Questions about Cam Spindles

[clevtrev]

The distance between the cam spindle and the centre of the large idler is equal to half the sum of the diametric pitch of the gears. 16DP x 48 teeth = 3" 79 teeth = 4.9375 sum = 7.9375 so centers are 7.9375/2 = 3.968"
Similarly the distance between HT pinion and Idler = 3.219"

Same for Comet.

 

[clevtrev]

If you look at the drawing you will get an eyeball check for the cam timing. Simply note that the slot in the shaft is pointing at the crank centreline, with the piston at top dead centre.

 

[ClassicBiker]

The distance between the cam spindle and the centre of the large idler is equal to half the sum of the diametric pitch of the gears. 16DP x 48 teeth = 3" 79 teeth = 4.9375 sum = 7.9375 so centers are 7.9375/2 = 3.968"
Similarly the distance between HT pinion and Idler = 3.219"

Same for Comet.

Clevtrev,,
I completely agree. Now, if I could impose upon you to check my math for the angles α, β, σ, and ψ.

If you look at the drawing you will get an eyeball check for the cam timing. Simply note that the slot in the shaft is pointing at the crank centreline, with the piston at top dead centre.

Well that is interesting as I was just wondering at what position the crank/piston was supposed to be in when all these dots were aligned. I take it then that; 1) We are talking about the Rear Piston being at TDC, and 2) the slot in the Front Camshaft being 90° straight down from the horizontal centerline that passes through both camshafts? So having said that has anyone set their valve timing by bringing the Rear Piston to TDC and made a couple of fixtures to align the slots accordingly, placed the Idler on its spindle then aligned the teeth of the Camshaft Pinions with the teeth of the Idler and tapped them on a little, before pressing them home properly?
I can't see the factory spending much time on the assembly line messing about with cam timing with degree wheels and dial indicators. What I do see is the factory assembling the Camshafts and Pinions in a jig, marking the Idlers in a jig, assembling all in the timing chest according to the dots, with the Rear Piston at TDC. Then I see them taking a little time to see which of the 5 keyways in the Half Time pinion best line up with the keyway in the Mainshaft.
Thoughts?
Steven

 

[bmetcalf]

Maybe the works had one of these?

http://www.vincentownersclub.co.uk/index.php?media/john-ulver-made-this.5250/

 

[Bill Thomas]

When I worked for Conways in the 60 s, They had one of those, But who ever made it, Made it Wrong !!.
So I have never trusted the marks since !!. Cheers bill.

 

[ClassicBiker]

Maybe the works had one of these?

http://www.vincentownersclub.co.uk/index.php?media/john-ulver-made-this.5250/

Bruce,
I'm sure the factory did have a fixture for setting the slot relation in to the dots, one for each Camshaft no doubt. I was curious if anyone had made fixtures when rebuilding the timing to set the timing by the slots only.
What I am really questioning is the angles involved. Using the numbers provided in the drawing the angle described as 46° 39' is actually 44° 57' and therefore the angle described as 43° 21' must be 45° 03'. Which if you were making the fixture described in the post, your post referenced, for the Front Camshaft you would be out 1° 42' (45° 03' - 43° 21'). As I'm rebuilding my timing chest with new Camshafts, Pinions, Spindles, Idler, and Followers I'm going to have to time everything. While I'm capable of doing this using a degree wheel and dial indicators and it is undoubtedly the most accurate, I wondering about a quicker and easier way of doing it that would provide satisfactory results.
Steven

 

[Bill Thomas]

What we found "off putting", On the last build, Was the size of the spacers for the steady plate, The engine was just a box of bits, Not all there.
When we got the new spacers they were thicker than the old type, And thicker than the books say, We didn't want to put any strain on the plate, So it took a bit of sorting as to how far in the spindles went !. Good Luck, Bill.

 

[davidd]

Here is a homemade jig:

The Factory probably had a standard that they used for cams. I used a Gary Robinson cam as a standard. To me, this meant installing the alignment pin on the right to hold the gear in the proper position. I thought that Gary might know something about that, so I copied his positioning. It seemed to me that the real issue is that if you ignore the markings completely, you want the cam pressed in when it is indexed properly on one tooth. That is, the the part of the cam that you want to have in the correct position when timing your cam is always one whole tooth on or off the mark because you can always move a whole tooth. Moving 3/4 of a tooth, for example, is not easy. I copied Gary's positioning hoping that it would be right, but at a minimum it would provide consistency.

Once the alignment pin was in, I put the Robinson cam on the jig and noted where the two dots on the gear fell with a sharpie. I put my loose gear on the same spot and pushed the cam in.

David

 

[clevtrev]

Steven, simply rotate the engine until the front piston is at TDC, the slot will be in line with the crank.

 

[ClassicBiker]

Steven, simply rotate the engine until the front piston is at TDC, the slot will be in line with the crank.

So we start with the Rear Piston at TDC and the slot in line but facing away from the crank, then rotate the crank clockwise 50° till the Front Piston is at TDC and line the slot up towards the crank, or 410° and the Front Piston is at TDC and line up the slot away from the crank? Or will both methods work?
Steven