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This one if for the guys who were around when the Mac 6 came along. Ted, Ron, Lyn, others.

I have the article in a KW that describes the changing of the 6 pto bearing to the 10 pto bearing. What I am looking for is;
A. Who can do the machine work these days?
B. What is a common bearing number as the IPLs won't help?
C. Does the crank PTO side need to be OD ground to match the 10 bearing I.D. and what is the finish Dia. for interference fitment?
D. Does the crank need annealing and re hardening if ground due to possibly grinding thru the hardening as exists?
E. Anyone have an excellent condition 6 crank for sale which would be a much quicker means to the end as my crank is pitted beyond use. Thanks. Tom

Tom,

E. i think i have a crank.
i was gonna sell it to Scott but there was another option Scott discovered.
we had discussed stroking the mc6 a common old school solution to having an older block that wasn't competetive.
this might help anyone trying to stroke one.
Scott i hope you don't mind.

" Hi Dave,
After all that, I don't need the crank after all. I finally bit the bullet and tore down the first engine and I am glad I did. It does have an Mc7-9 crank and a modern rod but the piston is different and the pin is placed higher so it doesn't stick out of the bore so much. I have never seen one, must have been a special for stroked Mc6's and maybe 10's. Anyway, it was a good thing you called because it got me to pull out my Mc10 thick ring piston and saw that the top ring is much lower down the wall. This morning I put that piston in the 2nd engine and it sticks up 0.100" but the top ring is still down the wall about 0.100. So with a 0.125 headgasket, everything went together swell. So now I have 2 stroked Mc6's. Can't wait to fire them up.Thanks for the call and it is good to get to know another vintage fanatic. I am sure I will be calling on you in the future.
Take care,
Scott Kneisel "

the important part of the thread that we discussed over the phone is the importance of the piston ring not going above the block deck.
that would create an unfortunate result!!!!!!
So you can put in a thicker gasket to make up for the longer stroke so long as the piston ring stays inside the liner

of course by telling you that i may not sell the crank but that's ok with me.
dave

Hey, Tom. Email me and I will send you the Racing Karts article from Sept. '61. I never did this, as I always ran super A, but the article seems complete. TJ
nosnhojkart@yahoo.com.

Dave, Ted,
Thanks for the replys. Dave I will be talking to you as you know about the other crankshaft in a few weeks. Ted, email sent, Thanks. Tom

When Cart Labs in Portland came up with a stroked Mac 6 crank in the summer of 61 Bob VanBeek built up and engine using this crank and special piston. He did not like the having to use a very thick head gasket as he was kind of sneaky and did not like giving away what he had. So I took the head and set it up in a lathe and machined out the piston side so Bob could use a standard head gasket. Next race he was out going like heck with what appeared to be a stock Mac 6.

Dennis Turk

how sneaky!!!
i love stuff like that.
will have to try it.
dave

I am currently working on a stroked Mac 6 also. In all the stuff that came with the Caretta I got from Al Lader there was a cart labs stroked crank Mac 6 crank. Now this crank is stroked .094 so the piston is going to be about .048 above the top of the bore. I found that a fellow in Canada had a chain saw piston that had close to .100 of piston above the top ring and it was a Plus 20 that I needed.

If you have a stroked crank in the Mac 6's your working on I am curious as to what amount of stroke these cranks add?

Also something we did back in 61 was to cut off a little from the top of the piston. this would change the port timing a bunch without messing with the ports. On a dino my stock stroked Mac 6 with .025 cut off the top of the piston and running a very thinner head gaskets and running with a Cart Labs Mac 20 cab setup for alcohol we were getting right at 12 hp at 14,000 Does this match up with anything you are getting out of your engine? I also took just a little off the head to make up for what we took off the piston. Really don't know what the compression was but we figured it was about the same as running the factory thin head gasket.

Also what are you setting the piston to cylinder clearance at? We always looked for .0045 to .005 with a new piston. If I remember correctly Mac piston clearance was .003 or .0035 cant remember now.

Turk

Just to add to this excellent Mc6 thread, The Mc10 bearing on the PTO is a 6203 bearing. Same as the inboard and also the same as the Mc101 bearings. This is a very common bearing and available all over. Comet has good quality ones for around $10. There are also a lot of really cheap ones from china but it is probably best to stay with FAG, General bearing or other brand names. They are probably still made in Aisa nowadays but to better standards than the no name bearings.

I also like the idea of turning some material off the inside of the head. Cool idea. I might take off my 0.125 gasket and do that on my stroked Mc6. That would make it look just like my other Mc6.

BTW, since I last talked to Dave, I found out that that special piston in my Mc6 is called a quick time piston which has the wrist pin set higher to open the ports sooner. Works great for these stroked engines but probably impossible to find for the small bore engines.
This is a great thread, thanks everyone,
Scott K.

Lots of people recessed McCulloch heads for stroker pistons in the early days, mainly on Mc-10s so the head shrouds would still fit. I like the Mc-6s etc. that McCulloch relocated the coil legs on and then welded them back onto the block with out any visable evidence of them having been altered. They learned the welding methods needed to weld the coil legs on from repairing broken ones on the saws. Meanwhile the tech inspectors checked the lamination bars to make sure the bolt holes weren't slotted to alter the timing......