Author Topic: CB750 F2 vs F3 (Read 9022 times)

SD750F · « **on:** February 23, 2007, 01:59:12 PM »

Okay I am seeking the wisdom of the forum. I am looking for the differences and how to determine the differences between a CB750 F2 and the F3? I have read a couple articles, looked at service manuals and I still have no definitive answer to the question I ask. Some blogs and other sources say the F3 was really produced in 1979, but maybe only in Europe and the Pacific rim including Australia and New Zealand...

So what can you tell me oh SOHC4 forum?

Scott

scondon · « **Reply #1 on:** February 23, 2007, 02:34:47 PM »

The tech sheet that covers the "upgrades" of the '78 F3(US) over the '77 F2(US) has only two or three items on it, one of which is the longer conrod bolt. I'll check tonight and see what the other items might be. In all appearance(except for paint) the F2 and F3 are identical. Well, side cover badge lettering is different and maybe tank badges.

SD750F · « **Reply #2 on:** February 23, 2007, 03:12:46 PM »

That is were the argument begins... Some SOHC individuals (not on this board) insist that I have a F2... Okay, this is what I have, an US 1978 CB750F... Some insist again that the F3 was only produced in the UK and the Asian Rim countries in 1979 and requires the 1979 manufacture date.

Waiting for more information...

Scott

mick750F · « **Reply #3 on:** February 23, 2007, 03:46:40 PM »

If you have an American market '78 750F then technically you have an F3. Although many people refer to them as an F2, they are called F3's in the Honda Shop Manuals. As scondon said the side cover badge is different, I didn't know about the conrod bolts, the F3 has a plug at the bottom of the collector for the breather tube and the needles in the F3 carbs do not have clips. There is also an emission control label on the frame beneath the left side cover. I believe that's it. As far I know paint colors were the same for both years...black or Candy Presto Red.

Mike

Jerry Rxman Griffin aka MuthaF'er · « **Reply #4 on:** February 23, 2007, 03:52:49 PM »

In the US there were 1977 F2's and 1978 F3's. This wasn't the case in other parts of the world. You would also find 1977 F1's in some areas but not the US. In the US the F first appeared winter/spring 1975 as the F0/F/ or as Honda parts fiche list them K0 Super Sport. In summer 1975 the 1976 F1 appeared, followed by the F2 as a 77 model and the F3 as a 78 model.

The best way to "prove" what you have is to give someone a list of bike serial numbers/engine serial numbers along with the numbers off your bike.

My bike is a 75F which i purchased in 3/75.

SD750F · « **Reply #5 on:** February 27, 2007, 07:38:22 AM »

Okay I have started taking some pictures for my rebuild thread and this is what I have:

Frame SN CB750F-2207945
Engine SN CB750E-3107922

And as you can see the prior owner did not take care of this bike. You should see the amount of road dirt and grease behind the engine on top of the swing arm! But after the cleaning, sand blasting of the frame and powder coating, I think it will look great again.

Scott

medic09 · « **Reply #6 on:** February 27, 2007, 08:16:46 AM »

Hey Scott!

Wasn't there a 750Four for sale just down the road from you? Whatever happened with that? Did they get what they were asking?

mordechai

SD750F · « **Reply #7 on:** February 27, 2007, 08:42:59 AM »

Mordechai,

If I remember correctly they wanted over $6500 for a K1... I picked up my 750F in the fall for $400 and am using it as a project over the winter. Just about to have the frame and supporting parts powder coated... I will do a thread on the progress just like I am doing on the remanufacture of the hand controls in Tips and Tricks.

Scott

jonbuoy · « **Reply #8 on:** February 27, 2007, 11:42:08 AM »

I'm not sure if I have an F3 or not. My motor number is for a K3 but the frame is an F. I have an engine temp gauge in my tacho, my choke is still on the carbs. Footpeg mounting brackets are one piece and different to any others I've seen - master cylinder bolts onto them too. I'm in NZ but this was a Canadian import so I think all in all its a mongrel!

Jerry Rxman Griffin aka MuthaF'er · « **Reply #9 on:** February 27, 2007, 12:58:16 PM »

How about we make it a FM for F Mongrel. Technically it would be an F if the frame is F.

SD750F · « **Reply #10 on:** February 27, 2007, 03:23:34 PM »

This is how I understand the frame and serial numbers. The 1978 Super Sport has the following:

Model Year:   1978
Engine #:   CB750FE-3100001
Frame #:   CB750F-2200001

So my Engine being a CB750E-3107922 indicates that it is number 7921 built in series for the US market? And the frame having CB750F-2207945 is number 7944 built in series? Okay why does all history on the engine indicate a serial number with"FE" when mine is only a "E" on the stamp? Is the history records in error? were there corrections made mid series? Or is it more complicated?

Curious minds want to know...

Scott

Jerry Rxman Griffin aka MuthaF'er · « **Reply #11 on:** February 27, 2007, 04:32:17 PM »

Scott,

Sounds like you have it right. There has been past discussion about the FE designation in literature but I don't know if there were any real answers. I have noticed in the shop manual on some models (don't remember which) that there were quite a few more serial numbers on engines than frame numbers when you'd think they would be close. Perhaps this is where the unknown FE comes into play. Perhaps exports ??

mick750F · « **Reply #12 on:** February 27, 2007, 05:14:35 PM »

Quote from: SD750F on February 27, 2007, 03:23:34 PM

This is how I understand the frame and serial numbers. The 1978 Super Sport has the following:

Model Year:   1978
Engine #:   CB750FE-3100001
Frame #:   CB750F-2200001

So my Engine being a CB750E-3107922 indicates that it is number 7921 built in series for the US market? And the frame having CB750F-2207945 is number 7944 built in series? Okay why does all history on the engine indicate a serial number with"FE" when mine is only a "E" on the stamp? Is the history records in error? were there corrections made mid series? Or is it more complicated?

Curious minds want to know...

Scott

The Honda Shop Manual I have lists the engine number for the '78F as CB750E-3100002 and subsequent...and the frame number as CB750F-2200001 and subsequent. There's no mention of the FE designation in the manual.

Mike

TwoTired · « **Reply #13 on:** February 27, 2007, 05:55:14 PM »

According to the "Honda Motorcycle Identification Guide" Published by American Honda Motor Co. All the CB750 F models had an FE in the serial number, 75-78.
They specify the 75 as an F0. They omit any F(number) designation for the remaining models. The product code is listed as 392 for 75-76 and 410 for 77 and 78.

How's that for clarity?

Cheers,

Jerry Rxman Griffin aka MuthaF'er · « **Reply #14 on:** February 27, 2007, 06:12:22 PM »

Clear as mud. No E in either of the numbers on my F0. I wonder if anyone has a FE and if so in what country might they be located?

TwoTired · « **Reply #15 on:** February 27, 2007, 06:44:26 PM »

The "Guide" says:
CB750F 750 Supersport (CB750F0)
Model year: 1975
Frame: CB750F-1000002~
Engine:CB750FE-2500004~

There is definately an FE on the black engine in my 78 750F. My 77 750F has a 78 CB750 K motor transplant (not black). Hmmm, wonder why?

Cheers,

SD750F · « **Reply #16 on:** February 27, 2007, 08:00:02 PM »

Thanks all, I think some of the mystery serial number designations have been solved. Now on to the frame refinishing and then I hope, a successful engine cleaning and check-out. And I am crossing my fingers that I have good valve guides and compression considering some of the comments made about the 77 and 78 black F series motors on this forum...

Scott

Jerry Rxman Griffin aka MuthaF'er · « **Reply #17 on:** February 27, 2007, 10:11:46 PM »

Quote from: TwoTired on February 27, 2007, 06:44:26 PM

The "Guide" says:
CB750F 750 Supersport (CB750F0)
Model year: 1975
Frame: CB750F-1000002~
Engine:CB750FE-2500004~

There is definately an FE on the black engine in my 78 750F. My 77 750F has a 78 CB750 K motor transplant (not black). Hmmm, wonder why?

Cheers,

Lloyd,

I figured out the mysterious E - Endangered

chung · « **Reply #18 on:** February 28, 2007, 06:57:01 AM »

My firt round with the Honda 750 was around 1982. I have been called a nut but I remember using the engine number to tell if it was a Super Sport engine. #CB750FE-xxxxxxx Confused the hell out of me in later years

I had one bike and 6 engines, not a good second gear among them and two broken cams.

As for year models. It's generally accepted that anything past june is next year's model. The parts Guys at the Honda Shops look for the year model that way on oloder bikes.

Look like you are the proud owner on an F3

Xcmandan · « **Reply #19 on:** April 10, 2017, 07:36:27 PM »

So, I've read everyone posts. But I'd like to know if the 77 and 78 cb750f engines are parts compatible? I have a cracked 77- 750f2 lower crank case. It's been welded(Badly) by past owners but I just discovered it. Also have opportunity to by a 78 f engine

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Pat_at_APE · « **Reply #20 on:** April 11, 2017, 09:20:43 AM »

I know for sure the 77 F2 cylinder head and cylinders are unique to that year/model. I'm not sure on the engine case but I think they were the same.

The 78 motors were more reliable. That is what I have in my F2 frame now.

Regards,
Pat at APE

Jerry Rxman Griffin aka MuthaF'er · « **Reply #21 on:** April 11, 2017, 10:49:19 AM »

77/78 F have same engine. Different than all the other 750 engines.

Xcmandan · « **Reply #22 on:** April 11, 2017, 12:05:38 PM »

I purchased this bike back a few months. I'm tearing it down and rebuilding the engine and I found that it was cracked and welded. Some kind of patch over it too. I have an opportunity to get a 78 cb750 ss engine. But I have to jump on it soon. Just wanted to find out if I can swap cases.

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Jerry Rxman Griffin aka MuthaF'er · « **Reply #23 on:** April 11, 2017, 12:56:10 PM »

Shouldn't be a problem. You have either a 77 or a 78 K engine (405)? The 77/78 F engine cases are the same except black. You going with the complete engine or you mixing and matching? Top ends must be swapped out cylinders up. Some of those parts are the same. The F engine is stronger (HP). Bigger valves and stronger cam in the F. Oil returns from the head are different. The valve guides wear out much earlier due to the more extreme valve angle used to get the fatter valves in. Bigger valves and stronger cam in the F. Could be something you'd want to look into. APE can re-do the F head. One thing you shouldn't attempt is to use 69 - 76 cases as the output shaft bearing is only a single row vs the double row. 10mm wider on the double row 77/78 thus 10mm sprocket offset all the way back to the wheel. Just verify that is a 77/78 K engine by the serial number and/or the output shaft bearing. Looking at the last 2 pictures I can tell it has the offset at the output shaft.

Xcmandan · « **Reply #24 on:** April 11, 2017, 01:40:13 PM »

Yikes, you guys all AMAZE me with your knowledge!!!!!!! This is my first build. So I'm learning as I go. I don't know what that 405 in the last photo was. But here's my engine serial number

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Author Topic: CB750 F2 vs F3 (Read 9022 times)