Topic: 75 cb750f OEM Sprocket..

[noelocol]

Hey Gents,

I was wondering if anyone could tell me what the stock OEM from and back sprocket sizes are for my 75 cb750f.

Im gonna count the teeth sizes but I need a reference point.

The reason why I ask is that when travelling at 60mph in 5th gear, Im revving at 5.5 and feels like I have one more gear to go....

My experience with riding a cb750 is limited so I have no idea how a cb750f should ride. But it acclerates like a bat out of hell!!..

I suspect that the previous owner had geared it up but wont know for sure until I count and compare.

Thanks for your help!

N

PS. Ive checked for clutch slippage and that not the problem.

[75750SS]

Stock gearing for 75 750F is 17 teeth front and 48 back.  Uses a 102 link chain.  5.5K sounds a bit high for 60mph.  Mine turns 4900rpm for 60 - 65 mph.  The gauges are less than accurate so it's really hard to tell what the actual mph/rpm is.

[ofreen]

Back when I ran a 17 tooth countersprocket, the tach would indicate about 4500 RPM at 60 MPH.  That's with a 48 tooth rear sprocket.

[noelocol]

THanks Guys...

So what Im getting is that a 17 front & 48 rear sprocket will get me 4500-4900 at 60 mph.
What RPM at 60mph should I expect  if I went to an 18 front w/ 48 rear?
(sorry for the rookie question, but I still dont get the gearing thing..LOL...)

What would be the OEM front & rear sprocked for an K5 or K6? and what kind of rpm is the standard K model getting at 60mph?

I havent counted the teeth on my rear/front sprocket yet but what would be the best guess if I've got 5500 rpm & 60mph?

Thanks

[ofreen]

What RPM at 60mph should I expect  if I went to an 18 front w/ 48 rear?

About 4200.

[noelocol]

Hello guys....

So I counted my sprockets and I indeed have 17 fronts & 48 in the back.
there is also a number "50" on every second link on my chain. (what the hell does that mean?)

So If Im getting 5500 rpm @ 60mph, what could be the problem? It always feels like Im on 4th gear!!..from what Im getting from everyone, I should be at about 4500-4900rpm for 60 - 65 mph

Thanks

Noel

[GroovieGhoulie]

The Fs will still rev higher in 4th and 5th compared to the Ks, even if the sprockets are identical (Ks had 18/48).  This is due to 4th and 5th being a little shorter than the K model gears, I presume for "sportiness".

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) 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.

ETA: That RPM is still crazy high.  Are you counting the gears, IE are you making it to fifth or is it getting stuck in fourth?   Could it be your tach?

[GroovieGhoulie]

Forgot to add that the 750s were geared (purposefully or not, I dunno), so that the speedo and tach needles should be oriented the same way when in top gear.  (It's pretty consistent regardless of RPM or speed.  Try it.)

Anyway, this was done (calculated maybe) on the original K0, which had 16/45 gearing, but 17/48 is identical to 16/45, and 18/48 is "close enough".  The higher top gear of the Fs also put it "close enough".

Based on this pic of my F1's instruments:



60 should be giving you 4200-4500 and 5500 should be giving you nearly 80 in top. (That's a WAG, but should be close).

Methinks you're stuck in fourth, or have a "custom" gearbox. 

Or a pocket bike rear tire.

[noelocol]

The Fs will still rev higher in 4th and 5th compared to the Ks, even if the sprockets are identical (Ks had 18/48).  This is due to 4th and 5th being a little shorter than the K model gears, I presume for "sportiness".

ETA: That RPM is still crazy high.  Are you counting the gears, IE are you making it to fifth or is it getting stuck in fourth?   Could it be your tach?

Thanks for all the info!!. That was AMAZING!!!..
I doubt that Im stuck on fourth, when I count the "shifts" I do go all the way to 5th gear. Yet when I shift up to 5th gear from 4th, the RPM doesn't seem to drop as much. When I do down shift, I do count 5 "clicks"...
If the gear box was getting stuck in 4th, it wouldn't "click" to 5th would it?

THanks again!!