WTB MAC 91, 92, 93 direct drive sprocket nut

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Tim McElrath
Posts: 9
Joined: Tue Nov 15, 2016 11:55 am
Vintage Karting items owned: Mc90~somethjng engine. Still need to ID
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WTB MAC 91, 92, 93 direct drive sprocket nut

Post by Tim McElrath » Thu Nov 24, 2016 12:09 am

Just picked up a direct drive sprocket for my mystery engine and its in the mail. Looking for the nut I need to hold the thing in place. If anyone has one or could tell me what exatcly im lookong for, it would be greatly appreciated!

REAR
Posts: 686
Joined: Sat Jun 16, 2007 10:19 am

Re: WTB MAC 91, 92, 93 direct drive sprocket nut

Post by REAR » Thu Nov 24, 2016 8:29 am

Tim,

No tricks here.

Standard American thread pattern bolt will do the job. If a regular right hand bolt won't thread on get a left hand thread.

R.E.A.R.

Tim McElrath
Posts: 9
Joined: Tue Nov 15, 2016 11:55 am
Vintage Karting items owned: Mc90~somethjng engine. Still need to ID
User Agreement: Yes

Re: WTB MAC 91, 92, 93 direct drive sprocket nut

Post by Tim McElrath » Thu Nov 24, 2016 10:46 am

Ok. I noticed the ones that hold the clutch on are a little different because they have the shaft and are keyed. For direct drive though, im not going to need any spacer ir anything, huh? Sounds good to me, ill give it a go when the sprocket gets here. Should be early next week.

This project has been a little more complicated than I would have thought. My dad raced karts back in the 60's and he had a mcculloch kart. Im building this thing kinda for him and he is the only mcculloch resource I have so i cant really ask him. Also trying to keep it hidden from the wife, so i have very limited access to work on this thing and take measurements and piddle around with it. I still done even know exactly what model the engine that I have is. I knew about yhe MACBOBAUST website when I bought the engine (sight unseen) and planned on consulting his website once the engine arrived, but his website has gone down. I dont even know where to look to track down the number on the engine itself.
I know boost ports, shaft, woodruff key, carb, and color scheme can all point to the correct model but I have no idea if all that stuff is even original on my engine. The guy I bought it from said he hadnt gone trough it more than verifying good compression and spark, which it has.

Sorry for the vent, I do appreciate the help. Happy Turkey Day everyone!!

REAR
Posts: 686
Joined: Sat Jun 16, 2007 10:19 am

Re: WTB MAC 91, 92, 93 direct drive sprocket nut

Post by REAR » Fri Nov 25, 2016 8:12 am

Tim,

There are no numbers stamped in the block anywhere ?

Most 91.92 93 series parts are all interchangeable so a accurate identification is really not that important.

Is the crankshaft 'keyed', or 3/4" straight like on a lawn mower on the pto side ?

If its 91-93 series kart engine the flywheel cover is black wrinkle and the cylinder cover is bright yellow on kart specific engines.

R.E.A.R.

Rob Voska
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Re: WTB MAC 91, 92, 93 direct drive sprocket nut

Post by Rob Voska » Fri Nov 25, 2016 1:52 pm

Crank if tapered is a 3/8-24 thread per inch nut. Might be right or left hand threads.
If it's a 3/4" straight crank it's 3/8-24 bolt.

Tim McElrath
Posts: 9
Joined: Tue Nov 15, 2016 11:55 am
Vintage Karting items owned: Mc90~somethjng engine. Still need to ID
User Agreement: Yes

Re: WTB MAC 91, 92, 93 direct drive sprocket nut

Post by Tim McElrath » Fri Nov 25, 2016 11:14 pm

As far as I know it IS a kart specific engine. Has the black krinckle flywheel cover. Has tapered/threaded shaft and had a small woodruff key slot. Has a BDC-14 carb on it (its marked). It also has three or four little holes in the block that look like they have freeze plugs in them, i believe these are the "boost ports". Not sure what purpose they serve. Crank side of case is yellow

REAR
Posts: 686
Joined: Sat Jun 16, 2007 10:19 am

Re: WTB MAC 91, 92, 93 direct drive sprocket nut

Post by REAR » Sat Nov 26, 2016 7:14 am

Tim,

If your crankshaft has a keyway cut in it a standard right thread nut will work for a direct drive application.

The plugs at the back of the block are for access to the transfer ports on the back side of the block. There is also 3 transfer under the intake manifold, those together with the boost ports on the back side of the block feed fuel to the piston top.

R.E.A.R.

Tim McElrath
Posts: 9
Joined: Tue Nov 15, 2016 11:55 am
Vintage Karting items owned: Mc90~somethjng engine. Still need to ID
User Agreement: Yes

Re: WTB MAC 91, 92, 93 direct drive sprocket nut

Post by Tim McElrath » Sat Nov 26, 2016 5:27 pm

So do I pull the plugs from those ports? How do I unleash the avaiablr power in this thing?

REAR
Posts: 686
Joined: Sat Jun 16, 2007 10:19 am

Re: WTB MAC 91, 92, 93 direct drive sprocket nut

Post by REAR » Sat Nov 26, 2016 6:22 pm

Tim,

No, do not pull the block off plugs. First things first, get your engine running and your kart together.

Once you run the kart you can decide if you need more power.

There are many avenues you can take to inprove the performance of your engine and internal engine modifications are only part of the equation.

Believe it or not a McCulloch motor even though its nothing more then a chainsaw motor is something you just don't tear into. Port sizes, heights, timing, carburation, exhausts, clutch speeds etc. all play into hopping up a McCulloch engine and if you don't know what your doing you can take a perfectly good engine and turn it into junk in a heartbeat.

As stated earlier, get what you have running. In the mean time if your still set on more performance find yourself a good motor man or buy a bunch of old magazines with hop articles.

Good luck...R.E.A.R.

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