Topic: UNSOLVED MYSTERY: 1977 Honda cb750K

[BenelliSEI]

Here’s a HONDA mystery question, for 2023. I’ve posted this before and all the answers have been suggestions and speculation, at best. Just to be clear, I don’t know the answer!

In all the cb750 books, articles, and manuals I’ve read, this “variance” is NEVER listed. It only appears on cb750K frames, built in 1977. On 1969-76 SOHC cb750K frames, the Left/ Front engine mount (just to the left of the oil filter housing and slightly above) is a welded lug on the frame. On the 1977 SOHC cb750K the frame has two sleeves that pass through the down tube, welded in place. A fabricated engine mount bolts to the frame and then takes the engine through bolt.

The really big surprise is on my 1978 cb750K (last year of the SOHC cb750), Honda reverted back to the welded lug style, just like on all pre ‘77 models. I’ve attached a few photos. I’ll be curious to see how many new answers we get this time. I’m amazed with all the recorded variations on these machines that I have NEVER seen this one noted or any explanation offered. Anyone the wiser??

JLH3rd reminded me of another interesting fact. The bracket has no parts number and does not exist in any parts books, fiche or records I have seen. Weirder still.

[BenelliSEI]

Pictures an original fabricated bracket.....

[CycleRanger]

Just my speculation, maybe since '78 was the last year for the SOHC K they were using up any old frames they had left?
Weren't there two factories making the SOHC? Maybe one factory started tooling up for the DOHC and frame manufacturing moved from one to the other?
I believe I've read that Honda had planned for the DOHC to arrive a couple of years sooner but development took longer than planned so they continued the SOHC models for an extra couple of years.
Dunno.

[jlh3rd]

yep...we did this before.....for anyone wanting to take a new stab at it....

this bracket is only on the 1977 model.
It is NOT shown as a part that can be ordered. The frame in the parts fiche shows the welded bracket...
It can be seen on the bike in the American Honda guide....the only honda literature that shows it.....

[jlh3rd]

Just my speculation, maybe since '78 was the last year for the SOHC K they were using up any old frames they had left?
Weren't there two factories making the SOHC? Maybe one factory started tooling up for the DOHC and frame manufacturing moved from one to the other?
I believe I've read that Honda had planned for the DOHC to arrive a couple of years sooner but development took longer than planned so they continued the SOHC models for an extra couple of years.
Dunno.

the '79 is flat, and not double sided....not the same...

[BenelliSEI]

yep...we did this before.....for anyone wanting to take a new stab at it....

this bracket is only on the 1977 model.
It is NOT shown as a part that can be ordered. The frame in the parts fiche shows the welded bracket...
It can be seen on the bike in the American Honda guide....the only honda literature that shows it.....

I’d forgotten that detail. I have several different parts manuals and the bracket appears in none of them. Yet, every K7 I have ever seen, is the same as mine. Adds to the “mystery”.

[BenelliSEI]

Just my speculation, maybe since '78 was the last year for the SOHC K they were using up any old frames they had left?
Weren't there two factories making the SOHC? Maybe one factory started tooling up for the DOHC and frame manufacturing moved from one to the other?
I believe I've read that Honda had planned for the DOHC to arrive a couple of years sooner but development took longer than planned so they continued the SOHC models for an extra couple of years.
Dunno.

Good idea, but I’ve never seen the part on a K8, just K7.

[denward17]

My K8 does not have it...

[BenelliSEI]

My K8 does not have it...

Correct..... only on the K7.

[CycleRanger]

Just my speculation, maybe since '78 was the last year for the SOHC K they were using up any old frames they had left?
Weren't there two factories making the SOHC? Maybe one factory started tooling up for the DOHC and frame manufacturing moved from one to the other?
I believe I've read that Honda had planned for the DOHC to arrive a couple of years sooner but development took longer than planned so they continued the SOHC models for an extra couple of years.
Dunno.

the '79 is flat, and not double sided....not the same...

No, I didn't mean to imply that there was any crossover between SOHC and DOHC parts, just that the upcoming DOHC production and subsequent delay may have affected SOHC production in some way.
Anyway, likely it will never be known unless some former Honda engineer can relate the tale.

Pity there's no way to determine the factory where a bike was built.

[jlh3rd]

got it.....yep...to me, the fact it's not on the parts list is weird.....

the '76 750A is the closest I've seen...but still one sided...

[BenelliSEI]

Weird is the word for it. So unlike Honda to never assign a part number!

[jlh3rd]

and it's not on the frame picture.....
I wonder if by some funny circumstance, it's in a Honda service manual showing engine removal.....and the part is shown, mentioned, or has a part # reference.....

[BenelliSEI]

and it's not on the frame picture.....
I wonder if by some funny circumstance, it's in a Honda service manual showing engine removal.....and the part is shown, mentioned, or has a part # reference.....

Interesting point! I have the original K7 supplement to the shop manual somewhere in the shop. I’ll dig it out and have a close look.

[HondaMan]

I bought a K7 from an estate (the widow) in Colorado Springs, circa 2007, and rebuilt it: the engine had been hit on the right side at the points cover by her husband's car in their garage, and sat for 20+ years after because it sheared off the spark advancer (basically it ruined the crankshaft) without damaging the engine cases. When I pulled that engine I took pictures of everything so I could document the "rebuild" to the guy who bought it later, but it did NOT have that fancy left lower bracket. It DID have a bent frame, so I had to strip the whole thing and then use hydraulics to straighten it ('twas a gamble, if it didn't work I was going to be out $500 for the bike), and the left-side frame was bent outward (toward the left) at that mount, about 3/4". That frame, though, was just like the '76F1 that I also had at the time, which also doesn't have that fancy thing! It was pretty simple to straighten, in the end, and worked out with wheels in align, and the works.

It had a Vetter, so I had a soft spot for it...
It had a build date of 10/76 on the steering head, making it a very early K7.

So, I don't have any clues about this, either!

[Flyin900]

Weird is the word for it. So unlike Honda to never assign a part number!

Not related to the mystery bracket yet another example of Honda omissions in the parts fiche.

Not unusual at all in a few models of their 1970’s Keihin carbs. There are a number of different Keihin models where the slo jet is pressed in and there is no reference to that jet existing in the carb. It’s in there yet no parts fiche shows it even exists. I have been fortunate to be able to remove and clean the existing ones, yet there is zero reference to it, or the jet size?

[jlh3rd]

I bought a K7 from an estate (the widow) in Colorado Springs, circa 2007, and rebuilt it: the engine had been hit on the right side at the points cover by her husband's car in their garage, and sat for 20+ years after because it sheared off the spark advancer (basically it ruined the crankshaft) without damaging the engine cases. When I pulled that engine I took pictures of everything so I could document the "rebuild" to the guy who bought it later, but it did NOT have that fancy left lower bracket. It DID have a bent frame, so I had to strip the whole thing and then use hydraulics to straighten it ('twas a gamble, if it didn't work I was going to be out $500 for the bike), and the left-side frame was bent outward (toward the left) at that mount, about 3/4". That frame, though, was just like the '76F1 that I also had at the time, which also doesn't have that fancy thing! It was pretty simple to straighten, in the end, and worked out with wheels in align, and the works.

It had a Vetter, so I had a soft spot for it...
It had a build date of 10/76 on the steering head, making it a very early K7.

So, I don't have any clues about this, either!

which just adds to the mystery.....
I've got no dog in this fight, but , up to a point, It's fun to try and dig for answers when it comes to Honda and authenticity........
so, the last time this thread was started, I went down to the old honda shop here and he had a '77 K....It had that bracket on it.........so now, maybe I'll check the frame #.....

[BenelliSEI]

Today I was working in the shop. Pulled out all the Factory shop manuals I have for SOHC cb750’s and found the 1977 Supplements for both the K and F.  Went through every page and photo and no mention of the engine mount, or it’s purpose. Nothing.

[BenelliSEI]

I also pulled an original Owner’s Manual from under the seat, on my K7. Guess what? You can clearly see the bolt on bracket for the front, left side mount......

[BenelliSEI]

Even stranger; I pulled out the Owner’s Manual for my K8 and check out this photo. It’s clearly a K8 (with the thin gold strip on the side cover and more sculpted saddle), but it also has the fabricated L.F. engine mount! Anybody have an early K8 with the extra bracket??

[grcamna2]

Will a K8 flat style motor mount bracket work in place of that special factory bracket on the K7 ?

[BenelliSEI]

Will a K8 flat style motor mount bracket work in place of that special factory bracket on the K7 ?

Nope. My K8 has a welded lug on the frame there (identical to 1969-76 cb750K) and the single bolt just passes through the frame lug and the engine.......

[newday777]

Even stranger; I pulled out the Owner’s Manual for my K8 and check out this photo. It’s clearly a K8 (with the thin gold strip on the side cover and more sculpted saddle), but it also has the fabricated L.F. engine mount! Anybody have an early K8 with the extra bracket??

What is the build date on your K8?
I have 2 78 K8s. The first is just a frame that I got in a package deal last spring and the second is a complete K8 I bought as a young man was wanting to make a Cafe 750 and I didn't want to sell him a K4-K6 that I have as I don't like them being cut up(he backed out though because of buying a house). I'll take a close look at them in a bit. Pretty sure they have the standard welded bung mount as the earlier frames have.

[BenelliSEI]

Even stranger; I pulled out the Owner’s Manual for my K8 and check out this photo. It’s clearly a K8 (with the thin gold strip on the side cover and more sculpted saddle), but it also has the fabricated L.F. engine mount! Anybody have an early K8 with the extra bracket??

What is the build date on your K8?
I have 2 78 K8s. The first is just a frame that I got in a package deal last spring and the second is a complete K8 I bought as a young man was wanting to make a Cafe 750 and I didn't want to sell him a K4-K6 that I have as I don't like them being cut up(he backed out though because of buying a house). I'll take a close look at them in a bit. Pretty sure they have the standard welded bung mount as the earlier frames have.

Stu.... will check the build date next shop day. Will be interested in what you find. Thanks.

[grcamna2]

Will a K8 flat style motor mount bracket work in place of that special factory bracket on the K7 ?

Nope. My K8 has a welded lug on the frame there (identical to 1969-76 cb750K) and the single bolt just passes through the frame lug and the engine.......

John,does the K7 engine have more ease of removal and installation when sliding the engine out from the left side of the frame with that separate motor mount part removed,compared to the other model/year CB750's ?