RGM multi-position cam sprocket (2019)

Curious if anyone has experience with this cam sprocket from RGM, now that my cases are assembled, I'm getting ready to dry assemble the top end and degree the Web12A cam I bought from JC.

I Had no inclination to go the vernier sprocket route, but while I was checking over their site I found this lightweight sprocket with 3 key slots milled, apparently it provides for a multitude of advance/retard options (no milling woodruff keys!). Description below, I've ordered the unit and will report back:

"Inspired by the original norton dommie racer, this sprocket has been carefully designed to eliminate all unnecessary material and thus be approximately 25% lighter than the standard component whilst maintaining its strength through careful choice of steel and heat treatment. The three carefully positioned woodruff key slots allow the choice of standard timing, 3 degree advance or 6 degree advance. Combining this adjustment with the 5 degree advance or retard provided by the tooth engagement of the intermediate gear gives a wide choice of valve timing positions. 2 degree retard. Standard. 1 degree advance, 3 degree advance etc"

https://www.rgmnorton.co.uk/buy/special-camshaft-sprocket-less-weight-adjustable-timing_4641.htm

Now if that is well made that is an excellent way to go. I used a vernier sprocket on my Dommie race bike and it simply wasn’t robust enough. I only ever used it for testing on the dyno never for racing.

If this is strongly made this is an excellent idea and if I were still racing would certainly try it.

In the early times I got around it by having a collection of standard sprockets which I found had slightly different keyway positions. I was lucky enough to be able to go through a big box of spares at Britishspares in their old location in the Hutt New Zealand

Looks like a great product to me.

Thanks for the heads-up. I'll definitely be buying one of those.
I wonder whether it will fit my 650ss (ie: is that end of the pre-commando cams the same as the commando cams?)
Anyone know for sure?
Maybe I'll be buying 2....

https://www.rgmnorton.co.uk/buy/special-camshaft-sprocket-less-weight-adjustable-timing_4642.htm
the previous one NO.....but that one yes , the first for commando the second for dommie/atlas!

marinatlas said:

https://www.rgmnorton.co.uk/buy/special-camshaft-sprocket-less-weight-adjustable-timing_4642.htm
the previous one NO.....but that one yes , the first for commando the second for dommie/atlas!

Click to expand...

Thanks for that - I really should read all the text before asking stupid questions, shouldn't I?

I guess this allows you to adjust the cam by 1/3 of a tooth

johnm said:

Now if that is well made that is an excellent way to go. I used a vernier sprocket on my Dommie race bike and it simply wasn’t robust enough. I only ever used it for testing on the dyno never for racing.

If this is strongly made this is an excellent idea and if I were still racing would certainly try it.

In the early times I got around it by having a collection of standard sprockets which I found had slightly different keyway positions. I was lucky enough to be able to go through a big box of spares at Britishspares in their old location in the Hutt New Zealand

Click to expand...

What exactly happened to your Vernier sprocket?
Do the pins work loose etc?
Cheers

baz said:

What exactly happened to your Vernier sprocket?
Do the pins work loose etc?
Cheers

Click to expand...

Yes they "could" get loose or break , I had one on my 920 but so far no problem , just to add more problem (or not ?) I had an automatic chain tensionner on that one !!!

marinatlas said:

Yes they "could" get loose or break , I had one on my 920 but so far no problem , just to add more problem (or not ?) I had an automatic chain tensionner on that one !!!

Click to expand...

I have heard of people having problems with them
I have one on my shelf,I think I will leave it there
Cheers

marinatlas said:

Yes they "could" get loose or break , I had one on my 920 but so far no problem , just to add more problem (or not ?) I had an automatic chain tensioner on that one !!!

Click to expand...

Yes that is the problem I had. I do not remember where I bought the vernier sprocket for the camshaft but the pin and locking mechanism was too light weight and it loosened off no matter how careful I was. The camshaft has a fair amount of torque applied to it.

I used a similar vernier sprocket on the magneto and it gave no trouble at all.

Great idea to sell a sprocket with multiple keyways. Back in the late '70s I bought the correct size broach and made two or three like it for my race bikes (but with more keyways and no lightening holes)s. The only problem I had was getting accurate locations. I made a jig to do so, but it wasn't accurate enough. In the end, I had to number the sprockets for identification, and just keep notes on where the keyways were located and how much advance/retard they gave. To cut the keyways I had to first anneal the sprockets. In an ideal world, I'd have re-heat treated them after, but I didn't (no high temp oven at that time). With the limited amount of mileage the race bikes got, the annealed sprockets worked fine, with no significant wear.

I've also used the adjustable sprocket (probably from RGM), shown below, with no problems, but again, only in a race bike with low running time. The method I've used most often to get the timing right is making offset keys. At first I hand filed them, but after I got a mill in the shop, I started using it to cut them.



Ken

acadian said:

I've ordered the unit and will report back:

Click to expand...

acadian, did you (or anyone else) install the RGM sprocket? I just installed one and the (new) chain is quite tight (like barily 1/16" deflection)

I'd be interested in feedback too. If it works it's a very useful addition to a race bike. Simple and strong is what you need racing in my opinion. Too many races lost by unreliable complication.

TomU said:

acadian, did you (or anyone else) install the RGM sprocket? I just installed one and the (new) chain is quite tight (like barily 1/16" deflection)

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I've had it in the bike for 2 years now, was able to get the advance I wanted fairly easily. So it does the job it claims.

Installed it with a new IWIS chain, fresh cam bushes, and rubber padded tensioner. So I recall noticing tightness in the cam chain as well, but it hasn't been a problem,

Hello!

I also installed this RGM-sprocket at my engine rebuild winter 2020/2021.
Put in the JS1 cam ….so as per cam manual the ideal adjustement is a camlobe-center with 102° before TDC.

Did measurement and calculating and my timing was 98° before TDC.
So i had to retard 4°.
This sprocket helped very well to get the 4° retard so that I got now exactly camlobecenter 102° before TDC.
this sprocket is good stuff and lighter than original.

post a drawing and a calculating sheet I made.....maybe it`s helpful for any member here on the forum who has also to retard the timing 4°…..

chris

If anyone's interested, below is the weight difference