CMB V5 45

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Terry Keeley

Well-Known Member
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Jul 24, 2002
Messages
7,116
Got to take a look at one finally, it's close to the VAC 45 except for a few changes:

The exhaust port is split into three with a main port and eyebrows.

The transfers are split into two making the whole thing an 8 port vs 4 for the VAC.

The piston is flat vs dished for the VAC.

The head volume has been increased to 0.35cc vs 0.29 + 0.02 piston dish for the VAC.  Trapped C/R is down from 13.7 to 12.1:1.

The squish band has half it's width tapered at 3* vs completely flat for the VAC.

The drum valve has some balancing cutouts.

Timing numbers are essentially the same.

Oh, and the cooling jacket is gold instead of blue.   :p

The motor I looked at had quite a bit of chrome globs around the ports, be sure to go around them with a small diamond file before running one of these!

CMB 45.jpg

Here's the complete story:  View attachment 2017 CMB V5 45.xls
 
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The Blue head 4 port VAC 45 had .35-.36 head and flat top piston for a long time!    I think only the first run had what you had, early versions also had less crankshaft counter weight.     The only changes to the V-5 were a slightly different head button config, sleeve ports that you mention and a drum with different timing and no ramp. And yes the cooling head!   
 
The Blue head 4 port VAC 45 had .35-.36 head and flat top piston for a long time!    I think only the first run had what you had, early versions also had less crankshaft counter weight.     The only changes to the V-5 were a slightly different head button config, sleeve ports that you mention and a drum with different timing and no ramp. And yes the cooling head!   
Have you run the V5?  How's it compare to the VAC?  :rolleyes:
 
I think V5 is better but I will say this, I like the v5 sleeve with old head and ramped drum :)           Opinions will vary !
 
Yes a ramped drum.  I’m not sure how much the ramp actually does but The newer one opens a little earlier than I like.   Again opinions vary ! 
 
question, is it possible to replace the drum housing of the cmb v5 with the drum housing carb angle of cmb 45 hr with  use drum valve of the v5 ?
 
Terry,

That looks really bad.  I am sorry.  Most do not look that way.

Martin,

One time I flattened the ramp using a Dremel.  Picked up 3 MPH.

Stu 
Ya, I've never seen one that bad either and I'm sure it's an anomaly.

I posted the picture not as a slam against CMB but just to be sure guys check before they run them.  That would have made a mess the first time the motor was fired.  :unsure:
 
It's too bad the manufacturer's couldn't add a groove like this to the exhaust stub so we could get away from those goofy headers with their leaky o-rings, springs etc.

Stu?  Ron?

exhaust groove.jpg

exh goove.jpg
 
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what is a good, or best, type of dremel bit to remove excess flashing (clean-up ports) ? 


You definitely don't want to get in there with a dremel tool, use a fine diamond file, the chrome globs fall right off.  Go around the edges of the ports both inside and out to be sure you haven't raised any burrs that can scratch the piston or the case.

http://www.ptctoolonline.com/9-round-diamond-file.html

in-514.gif
 
 
Got to take a look at one finally, it's close to the VAC 45 except for a few changes:

The exhaust port is split into three with a main port and eyebrows.

The transfers are split into two making the whole thing an 8 port vs 4 for the VAC.

The piston is flat vs dished for the VAC.

The head volume has been increased to 0.35cc vs 0.29 + 0.02 piston dish for the VAC.  Trapped C/R is down from 13.7 to 12.1:1.

The squish band has half it's width tapered at 3* vs completely flat for the VAC.

The drum valve has some balancing cutouts.

Timing numbers are essentially the same.

Oh, and the cooling jacket is gold instead of blue.   :p

The motor I looked at had quite a bit of chrome globs around the ports, be sure to go around them with a small diamond file before running one of these!

View attachment 100128

Here's the complete story:  View attachment 100129
Any sharp edge on the ID of a cylinder bore will cause the chrome to buildup on that edge. Careful removal, before chroming, of those sharp edges with an Exacto knife & brush hone eliminates this problem. 

Jim Allen

P8290016.JPG

P8290017.JPG

P5020003.JPG

P5020004.JPG

P6200009.JPG

P9080022.JPG
 
Any sharp edge on the ID of a cylinder bore will cause the chrome to buildup on that edge. Careful removal, before chroming, of those sharp edges with an Exacto knife & brush hone eliminates this problem. 

Jim Allen

View attachment 100151

View attachment 100152

View attachment 100153

View attachment 100154

View attachment 100155

View attachment 100156


Jim,  I see Nelson engines are still using double hemi heads. The Super Tigre X-40 Pylon engine (1973) used the double hemi.  Worked great in boats too. It was a popular after market part available for many engine brands through out the 70s and 80s.
 
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