Vintage Karting Forum

Hi everyone. Does anyone know if any Macculloch chainsaws came with a crank with a taper shaft with keyway,? And would they work in a 250mac chainsaw? I!am wanting to try putting a crank in my 250so I could use a outboard clutch. I know I could put a special clutch that Jim makes for the stub crank on a 250saw but it,s only for inboard,and I don,t think I have enough clearance with my a bone kart. Thanks for your help. MEl

You just need to make a engine mount with a 5/16" steel base plate that won't flex and have it hang over the edge of the mount to give you the clearance you need. I've run A bones and others this way for years. Way better than using an outboard clutch.

i think ..im pretty sure that you can find taper shaft saw crank fairly easy..ask chuck stroker ace ..I think maybe them guys use em to convert saw motors and make mc10 clones ..I think ..??

Hi Mel,
I "second" what Steve W said!

Some guys on here, and on the chainsaw forums, know their Mac interchangeability charts inside & out.  I sure don't, and finding a GOOD tapered crank that will fit could be a real hassle.

McCulloch recommended against using outboard clutches (in the owner's manual, I recall).  The crank diameter is on the small side when it comes to handling the bending loads from having the sprocket hung way out on the end.  Just as important, in order to get a reasonable ratio without having the axle sprocket dragging on the ground, most people use a 9-tooth driver.  Unfortunately, with such a small driver, the wall thickness of the clutch nut ends up being very thin, and they have been known to break, leaving you with no way to remove the stump.

Since you're running an A-Bone, you already have a swing mount.  That's the MOST important thing for avoiding crankshaft breakage, IMO.  With a swing mount, when the axle flexes over bumps, the chain tension won't instantaneously "go to the moon" and snap your crank.  With respect to chain tension vs. axle flex, the optimal location for the axle sprocket is between the axle bearing and the wheel, but it's not mandatory.

That said, you'll need to watch for interference between your chain (Space Chain) and the engine block.  You'll probably need to tap the PTO seal into the block a bit (use a deep socket as a driver) and accept that the chain will maul the block a bit.  Before you put the clutch on, smear a little RTV around the joint between the PTO seal and the block to help it stay put and prevent leakage.

Sorry to drone on.  Now I got Brunhilda over my shoulder; gotta run!

mel, a mc49 crank is the direct substitution for a saw crank with the rooler bearing stub shaft.
as to whether you should do this conversion i'd say no.
steve w. is absolutely correct about how you can mount your motor and get the required clearance.
if you ask nicely i'm sure he'd post pix of what to do.

Steve m., is of track about tapered cranks in saws.
 the standard saws with the mc49 stroke spec did away with tapered cranks early on and went exclusively with stub cranks.
and mc10 clones aren't even in the same discussion as mc standard saws conversions. 
no shade on steve on this , saw interchangability s a complicated subject that i happen to know a little about.
we had a ton of info but i made the mistake of posting it on two sites that later went away. 
redoing this info takes time.

to answer your question.
there are mcculloch saws with tapered cranks some even are found in mc250's.
 the issue is they have pto BALL  bearings not roller bearing.
mcculloch  did away with pto roller bearings on tapered saw cranks about the same time they shifted to stub cranks on the pto roller bearing equipped saws.

so your options are 
replace the saw crank with a mc49 crank and use any mcculloch tapered clutch
you can get an extension shaft and use a straight bore clutch either inboard or outboard clutch (outboard clutch not advised) 
you can use jim's excellent max torque inboard clutch made for stub shafts , modify your mounting ideas and forget about the clutch

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look closely at that setup. Offset mount, mac 49/ 250 saw with stub crank inboard. Won a lot of races with that setup. bullet proof.

Thanks everyone for your opinion, very much appreciated. IT looks that Making it inboard clutch is the way to go.The 250 Mac was given to me and it looks that it would make a great motor to run the 49 class but want to keep cost down as much as possible. Looking forward to running fremont