Was looking through my 1955 KH Rider’s Hand Book for ignition timing specifications and found them given in terms of piston position (inches BTDC) for both KH (19/64”) and KHK (11/32”). I was interested in knowing what crankshaft angle these down-bore distances correspond to, so calculated the crankshaft angle corresponding to the piston position, which is shown in the table below.
Thought it would likewise be interesting to check the timing provided in the KR Competition Racing manuals and found a discrepancy between a couple manuals. I have one “early” and one “late” Competition Racing manual for which I have no issue date. The only means I have of estimating the date of each manual is to note the cam offerings described in each. The early manual provides specifications for H and J cams that have -66R and -67R part numbers respectively. The later manual provides specifications for J/K and J/L cams that both have -69R part numbers, so it would appear the manuals are perhaps a couple years apart. The early manual is consistent in it’s written description of ignition timing, providing piston position of 7/16" BTDC and crankshaft angle of 36 deg BTDC, along with an image of the flywheel mark at the edge of the timing hole. However, in the later manual the written description calls out the same piston position (7/16” BTDC) but couples this with a crankshaft angle of 38 deg BTDC along with the same image of the flywheel timing mark at the edge of the timing hole used in the early manual. Thought this was an interesting disparity so again determined crankshaft angle vs piston distance for the KR, which is shown in the table below.
Placing a degree wheel on my KHK flywheel confirms a difference of ~ 28 deg between the TDC dot and timing mark line.
Found it curious that the KH and KHK were timed considerably later than the KR. Perhaps the K Model ignition timing was set later than the KR to avoid detonation, as these engines are stuffed up with their small diameter 2-into-1 pipe set up relative to a KR with open pipes, possibly operate at a “significant” temperature and are often subjected to low speed lugging all of which is a perfect recipe for detonation to occur. In light of the possibility of lugging operation and fuel quality of the era the modest timing may have been required for survival. I would guess that if a K model consumer engine were operated without lugging, i.e., run free and fed modern high octane fuel it could tolerate quite a bit more spark advance than the specification calls for.