What Model???

[sswinno]

I guess this has been covered a zillion times but I'm struggling a little and getting contrasting info on what bike i have log book says it a 1978 CB 750 736cc but looking online with engine numbers it says it a 1976 K6. So if anyone can shed some light on this it would be massively helpful. This bike has been sat in my garage for 10 years so i would really love to get it up and running

Engine no. CB750E 2547445
Vin CB750F 1025342
4 into 2 exhaust
Disk brakes front and rear
Many thanks in advance
John

[Re-run]

Well the 4-2 is aftermarket. I don't think any cb came with that. It was either 4-4 or 4-1.
Disk brakes front and rear were the F model. You didn't say if you had 2 up front or just 1.
Do you have spokes, or comstars?

The frame number sounds like a 75 F bike. I don't have the engine numbers, but those usually did not match frame numbers except for the first few production runs.

So, it sounds like you have a F bike that has a aftermarket exhaust. If you got a pic of it, we could tell you for sure.

it may also be that you have a bike that is using parts from many different years. Good news is that the cb has a parts compatibility of about 95% or so

[TOOLS1]

Your frame is a 1975 "F", and your engine is a 1976 "K-6" so someone has done an engine swap. I hope your title matches your frame. That's what counts.
TOOLS

[Re-run]

I thought it may have been a k6 engine but I didn't have the numbers to look at. The previous owner probably slagged the F engine and dropped in a 76. Can't think of any other reason to put in a K engine in place of the F.

[sswinno]

Thanks guys for your replies i made a mistake it is a 4 into 1 exhaust my apologies and just one disc up front and spoked wheels. Seems like a bit of a minefield when trying to id the bike, i must admit feeling a little disappointed if it isn't the original engine for the bike.
thanks again for the info very much appreciated.

[Re-run]

That makes it more clear. definitely an F model with a k6 engine.

[sswinno]

So why would you change the engine and what is the difference between the 2 

Sent from my iPhone

On 18 Feb 2015, at 18:35, Re-run [via Honda CB750'S] <[hidden email]> wrote:

That makes it more clear. definitely an F model with a k6 engine.

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NAML

[Re-run]

Well, likely something happened to the original engine. That is the only reason I can think of to change out the F engine, since it was a hotter engine than the 76 k engine. Busting a hole in the crankcase was not unheard of if the chain broke.

Not a whole lot of changes. I think mainly the cam was hotter in the F. maybe a couple other tiny things but nothing major.

[shinyribs]

The F had a little hotter cam, other than that, I don't know of any differences.

There are slight differences on the cylinder head fins between years, but almost impossible to really notice. Some early motors ('74 and earlier?) had chain oilers on the output shaft. Some of the later engines (iirc, starting in 77?) use some different oil seals around the cylinder studs. Some engines have extra bolts in the cam tower/rocker arm area. I think they started in '76, but again, not sure. There were some slight differences in clutches and stators,too. But like Rerun said, most all of it, thought different, is all interchangeable. Now, the black 77-78 engines had a totally different topend, but the bottom end is still the same.

Basically all of the 69-76 k & F engines are the same except the tad hotter F cam. Maybe someone did the the original engine to your F, but they were savvy enough to keep the cam. But as far as going out and riding the bike you'll really never see much difference.

[Re-run]

Yep, that's about it. The 77/78K used the 75/76 f engine. Honda had to put some snort back into the K bikes and so put in that engine, with the cam.

It's nice to have bikes that have such a high compatibility for parts. You don't find that much anymore.

[sswinno]

Massive thanks to all you guys who took the time to answer.
I have some serious work to do on the bike and knowing what bike I have is a great start, no doubt I will be asking on here again sometime soon  for your invaluable advice

Top guys thanks again
John