MAC 67 and OS drum possible????

[EatMyShortsRacing]

Yes it seems a crazy idea but it would solve a problem for me. I am building a Chisel nose 1/8 scale and I positioned the engine last night and found to my dismay the carb sits above the deck line and out in the open. I am wondering if it is possible to fit the OS drum rotor to the MAC? I do have a 91 Drum and carb sitting around at home...

 

[TimD]

Craig,

What about a CMB 67 green head rotor + housing - same manufacturer?

No idea on the OS conversion - I have heard of fitting the OS housing to a picco before but not a MAC. I'm doing something similar with different engines / parts at the moment. There is a lot of measuring and checking involved!

Tim.

 

[Don Ferrette]

Craig,What about a CMB 67 green head rotor + housing - same manufacturer?

No idea on the OS conversion - I have heard of fitting the OS housing to a picco before but not a MAC. I'm doing something similar with different engines / parts at the moment. There is a lot of measuring and checking involved!

Tim.

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The CMB drum housing is too small diameter. Know this for a fact as you can't fit a MAC drum housing into a CMB case (tried it ) The Picco drum housing will fit into the MAC case (won't fit CMB case for same reason as MAC) but I don't know about the clearances and/or timings. OS might also as Tim said that used to be a popular conversion on the old disc EXR's.

 

[TimD]

MAC 67/84 rotor housing will fit in a K67/82 B) Shame it's not ballraced and balanced like the K item, the port shape is better.

Pic' of housings

 

[EatMyShortsRacing]

MAC 67/84 rotor housing will fit in a K67/82  B)   Shame it's not ballraced and balanced like the K item, the port shape is better.Pic' of housings

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and the K into the MAC I gather????

just thinking if the K assembly would end up lower in the boat???

 

[TimD]

The K housing will not solve your problem Craig - the carb still sticks up in the air!

Just thinking out loud but what about rotating the rotor housing 90 degrees and drilling a new hole in the rotor for the crankpin to get the inlet timing right? Feasible?

 

[Don Ferrette]

Just thinking out loud but what about rotating the rotor housing 90 degrees and drilling a new hole in the rotor for the crankpin to get the inlet timing right?  Feasible?

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As cast there is not enough "meat" to go 90 degrees on the drum rotor. :huh:

 

[EatMyShortsRacing]

Well then either the fuel connections or the throttle linkage become impossible to service. Was almost going to lay the engine down on its side but I'd hate to need to change a plug in pit time!!!!

D'oh!!!!!!!!!!!!!!

 

[Don Ferrette]

Well then either the fuel connections or the throttle linkage become impossible to service.  Was almost going to lay the engine down on its side but I'd hate to need to change a plug in pit time!!!!

D'oh!!!!!!!!!!!!!!

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Just drill a hole in the plug side of the boat! :lol: :lol: :lol:

 

[EatMyShortsRacing]

Well then either the fuel connections or the throttle linkage become impossible to service.  Was almost going to lay the engine down on its side but I'd hate to need to change a plug in pit time!!!!

D'oh!!!!!!!!!!!!!!

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Just drill a hole in the plug side of the boat! :lol: :lol: :lol:

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Or put a right angle tube into the head button and extend the plug out???

 

[Ken Retallick]

I join up here and what do i see? Craig building a Scale boat....

Having all the parts here, i had to go and have a measure.

What you want to do is possible with a few adaptors etc, but the biggest prob is you would need a hardened steel washer to keep the needle rollers in the rod as the OS drum flange is a smaller diameter.

Could be a weak point.

 

[ScottVanSlooten]

If the OS 91 housing would fit it would be the way to go . I have put them in other motors like the ops 67s and they work great. Scott

 

[TimD]

the biggest prob is you would need a hardened steel washer to keep the needle rollers in the rod as the OS drum flange is a smaller diameter.Could be a weak point.

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What about, dare I say it, a bushed rod....

 

[Mark Anderson]

If the cmb housing is a little smaller it would be a very easy project to machine a bushing. The more important measurement is the depth into the case and the crank pin slot width. The os sounds like it would be a problem with the needles.

Mark

 

[Don Ferrette]

If the cmb housing is a little smaller it would be a very easy project to machine a bushing. The more important measurement is the depth into the case and the crank pin slot width. The os sounds like it would be a problem with the needles.
Mark

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Now that is feasible, bolt pattern for both housings are the same.

 

[Ken Retallick]

If the cmb housing is a little smaller it would be a very easy project to machine a bushing. The more important measurement is the depth into the case and the crank pin slot width. The os sounds like it would be a problem with the needles.
Mark

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Now that is feasible, bolt pattern for both housings are the same.

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I also measured a CMB green head housing up. would be a simple enough machining job as Mark said, but if i recall correctly the stroke is slightly different between the MAC and CMB, if so you would need to adjust the crankpin hole to fit.

Still simple and do-able.

 

[Joe_Knesek]

If the cmb housing is a little smaller it would be a very easy project to machine a bushing. The more important measurement is the depth into the case and the crank pin slot width. The os sounds like it would be a problem with the needles.
Mark

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Now that is feasible, bolt pattern for both housings are the same.

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I also measured a CMB green head housing up. would be a simple enough machining job as Mark said, but if i recall correctly the stroke is slightly different between the MAC and CMB, if so you would need to adjust the crankpin hole to fit.

Still simple and do-able.

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As long as you can find a rotor, building a new housing is not that hard to do. I had a new housing made to use a Rossi drum rotor in a Picco before Picco's had drum rotors.

 

[Rudy Formanek]

If you need a hardened washer for the crankpin (to keep the needles in) OPS had a set of needles and washer for thier super 67/80 motors, used to be about $8.00 US , might have to drill/grind out the inner hole to match your rotor take off pin diameter. The needles might even work for you so they just don't rattle around in your spares box.