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Camshaft & Crankshaft Centerline Dimensions Relative to Case Deck

Submitted by robert_holly on Tuesday, 7 October, 2025 - 16:50
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Commando

Hello, all.
 

​I have a set of cases in the mill right now that have a total variation across the deck of 0.013" which can be seen in the image below.

Deck Height Variance

I would like to bring this back into spec. as much as possible, so I am looking for some reference dimensions, namely, the centerline dimensions from the camshaft and the crankshaft to the target deck height.  This is shown in the image below.
Commando Crank & Cam CLs To Deck
Does anybody have these dimensions on hand that they can share?

Thanks!

-Robert
 

Attachments
Initial Setup.JPEG
Precision Ground Dummy Crank & Cam.JPEG
Truing Crank CL Along X Axis.JPEG
Sweeping Deck.JPEG

Submitted by paul_griffiths on Tuesday, 7 October, 2025 - 19:42

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Have you clocked the cylinder base for this engine?
Have you bolted the two together and checked for gaps with feeler gauges.
Seems like a lot of trouble to go to with little to gain that can't be solved with modern sealants and gaskets.
But hey, if this is an exercise in seeking perfection, please keep us informed as to when you eventually get te bike on the road.

Hi, Paul.

Thanks for the response.  I have done what you have suggested.  This is how I know I have an issue.

Initial Setup

Truing Crank CL

Deck Height Variance

Sweeping Deck

If you look at the third image above, you'll see that I have a to variation of 0.013" across the deck. I do not consider this variation to be minor. 

Everything critical in the engine is referenced from the deck; when the cylinders are bored, they are bored relative to the bottom of the barrels.  Because the barrels meet the face of the case deck, the crankshaft should be dead parallel to the deck or else the barrels will be askance and you will lose a lot of power to unnecessary drag with the added disadvantage of increased wear. 

Finally, you can have similar issues if the barrels aren't correctly configured fore and aft.  A good reference to achieve this correct "ideal plane" would be from the factory blueprints which should provide the centerline dimensions I am seeking.

Any input on this front that you could offer would be greatly appreciated.

Thanks,

-Robert

 

Attachments
Deck Height Variance.jpg
Sweeping Deck_0.JPEG

Submitted by neill_watkins on Tuesday, 7 October, 2025 - 20:18

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Without giving it too much critical thought I would say you're governed by the lowest dimensions.
The 0.000" on both sides at the rear and the -0.007" at the right front. The left and right datum is easily set true with the dummy crank

Can you not just rotate the cases to split the difference between the front and rear 0.000"/-0.007" lock it down and skim it flat? 
Will probably be as good as most and if they're 850 cases, they use sealant without gaskets as Paul suggests.

My DIY fix for nice flat faces on my Mk3 was to bolt the cases together and lightly hand skim them on a flat bed with 240 wet & dry. Mainly just to clean up the surface, no obvious mismatches.
Aligned perfectly using straightedge and eye with crank fitted and never any leaks sealed with Permatex Ultra Grey sealant and a good PCV valve.
 

Submitted by robert_holly on Tuesday, 7 October, 2025 - 20:52

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Hi, Neill.

Thanks for the feedback.

I am governed to an extent by the lowest point, but what I don't know is what's been done before and if by splitting the difference I might be going in the wrong direction.  And while I could certainly cobble the whole affair back together and use any number of sealers, but that's not how I operate, and I'm not looking to be "as good as most."

My goal with my engine builds is to "blueprint" the engines, at least as a starting point or baseline condition.  By "blueprinting," I mean to bring the engine as close to the original specifications as intended by the engineers.

With the goal of blueprinting this engine, the missing piece is the answer to this questions I have posed.  Perhaps it would make more sense for me to reach out to the archives to see if they have any of the historical drawings on hand.

Thanks again!

-Robert
 

Submitted by tony_ripley on Tuesday, 7 October, 2025 - 20:42

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Hi Robert,
Just sent you an email with a drawing. It may be no use whatsoever but it is the best I have.
Regards

Tony

Submitted by david_cooper on Tuesday, 7 October, 2025 - 22:27

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It looks as if each side is planar to within 0.001 on the right and 0.002 on the left.  Perhaps the two halved didn't leave the factory together?  There is a step of 0.003 between them.  So you need to establish the exact height (or heights) of the plane faces of each half relative to the crank.  Presumably you should insert a mandrel through the main bearings to find out what's up.  If they do match - shouldn't the cases be finally tightened together with the barrel (or another flat surface) is in place?
 

 



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