfer with crank clearance stay with the origional the CP125 has an odd decompressor and is different to the one fitted to the SP125 yes the two engines mentioned suffer the same hassle fixed cylinder heads but i have and do run them on my hotsaws great engines proberly won;t catch a 101 but hey whose racing for sheep stations ??

McBob.

[Sterling Brundick]

David: I'm rather new at this, trying to attach pictures. But I think I got it right.

[mcbob]

To my MK 1 eyeballs thats a CP125 yes sir if you look at the DSP leverfor the decompressor it's a lever that trips a valve open the SP125 use a push button finger operated that blows shut once the engine fires.

McBob

[Tom Smith]

I don't think a CP125 is a very good candidate to convert into a kart engine because it doesn't have what's known as a 'booster port' in McCulloch nomenclature. It does share pieces with an Mc-101 but there are other saw power-heads that are closer to an Mc-101.
You'd be scrapping a decent saw to make a marginal kart engine going that route. Same goes for the SP-125 and SP-125C, the so called kings of the McCulloch saws. Truth is the best saws had the opposite swap, they put Mc-101 kart engines in the saws. I've seen a picture of a twin engine two-man McCulloch saw used for cutting giant redwoods in Northern California that had about a 30 foot bar, one power-head on each end, and the power-heads were both on tri-pods.
The life cycle of those McCullochs they used for cutting giant redwoods was about 3 weeks.
There is no shortage of the later generation McCulloch kart engines which would be much more practical. I know where there's a pile of them.
If for some reason you decide you do really need an Mc-101, get a nice stock Mc-101 to start out with.

[steveohara]

I agree with Tom. That saw in original configuration and complete like yours is worth some good money to the saw community. I would sell it and use the proceeds to buy a proper McCulloch kart motor. Parts and help with prep, repairs and tuning will be much easier to come by for the kart motor and I would expect a stock 91B1 or similar model to out perform the larger saw motor on the track.
Good luck.
Steve O'Hara

[Jacob Jay]

Also keep in mind that there are considerable differences internally between the CP-125 and any of the 101 engines and the SP-125 series and the 101 engines. The CP-125 uses a piston with a 1/2" wrist pin but the crown height is taller than a 101 piston. The SP engines use the hockey puck style pistons with the long 9/16" pin and loose needles encapsulated in the small end of the rod. These pistons are also taller than the 101 pistons.

The saw engine that most closely resembles the 101 is the 797/Super 797. The regular 797 basically uses the same piston as the M/C101. Thin rings, 1/2" pin, same crown height, same rod, etc. The Super 797 usually came with a thick-ring piston. I've seen 797s with cast boost ports, no boost ports, and a boost port with the removable cover.

These fixed-head saw engines have very large combustion chambers which means much lower compression ratios than the karters and lower port timing. The saw engines were designed to make peak power at a lower RPM.

[david a luciani]

as i said almost certain.
some of the best engine guys have spoken and i'd take their advise.
unless you're not in the states there are better options and cash will get you a decent kart motor.
figure the least you should get is a couple of hundred and i've seen them go into the 500 range.

of course if you're willing/have to use the motor or just want a decent kart motor it'll be all that.
along the lines of a mc30 or so for power and since we ain't racing it shouldn't matter.
if you have good machinist skills you can add the booster ports or finger ports for more power.
if theres stuffer issues get a gem super stuffer and remove the interfering metal.
rebuilding could be a hassle too but there are the center bearing pistons available now and then.
dave

[Kyle Tros]

Hey Tom,

I need a later generation Mac Kart engine. Can you point me towards the pile ?
a Mac 49 or maybe a 91 I would guess for a Rupp A-Bone replica.
Any advice is appreciated.

Thanks,
Kyle