Vernier cam wheels...

Are they a good, or bad idea ?

I was told by Mick Hemmings (when discussing my cam timing with him) they are a bad idea as if the locating dowel pin fails (which is apparently likely over time) then the engine is wrecked. The normal method of adjusting the position of the chain and gears is far more reliable and the only real benefit of vernier system would be easier adjustments to figure out best set up but once done an timing found replace with solid item that can give the required timing. Also for a road engine the gains if any of adjusting in less than the 5 degrees of the normal method were not significant and so not to bother with them in his opinion which is good enough for me.

Hi Eddie

Ran one on the 750. Would not start on the rollers, found the pin, no drive to the cam unbelievable no damage. Geoff cuts new keyways as per Triumphs.
Use standard ones now.

Chris

Norton Inters and some varieties of manxs had the cams individually adjustable against each other.
This gives almost infinitely adjustable cam timing, although obviously the range that works well is in quite a narrow band. I don't think I've ever heard of the peg failing in this system.

Commandos can't adjust the inlet against the exhaust timing, so adjustable timing is far less useful, as mentioned.

I went away from the vernier sproket.
I asked a friend of me to make two different offset keys to me. He did and now I using these two keys and mixing with gears l can adjusting the cam for each degree all the way around . I have engineering drawings, if anyone is interested.

I've used the Fair Spares/Norvil Vernier sprockets off and on for a couple decades, with mixed results. I originally tried a version they made with an aluminum sprocket. It beat the holes to death rapidly and was a real failure. I've used their steel version on several engines successfully, but it also eventually wears the pin and holes. Back in the '70s I made offset keys, starting with a larger width key and filing it down by hand. Later, when I acquired a milling machine, I did the same on the mill. I also tried cutting extra keyways in the sprocket. That worked well, but I had a hard time indexing the broach accurately, so the keyway locations varied a lot from what I intended. Still, after I set them up and measured the changes in timing for each keyway, and carefully took notes of the results, they worked quite well. All of these methods worked satisfactorily, but some were easier to use than others. Now, I mostly just use the offset keys I have on hand to get the timing right, at least on the race bikes. On the street bikes, I've just been using the stock timing marks, and not worrying about it. On a highly tuned race motor, even a couple degrees of timing change can make a difference. On a stock or mildly modified street motor, I'm not sure it's worth the effort, unless you are using an aftermarket crank with questionable keyway locations, or a reground cam from a not-so-fussy grinder.

Ken

Nigel, I run a stepped key on my JS2 cam.
Thought of the vernier set up originally, although after all the comments on the forum and advice from other racers, decided against it.
Regards Mike

I simply broached two more keyways at random after softening the sprocket. Helpful if you are fitting a 2 into 1 exhaust. However on my bike the exhaust valve now closes too early.

I have a vernier cam sprocket in my spares. IIRC the pin just locates the sprocket and once the nit is tight there should be no stress on the pin. I' ll have a look at the week end.

pommie john said:

IIRC the pin just locates the sprocket and once the nit is tight there should be no stress on the pin.

Click to expand...

That's what I thought ...

Fast Eddie said:

pommie john said:

IIRC the pin just locates the sprocket and once the nit is tight there should be no stress on the pin.

Click to expand...

That's what I thought ...

Click to expand...

I have a PW3 chilled iron cam which cannot have a high torque setting on the sprocket nut for fear of breaking the end of the cam. I would not trust the 15 lb/ft torque setting it uses to "clamp" a vernier sprocket securely.
Such design of sprocket do work on other types of engine so maybe it could be that the materials used in commercially available items are not suitable (for reasons of cost etc).
Given many people make themselves an offset key with not much difficulty is there a market for a high quality and cost sprocket? A set of commercially made offset keys would be easier to produce profitably i image.

Having seen your latest engine build project Eddie (nice stuff im jealous as am sure are others) which will require special fine tuning a vernier sprocket may have a (temporary) use but would you trust it as a long-term fitment?

toppy said:

Fast Eddie said:

pommie john said:

IIRC the pin just locates the sprocket and once the nit is tight there should be no stress on the pin.

Click to expand...

That's what I thought ...

Click to expand...

I have a PW3 chilled iron cam which cannot have a high torque setting on the sprocket nut for fear of breaking the end of the cam. I would not trust the 15 lb/ft torque setting it uses to "clamp" a vernier sprocket securely.
Such design of sprocket do work on other types of engine so maybe it could be that the materials used in commercially available items are not suitable (for reasons of cost etc).
Given many people make themselves an offset key with not much difficulty is there a market for a high quality and cost sprocket? A set of commercially made offset keys would be easier to produce profitably i image.

Having seen your latest engine build project Eddie (nice stuff im jealous as am sure are others) which will require special fine tuning a vernier sprocket may have a (temporary) use but would you trust it as a long-term fitment?

Click to expand...

Well Toppy, as you say, I certainly do not wish to fit anything that could be a weak link and cause wider damage in the event of failure.

But then again, I intend to fit out the timing chest with new components (so I can leave the 'old' motor in one largish ready to use lump), so if I'm buying a new camwheel anyway, I thought I'd try and ascertain if the vernier option was a good one. So far, the vote seems to be no!

And I totally agree with you ref the offset keys, about time someone with a CNC mill knocked a batch or two out I reckon!

Fast Eddie said:

And I totally agree with you ref the offset keys, about time someone with a CNC mill knocked a batch or two out I reckon!

Click to expand...

Not a lot of profit in it I shouldn't think, except gaining a small but grateful following

pommie john said:

I have a vernier cam sprocket in my spares. IIRC the pin just locates the sprocket and once the nit is tight there should be no stress on the pin. I' ll have a look at the week end.

Click to expand...

I think the key word here is "should". I can't argue with that in theory, but in practice, with the Loctite applied and the nut properly torqued, I have still seen significant wear on the pin and sprocket. I suspect part of the design problem is with the small size of the pin and the close spacing of the holes in the sprocket. I've seen similar systems on other engines that had no wear problems, but they all had larger pins. I've thought that using a splined hub and sprocket instead of the pins and holes might be a clever idea, but never followed up on it. The offset keys work quite well as long as the amount of offset needed is small, and in my case it always has been, so the motivation for a different solution just isn't there.

Ken

I usually set the cam timing with nil tappet clearance, then adjust the tappet clearance for running. With the three keyways broached into the cam sprocket it is easy to simply wind the cam up against the spring tension in the valve train, align one of the keyways, then simply push the sprocket on. If you use stepped keys, don't you have to put the sprocket on and if you've got the wrong key, pull it off again and change the key again until you get the timing right ? Seems to me that my answer of broaching two more keyways into the cam sprocket at random, is much simpler when it comes to setting the valve timing.

The cam my bike had in it when I got it had 3 keyways machined into it by the manufacturer (an aftermarket item said to be by "Dickenson" but i have no prove or information on it). Unfortunately the lobes had all lost their surface hardness and it was ruined but the extra keyways gave the ability for fine adjustment something makers of new cams could do but as with making special keys or sprockets it down to cost again i suppose.

acotrel said:

I usually set the cam timing with nil tappet clearance, then adjust the tappet clearance for running. With the three keyways broached into the cam sprocket it is easy to simply wind the cam up against the spring tension in the valve train, align one of the keyways, then simply push the sprocket on. If you use stepped keys, don't you have to put the sprocket on and if you've got the wrong key, pull it off again and change the key again until you get the timing right ? Seems to me that my answer of broaching two more keyways into the cam sprocket at random, is much simpler when it comes to setting the valve timing.

Click to expand...

I agree that a sprocket with extra keyways is a good approach, but if you just broach some randomly, there's no guarantee that they will be in useful locations. Building a jig that would let me broach the new ones in precise locations was more effort than I thought it would be worth for just my own use. It's not that it couldn't be done, just that I didn't see enough benefit for me to do so. Also, back when I was doing this I had to anneal the sprocket completely to cut the keyways, then harden and temper it, using just a torch and color judgement. Now that I finally have a proper oven for heat treating, that part would be simpler. I'd really like to be able to have a local job shop make some to my specs, but it just doesn't pencil out financially. When I made my last sprocket like this, I added four extra keyways, trying to get them plus and minus one degree and plus and minus two degrees. My jig was not adequate for that, and the keyways ended up more randomly. It still worked, but I had to set it up on an engine and degree the cam on each slot just to find out what the timing changes were. Not a practical procedure for a production process.

As an aside note, the other problem I had with the Vernier sprockets from Fair Spares was a lot of runout. They were even worse than the factory ones in that respect.

Ken

Ken

I think that it doesn't matter where the extra keyways are broached, but preferably not exactly evenly spaced. I can usually get the timing within a couple of degrees of where I want it, and I always check with the degree wheel on the crank, using nil tappet clearance and the dial mic. on the valve. It is academic anyway, because what I am usually doing is either maintaining a previous set of timings, or I am systematically changing the timings to find what works best with the exhaust system.
I don't believe that cam timings are so critical that 3 degrees error at the crank makes a substantial difference to the result.

From memory, I think that one tooth error on the cam sprocket causes about 15 degrees error in the valve timings. With three keyways broached randomly, you should always be able to get your desired timings within a couple of degrees ?

We might have to agree to disagree on this one. My mentor on the subject of cam timing, who had more hours of Norton dyno time developing cams than anyone else I know of, told me that for his race cams I needed to be within one degree of the specified timing or I would be losing power. For a street bike, not such a big deal, but for a race bike, the maximum horsepower is achieved by paying attention to all the small details, including precise cam timing.

Ken