The following is taken from OVR, June 2017.
Frequently you cannot rely on the pinion marking when setting up the valve timing on a Vincent. The only accurate way is to actually measure what is going on. And this can be a bit of a chore if done in the conventional manner – that is by taking the measurement off the top of the valve stems.
The issues encountered are the need to get to the top of the valve stems to mount your indicator gauges; on both singles and twins this requires the removal of the Upper Frame Member/Oil tank. Having done so then as you rotate the crankshaft you are then fighting against the valve spring pressures that seem to always be pushing the crank just past the point where you actually want it. In all it can be a time consuming and frustrating experience.
Of course this work requires removal of the timing case cover as the valve timing is set by the relative position of the cam pinion (2 of them for a twin) and the adjustable half time pinion. Another issue is that the cam pinions themselves prevent access to the cam lobes, so you cannot easily see what is going on. Here is one solution – I’m sure it been done before though I have not seen it documented anywhere. All you need do is remove the fuel tank, the spark plug, the pushrods and the timing side cover.
Required is a pair of 1/4” diameter Pushrod Replacement Rods, each around 10 inches long – these are simple to make. One end is gently rounded so that it can sit securely in the pushrod cup on the end of the camshaft followers ET29, the other end is fitted with a brass sleeve so that the shaft of the dial indicator is located securely.
Here is the raw material for a pair of homemade Pushrod Replacement Rods, purchased on eBay for less than A$10.
below is a finished pair of the Rods.
I made my own from ¼” OD stainless steel rod with a short length of ¼” ID brass tube fitted over one end, forming a cup to locate the probe of a dial gauge. As it is an interference fit, I heated the brass tube (to get it to expand) then carefully pressed it onto the rod. Once cooled it was firmly secure.
This is close up of the (almost) rounded ends to engage in the cam follower cups
Below, the opposite end of the rod with a brass ‘cup’ to locate the end of the dial gauge
In use, you remove the tappet adjusters ET27 and the pushrods ET43 then insert the Pushrod Replacement Rod through the tappet adjustor hole in each of the rocker ET25, making sure that the rounded end is located in the pushrod cup on the end of the camshaft followers. Use magnetic dial gauge holders, locked onto the face of the UFM, to mount a pair of dial gauges with their business ends sitting in the brass cups of your rods.
For a twin you will need 4 pushrod replacement rods and 4 dial gauges, but only a pair of each for a single.
As you rotate the crankshaft the indicator gauges will show the lift of each camshaft follower
The actual amount of valve or more correctly in this instance, cam follower lift is not important. What is important is the
comparative lift of the inlet and exhaust.
For almost every road going Vincent camshaft I have encountered the sweet spot for camshaft timing is to have equal lift of the inlet and exhaust at a point 4 degrees BTDC on the exhaust stroke.
So with the half time pinion key E81 removed, set the crankshaft to 4 degrees BTDC and secure it in that position. Now rotate the large idler ET50/1 while watching your TWO indicator gauges. The first thing to do is have the camshaft in the position where BOTH valves would be fully closed and at that point set both of your indicator gauges to zero. Now rotate the large idler to the point where BOTH of your indicator gauges are showing equal lift. Keeping all steady, rotate the half time pinion on the drive shaft (ET17/1) till you find the position where the keyways in the pinion and the drive shaft are in alignment then fit E81
[1] the half time pinion key. Job done!
If you are using mechanical dial gauges it can be a tad tricky as each gauge will move in an opposite direction – that is one goes clockwise and the other anti-clock wise, BUT if you use digital readout style gauges it’s a doddle.
Now you've accurately timed the cams without the use of timing marks. If you've followed the above procedures, your timing will be far more precise than 90% of the Vincent motors still in existence.
[1] The fit of the E81 key way is quite important, as all too often the fit is a bit loose allowing the pinion to move, chattering back and forth on the mainshaft, it sounds not unlike a big end gone. Get a new E81 and lap it on your oilstone ensuring it is a tight fit.
