Inter Vertical Shaft Measurements

Should float Bill.  When assembled, correctly shimmed to align the bevels and no tube the couplings should be a press fit into the slot; there should be no air gaps.  For the tube seals Stu Rogers makes a spacer/ carrier and oil seal either end arrangement that works well. The rocker stuff needs answering by someone with more experience than me.    

cheers

Jon

Hi Bill.

I think it would be easier to discuss your questions over the phone  as they are a bit involved. I am happy for you to give me a call. My mobile number is under North West Branch details as I am secretary.

Regards, Nick 

(Sorry to post repetition but this overlapped)

I'd like to hear the answers, especially about replacing the rubbers.  I foolishly did not change the crush washers when I had it apart early in the year.  I don't understand the way it seals (which is why mine leaks).  The crush washers seal (or in my case leak)  between the flange of the nut and the housing, and the rubber ring  must be there to seal between the nut and the tube.  That should surely be simple enough with an O-ring - or even more than one, as Bill suggests?  I see Paul Norman advertises new nuts specially designed to take O-rings. 

The tangs should be clear at their ends so the discs are close to the ends of the shafts at top and bottom to make sure the tangs are have as little bending as possible.  It's suppose to be  trial assembled with cam box reasonably well tight so you can measure the shaft goes up and down the correct amount (I think George Cohen's notes say something about 15 thou minimum, but maximum is a bit vague).  Ian Bennett  (http://bennett-cnc.co.uk/)  sells different couplings.  I think they come in 20thou steps so if you have say 12 thou and want to have more than 15 you end up with 32.

The tangs should be snug within the shaft slots. It looks like Bill has 5 thou - seems a lot but perhaps others know?

A really good section drawing would help.

The  vertical shaft could sit on the lower bearing inner race depending on the thickness of the lower Oldham coupling fitted. I would prefer just touching or a few thou clearance.

I use O rings to seal the vertical tube and they seem to work well. That is also what Paul Norman recommends.

You do not want the tang of the Oldham coupling bottoming out in the vertical shaft groove otherwise you will have a gap between the end of the shaft and the full diameter of the Oldham coupling. The thickness of the full diameter should be controlling the free movement of the vertical shaft.

The tangs on all the Model 40 Oldham couplings I have are approx. 3/8” long and the parts book shows couplings being the same part for the CJ, CS1, M40 and M30.

Bill says “I have a gap of 47 thou between the bottom bevel and the bevel housing when the vertical shaft is resting on the inner bearing and a 3/16 vertical shaft coupling is fitted. Could I put a 50 thou spacer under the bearing to cure this problem?”

But you also say you do not have the retaining collar on the bottom bevel which is important otherwise you might get too much vertical movement in the lower bevel. If you have the collar fitted your vertical shaft may not then be resting on your housing bearing. All items of the bevel train need to be restrained within the correct tolerances. One item out of tolerance will affect another item.

The running tolerances of the two pairs of bevels have to be set via shims before you can set the free movement of the vertical shaft via the different thicknesses of Oldham couplings. Therefore the collars have to be fitted to the top and bottom bevels to restrict their vertical movement.

If the top of the vertical shaft has been reduced perhaps that has been because the correct thickness of Oldham coupling was not available.

The Oldham couplings to my mind should be a good fit in the vertical shaft without any side play.

The side cups on the rockers should be a tight fit or light tap fit and should oscillate with the rocker on the corks. It is a very poor design for retaining oil in the cam box.

I think your suggestion of machining the cups could end up causing more oil leaks.  

Whoever built the engine before you bought it does not seem to have done a very good job of the bevel train. Maybe he could not get the correct parts or  have access to engineering facilities. It would be worth checking other areas of the engine if you have not already done so.

Regards, Nick

Nick...did the side "cup and cork washer" arrangement change? I think I read it somewhere. I seem to remember Barry Strickland (I think...) saying that although people put a lot of effort into sealing above and below the rockers, much of the leakage comes from the sides?

Hi David.

My engine is 1936 but checking the 1950 parts list the steel cup and cork washer are still the same.

So it does not look like they changed but the Manx 40M was very different.

My bottom bevel overall length is 2 3/8”,  the bottom bevel housing where bearing sits on pedestals  to top of bottom bevel casting is roughly 32 thou under an inch.  You will pick up roughly 15 thou if you have the bottom bevel washer (part number A11/756) installed below the bottom bearing.  

3/16 oldham coupling on bottom of vertical shaft as constant and make up difference with top oldham couplings. Take a look at Paul Norman’s site as he does some very detailed write ups of these engines/components.  

My model 30 Inter engine is a 1948 for reference.  Let me know if you need other measurements as it’s apart in the midst of a rebuild.

Good luck 

Pat

Hi Bill

Please remember that the Inter engines should have been carefully built and were individually tested by the factory. Parts at the time could not be made economically to the tolerances of today. Therefore the bevel train was setup on assembly with selective assembly, metal shims and different sized Oldham couplings to bring everything within the required tolerances. That is one of the reasons the overhead cam engines were more expensive to produce than the OHV engines and cost a lot more. 

Therefore I don’t think that comparing all your dimensions with anybody else’s is going to help you very much. I do think that you will have to build the engine with the components that you have and bring all the tolerances within excepted limits. Different thickness of shims can be bought or made but different size Oldham couplings will be a bit more difficult, although Ian Bennett Engineering Ltd UK (Bennett-cnc.co.uk) does make and sell them.

I have 6 Oldham couplings but when I built my engine back in ’86 none were the correct size I needed and had to make my own of the required size. I did have easy access to engineering facilities.

As an example to tolerance variation the tang widths of my spare Oldham couplings, some new and some used, vary from 0.214” through to 0.220”, most are around 0.217”. But on each coupling the 2 tangs do vary in width by between 2 and 3 thou. Only coupling has both tangs the same width.         

Sorry if this does not sound very helpful but these engines do require more careful, precise and individual assembly compared to the OHV engines. Once done the setup can be expected to last for a very long time. Mine has lasted over 40K miles without altering the bevel drive train.

Regards, Nick

The bevel gear tooth forces develop axial thrusts in service which will be huge compared with the weight of the shaft, so can easily carry the shaft. So that's not a problem. Even if the shaft weight sat on the bearing, it would lift off as soon as the engine turned over.

Is silver steel the correct material? I understand it's a bit brittle? Those sharp corners alongside the coupler tangs worry me much more than the weight of the shaft. If I were designing it, I'd like to see small matching radii.

Hi Bill.

Thank you for describing your problem again, it is much clearer now. I can't help with the dimensions you ask for as my engine is fully assembled.

I have found the articles Paul Newman produced when building his Inter. One of which explains the setting of the vertical coupling assembly in great detail and covers the Oldham couplings and adds some specific detail i did not know.

http://www.racingvincent.co.uk/14%20Norton%20Site/Manx-Norton-01F.htm

One of the specifics he mentions is that the bottom Oldham couple should be 3/16" thick and the lip of the vertical shaft should rest on the bottom housing bearing. The vertical shaft clearance then being taken up with the top Oldham coupling.

I agree with David that silver steel is not a good choice for the couplings. I can't remember what steel I used but it was something tough such as EN16 or 24. I also has them case hardened.

Hope this goes someway in helping you to decide what to do.

Nick