CMB 67 green

[David Ashcroft]

I have a CMB 67 Greenhead like new with the cast rotor housing.
I remember years ago reading about the ideal inside diameter for a good seal of the rotor to brass face,,but I cannot find it while searching..
I have measured 0.708"-0.709" ID of the brass in the housing..
Can someone confirm the ideal ID so can lightly either sand or not ,,or are those measurements good.

 

[Mike Cathey]

The only rotor clearance issue I have heard of is between the front casting and the case and that's easily gotten around by stacking 3 (factory) gaskets (or a couple of the thick ones you can get from Bill Brandt at Rattlesnake RC) so the rotor has some room to float when the motor heats up. The Picco 67 squarecase motors were notorious for that and broke a lot of rods because of it.

On the older CMB Hydros I think Stu Barr did recommend drilling a small hole in the front case at the back of the transfer opening for extra lubrication for the rotor. There's probably a post on IW about it.

 

[Stuart Barr]

David,
The cast housings and the new billet housings are fine. No clearance issues. The first generation billet housings were too tight. Best fix was to lap the drum to the housing to fix.
Stu

 

[David Ashcroft]

The only rotor clearance issue I have heard of is between the front casting and the case and that's easily gotten around by stacking 3 (factory) gaskets (or a couple of the thick ones you can get from Bill Brandt at Rattlesnake RC) so the rotor has some room to float when the motor heats up. The Picco 67 squarecase motors were notorious for that and broke a lot of rods because of it.

On the older CMB Hydros I think Stu Barr did recommend drilling a small hole in the front case at the back of the transfer opening for extra lubrication for the rotor. There's probably a post on IW about it.

Mike yes I will be cutting a small vertical channel on the face of the rotor casing for lube ,,I vaguely remember the clearance I had ,(Lost my papers) when using a thin feeler gauge to check clearence,,I will keep searching .Thanks

 

[David Ashcroft]

David,
The cast housings and the new billet housings are fine. No clearance issues. The first generation billet housings were too tight. Best fix was to lap the drum to the housing to fix.
Stu

Yes I remember lapping ,,ok no problem thanks Stu..

 

[Terry Keeley]

https://www.intlwaters.com/threads/galled-drum-valve.56099/

 

[Mike Cathey]

It's pretty much a given that you have to go through every new motor before you even turn it over by hand.

I think the only motors I ever trusted straight out of the box to the boat were the Mac's because Andy was going through every one of them before he shipped it. Talk about a full time job. That could go from fun to monotonous really fast. As I recall that's the deal he wanted from CMB to provide motors ready to go with the exception that you only had to perhaps adjust the head clearance for application and it never quite worked out that way.

 

[David Ashcroft]

https://www.intlwaters.com/threads/galled-drum-valve.56099/

Thanks Terry

 

[mr_fons]

Can you please provide a picture/diagram as to where to drill lubrication hole?

 

[Tom Foley]

I had this problem with the VAC 91 and sanded the inside of the rotor housing with 400 , then 600 paper and wd 40 the cleaned and made a judgement call on the clearance . also made a larger radius on the drum housing opening and added two additional oil grooves to the face of the rotor housing . Oil has to have someplace to go otherwise it will only serve to cool not lubricate . No more problems for the last couple of seasons . Jerry Crowther clued me in to this problem after I dropped an engine in the twin for an unknown reason .

 

[Ray Sametz]

Can you please provide a picture/diagram as to where to drill lubrication hole?

2 options slot or pin hole.

 

[David Ashcroft]

Can you please provide a picture/diagram as to where to drill lubrication hole?

Look at Terry's post there is a link ,click on Galled Drum Valve.

 

[mr_fons]

Thanks gents..

 

[David Ashcroft]

Thanks gents..

Mr fons
The rotor housing to case gasket is around 0.005" I have added a extra gasket which can allow a little floating away from the rotor house face and the rod to drum itself..