MCCULLOCH The official McCulloch thread

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My 4 a.m. (local time) brain starts wanting to know about what happens in the crankcase with those two intakes and any mathematics and resonances and mass and inertia and turbulence and interference possibilities?
Don't dismiss it.
Back in the 70's~80's, I think it was Morbidelli who was said to have looked at everything they could imagine for resonances and all this other stuff.
The article I read back then, the writer claimed they had pulled in someone with musical instrument background to help ponder the air flows and what mattered about it.
For that era, They managed to get some rather impressive HP numbers out of their race bikes as a result.

 

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Oh and are we gonna get to see the innards of the twin carb motor? Any deflectors or puttied or otherwise filled corners and such? Little radius's and etc..

It's just a heck of a thing when you're reduced to livin' vicariously through web pics!

 

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The crankcase bottom/stuffers in the mount looked to be pretty conventional.

Nothing special in the bottom end of the saw.



Someone has done some work under the intake, some transitions into the intake ports, added some holes in the cylinder wall (I think that is mainly for lubrication), and cut away the third port wall which I understand was a common practice on kart engines.



I have a MAC40 in a saw that AWOL worked some magic on, in his case he filled the third port with epoxy which I understand increases crankcase compression and improves the flow into the combustion chamber. The notch in the cylinder wall was from a rod failure, as is the damage you see around the intake in the bottom of the photo. JB Weld to the rescue.



On this one he also made some changes to the piston, I can't say I know where he was going with that work, but it does run pretty well still.





Mark

 

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Seemed like most of the kart crowd was pretty tight lipped about the internals, back then. Thnks for the images. Nice to see some things when these kart motors show up.
On Yamaha dirt bikes, which had a reed valve (70's era), we would ad a couple of holes in the intake side of the piston and trim out a little of the top of the intake tract, past the reed block. Made for nicer mid-range torque.
Just always spin your sandpaper in the piston holes. Leaving file any marks going across the metal thickness tended to promote cracked pistons, as any marks going in and out, are stress concentraters