ET: Engine (Twin) Checking the Cam timing on a twin
- Thread starter Freebird
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I copied Eriks design using one pushrod cut in half and one old clutch pushrod cut in half with two bits of flat steel for the landing surface. It was easy to use and cost nothing to make - Our postman supplies the elastic bands 
The most accurate way to measure the lift is to take out the valve adjusters and use a length of old hollow car aerial or similar cut to length between the pushrod and the dial guage.
Quick test. With rear cylinder on the exhaust stroke. Crank 4 degs BTDC. Notice that the slot in the rear cam end points straight up the centre of the cylinder. The slot in the front cam end points vertically down. Ignore the dots. Watch the slots.
The slots are accurate because they are used in the setting of the cams in the pinions.
PS- in this setup is a good chance of checking ignition timing. One complete rotation of the crank and the rear piston is on the firing stroke, the slot pointing at the crank. In this position, the mag points or whatever, fully retarded, should be about to open.
The slots are accurate because they are used in the setting of the cams in the pinions.
PS- in this setup is a good chance of checking ignition timing. One complete rotation of the crank and the rear piston is on the firing stroke, the slot pointing at the crank. In this position, the mag points or whatever, fully retarded, should be about to open.
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I am not sure about the rubber band system there are many variables between the push rod ends and the movement of the valves I have about 15 rockers and the difference in the curve of the fork faces is amazing then we have adjusters, stem collars... I think i will stick to the valve cap method for the twin and reverse assembly for the comet
And the whole shit in this is the backlash on gears.
As the other cylinder is also in mesh.
Best do it with only the inner valve springs mounted
As the other cylinder is also in mesh.
Best do it with only the inner valve springs mounted
You just set them up per the book......they are not fussy or exact like a modern engine.......there are so many variables that can be out on these engines and they still seem to run.......different barrel heights, different comp pistons, ignition that is 30 odd degrees over advanced.......and so on......years of use and abuse from some owners, but they keep on going like an old steam engine.
It certainly is worth always trying to do your adjustments with the engine in forward stress and certainly 4 degrees BTDC can be 6 or 2 and I doubt that anyone could divine the difference