McCulloch Algebra

[cpr]

797R = (790-6ci)+x

Solve for x

x=MC-101

I salvaged this heap of a 790 from the boneyard of forgotten yellow thunder. The price was right and I had a plan.

I reduced it to a pile...

Sorted the bits I needed for this build and packed the rest off to promac610. You can follow the restoration of a mighty 6ci McCulloch here: http://www.arboristsite.com/chainsaw/170558.htm

In the meantime, I started cleaning, planning, acquiring bits I didn't have and waiting a painfully long time for the box punters to make the bench look like this...

and the biggest part of "this" is a stock port MC-101.

These are brutal screamers as karts, but for this "semi-stock" appearing (for reasons we'll learn later in the process) saw, it will be strong, but not as strong as it could be. The reason is air and fuel. The stock tank and carb mounts suffocate the engine. It introduces a 90 degree bend to the airstream, makes it pass through a perpendicular to flow reed plate (that I can only get 2 measly reeds into, albeit they will be made as large as possible), and the carb well can't accomodate a massive pumper. The 48890b flatback that is going to be used is the largest bore carb that will fit the saw and the tank throat will require grinding to match the carb's bore. But for all that the 48890b is the biggest, and that these are the baddest things in the woods, they're still snuffed... check out the Tilly that came with this motor.

 

[Sprintcar]

And this bone yard is where?

 

[Brian13]

Just getting my front seat, to watch this. If you can while you have the engine apart could you get a port map?

 

[cpr]

I've begun mocking up some things and doing light assembly to check clearances and see where issues are going to arise.

First is to match the carb to the tank half. You can see a lip at the top of the funnel in this shot. This is looking up through the fuel tank and into where the carb would be. Once the hole is enlargened to flush, it will mate to the carb exactly and provide a nice flow to the reed plate where it'll go all over anyway...

Then there's the reeds. Below is the stock 790 plate laid over the 101 block. The 2 ovals are the reed passages, the right hole is the third port transfer on the 790 block (101s don't have that, they have boost ports instead). The small hole above and centered between the reed holes is the impulse passage. There's no room to lengthen the reed passages because the tank funnel is the same, nor can the left reed port be widened to the left for the same reason. Space is available between the reeds and to the right only. I am going to fab my own reed with a SP125 keeper and use a Mac 15 blank plate (bottom carb on that saw) to make a new reed plate.

BTW, the more I look at this photo, the more I am inclined to play with the spacer block to "cheat" the reed ports toward the bottom of the crankcase... hhmmm.

NOS head.

New piston and rings, .004 over.

Aftermarket H-beam rod. Reckon she'll take some revs?

Once the mockups are done, the tanks and covers are getting stripped and powdercoated black. The fan shroud and hood are chrome, but not great. I may replace them later on. I've coveted these for a long time and I want this thing right. 52" roller nose and new chain are due in Tuesday. I have a list of miscellaneous hardware, gaskets, and small parts to get to finish, but the major stuff is now ready.

McCulloch's design team sure had wierd ideas sometimes, but the swap-shop interchangeablilty is dad-gum handy for builds like this.

I hope you all enjoy this as much as I will and I'll try to document everything as we go.

 

[cpr]

Just getting my front seat, to watch this. If you can while you have the engine apart could you get a port map?

Courtesy ozflea aka mcbob.

http://www.arboristsite.com/chainsaw/160244-9.htm#post2876153

 

[cpr]

And this bone yard is where?

Here...

 

[Brian13]

Thanks, I saw that and thought nothing of it. Sometimes my mind is lost LOL. Awesome looking build though. Hoping to do this myself in the future, so I will be paying very close attention.

 

[Sprintcar]

Here...

Sweet, there is a guy in Dike, Iowa that would have a field day in there.

 

[Ambull]

Don't listen to anything this guy says. He has more than one project saw, so he is a loser, lol!!!!!!!!!!!!!!!!!!!!!!!

In all seriousness, I am liking it so far CPR!!!

 

[Rounder]

Mouth watering stuff.....-Sam

 

[54stude]

Are you sure there is not a way you could sneak that huge cart carb in there with a very modified airbox lid or velocity stack? If this is just a cookie cutter gtg saw, maybe you could stick a smaller gas tank into the tank, and grind until it fits?

Maybe build a manifold with a steel weld elbow and a few flanges?

You do do a "high top" airbox cover like a pm800 maybe?

 

[Brian13]

It can be done, but I think he is going for a stock appearing saw.

 

[cpr]

Are you sure there is not a way you could sneak that huge cart carb in there with a very modified airbox lid or velocity stack? If this is just a cookie cutter gtg saw, maybe you could stick a smaller gas tank into the tank, and grind until it fits?

Maybe build a manifold with a steel weld elbow and a few flanges?

You do do a "high top" airbox cover like a pm800 maybe?

It can, and has, been done...

It can be done, but I think he is going for a stock appearing saw.

Correct, I'm going for the "dealer installed option" aesthetic, but with tweaks to maximize the given paradigm.

I have this ported one waiting for the full-house alky/piped/to-hell-wth-stock-appearing voo-doo treatment...

Crawl, walk, run...

Respect the yellow and black.

 

[rwoods]

I'm glad your engine finally arrived. Personally I favor the stock appearing approach. I look forward to keeping up with your progress.

SawKing has videos of stock appearing, elevated tank and fully modified models on YouTube for those interested in seeing some of the possible variations. Ron

 

[Duke Thieroff]

Here...

!!!!!!

My lord!

It can, and has, been done...



Correct, I'm going for the "dealer installed option" aesthetic, but with tweaks to maximize the given paradigm.

I have this ported one waiting for the full-house alky/piped/to-hell-wth-stock-appearing voo-doo treatment...

Crawl, walk, run...

Respect the yellow and black.

Looks as if you're quite the capable saw builder. I'll have my eye on this one man.

I can't believe you have a Kart motor and one of Aaron's posts together in the same pic.

That's like the semi pretty girl taking her ugly friend with her to make her look prettier and boy, does that kart motor look pretty in that pic.



Chris

 

[RandyMac]

!!!!!!

My lord!



Looks as if you're quite the capable saw builder. I'll have my eye on this one man.

i can't believe you have a kart motor and one of aaron's posts together in the same pic.

That's like the semi pretty girl taking her ugly friend with her to make her look prettier and boy, does that kart motor look pretty in that pic.


Chris

lmao!!!!

 

[Brian13]

Have you thought about making your own reed plate, rather than trying to fit another. It may work out to be the same with more work involved, but maybe that might allow a larger set of reeds?

 

[RandyMac]

I have seen Mac Kart reed plates that were "V" shaped, with four reeds, they came out of stock appearence class saws.

 

[cpr]

I have the V4, but it's going to take a lot of tank mods to get in there. I don't have the welder or skills to do it. The yellow one is going topless with a big ole carb. The donor 1-72 is waiting for that one on a shelf.

Thanks for the kind words. I'm more of a saw assembler than a builder right now. I didn't do the bottom end of the motor on this one and the ported one was built by a race shop here in Detroit.

 

[leeha]

Sweet project Chris, Glad the 101 finally arrived.
These are the threads i like.
Being creative and having it work is very rewarding.
Good luck, Looking sweet so far.



Lee