Stepped key for cam timing

jseng1 said:
Made some stepped cam sprocket keys to make cam timing adjustment easier. Gives about 2 deg advance or retard adustment depending on which way you install it.

Stepped key for cam timing
Click to expand...
Question: How do you keep the sprocket from turning on the cam while tightening?
 
marshg246 said:
Question: How do you keep the sprocket from turning on the cam while tightening?
Click to expand...
By making sure the key is fitted! The stepped key will/should have been made from a thicker woodruff key than the standard one so both top and bottom of the key will fit the cam and sprocket without any play. Ive made custom woodruff keys before by cutting up a scrap bolt as the material is very suitable for this application, the only problem is holding the thing to file/machine to the right size
 
Last edited:
dobba99 said:
By making sure the key is fitted! The stepped key will/should have been made from a thicker woodruff key than the standard one so both top and bottom of the key will fit the cam and sprocket without any play
Click to expand...
Yes, if the key is cut twice. The picture JS posted does not appear to be that and many others have documented filing off one side or the other of the part that fits into the sprocket.
 
marshg246 said:
Yes, if the key is cut twice. The picture JS posted does not appear to be that and many others have documented filing off one side or the other of the part that fits into the sprocket.
Click to expand...
jseng1 said:
Yes it is full width in both sections - where it fits into the cam and also where it fits into the sprocket. Below are photos of each side of the key.

Stepped key for cam timing


Stepped key for cam timing
Click to expand...
Nice job Jim. Did you machine a thick key down to size or made them from scratch?
 
As a non-tool room type I used a file on a stock key on one side. As Jim notes somewhere in his installation notes for his cams, you can insert a shim in the empty side you wish (ie, if it makes you
feel better). Once home on the taper I doubt the cam will slip. Hasn't on mine. But that said I am
certain I will blown out of the water with stories about how wrong I am.
 
Onder said:
As a non-tool room type I used a file on a stock key on one side. As Jim notes somewhere in his installation notes for his cams, you can insert a shim in the empty side you wish (ie, if it makes you
feel better). Once home on the taper I doubt the cam will slip. Hasn't on mine. But that said I am
certain I will blown out of the water with stories about how wrong I am.
Click to expand...
As you say, that’s doable. I’d still be happier having a couple of these to hand though just makes such messing around quicker / easier.

One minor detail tho… it’s not on a taper…
 
Although more agricultural in many other senses the ES2/Model 50 is far more advanced than the twins in having separate inlet and exhaust cams.
I had 2 extra keyways machined in the cam gears (at 120 degrees) giving the ability to separately vary the timing of the inlet and exhaust valve action, something that is impossible with a commando without a new cam (or cams)
I recall the gears had 40 teeth meaning 9 degrees per tooth - 120 gave you a 1/3 tooth variation (3 degrees)
You could do similar with the pinion (20 teeth) which would give 6 degrees movement for both inlet and exhaust.
 
Last edited:
robs ss said:
Although more agricultural in many other senses the ES2/Model 50 is far more advanced than the twins in having separate inlet and exhaust cams.
I had 2 extra keyways machined in the cam gears (at 120 degrees) giving the ability to separately vary the timing of the inlet and exhaust valve action, something that is impossible with a commando without a new cam (or cams)
I recall the gears had 40 teeth meaning 9 degrees per tooth - 120 gave you a 1/3 tooth variation (3 degrees)
You could do similar with the pinion (20 teeth) which would give 6 degrees movement for both inlet and exhaust.
Click to expand...
”far more advanced”…

Like a Triumph you mean… ?
 
Onder said:
As a non-tool room type I used a file on a stock key on one side. As Jim notes somewhere in his installation notes for his cams, you can insert a shim in the empty side you wish (ie, if it makes you
feel better). Once home on the taper I doubt the cam will slip. Hasn't on mine. But that said I am
certain I will blown out of the water with stories about how wrong I am.
Click to expand...
What's wrong with using a thrupenny bit and a junior hacksaw!!
 
A single camshaft may have had production engineering advantages, so in that way, a Dominator would be more advanced than a Triumph twin.
 
If the exhaust cam is moved in a Triumph motor, it is difficult to get more torque unless the exhaust system is altered. in a Commando motor, both inlet and exhaust move together. More advance in the inlet lobe can move the revs at which the power band comes on strong, and advancing the exhaust lobe might work better with a more restrictive exhaust system. So advancing the cam in a Commando motor might not be a bad thing, unless it affects the heat build-up.
I do not worry too much about cam timing, wherever the power band might be, adjusting the gearing takes care of it.
In a Triumph twin, E3134 race cams were pretty much the best. They needed separate pipes with megaphones to the factory specification. They were a 1953 race kit thing, when noise did not matter - but the power band was very strong and well defined - too harsh for smooth riding. They were the only cams with which I ever bothered about getting the timing really right.
 
Two degrees variation in cam timing in a standard Commando motor should not make much difference unless you are not prepared to adjust your jetting. With my bike, I set everything up and get it running, and then adjust the carburation. Changing the exhaust system can have a bigger effect, than changing the cam timing.
When I adjust my jetting, it usually only ever involves moving the needles one notch.
 


Write your reply...

Similar threads

P
  • Locked
1972 750 Commando cam timing
Replies
15
Views
1,714
johnm
johnm
T
  • Locked
Lobe Center (Cam Timing) Help Needed
Replies
14
Views
2,069
thunderbolt
T
G
A50 cam timing
Replies
3
Views
2,342
L.A.B.
L.A.B.
Fast Eddie
E3134 cam timing
2
Replies
24
Views
7,764
acotrel
acotrel
acotrel
Exup and exhaust cam timing
2
Replies
20
Views
4,270
acotrel
acotrel
Back
Top