I guess we should not be surprised that Greg has had to deal with all sorts of problems, including variable camshaft lengths. He has no way of controlling what shows up at his door for fixing.
I build with all new gears and spindles. It may seem excessive, but the reliability of these engines is incredible with a new timing chest and I feel that is a very important requirement for a racer. I use only Megacycle cams because of the quality. I use all the Maughan parts for the timing chest, including the big idler boss. I use the shoulder of the large idler boss as the datum, but I have never had a cam that exceeded the height of that datum. In fact, the datum from the idler boss is quite a bit higher than the instruction sheets anticipated, so those stated dimensions are often of little use to someone assembling a new timing chest.
There is no washer called for behind the camshaft between the shaft and the case, but when lining up the followers with the cam lobes I am always forced to install one in that position. This means that I have to install the same size shim under the other gears to keep the steady plate level. Fortunately, the Arbor shims from McMaster Carr are up to the job and I have never found any cupping or softness when using them.
I suppose the answer is that you need an initial datum location when setting up a new timing chest and the shoulder of the large idler boss is quite tall and easy to install in place. If you have to shim behind the cam to align the followers to the lobes then the top plane of the cam gear becomes the new datum that requires the remaining gears to be adjusted to this new dimension with the object of keeping the steady plate flat.
Bill is spot on about the Simmonds nuts on the cam spindle. I run a tap through the nut to score the nylon. I also run them on and off an old cam spindle held in a vice. There is nothing worse than tightening up this nut and having the 5/16" threaded stem break off due to the high friction fit provided by the nylon insert.
David
Thanx for the mcmaster carr, i ordered a bunch of shims today, after having some lasered form C70 hard steel (at a price...) at 0.1 till 0,6mm all diameters...
for spindles i use my own made from Bohler K340 to 62-64 HRC than machine down to suit, and indeed
@greg brillus you are right when 0,05 interf fit it bulbs a bit at the cylinder surface, (scraped down) but a new case will hold it better. After machineing sometimes i do Nitride them to 70Hrc. (annealing K340 is only at 550degr)
when one wants two properities in a part (hard surface and though middle), i made two parts, get rid of the nyloc nut and made bolts from 1000N/mm2 (say 12.9 bolt) with M8x1 and hole 2 mm.
when one carbonize the standard spindles, one should blank off the thread, but thats cumbersome, so not done, so now and than it snaps. (nicht zu verwirren mit Schnaps
@erik )
Cheers