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For those in need of cranks for a Mc5/6/49, there are a ton of stepcrank chainsaws that are perfect donors. The majority of the standard series saws with kart based motors are 80 cc's with 1 3/8 stroke. So its destroking a Mc6. But there are a few saws with the 1 1/2" stroke that should work. The early model saws have removable heads. Good donor step cranks include the D=30, D-36, 1-40, 1-41, 1-42, 1-43, 1-45, 1-46, 1-50, 1-51, 1-52. 1-53, D-45, Mc15, 200, 250, 300 and some more newer models. The D-30, D-36, and 1-40 have smaller counterweights, but still work fine in the rpm range these run. The models with removable heads are basically identical to the Mc5/6 blocks. These include the D-45, 1-50, 1-51, 1-60, 1-61, and 1-62. They are perfect replacements with exception to not having the third port induction drilled. Models 1-60, 1-61, 1-62, and 1-63 models have the correct tapered crank. The other models with removable heads include D-30, D-36, 1-40, 1-41, and 1-42, share the same block but not all of the intake/exhaust ports are drilled. The others listed are fixed head models and most do not have all of the ports drilled. Some 200/250 blocks have all of the ports including the third port induction, while others dont. So there are at least a few possible perfect Mc49 clones with no additional work. My preference is the 1-50/60 series block with removable head so the boost ports can be easily added and compression ratio changed.

Back in 1961 when my dad was racing, a buddy of his had connections to a chainsaw dealer and supplied a large amout of Macs to local racers. Being cheap and always looking for an edge, he was buying certian chainsaw blocks without all of the ports drilled to replace the Mc5/6. Then he would add the ports to his liking. Most of these did not have the third port induction added. So he first started adding two large squared ports instead of the three small ones equipped on kart blocks. Later he started adding one large round booster port in back like they had been having great success on the Power Products AH-61. One motor I remember seeing had two boosters that were drilled thru the block just like the other intakes. Then the passages were opened up and welded over. He said they ran good but took too much trouble. Then he was just plunging three small boosters like was becomming a popular mod to the actual kart blocks. I asked why he didnt plunge down two large boosters on the saw blocks without third port induction added like the newer 91 motors. He said they never thought of that at the time. Something else he did make use of was taking advantage of the blocks with just the two outer exhaust ports drilled. He said some guys were already doing this on a few resleeved blocks and where he got the idea. Well after digging thru a bunch of junk I found the end mill that had been ground to fit exhaust ports on the early motors. So I just had to try it out for myself. One pic is a stock 1-45 with only the two outer ports drilled. The center port is undrilled and just clean aluminum. The other is one I just opened up the exhaust ports like they started doing back then. I also have a rotary table set up on the mill to drill the other intakes that are blank and plunge two large boosters on the back side that never had the third port induction added. Adding boosters to one of these saw blocks really steps up the power. Installing a Mc7-91 crank really brings one of these motors to life. Hope this is helpful to some of you. If so I will follow up with more info and pics.

Terry,
What a great mod for the 2 port saw blocks, just like an Mc91.
I always have drilled out the center port and squared them all....Duhhhh I never thought of doing what you and your dad did but I will now!!

I have used quite a few of the stepped saw cranks and added extensions for a 5/8" clutch. I also did some with a 3/4" PTO but with one of those it is hard to get enough gear for the small engine. Noram makes an 11 tooth 3/4 bore clutch that works but you need a BIG axle sprocket.

Anyway attached are pics of the modified stepped crank and thank you for all the info and tips.
Happy Vintage

hi Terry,
great information here.
love the oval exhaust ports.
on the saws you wouldn't happen to have a list of saws with closed ports would you?
the reason i'm asking is if you or anyone else does it would be great to add to mcbobs site for ease of reference.
if you look at the site he recently revised a section listing which saws are super series or standards.
i also has a slightly more complete list of cranks and connecting rods too.
that should make everyone's life easier when looking for saw clone or interchange parts.

dave

As fas as the clutches are concerned I happen to have a small universal grinder. Actually used to be a piston grinder, but converted over for general use. I ended up grinding the 5/8" step down to 9/16". Then retain the original chainsaw clutch guts with 7/16 left hand thread hub and use either a rev-grip 9 tooth drum inboard or drill stock saw drum to bolt a 9 tooth 35 or 10 tooth 219 sprocket from a Horstman disc clutch. Nice, clean and stronger than original tapered key. Again this is some of the stuff that is being brought back from the past.

On one of my Mc10s, I bolted up a gear reduction from donor chainsaw. It has all of the casting cut off not needed for kart use. It made a gearbox extremely small and lightweight. Less than half the size of a Margay box. The driven output shaft fits a 35 chain gear to sprocket on axle. Sealed up with one big plus. The final gear is changed just like a standard setup. No need to tear in to the box to change ratios. No 70 to 84 tooth sprockets to bend. And no 9 or 10 tooth clutch drums that wear out and kill the chain. Again some more blast from the past. But I will leave this for another post in the future.

I know most of the saws that should have only two exhaust and intake ports drilled. Unfortunately I have seen the same models come both ways.I will compile a list that I know for certian and follow up. I do have everything relevent to a Mc 10, tho most has already been posted by others before. Also a Mc 20 and Mc 30 clone. One saw motor actually has factory squared exhaust ports just as the Mc30 came. This was a big suprise to me.

Yes,
I rebuilt a 740 saw once and that had squared exhaust ports and the same crank as an Mc30.
I was surprised to see that too.
Scott

Scott Kneisel wrote:Terry,
What a great mod for the 2 port saw blocks, just like an Mc91.
I always have drilled out the center port and squared them all....Duhhhh I never thought of doing what you and your dad did but I will now!!

I just realized how brain slow I am. My dads buddy had mentioned about seeing the two oval ports originally done on some resleeve blocks in 1961, so then copied. But way long before it was a consideration with McCulloch, a lot of the Clinton chainsaws in the mid 50's, then later in 1959 the E-65, already came with same configuration. I have been stepping over an old D-2 saw motor on the floor for the past month. Its nothing more than a small bore bushing motor, but those exhaust ports have been staring at me the whole time. DUH!

Another easy way to install a kart clutch on a stepped saw crank is to use the right clutch assm. and it will screw right on with one only having to know the correct direction to turn it. They have a 1-1/8" hex for installing and removing.

on the saws you wouldn't happen to have a list of saws with closed ports would you?

McBob has a a decent section with which I helped contribute with my 1-50 saw block that has a list of the saw blocks that can be used to recreate the 5 or 6. It lists the number of ports that are open. Hope this helps.