I'm also now curious about the F3/K7-8 heads: did they share the same guide wear situation? According to the info I have for the 'F',(Honda's published shop notes, which were not always 100% accurate), the cam on the F1-F3 was the same as the cam on the K7/8. It has a bit more duration, and is a little later, than the 'K' cams. I have one K6 engine in my parts collection, and it also has the F1 "late" cam, so I suspect it sneaked into production before it was published as being there.
Not to my knowledge. The F0 and F1 heads had the same sized valves as the K-series, but the cam was more aggressive and tuned to work with the 4-into-1 exhaust and its resulting higher-RPM powerband. Since a 4-into-1 moves the powerband up the rev scale, the cam was adjusted to fit that "character". The 4-into-4 is meaty all through the rev range and cammed accordingly.
A note on the redline, the F0 and F1 brought back the higher redlines of the K0. The K0 had the 8500-9300 red zone. The K1 and later had the 8000-9300 red zone. The F0 and F1 were 8500-9600. According to my "Seat o' the Pants Dyno", my F1 has power higher up the rev scale and really doesn't "come on" until revved, while my Sandcast feels like it has more "grunt" all over.
Redline comparo. Note they start at the same 8500, but the F1 "discovered" 300 more RPM at the end.
F1 tach:
The K7/K8 engines are the F0 and F1 engines, but with different carbs and 4-into-4s and the internal gearing is similar to the K models, since the F had a shorter primary ratio (one less tooth on the countershaft gear) and shorter 4th and 5th, along with 17/48 sprockets from the factory.
Here are the gearing differences between the K series and F0-F1 bikes:
Gearbox Differences:
4th:
K - 1.097:1
F - 1.133:1
5th:
K - 0.939:1
F - 0.969:1
Gears 1-3 were identical.
Combined with the overall gearing changes (sprockets and primary) from the K, the overall drive ratios are:
K:
1st - 11.38
2nd - 7.78
3rd - 6.07
4th - 4.99
5th - 4.27
F:
1st - 14.01
2nd - 9.57
3rd - 7.47
4th - 6.35
5th - 5.44
Source: Cycle Guide Road Tests of 1975 K5 and 1976 F1.
Nice synopsis, Groovie!
Where did you find those beautiful tachs? I'm so jealous...
I might add a couple of notes, more curiosities than useful, to this collection:
1. The first K0 bikes had tachs with red zones that started at 9200, went to 10,000. My friend Jim had one of these (first 750 sold in Peoria, IL, in 1969), and it was good for 10,000 RPM even after it had 75,000 miles on it. These tachs disappeared almost immediately, as we noticed that two months after he got his bike, they were coming with redlines starting at 8500, like the K0-K1 everyone knows.
2. The K0, up until late 1969, had 16T coutnersprocket and 45T rear, and a master-linked chain. A warranty retrofit kit came out in late 1969, with 17T counter and 48T rear, and a little sheet metal chain guide around the countersprocket, and an endless chain that required removal of the swingarm to change.
By the K2, the chain guide disappeared and the counter went to 18T, with the 48T rear, still, and the endless chain. By the K3, a rivet-type master link replaced the endless chain.
These powerband of the K bikes really likes the 17T front sprocket. It is harder on the chain, but using a good chain like a Diamond Powersport or Reynolds still yields over 25000 miles of service. Using the 18T is nice if you tour a lot, as it drops about 400 RPM at highway speeds for a less buzzy feeling. My bike has always made better MPG, though, with the 17T front, which indicates overgearing at 18T. Unless, of course, I was touring Kansas...
