MCCULLOCH The official McCulloch thread

[legdelimber]

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.

 

[legdelimber]

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!

 

[heimannm]

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

 

[legdelimber]

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

 

[edju1958]

I got the crank & piston for the PM55 today.I can't even feel the scratches with my fingernail.I'm wondering if I can clean it up with emery cloth & it'd be good to go.Supposedly it came out of a running saw.

 

[heimannm]

Polish it with some Scotchbrite and go cut wood.

Mark

 

[jacob j.]

McCulloch find of the day: https://www.ebay.com/itm/226832116898

I'm gonna need an OPE member to take one of these and clear four acres of Scotch Broom and Poison Oak.

 

[lehman live edge slab]

McCulloch find of the day: https://www.ebay.com/itm/226832116898

I'm gonna need an OPE member to take one of these and clear four acres of Scotch Broom and Poison Oak.

View attachment 470416

If it’s like my 1-41 the operator will be too tired to cut anything after he gets it started and if he did I guess he’s in for a few fun days afterwards. Cutting and taking a bath in calamine lotion.

 

[Sloughfoot]

If it’s like my 1-41 the operator will be too tired to cut anything after he gets it started and if he did I guess he’s in for a few fun days afterwards. Cutting and taking a bath in calamine lotion.

Goo Gawd that thing is massive. Gonna stop whining about my 4 stroke Honda.

 

[heimannm]

Requires two workbenches.

 

[lehman live edge slab]

Stihl made a similar ones with an 07,08 and 041 powerheads. Then the made the lightweight one with an 020av on it .

 

[Sloughfoot]

Requires two workbenches.

View attachment 470465

What's the displacement and h.p. rating on that beast? My Honda with a GX35 is 36 c.c. and a whopping 1.3 h.p.

 

[Woodslasher]

What's the displacement and h.p. rating on that beast? My Honda with a GX35 is 36 c.c. and a whopping 1.3 h.p.

80cc, I dunno the hp rating.

 

[hacskaroly]

What's the displacement and h.p. rating on that beast? My Honda with a GX35 is 36 c.c. and a whopping 1.3 h.p.

The 1-41 chainsaw is 80cc, power head only = 19.5 lbs

 

[heimannm]

That one has a 250 power head attached but the 80cc and weight are the same.

Mark

 

[Sloa]

Beautiful fall colour.

 

[Woodslasher]

Only 3 years after I got it, I finally got the clutch lapped to the crank and put my CP125 in some wood. It still needs to be tuned just right, but I'm just ecstatic it got this far.

 

[FergusonTO35]

McCulloch find of the day: https://www.ebay.com/itm/226832116898

I'm gonna need an OPE member to take one of these and clear four acres of Scotch Broom and Poison Oak.

View attachment 470416

They might as well have made a brush cutter attachment for the two man saws.

 

[LAWN BOY]

McCulloch find of the day: https://www.ebay.com/itm/226832116898

I'm gonna need an OPE member to take one of these and clear four acres of Scotch Broom and Poison Oak.

View attachment 470416

That is a cool piece of literature. I have a model 35 brushcutter that works...

 

[jacob j.]

Only 3 years after I got it, I finally got the clutch lapped to the crank and put my CP125 in some wood. It still needs to be tuned just right, but I'm just ecstatic it got this far.
View attachment 470510

Heck yeah Mr. D - awesome!