E: Engine Setting MkII Cams With No Timing Marks...Equal Setting?

[ClassicBiker]

I set my Shadow to equal lift at 4 degrees BTDC, MKIII cams and new pinions from the Spares Co.. After setting the front cylinder I turned the engine back to the rear one being 4 degrees BTDC and it looked just like the diagram in Richardson's. I'm quite happy with how the Shadow starts and runs.

 

[vibrac]

You were lucky with a twin its normally a compromise its a fine day when the range between 6 and 2 BTDC encompases the two cylinders

 

[ClassicBiker]

A little bit of luck and magic markers. I pressed the cam pinions on myself. Once the rear cam was at equal lift and the crank was at 4 degrees BTDC, I aligned the timing marks of the large idler, the half time pinion, and the rear cam pinion. I gently tapped the rear pinion on the cam, just enough to hold position. Then I removed the lot and pressed the pinion on. The tool I made to turn the cam shafts under the spring pressure also doubled a surrogate cam, the pinion being a sliding fit and able to spin on it. Once my rear pinion was pressed on the cam shaft I put it on its spindle and the large idler on its spindle, timing marks aligned. I also placed the front cam pinion on the tool and that on the cam spindle with the timing marks aligned. I then rotated the crank 410 degrees which would be 4 degrees BTDC on the front piston. I marked all the pinions with magic marker. I turned the crank backwards enough that once I had installed the cam I could rotate it to equal lift without the valves hitting the piston. I then turned the engine forward until my temporary marks aligned. I aligned the temporary mark of the front pinion with the larger idler's and gently tapped the pinion on just enough to hold position. I took it all down again and pressed the pinion on properly. I then reassembled to the temporary marks with out pushrods and rotated backwards 410 degrees. The permanent timing marks all lined up and it was then that I noticed the slots in the cam shafts orientation. Doing it the way I did, I felt very confident I would have equal lift at 4 degrees BTDC for both cylinders as I was placing the pinions on the camshafts with the crank correctly positioned and teeth engaged. What didn't occur to me until that light bulb moment was the significance of the slots in the manufacturing and gauging process. As the cams I used were supplied by the Spares Co. I suspect the slots are still used as datums in the same fashion as originally designed and I also suspect the Spares Co. uses drawings from the Drawing committee and they probably updated the camshaft drawings to the latest drawing standards but maintained the original datum scheme.

 

[bmetcalf]

Get one of these:

https://www.vincentownersclub.co.uk/media/john-ulver-made-this.5250/

 

[ClassicBiker]

Making one of those would indeed be easy, but the point of doing it the way I did was to ensure that the valves would be at equal lift when the timing marks aligned, regardless of the variation of the cam due to manufacturing tolerances. I also did not initially assume the relationship of the cam lobes to the cam slots. If I were to use camshafts other than those supplied by the Spares Co. and I wanted to set them up at equal lift I would repeat the process. Because there isn't anything to say that XYZ co. didn't design their cam with the lobes equal lift point 90, 180, or some other number of degrees from the slot, unless they released that information.

 

[Monkeypants]

I was dreading this procedure with the 1360 engine. These were MK5 cams. I asked Terry if the equal lift at 4 degrees BTDC method would work and his reply was " It's the only way with the MK5 cams"
It turned out to be one of the easy jobs. It was much easier than fitting the oil pump sleeve. That was a bit of a nightmare first go round.
For the cam timing, I just squeezed the cams and camwheels part way together with soft jaws in the vice. With some effort, the cams could still be slipped relative to the wheels for timing adjustment .
A bit of playing around got everything in place, equal openings at 4 degrees btdc +- 1 degree fore and aft cylinders.
Then make some marks in case you have to pull everything down again, which I did for dynamic crank balance at 1500 miles.

Glen

 

[jim burgess]

I have a Mk 2 cam that gives the following figures with 1 thou nip and measured on top of the valve stem with 5 thou lift.
Inlet opens 58 BTDC
Inlet closes 80 ABDC
Exhaust opens 71.5 BBDC
Exhaust closes 59.5 ATDC
​

"THE BOOKS" say it should be...
Inlet opens 55 BTDC
Inlet closes 68 ABDC
Exhaust opens 73 BBDC
Exhaust closes 50 ATDC

I have not run the bike like this yet, but I did run it timed by the marks on the wheel which gave timings of
Inlet opens 46.5 BTDC
Inlet closes 91.5 ABDC
Exhaust opens 60 BBDC
Exhaust closes 72.5 ATDC

With these settings the bike sent me to A&E with a suspected broken ankle. I cannot make any adjustments to the relationship of the exhaust and inlet cam timing because of course they are fixed, I might be able to get the inlet opening closer to 55 but that would leave the inlet closing at about 77. So, the cam is marked with a 2 (so a MK2?) on the outer face, I am wondering if these cams were ever made with quietening ramps as per Series D? Or to put it another way how are series D cams identified on their ends? There is a possibility the 2 marked on the end face is preceded by a feint horizontal bar... Horizontal bar! what a lovely idea!

Any advice and guidance gratefully received.
Cheers
Jim

 

[davidd]

I would note that the equal lift method was the Vincent Factory's method of timing a cam. That was the position where all of the gear markings were stamped for correct alignment.

I have mentioned before, it is not possible to set a cam accurately at its highest lift. This is because the point of highest lift on a cam has some similarity with the point of lowest lift; it lasts for some time. When the follower is traveling over the highest point of the cam, it usually reads that same maximum lift number for several degrees. As a result of this "dwell" at the peak, which can last as long as 7 degrees, you would be forced to select one of these spots as the place to set your cam timing.

The cam does the exact same thing at the lowest lift, which is the base circle. This is why we set the "lash" there. The base circle has a much longer dwell, which makes it very easy to find. The shortest dwell at the peak may last only 3 or 4 degrees, but which one of those 3 or 4 spots should you choose for timing?

Frankly, the cam timing can be away from the 4-degree spot and work well. Andrews cam would often recommend zero degrees with no serious ill effects. Many owners rise to the challenge of attempting more precision than may be necessary, but often rising to that challenge will usually offer the default of consistency at worst.

David

 

[fogrider]

Jim, it's a pity you did'nt note where the inlet valves were at full lift while you were watching the degree disc.. Mk 2's work out at 97 deg after TDC. Doing it at full lift gets you away from the ramps which, to me, complicate matters by the tiny readings from shallow ramps. It's so easy to find the top of the lobe with a dial gauge.
A degree or so away from 97, either side , won't make any noticeable difference, they just need to be the same as close as can be achieved.
The big differences in your readings seems to demonstrate how dodgy it is going by the " works" method.
Try full lift, It works , have a go !
Regards, Terry.

 

[oexing]

Forget all these funny numbers, they are not relevant for the performance of the engine. The critical point is the timing around overlap. So you set valve clearance at nil on the base circle and put two clocks on valve spring caps. Then turn each cam to overlap position and equal lift. Easiest way is to have extra light springs fitted for easy turning the cam by fingers. I then mark the engine case and cam gear tooth at suitable places for that equal-lift-position. So you have two marks on engine case for front and rear cam, plus two marks on gears of front and rear camshaft.
So then have a degree wheel on the crank with zero at TDC , checked by piston stop method, meaning an old spark plug gutted for a length of bolt in it.
So you turn the crank at 4 degrees BTDC and the rear cam for equal lift with your marks on gear and case aligned. In this position slip the half time gear on the crank end after trying all slots for best fit.
The front cam timing will be next when you turn the crank one turn plus 50-4 degrees as the front cylinder is 50 plus from first pot. In this position at 4 degrees less from front TDC the front cam should align with your marks for front equal lift. But then it depends on the pressed on gear and large idler for getting a good match for your marks. So sometimes you´d have to press out the front gear and reposition for best fit possibly.
Any funny numbers from handbooks are useless as they were only correct with all new components at best, but I don´t believe this at all, too many variations in production in real life.

Vic