5 degrees advanced cam timing

lcrken · Oct 25, 2015

jseng1 said:
lcrken said:

The magazine says you can put the cam key in a vise, and knock it over with a chisel to get an offsest key. A more precise method, which I've used several times, is to start with a wider key, and file both sides to get the same sort of dogleg offset.

Ken

Click to expand...

I've looked everywhere and can't find a thicker key with the same shape (height, radius etc). How about some help here.

You have to start with a larger key to get the right width, and then file/sand/grind/mill it to the proper shape. I'll see if I can't hunt up some examples and take pics.

Ken

Deets55 · Oct 25, 2015

lcrken said:
jseng1 said:

lcrken said:

The magazine says you can put the cam key in a vise, and knock it over with a chisel to get an offsest key. A more precise method, which I've used several times, is to start with a wider key, and file both sides to get the same sort of dogleg offset.

Ken

Click to expand...

I've looked everywhere and can't find a thicker key with the same shape (height, radius etc). How about some help here.

Click to expand...

You have to start with a larger key to get the right width, and then file/sand/grind/mill it to the proper shape. I'll see if I can't hunt up some examples and take pics.

Ken

Could you start with a piece of bar stock with the correct radius and the cut it to the required width and height?

Pete

lcrken · Oct 25, 2015

Deets55 said:
[Could you start with a piece of bar stock with the correct radius and the cut it to the required width and height?

Pete

Don't see why not. The keys aren't hardened. If one fails, in most cases it's better to have it shear instead of ripping the keyway out of the shaft with a hardened key.

Ken

johnm · Oct 26, 2015

" Even easier is to use Vernier cam gears, and I've done that in the past with the ones from Fair Spares (now Norvil), but the ones I bought were not very concentric, and had a lot of sprocket runout. Only one out of the three I bought was usable (at least by my standards at the time). "

This is exactly my experience. I would not use any vernier I have seen except for short term experimental purposes. I have had two come close to destruction.

Based on my experiments 5 degree steps will give sufficient flexiblity for almost all desired outcomes.

Brooking 850 · Oct 27, 2015

Jim as you know I have a stepped key on my JS2 cam with the step being clock wise from the indent on the cam as you look at it in the installed position.
As ken stated, we also started with a fatter key close to the radius of the original, the rest was hand work with a file. Took a while !!!
T o get the minimum valve clash with that cam, I ended up three teeth on from standard Norton timing marks between the crank pinion and the idler and it is in fact 9 pins between idler /cam sprocket teeth.
Intake Vv at TDC has 0.174" of lift and the exhaust Vv at TDC has 0.152" of lift thats with both sets of tappets set at 0.005" when setting up
105 Intake at full lift with zero tappet.
Just an aside, I had a race meeting this last weekend, there was a mobile dyno there , so after the last race for the weekend while the bike was still very hot, pulled a quick run just to get a read out on air/fuel as I am testing the new 2 into 1 exhaust.
Also the power/torque curve as I need to see where we are at, surprised myself, as it was still making power with this system before I hit the rev limiter at 7500rpm.
I will be posting pics and details in a new thread.

Matchless · Oct 27, 2015

The easiest thing to do is take the cam sprocket & crank gear to an engineering company that does wire erosion. Get two extra key ways in each. Very accurate & not to expensive.

jseng1 · Oct 27, 2015

Brooking 850 said:
Jim as you know I have a stepped key on my JS2 cam with the step being clock wise from the indent on the cam as you look at it in the installed position.
As ken stated, we also started with a fatter key close to the radius of the original, the rest was hand work with a file. Took a while !!!
T o get the minimum valve clash with that cam, I ended up three teeth on from standard Norton timing marks between the crank pinion and the idler and it is in fact 9 pins between idler /cam sprocket teeth.
Intake Vv at TDC has 0.174" of lift and the exhaust Vv at TDC has 0.152" of lift thats with both sets of tappets set at 0.005" when setting up
105 Intake at full lift with zero tappet.
Just an aside, I had a race meeting this last weekend, there was a mobile dyno there , so after the last race for the weekend while the bike was still very hot, pulled a quick run just to get a read out on air/fuel as I am testing the new 2 into 1 exhaust.
Also the power/torque curve as I need to see where we are at, surprised myself, as it was still making power with this system before I hit the rev limiter at 7500rpm.
I will be posting pics and details in a new thread.

Mike (Brooking) I would need a photo to make sure I understand your timing adjustments. Whatever you did it came out right according to your valve lift at TDC. I am not surprised that you make good power at 7500. Another racer got his 850 up to 8400RPM with the same JS2 cam. Looking forward to more info in your coming thread.

Matchless - Your EDM technique is interesting. I'm a little frustrated with the stepped key modification and I'm tempted to take the easy way out -Just mill or file a step so it can be retarded or better yet - mill the step and simply solder a strip of brass shim stock on the other side so it can be reversible (advance-able). It would still need a little filing but anyone could do it with common tools.

johnm · Oct 27, 2015

" I'm a little frustrated with the stepped key modification and I'm tempted to take the easy way out - "

Jim. Don't know if you are thinking about this for customers or just yourself but for my own use I found when I went through a box of cam shaft sprockets at British spares and Cycle Works in the Hutt here in Wellington I was able to find 4 or 5 original sprockets which had sufficient range in the key way location to be able to cover all cases.

Just keep an eye out for sprockets at any swap meets etc and make a collection.

5 degrees advanced cam timing

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