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Camshaft wear on Dom 99


My 1956 Dominator 99 has a bad clatter from the engine. Very audible.

It is not a bearing rumble. nor a tappet rattle, nor a chain slap.

It seems to be coming from the front of the engine.

The engine has not been run much since rebuilt - probably 15 years ago.  Probably not done 100 miles. Compression test shows 120 psi both cylinders (at 1000m alt)

I suspect a camshaft/cam follower problem.

Does anyone have any experience or suggestions on this before I strip it down?



The old 'long screwdriver to the ear', with the tip pressed against the cases,  barrel, etc?

Useful in pinpointing where it is loudest?

Also 1956 is a dynamo model? Is it dynamo or its drive gears?

Regards, George 




Later bikes suffered with cam issues but the Dommies  with an intact cam tunnel  are normally very reliable,Both Nortons in our family are orriginal and still perfect. If a piston has picked up they can be very clattery. If its a loose pushrod they can be positioned without head removal,but may be a bit bent.


...for your suggestions.

I will check each. However, I don't think it is a pushrod problem, the noise is too harsh for tha.

It is a dynamo model, I looked inside the timing cover, all looks ok.

The noise is definitely loudest at the lower front of the barrel.

Yesterday I took off the valve covers, slowly turned the engine over and saw that the one inlet valve didn't open smoothly, there was clearly a small 'jump' as it started to open.

Looks like cam/follower problem?  I'm going to put a clock gauge on each valve and measure the profile vs engine rotation to get a complete idea of what's happened to the cam.

Regarding the piston nipping up, this is a real possibility, I bought the bike having been told the engine had been rebuilt. However, the clatter is worse when cold, which is a symptom of this problem.

In any event, the motor must certainly be stripped down to find out.

Thanks again.



Just a thought!, If a pushrod is not located on the rocker it sits to one side trapped but can still partially open the valve . With the adjuster removed a wire hook can pull it into position. Been there done that ,and have a spare rod to replace the slightly damaged one thats been working for 25 years.


Hello now think about on this one if this Norton has been layed up for some time then how as the cam gotten worn And this chatter is could be a be the Cam bushings that's getting worn And not the cam

Anna j


I've taken off the covers and inspected the movement of the rockers as the cam turns.

On both exhaust valves there is a distinct snap/click as the cam passes over its peak.

It can be felt clearly with a hand on the rocker as well.

So, it's a worn cam or worn/broken tappets.

Can the cam be removed without splitting the cases? Of course the barrels must come off.



But the tappets are in the barrels, so you might be lucky!


Just adding to the guessing the camshaft passes through full lift, the pressure of the valve springs will give the cam lobe a hefy push on its rotational journey. This in turn will cause the camchain to reverse its tension and give the tensioner plate a good whack with the chain. Hence the snap/clip sound. Perhaps the camchain is so slack that the noises are all down to this single item. Its a lot easier to pull off the timing cover to check this chain that dismantle the engine.


I read somewhere that the tensioner packing plates have to be fitted with long ends in opposition ,otherwise the chain tensioner will not work fully.  The diagram does not appear to show the correct set up. Could this be what has happened to Richards motor?. or does it do the opposite ,not enough slack to fit a new chain?.


I've got the head off and as expected it hasn't shown me much.

The point about the cam chain is interesting. I did have the timing cover off recently to check the chain and saw nothing wrong. I'll look at it again in light of what you have told me.

If there is no problem there then it's barrels off. I should able to see the problem then.



Surely if a closing valve spring is going to kick the cam forward, then the following opening valve spring will exert a force in the opposite direction keeping the cam under constant load throughout it's rotation.  


I thought Ian's point was a reason for having one cam instead of an inlet plus exhaust. There's less fluctuating load in cam drive on the Norton twin than on B's and T's.


Hullo all,

Well, head is off. Everything looks good inside as expected after only a few miles. However, I found that the pistons could be moved/rocked sideways about 1/2 mm. Didn't look right.

I then took the barrel off. Piston/bore clearances are fine, about 4 thou. Big end bearings are fine, no play at all. The faces of the tappets/cam followers are worn, quite badly ridged. The cam itself seems to also have a ridge on it but can't tell for sure yet.

The big problem is the gudgeon pins are loose in the small end bushes. by quite a large amount. The vertical clearance pin to bush is about 10 thou. The pin can actually be rocked in the bush noticeably. Those who (should) know tell me this would cause a lot of noise.

So, not good news. The engine must be split to get the conrods out for new bushes. Then I can get the cam checked properly.

I am trying to find someone here in SA who will dress down the tappet surfaces (how much can come off the hard surface case?).

I will also get an opinion as to whether the cam can be built up and ground.

The cost of buying new ones to be delivered to SA is astronomical (about P500 for four followers and the camshaft. Add about 70% for shipping, duty, vat, courier etc), about R20000. I need to see what I can get done locally first.

While I was checking all this, I noticed that  the pistons are stamped on top with "67". They measured about 66.95mm. The specifications state a diameter of 68 mm for the 99. The engine case is marked 14 - 73258, correct for the 99.

So I checked the stroke. It is 72 mm. It should be 82mm. This seems to mean that it is a 88 not a 99.

So someone has fitted a 88 crankshaft, barrel, pistons (+ 40th), pushrods and cylinder head into a 99 case.

Is the diameter of the lower part of the barrel the same for both engines? 

Is this possible? 

(I often wonder why I get involved with these things!!) 




Count the fins down the side of the barrel including the shorter ones.

There should be 8 for an 88 or model 7 and 9 for a 99, 650 and 750.

The pre-1960 crankcases can be built up as either a 500 or 600cc engine. Apart from the crankshaft, pistons and barrels all the other parts are inter-changeable. 


I have successfully ground Dominator tappets in the past and had no trouble with them. They must be ground in a fixture. NOT BY HAND and must be kept cool while grinding otherwise the stellite may crack. Make sure the pistons are in the correct holes! I know a bloke who put them in the wrong holes once and had this trouble. Little end bushes can be replaced in situ if you are careful. You will need to make up a puller/inserter and push the old bushes out with the new ones and then finish ream them to size.


Thank you both for your advice.

The barrels have 8 fins, so it's settled, it's a 500.

Bill, what do you mean by "make sure the pistons are in the correct holes"?

Are you referring to the tappets as pistons? So put the tappets back as they came out?

I think that I will split the crankcase. I need to examine the cam closely and, anyway, I don't have the equipment (or experience) to ream the bushes in place. I'll check the bearings and other bits as well.

Thanks again.


I have found that the cam follower/tappets are badly worn, but the cam itself looks fine (someone sure took a short cut with this engine!). The bike has only done about 50km since the rebuild.

So as I probably won't be replacing the cam, I won't have to remove and split the engine if I can replace the small end bushes in situ.

Do new bushes bought from AN or Norvil need to be reamed?

Considering the price of new tappets, I will get mine built up and reground. 


...they distort as they are pressed in and need then to be reamed back to the correct clearance.


The pistons are handed.  The exhaust cutaways must go to the front outsides of the barrels. The inlet cutaways together at the rear.

Like pistons, try and replace the tappets / follows in the same tunnels they came from. This is good engineering practice. Your suggestion of getting the tappets refaced is ok if done by somebody who knows what they are doing. There are quite a few stories about rebuilt and /or refaced tappets breaking up. Why not try and source a set from within the Club. Around £40 was the going rate for a good set not too long ago.


On some engines one pair of valves is bigger than the other. So the piston pockets need to be the right way round as well.  I think some pistons have 'front' marked on them. A pair I have here do not...


My pistons are marked RH and LH, so no problem here.

We have a cam specialist here who makes cams for racing engines, has done for years so should have no problem.

Re fitting new small end bushes. They  must be reamed. Can it be done with the rods still in the engine? Is it done by hand or must it be done in a machine? I don't want to take the engine out of the bike and split the engine to get the rods out to have two small bushes reamed.


My pistons have the same size valve recesses inlet and exhaust.

The LH and RH stamp is located in one of the recesses, facing forward when I took them out. So I know which is the front and which side to fit them.


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