The Kart Engine Thread

[cpr]

Feel free to share your knowledge of the McCulloch, West Bend, Power Products, and Homelite engines here. Please try to keep it to the kart engines, tech, resources, tricks, etc.

I'll start off with a question. I have several MC-10 based 87cc McCullochs. While I have never been able to verify that the blocks are different, meaning port timing and sizes, the heads are different on the saws. The saws have the spark plug opposite the exhaust port. With 2-stroke motors, the theoretical advantage of placing the plug opposite the exhaust port for maximum mixture combustion before port opening is intuitive, I have to wonder what other differences there are. Is the central plug MC-10 head more conducive to power with flame front propogation in all directions around the head and across the piston? Is the combustion chamber smaller on the kart head than the saw head? I know hood clearance would be necessary to acommodate the plug like on a D-44, but could I pick up some saw performance with a head swap?

 

[Brian13]

Subscribing . Do you know if the Mc-10 has a thinner head gasket then the S44A does?

 

[cpr]

Don't know Brian. I have seen various thickness head gaskets, though.

 

[Jacob J.]

First off- the kart blocks do in fact have different port timing than the saw blocks, by and large. The kart motors were designed to make their power at a higher RPM, and the saw motors were made to peak much lower. This was as much to do with cutting attachments of the day than anything. It wasn't advantageous to design saws running hardnose bars and 1/2" or 9/16" pitch (mostly semi-chisel or chipper) chain and try to get them making peak power at 9k in a 87-103cc motor.

Yes, for the most part the kart heads have a smaller CC than the saw heads. There is a performance gain from swapping heads but you have to make sure you have the head with the correct bolt spacing. Also, I can't remember for sure, but I think the larger, square kart heads wouldn't fit under some of the saw shrouds without modification.

Some of the kart guys are converting the saw engines over to replica kart motors. It takes a lot of work in changing port timing, (in some cases) ignition timing, external parts, and utilizing the kart intakes and exhausts.

I sure wish there was more of a secondary market on the aftermarket stuff for the West Bends and Power Products motors. I had to wade through a ton of crap to find a Wiseco thin-ring West Bend 820 piston. It only took about 12 years. umpkin2:

 

[Busmech]

Kart pistons

I guess I was lucky I got a wiseco thin ring 820 piston off ebay last year after about eight years search. I have several mac 101 pistons, all from ebay, rods are the thing I am having a problem finding.

 

[cpr]

Figured this would draw you out JJ. You've probably got as much exprience as anyone here with these, thanks again and in advance for sharing your thoughts.

Let's develop the theory a little more. Does higher rpm automatically mean more hp? In the abstract, it might, but as you note, this may not translate to a faster cut. Thrown into 30" plus of hardwood hauling some FAT chain, the saw blocks may enjoy a torque advantage that going to a kart block may not soon surpass.

MC-10 heads seem to be "affordable" vs entire engines. May have to do some experimentation in the future.

 

[Jacob J.]

No, higher RPM doesn't translate necessarily into higher HP automatically. I actually prefer in many cases, the saw blocks, especially in larger displacement. My latest project involves cutting the heads off of three SP-125 blocks, having them bored out .050" over and chromed, and then fitting custom heads to them. Two will get all-new manufactured heads while the third will get a custom WB-820 head that has larger cooling fins.

One of the biggest complaints I heard from guys (including my dad and grandpa) who ran the kartsaws in the woods was the high temps they ran at. After I tore down all my dad's saws I could easily see what he was referring to. There was a lot of really baked-on stuff that had seen high temps.

Hopefully we can get Lee involved in this thread as well, since he's built up some of the kartsaws. Jay (Bigbore577) and Hoss both have 101b kartsaw rigs.

Another of my kooky ideas involves a Homelite 990 saw chassis, an Mc-7 crank, an Mc-90 .010" over domed piston (thin rings), an Mc-93 rod, and a Mikuni 34mm carb. It's a witches' brew but might make a good runner.

 

[Jacob J.]

Another good thing about those early saw blocks like the D-44/55 is that they have the steel sleeves, so there's flexibility there in adapting them to handle a particular load range. Some of the kart blocks don't give you that option.

 

[heimannm]

I'll watch, and hopefully learn something here.

Mark

 

[ttyR2]

Though y'all might like to see some pictures from early '60's Hot Rod magazines specific to karting. Some McCulloch action:

Mac 55's:

Mac 99:

Triple Mac's:

Dual MC-6's:

 

[crmyers]

Great pics, this thread is looking better and better.

 

[Bill G]

Here is a Mercury-Disston KB7 on a kart.

 

[blsnelling]

Very cool info. I know little to nothing about these engines, but I find them intriguing.

 

[nmurph]

Bill, get that pic up. that is a combo i have not heard of for a cart motor.

 

[Bill G]

I am trying to figure out the pictures now that all changes have been made. I will try again as an attachment. Someone please post it directly if I get it attached.

Bill

 

[blsnelling]

Here ya go Bill.

 

[Bill G]

Now how did you get the pic to show up

 

[blsnelling]

Now how did you get the pic to show up

Do a quote of my post and you can see the HTML. All you have to do is copy the URL of the pic, then click the image icon just above the message body you're typing, and then paste it in.

 

[Bill G]

I can understand that simply enough because the pic was hosted here once I posted it as attachment. What I need to figure out is how to do it from a pic saved on my camera.

Bill

 

[Bill G]

Here is a Disston DA 211 with AH 58 cylinders and pistons