Camshaft woes.....no end float

A carefull check  of new against  old  and  correct the difference would be my way. We have to accept that quality control has gone and do the best we can.

The cam is not recoverable, return it. 

A used sleeve gear may have a slight deformation on the inside edge where the sprocket stops when it is tightened on to the sleeve gear. Remove any high spots and the sleeve gear will allow the bearing to seat correctly. 

Marcus, I have just measured an original cam and the measurement should be 28.75mm or 1.132 inches. That is from shoulder that cam gear goes against to rev counter gear.

I fitted a new AN cam last year and end float was correct without any messing about.

Hope this helps.

Ian

To be honest I didn't measure mine when I assembled it. The cam spun nicely and didn't seem to flop from side to side so I just stuck it together. I can't see that 20 thou would be a problem in that situation. In an ideal world a bit less would be desirable but I don't think I'd be messing about with shims to make it less as that tapered washer is hardened so putting a shim in there could be problematic.

What you have done is not a problem. From the engine builders of the past one said hit it through with a mallet, and another which I agree with, is what you have done. It should be only just loose enough to just press through with a struggle in the hands, too loose and it may not act as an inner race. 

Is the gear notchy in the bearing or against the 4th LS gear? This is the first I have heard of this, and considering who we sell them to including RGM and how many we sell, if there was a regular quality issue with the sleeve gear we would have heard and so would have RGM and they would have certainly told us.  

The AMC gearbox is nice, but the un-noticed quality of gearboxes from the 60's and 70's is really variable, some are worse than others and this is easily spotted once they are apart. The gears give it away when you look at them.  

The cam problem I have seen many times, adjusting the thrust washer will cure it, but remember this if you replace the cam in the future with one that is correct or sell the bike to a new owner so they know not to use the old thrust washer if they replace the cam.  

Cam issue Mk3  

Hi Marcus

I’ve had the same cam problem. In 2018 two of the lobes wore down badly and the bike wouldn’t run. I got an AN standard camshaft from RGM as AN were out of stock. I did a full rebuild with rebore and crank grind, big ends etc. I discovered like you that when I tightened the camshaft retaining nut that I had almost no clearance - probably 1 or 2 thou only. I discussed issue with AN who offered to replace it and mentioned that a number of cams were affected with insufficient length from tacho worm to shoulder. My concern was that the cam may have other deficiencies like soft lobes but was assured this wasn’t an issue.  Anyway my fix was to make a 10 thou shim which fits under the timing side sprocket thus extending the shoulder portion of the camshaft. Once nut is tightened I have about 12 thou clearance.  Only snag is that I’m coming to the end of a one year restoration and I haven’t started the engine yet!!! Here’s hoping all will be ok.   

Ian.   

Hi Gents,

Thank you all for this thread. I am just struggling with the same camshaft issue and the information contained here has helped enormously. I would like to add that the camshaft I'm struggling with was supplied last week by RGM and comes from 'Hepolite'. They market it as being manufactured in the UK and being 'chilled iron' but no other 'fitting' information was supplied.

This omits one very important point with 'chilled iron' camshafts, which has been mentioned above and that is that you must not tighten the camshaft nut very tightly or you'll snap the end clean off! Some years ago a friend of mine did this when fitting a PW3; the end snapped and he so did he!

I've since bought a couple of PW3 camshafts from Mick Hemmings, which are from 'chilled iron' and these came with written instructions not tighten above 15 ft/lbs and to use lock tight to compensate. I followed Mick's instructions with my track bikes and have had no trouble in 5 years. I shall be doing the same with this Hepolite camshaft assuming I can get it to fit!

Thanks

Ian

Hi,

I've just spent an afternoon trying to find the missing end float on my new camshaft. I now think I've found the problem I have, which may well be different from what other are experiencing. However, it might help some poor soul one day, so I thought I'd add it to the thread. 

I'm working on a 1970 Commando with a timed breather on the end of the camshaft. When I put the standard camshaft thrust washer and camshaft through the timing side crankcase only and add the camshaft sprocket it all rotates as you would expect. When I add the breather and drive side crankcase to the equation and tighten the cases together it all binds up. 

On close inspection of the timed breather disc I find that, on the original camshaft, it sits down flush onto the camshaft. However, when the disc is pressed down onto the new camshaft, I find I can get a 30 thou feeler gauge between it and the camshaft. On even closer inspection it's clear that the cut outs on the new camshaft are not as deep as on the original. 

I also assembled the cases, camshaft and breather disc but without the camshaft thrust washer. With that assembled the camshaft end float was 0.095 thou. With the camshaft thrust washer being 0.123 thou wide, I find I'm missing about 0.028 thou. About what is taken up with the breather issue. 

I'm going to have a think about it and talk to a couple of people. If I find out anything relevant to these issues I'll add to the thread.

Regards,

Ian

what is obvious from this thread is that cam manufacturers are not using simple go/ no go jigs to check that cam is to spec. in vital dimensions. This is unacceptable.

Well spotted, but keep looking.

Jan makes a point - but I wonder if they simply do not have access to all the original tolerance data?  Maybe they are being reverse engineered, and the original tolerance details are not followed?  Indeed the cases themselves might have been out of tolerance since they were assembled in the 1970's?  End float should not need to be more than enough to allow it to turn, since the alloy cases will rapidly expand more than the cam anyway.  A firm called NOC Ltd allegedly has lots of drawings, doesn't it?  Or are they all for the Dommie?

Given the greater expansion rate of the aluminium alloy crankcase and oilite camshaft bushes versus the nitrided steel/chilled iron camshaft, a degree of endfloat when cold more than just ability to rotate would surely be necessary, as crankcase expansion would be both radial and axial?

Andy

A Newman cam will be chilled cast iron, note the earlier warning about the torque used on the nut being a lot less than the factory setting, Use the factory setting and you will scrap the cam. Other than that they have a good reputation.

.. is not fit for purpose and you should get a refund from Norvil. Of course the flaked off bits will be floating around in your crankcase so to be safe it would be a full engine strip (although of course you need to do that to fit the camshaft).

Case bushing is .986" +/-

Very similar for all NHT 750/850 cases & bush styles 20M3S/200K/300K/325K

Cam from thrust washer to drive gear 1.011" typical

Thrust cone washer .125"

If the cam shaft journal is short a few thou, I would probably grind/cut the tach gear a few thou.

Hi. I too have a new camshaft from Norvil - but haven’t fitted it yet! The instructions on running in the camshaft seem a bit strange to me. The instructions say that on the very first engine start with the new camshaft, the revs mustn’t drop below 2000rpm for half an hour. I guess that this is to make sure that there’s sufficient oil getting to the camshaft lobes and followers to prevent pick-up. But what exactly is happening - why does the camshaft need to be ‘run in’? Are the lobes getting some kind of work hardening in those early minutes of engine running? It all sounds a bit ‘black magic’ to me.

Regards

Tony

And you think the lobe next to it is OK?, something serious is amiss there. Work hardening on the lobes can happen, but then you really have problems as that is caused by hammering. Work hardening on its own is not an issue.