Hi Mark, I think I may have found an error in your book. While measuring my (F3) cam today I got consistent exhaust lift values of 7.50-7.55mm. Every other source I have (Honda, Clymer, Haynes) claims 7.43-7.52 mm. Your book says 7.06-7.26mm on page II-3.
Your values for inlet lift (7.64-8.00) is a lot closer to my measurements (7.99-8.04) and Honda's values (7.93-8.02), also copied by Clymer and Haynes, and the same for your clearance values.
Is the F cam just off that much from the K0-K8 cams? Or is it an error in your book? It could be my fault too, but I'm fairly decent with a calliper, and even if there was measurement error on my part, it'd be cancelled out by occurring in both measurements anyway, assuming a consistent measuring bias [ (y+x) - (y'+x) = y-y' ].
First (hopefully not to avoid the point, or sound defensive...), this book was written more about getting these 35+-year-old bikes back on the road in a reliable condition than it was about making them into a high-perf ride: the latter is more for the upcoming book, "750 Performance" (or whatever it ends up being called
).
The cams quoted in this first book are specifically the K2-K6 cams, empirically derived from actual measurements in the 1970-1975 era. There are some differences in the cams made after 1976. Also, the numbers I have in that "Inspection" chapter are my averaging, from engines with more than (typically) 20,000 miles on the clock, which still run (ran) well, but were torn down for other reasons. Even my old K0/K1 manual shows the spec you're citing (about 7.5mm), but I seldom found that much lift on the cams I measured, even on new engines "in the day". The K0/K1, with the HM300 pipes, had more like the 7.5mm exhaust lift: the HM341 pipes needed less because of the restriction increase (or so it appeared, at the K2 era). If you had a K1 cam in a set of HM341 pipes, the sparkplugs would gas foul very quickly: some of our frankenbikes at SOHC4.net show this plainly when someone drops a K1 engine into a K4 frame, or that sort of thing.
Beginning in late '76 production, the cams changed in several ways. The casting marks on the cams roughly tell the story: there is an "R" number cast on the rough camshaft that declares the mold it came from. The ones with numbers of "R6" and earlier are generally considered to be the "early" K cams. The 1977 and later era had 2 distinct cams: one was the F1/K7/K8 cam and the other was the F2/F3 cam. I don't have accurate specs for the differences between these myself (as I did not keep the kind of notes on them like I did on the earlier bikes), but the ones I have measured show more lift and slightly more duration, on the F2/F3 cam, than on the other late (K7/K8) cam. Both of these post-1976 cams have lobes that open 5 degrees later than the earlier cams did (for emissions reasons): if you insert one of these cams into an early engine, the midrange power falls a little flat and the top end perks up. Vice-versa, too, with swapping cams the other way.
All this said, the cam lift lift varied widely (wildly?) in production of the K0-K6, as did the timing. One example: on several K3 bikes I measured in early summer of 1973, I got 3 different valve openings on each engine (measuring at the intake valves of #1, #2, and #4, as the fuel petcock was in the way of #3), spanning more than 3 degrees between the intake openings on any one bike (and not the same between the bikes). Likewise, the lift (as measured by indicating from the top of the rocker, though the valve cap hole) varied more than 0.0050" on these cylinders on any given engine, none of which had 1000 miles on them. Honda never seemed to be much concerned with this accuracy(?). The worst examples of this type came from "new factory" bikes, where there seemed to be a real scramble to make enough machines in those days. But, it didn't seem to make that much difference in the way the bikes ran, either, until one tried to reach 100+ MPH.
Generally, the lift figures of 7.8 to 8.0mm were 'normal' for the inlet and 7.1 to 7.3mm for the exhaust side on the K2-K6, despite Honda's quoted specs. And, they actually varied that much on the bikes I measured.
