E: Engine Valve Timing

Bill Thomas

Well Known and Active Forum User
VOC Member
I think one of the books tell us the breather goes the wrong way ?,
Not bothered me too much as I don't use the standard one.
I don't think you need marks doing it my way, If you have trouble on the road,
It's TDC with the valves rocking on the wrong stroke, On either cylinder.
The halftime pinion keyways don't make much difference, It's only a way of giving you half a tooth ish.
Another way of checking the timings right is to look at where the brass bit on the mag' pickup is on the firing stroke.
 
Last edited:

davidd

Well Known and Active Forum User
VOC Member
the rear cylinder is on the top of the exhaust stroke and the front is 50 degrees from the top of the compression stroke.
I am certain that I posted these before. I keep one for the twin and another for the single as a reminder.

Equal Lift 4 Deg BTDC Twin.PNG


Equal Lift 4 Degrees BTDC.GIF


David
 

ClassicBiker

Well Known and Active Forum User
VOC Member
David,
Yes, you have posted that before, but I can't remember whether it was on this or the old forum. Anyway now that you've posted it, it brings to mind something I read either here or on the old forum, and it raises a couple of questions. I remember reading that with regards to the twin drawing above, that the slot in the rear camshaft is in line with a line drawn from the crankshaft center through the rear camshaft center. While at the same time the front camshaft slot in perpendicular and down ward to a line drawn through the two camshaft centers. If this is the case I would think it would be easy enough to make a jig with a pin to fit the in oil quill hole in the end of the crankshaft and holes to fit over the camshaft spindles and pins to align the camshafts. If it were a plate it would need a large hole for the large idler to fit through, but if it were "V" shaped that might be avoided. If the former is true has anyone attempted to make the latter?
Steven
 

oexing

Well Known and Active Forum User
VOC Member
Would you really rely on any slots, marks, dots on unknown parts with unknown history ? I did have dots on these genuine Andrews cams but would not care to dig into scetches and procedures for setting up the timing gear from books. I only trust in my measurements of equal overlap at the valve ends as shown above. So I really KNOW about the actual timing and not rely on somebody having pressed up the gears on the cams to specs and marks, slots, dots and what not.
Also, my marks on each cam tooth which align with the chisel mark on the engine case at equal lift can be checked any time I like for self assurance. Just find TDC for one pot at overlap and the corresponding alignment must be allright. All slots, dots etc. are void when you turn the crank a few revolutions as the idler gear has different numbers of teeth. So you can only start from very first step to check anything.

Vic
 

vibrac

Well Known and Active Forum User
VOC Member
I agree with oexing dont trust the slots use them in the first instance to do a rough set up but then refine. After all if you are putting new cams in chain wheels you may not have a jig to align the parts up and in any case using the 4 degree method a wheel is a wheel and any old marks dont matter
 

timetraveller

Well Known and Active Forum User
VOC Member
Posting #2 above. If you do not know the cam profiles then what are you timing for? I remember one set of cams that were so extreme that I had to time them with the lift half way down the stroke as the valves were hitting the pistons near TDC. By all means use short cuts once you know what you are dealing with.
 

ericg

Well Known and Active Forum User
VOC Member
I agree with oexing dont trust the slots use them in the first instance to do a rough set up but then refine. After all if you are putting new cams in chain wheels you may not have a jig to align the parts up and in any case using the 4 degree method a wheel is a wheel and any old marks dont matter
Tim, does this means that one can press a cam in its pinion in any position and end up with no problem when using the 4 deg method? I have a brand new TP 105 cam in one hand and a new cam wheel in my other hand for my Comet project.
 

ClassicBiker

Well Known and Active Forum User
VOC Member
As I said I timed mine by the 4*BTDC method.
But others on here have timed their cams to the timing marks on the pinions, using the slots, and then aligned the all the timing marks and called it good. I would suspect for expediency in manufacturing the machines originally, the cams were aligned to the marks on the pinions. Which in turn were align to the marks on the large idler. With the crank in position the and all the marks aligned the half time pinion was the last one to be placed once the assembler determined which key way lined up best with the slot in the crankshaft itself.
These machines were a mass produced item. So methods were devised to make assembly as quick a process as possible.

In these threads the relationship between the dots and slots are outlined.
So I would be willing to bet that the slots are datums for the manufacturing of the standard cams and that you could time the cams from them.
 
Top