Thanks Hondaman! So for an engine I am going to flog a 72 would be better than a 76? I am getting the feeling that the older engine were just plain better all around is there any truth to that?
If so I will keep the 76 with 3,300 miles and put in back in it's frame. The PO left it out in the rain with the plugs out so I had to take the top end off, but everything inside other than the cylinders is mint.
Well, the older engines last longer, for the most part. They also take abuse better. Up to the K2, they made almost the same HP stock that the 76-77F0/F1 made at the rear wheel, too, because the losses in the later bikes are higher. The tranny in the older bikes is a wide-ratio gearbox, which has lower stress internally when you're romping on it, so it tends to last longer. The oil flow through the older engines is more uniform (after the K0), being more heavily toward the bottom end in the K6 and later bikes.
These "little" things can be adjusted, though, depending on what you're doing with the build.
For example, the F engines (and K7/8) made from 1976 to 1978 have stronger rods and rod bolts than the earlier engines. The later engines were engineered to produce peak HP about 1000 RPM higher than the early design, so the oil flow to the crankshaft was increased by restricting the top end flow. This cost the top end quite a bit of life (especially the valve guides and rocker shafts) and increased the heat in the head area.
The K0-K1 engines were made to produce more HP at 7500 RPM than the K2-K5 engines, but the K2-K5 engine make more torque where you ride the most often (3500-6500 RPM), making them feel more lively on a day-to-day basis, or when touring at 55 MPH (which was the Democrat's solution to the oil supply problems in the early 1970s). All of the K0-K5 engines make more torque in the midrange than the post-1976 engines, because the cam was retarded 5 degrees during the 1976 models, for emissions reasons. But again, all of this stuff can be adjusted to suit your riding style, if you're building.
My personal ride is set for peak HP at 8000 RPM, but peak torque comes at 4400 RPM. This took a combination of LESS than stock cam lift (0.020" less, or 0.5mm less), with 2-3 degrees more duration on the cam, and the cam is advanced 2 degrees from the stock (5 degree) setting, to open at 6 degrees BTDC and close at almost the same time as in the K0 engine. To this I added a hemi head, polished valves, pocket porting over the inlet valves, stronger spark advance springs for a later full advance, leaner mainjets (5% leaner than stock), deeper float bowls (25mm instead of 26mm), K&N air filter with stock K2-size airbox openings, HM341 pipes, 17T countersprocket with a 1-row output shaft bearing, free-spinning rocker shafts, and 0.25mm oversize pistons (which are about to become 0.5mm oversize, as they have 90,000+ miles on them now) with 1-piece oil rings. I run the rod bearings at 0.0015"-0.0018" clearance, the crank at 0.0012", and stock oil pressures with 20w50 weight oils (sometimes 15w50 for colder weather). I also run 110/90 rear tire size, and only Honda rear sprocket, with Diamond XDL (also called Powersport) chain. This makes for a very lively ride that doesn't care what altitude, fuel grade, or hiway speed I ride: it is always happy and snappy.
Now you know my secrets!
