Mc45D......was it real!!

[Butch Kavanagh]

wasn't ormel duke going to write a book or something ? seems that was mentioned in some of the old karting worlds. i've searched in the past and agn this am and nothing for any articles.

[ted johnson]

Steve, according to the picture in the Sept., '62 Karting World magazine, the tops of the exhausts only were squared. The gully porting was to provide extra crankcase charging at TDC from the third port. Most modifiers added a bottom carb, so the case charging effect of the third port was negated. In fact, with a bottom and top carb combo, you'd get a "rooster tail" of fuel out of the top carb. That's why you see a lot of vintage Mac blocks with the third port cavity epoxy filled. If we ran dual carbs, we used the GEM dual bottom engine mount/manifold and put a plate over the top manifold block opening and filled the third port cavity. If we ran 3 carbs, we filled the third port cavity in the block and the single top manifold, running the GEM dual on the bottom. That caused a beast of a time when we wanted to add 9-porting ! TJ

[Frank Payne]

I have 2 stock, unmodified 30s with 2 different styles of exhaust port. One is the aforementioned triple squared port arrangement, the other has a single open port that is smaller across than the triple ports but since no ribs the area is probably the same.

[Don Tomich]

There was a Mac45D in Australia, or at least that was what everybody called it. Chrome shroud and twin carbs. one behind the other on a V angle.
Don Tomich

[Ronald Cubel]

Great now we are getting somewhere

[Don Tomich]

Just had a look at Macbob's website and the 45D is shown there. In the ealy 70's we had a stock Mac class in which you were able to legally interchange parts from other 100cc models and the 45D manifold with two small flatbacks was a popular set up on Mac 91's etc.
Don

[Tom Smith]

Steve, My Mc-30s have the tops of the 3 exhaust ports milled square, it appears that it was done in two operations since they used two different diameter cutters. They also machined around the bottom perimeter opening of the top passage to remove the bottom 25-30% of the transfer ribs/reed stops. The corner radius at the bottom looks to be 1/2". The 2 ribs have cross cut tooling witness marks from a vertical end mill on the bottom and you can plainly see the tool cutter finish/ slightly larger opening around the side of the passage. The fact that the bottom of the ribs are gone is another clue they done done something in there Clem.
I also came across a saw block that had the same modified exhaust ports. I'd bet it was machined at the same time the Mc-30 was in production by mistake.
They had photos of an Mc-45D on their web site. I wonder if they were smart enough to know why a dual pyramid reed manifold was used.

Mc-30 + 450 .JPG

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Mc-30 pto .JPG

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Mc-30 ex port .JPG

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[steveohara]

Tom,

Thanks for posting the pics. It clears up some questions I had about the 30. I have a 30 block that has what look like factory squared exhaust, gulley porting and those same machine marks in the area where the reed cage points. Unfortunately someone ground all of the reed stop ridges out and tuned on the transfer port inlet shape a bit. Not a horrible excuse for a 30 except that it has a bore that is .110 oversize and finding a piston for it is not likely!
If anyone has a stock 30 block in decent shape and wants to sell or trade it off please let me know.
Steve O'Hara

[Jeff Campbell]

Steve,
Yes the MC45D was real.

It was real, it is listed on McCulloch's engine production summary:
http://rearenginekarts.com/McCullochSummarySheet.PDF

...but class rule changes at the time banned multiple carbs on stock engines and guys running modified motors wanted other manifold / carb options.

Jeff

[Bill Hermsted]

did the speed trick of the day,filling in the Mc 45 third port chamber and installing an Mc91 piston,really increase top end?
It seems this added a lot of stuffing,since the chamber became part of the crankcase when the dividing wall had that window cut in.
I wonder if a contoured plug can be made to fill this chamber, and then pulled out easily if you wanted to make the motor stock again.
take care, Bill









lly increase top end performance?