After a year of building modifying and fitting parts to the Grey Flash Project, the fact it only took about 3 hours to return it to just an engine sitting all on its own on the bench, is a bit of a shock. And so was the weight of the box of items I took to the plating shop for a dose of electrolysed nickel. The tank is due back from the painters next week together with some matching aerosols for the parts as yet unpainted (they make them up from the same batch of paint that they paint the tank with), so now in the interval I can finalise the engine. First of the remaining engine jobs is to cure forever any leakage from the valve lifter hole, a simple two diameter alloy plug with an ‘o’ ring a smear of sealant and a bsf cap head screw and washer filled that leakage source. I did not have to make the dynamo hole plug had kindly sent me a real set so I also fixed them in place. I am now ready to set my valve timing. I have a set of MK2’s and there are no timing marks to be seen, not that it matters since my method of timing does not need them. I learnt about this method a few years ago, it does fly in the face of nearly 100 years of method, but it made a lot of sense to me. Using it, avoids all the problems associated with getting a clean accurate set of figures for opening and closing of the valves. The method is predicated on the fact that within a few degrees, the point at which valves are just cracked open or are just closing has really little effect on the engines performance, but, where they are when the piston is at the most important point in the intake exhaust cycle, does. So here is what I do. (Traditional method followers are advised to skip the next 350 words) The halftime pinion has no key yet; the cams, all the cogs and the steady plate are fitted. The engine is rotated to TDC by feel in the plug hole (I have a handle of the drive side shaft) then the big idler is used to rotate the cam until the push rod exhaust is descending and the push rod inlet is ascending when they are about equal height I stick my ” hand key” in the Half time pinion (just a piece of steel sharpened to key shape with a hook end to get it out. I add my timing disc and my petrol tap/spoke pointer in the oil filter union hole. I measure with a digital vernier depth gauge the spring height from valve cap to upper guide floor on both valves when fully closed. (On this motor the two figures differed by .036”) I then assemble enough shims and washers on the shortest valve assembly so that both readings match (hold the washers with a dob of plastecene) Now using the spark plug stop method I set an accurate tdc with my timing disc and pointer, now I add the E adjusters (Allen head type) screw them in a couple of turns and rotate the engine backwards and forwards till the respective push rods are at rest and reduce each pushrod clearance to zero. Now starting from about 20 BTDC I rotate the engine forwards and measure the reducing height of the inlet valve and the increasing height of the exhaust and when both read the same I finally look at the timing disk. If it reads between 4-6 degrees BTDC job done. If not (and I have only been lucky once) I back off, move the half time pinion keyway and try again (of course the second and subsequent times its easier since I now know the actual ‘equal valve height’. The vernier gauge part in the above scenario is not essential, if you are happier with 2 ‘cap’ dial gauges then use them, but I just find swapping about with the vernier easier than watching two dial gauges rotating in opposite directions while decrementing and incrementing. Does it work? Well nothing compensates for a badly ground cam but you can check the opening and closing points conventionally afterwards (now you know the ‘height’ a 5 thou lift its a doddle), but I have used this method for my road comet trials outfit, our old Egli single racer, the comet racer. The Alphabet road twin, and the 1275 twin racer (it’s a bit more complex getting both cylinders into the sweet zone) and its always given good results.
The Blog Oldracers posts - Grey Flash Diary Mar 2013