Topic: f1 and f2 engines

[monkeyrocco]

my apologies for being a tit i have just posted this question under club mercandise 
does anyone know if there are any major differences beetween a 750 f1 and a 750 f2 motor ? the reason i ask is i have a f2 with 48k on the clock there is nothing wrong with it but i have just got a f1 with only 20k on it, is it worth the bother to swop ? 

[Lumbee]

...from http://www.hondachopper.com/engine/engine_mods/modifications.html

CB750FE-2500004         F1
          new camshaft, carbs w/additional idle air. New pistons, compression ratio 9.2/1. New case w/o primary chain oiler. Final drive gear ratio 43/50 i/o 48/50. 4th gear on main shaft 31 i/o 30, 5th gear on countershaft 31 i/o 32
CB750E-2600014 and CB750GE-1000014         F2
          new cylinder head with bigger valves (34/31mm i/o 32/28mm), larger combustion chamber, larger carb mount rubbers, stronger cam chain, new camshaft, harder valve springs, new retainers, cotters, new pistons compression ratio 9/1. New rod big end bolts and bearings, harder clutch springs, additional fins on crankcase, larger fins on oil pan, "oil cooler" - finned plate between oil filter case and engine. Final drive 15/43 or 14/43.

[JohnG]

The carbs on the F2 are a different size than the F1 so you would need to use the rubber intake manifolds from your old motor if you kept the same carbs. I dont think the manifolds from the F1 motor would fit your F2 carbs.

[Don R]

If it's running well I would rather have the original engine. Then again if they're not very original bikes and it smokes, leaks rattles and runs poorly etc. it might be worth the trouble.  The late F1's are supposed to have softer vavle guides than the early f1's. The F2's all got them.  My .02c

[monkeyrocco]

thanks guys , i have the complete f1 including carbs however the f2 is perfect no smoke or rattles just a small oil leak from the centre of the head somewhere so the motor will have to come out anyway. originality does not matter as its a cafe anyway.i was just wondering is there any reliability or major performance issues  that favours the f2 over the f1 

[bryanj]

F2 has more power if original BUT exhaust valve guides wear out very quickly

[monkeyrocco]

thanks for the info guys, i have just checked the engine no on the f1 it is cb750e-2706358 is this a k7 ? 

[fire113]

...seem to be a K7, K7 engine No. from 2700001 to 3000000.

[monkeyrocco]

cheers for that info, so i supose my question now is whats the best a f2 or k7 reliability etc ? 

[Jerry Rxman Griffin aka MuthaF'er]

Yeah, that looks to be K7 HOWEVER the European stuff was different than here in the States such as no F0 or F3 there. Turn signals, front fender, rear fender different and a couple other things in 75/76. Not sure if the European F2 had the 'black' big valve engine. '75 F here was a 4 month run in 1/75 to first week 4/75. Color changed and it then became the '76 F1. Same silver engine. 77 and 78 brought the new F with the black engine and Comstar wheels.

Sooo... you mention F1 AND F2. Silver engine in your F1? Black engine in your F2? there is a fair amount of appreciable differences in the F0/F1 engine and the F2/F3 engine.

The K7 engine is in fact a F0/F1 engine with the cam timed 5 degrees differently. Otherwise identical. Soooo, did they use the K serial numbered engines in the European F's? 

The F2/F3 engine reportedly had a 6-7 HP increase but the F0/F1/K7/K8 engine was the next strongest and probably equivalent to the 69/70 750 before they de-tuned them for reliability purposes once they had made the '750 statement' to the world.

[Jerry Rxman Griffin aka MuthaF'er]

cheers for that info, so i supose my question now is whats the best a f2 or k7 reliability etc ? 

Reliability depends on which F2 engine you have. Is it the black engine with the larger valves? If so then the K7 would be the more reliable considering the F2/F3 has premature valve guide wear issues. Other than that they are both Hondas! 

[monkeyrocco]

big thanks for all the help, the f2 is the big valve black engine, i think i will ride the f1/k7 as i have the full bike and decide from there, thanks again guys