CMB V5 45

[Terry Keeley]

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.  

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!



Here's the complete story:  View attachment 2017 CMB V5 45.xls

 

[mtruex]

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!   

 

[Terry Keeley]

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? 

 

[mtruex]

I think V5 is better but I will say this, I like the v5 sleeve with old head and ramped drum           Opinions will vary !

 

[David Bryant]

I like ramped drum

a ramped drum from an older CMB .45 ?

 

[mtruex]

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 ! 

 

[Mike Hughes]

WOW, you can see the chrome in the pic. That looks bad from here.

Mike

 

[Jim Mamaril]

Mine didn't look like that.

 

[Stuart Barr]

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 

 

[gilbert galli]

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 Keeley]

I think V5 is better but I will say this, I like the v5 sleeve with old head and ramped drum           Opinions will vary !

Lol!  C/R is king, especially for what your doing! 

 

[Terry Keeley]

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:

 

[Terry Keeley]

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?

 

[David Bryant]

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

 

[Timbo Whalen]

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

Give these a look- 

https://www.mcmaster.com/dremel-compatible-rubber-bonded-grinding-points

 

[Stuart Barr]

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 ?

No.  Different stroke.

 

[Terry Keeley]

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

 

 

[David Bryant]

thanks!

 

[Jim Allen]

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.  

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

 

[Andy Brown]

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.