Topic: Is my CB750 engine a K6 or an F?

[Terry in Australia]

I'm told that it's a K6, but I can't be sure. The engine No is CB750E-252XXXXX. Does anyone know? Cheers, Terry.

[octagon]

hi terry,
my 76 750k motor number goes cb750E-244xxxx. i have a 75 750k parts motor and the number on it is cb750E-240xxxx.
as far as i know, which isn't far, f series motors start with cb750FE

[bryanj]

According to the ID book Terry, K6 start at 2428762 and the F starts  FE-251094 BUT i have yet to see an engine with the FE  designation so i would suspect an F.

Only sure way to know is the numbers on the pistons, which i believe are different but have no 1st hand experience of

[Damfino]

The day that Terry doesn't know what engine he has, is the day that this entire forum implodes...

[Jerry Rxman Griffin aka MuthaF'er]

Mine is CB750E-2501954. First year there were ~ 15,054 made. I believe in 76 the numbers continued in sequence with 75 and go up to ~50,000 or so. If you truely have five X's then you have one too many numbers for a 75/76 F engine. Boy, you sure lucked out there mate as I know how much you love the F's  Now if it is in fact a K6 at least you won't wear it out with all that LOW hp 

[Terry in Australia]

Ha ha, thanks guys, no trap, I'm just a tad confused. My K6 frame number is 258XXXX, and the engine I bought for it is 252XXXX. I I initially thought that would make the engine a K5, but I now understand that the K6 engines started at 244XXXX, but I don't know when they finished.

No biggie, the wicked 836cc race engine in my K1 is definitely a K6, (247XXXX) and as I've finally managed to blow the head gasket I might pull it out, take it back to stock and install it in the K6's frame, and rebuild the 252XXXX with all the 836's goodies and my APE crank, undercut gearbox etc.

If it is an F engine Jerry, it'll be good to breath new life into it, F's are pretty rare here, I think the "good taste police" had most of them scrapped as soon as they arrived on Australian shores. The engines were good, but the rest was just so disappointing, I believe the designers went on to design Lada cars, and "chrome and glass" office furniture.............. 

[Retro Rocket]

I have an early "F" engine in my shed Terry, i'll have a look at the numbers tomorrow....   {i thought it was a trick question as well  }

[GammaFlat]

Is my CB750 engine a K6  or an F

It's an F'n K6

[Terry in Australia]

I have an early "F" engine in my shed Terry, i'll have a look at the numbers tomorrow....   {i thought it was a trick question as well  }

Thanks Mick, I'd really like to know!

[Terry in Australia]

Is my CB750 engine a K6  or an F

It's an F'n K6

Is that a play on words Gamma, or are you speaking with some Authority?

[GammaFlat]

Is my CB750 engine a K6  or an F

It's an F'n K6

Is that a play on words Gamma, or are you speaking with some Authority?

I have a K6 at home.  I'll report numbers later

[Terry in Australia]

Is my CB750 engine a K6  or an F

It's an F'n K6

Is that a play on words Gamma, or are you speaking with some Authority?

I have a K6 at home.  I'll report numbers later

Thanks mate!

[mick7504]

Hey Terry

Having a look in the John Wyatt "Original Honda CB750" book, this is what he writes:

K6 Release Date 1976
Eng    CB750E 2428762
Frame CB750 2540001

CB750 F0 Release Date 1975 (USA)
Eng     CB750FE 2500004
Frame CB750E 1000002

CB750 F1 Release Date 1976
Eng    CB750FE 2515094
Frame CB750F 2000003

CB750 F2 Release Date 1977 (USA)
Eng    CB750FE 2600004
Frame CB750 210011

CB750 F3 Release Date 1978 (USA)
Eng    CB750FE 3100001
Frame CB750E 2200001

Out of curiosity, I've got a set of cases numbered CB750E 261xxxx (Not FE) which sticks it into the F2 designation so I don't know where the FE came from.
Anyway mate, according to this, she's an F1 that you've got there.

Mick

[Jerry Rxman Griffin aka MuthaF'er]

Mine is an early F. Build date 1/75 - the first month with engine serial number CB750E-1001954 and frame CB750F-1001606.  I take exception to John Wyatt's book info on the engines. CB750E not CB750FE. The only "F" designation is in the frame serial number. That is speaking as an original owner of a 75 CB750F in the States. Can't speak for other countries though. I have my vin tag in my hand and the engine on the work bench so the numbers are obvious. Let's see what Retro comes up with too. I can provide pictures for any doubters.

OK Terry, these F bikes make GREAT works of art! My powder coated frame has adorned my living room for quite a while and now that the EX is gone I may just take your idea to task. I have been wondering what I could do for a coffee table. I just need to get a thick piece of glass cut  Thanks for the idea. Hell, it would be easier to just put the damned thing back together 

Does your engine have that extra 8th digit in it or is it a 7 place number?  If it is a 7 place number then you have a late 76 F engine. If it is a 8 place number then you have a boat anchor, err a K engine.

[longshanks]

My K6 engine reads cb750E-242xxxx

[Retro Rocket]

I have an early "F" engine in my shed Terry, i'll have a look at the numbers tomorrow....   {i thought it was a trick question as well  }

Thanks Mick, I'd really like to know!

Gday mate, my engine number is, CB750E-2522625

[mick7504]

Curious minds want to know where this FE fits in now and also the Eng numbering sequence for the early
F models. 

Having a look on the Satanic Mechanic site, Axl has the F1 Eng No starting with CB750FE 2500004 which John Wyatt calls an F0 (or an F) http://www.satanicmechanic.org/enginemods.shtml

Jerry, what you have, just cannot be disputed, although it disputes all other information out there.

[GammaFlat]

My K6 is CB750E-2468528. 

[Retro Rocket]

I have never seen an "FE" designation at all, and my engine is definitely an F

[mick7504]

I have never seen an "FE" designation at all, and my engine is definitely an F

Same here too mate.
The raised casting with the eng no. on the one I have runs @ 90 deg to the crank.

[Retro Rocket]

I have never seen an "FE" designation at all, and my engine is definitely an F

Same here too mate.
The raised casting with the eng no. on the one I have runs @ 90 deg to the crank.

Not home now but i am sure mine runs the same way to the crank......interesting.....I'll recheck when i get home....

[Retro Rocket]

My casting and numbers run parallel to the crank.....

[david 750f]

There seems to be some confusion on the F engine serial numbers.

I have an original Honda parts list from the 70's that has the frame and engine serial numbers for the F models. (North America, Europe and general export models)

It clearly states that there is NO "F" in engine serial numbers only in the frame VIN.

Engine numbers for the 1975 CB750F run from CB750E-2500004 through 2515085.

Engine numbers for US and the rest of the world for 1976 start at CB750E-2515094.

The only way to disprove this would be to have a photo of an F frame with a F in the engine serial number. In over 20 years of looking at serial numbers I have never seen an F in a engine serial number.

It appears that Terry has an early 1976 CB750F motor.

[Retro Rocket]

It appears that Terry has an early 1976 CB750F motor.

Looks like Terry and I have F1 engines........Thanks....

So what are the differences between  our F1's and the K model engines.?

[AHuff]

No F's on my engines either.

75 F0 build date of 3/75 CB750E-2512992

76 F1 build date of 4/75 CB750E-2518086