Topic: CB750 Question-First post

[solo 2]

Hi, while I'm new to this forum I'm not new to bikes,mods,rebuilds etc.. My first bike was a 78 CB550K, still one of my favorites. I've been playing with Yamaha 2 strokes for a year now and decided that this winters project would be a CB750 cafe possibly. I've done a fair amount of research on these things lately and had a question about differing years. While I'd like to get a nice 70-76 to start with they're getting hard to come by and pricey around here, everyone wants 2G for a beater I've been looking at a couple of 78's in reasonable shape. I was reading Carpy's web page and he talks about the frame being longer. So I guess my question is what are the differences, do parts from earlier years fit the 78 and if I'm ditching the tank and seat does the year make much if any difference.

Great site, lots of good info/ideas. Appreciate any help I can get.

[Hondawggie]

Good question, I've wondered this too.
So I busted out my Zedder Honda Cross-Reference.
Not all inclusive here but some early parts fit on the '78 bike, such as:

- wheel spokes
- oil pan
- alternator cover
- connecting rods
- crankshaft
- oil pump
- coils
- turn signals (except the earliest cb750s)

Here's some things that only work up to the 1976 K6 bike:
- crankcase assy.
- pistons
- camshaft
- mufflers (the '69 - '71 bikes had hm300s, the '72-'76 had hm341 mufflers)
- headlight
- seat pad
- master cylinder (front brake)

Lots of stuff is model-year specific (wiring harness in some years, gauges, seat pattern, etc.)

Now, the stuff above is from Zedder's cross reference, the pro's on the board here might be able
to say more accurately what early stuff will fit the '78.  Looks like a lot of stuff will, though.

If you're trying to keep it model-year correct, you can get Zedder's Honda X-Reference on ebay for $30.  I thought that was pretty cheap considering all the time it would save me and it really has since I stick to model-year-correct when I buy parts.

[Retro Rocket]

Any year engine should fit in any year {sohc} frame. The "F" frames are longer at the back after the rear mudguard mount and the seat mounts are different as well. "F" tanks will fit "K" model bikes. "F" model bikes have a completely different wiring harness to the "K" and the later model SOHC bikes have longer swing arms as well. Not up to date on later "K" model bikes....

Mick

[cookindaddy]

I'll answer your question a slightly different way.
I just finished rebuilding a 78 750K to original condition. It took me two years but I had lots of good riding along the way.
I paid way too much for the original bike because I was a newbie and I didn't know better. It was a pile of crap for $2000.
I started buying parts and generally found them easy to get. Most people have and prefer the earlier models (up to 76). But Honda made about 100,000 of the 77/78 so there are lots of them still around.
I then bought a 77 750K parts bike for $300 and that was a great find. I ended up rebuilding and using the engine from the parts bike for the 78 while I rode the 78.
Yes the 77/78 are a bit longer (about an inch and a half in the back section) and that means that pipes from the earlier models don't fit, you have to have the HM405 pipes.
The front brake master cylinder on the 77 does not have the pressure switch built in, it is on a block on the triple tree, the 78 has the brake switch in the master.
My 78 had the roller bearings in the triple tree, the 77 had lots of balls.
The side cover trim on the 77 is different from the 78.
But for all other practical purposes, the K7 and the K8 are the same bike. I generally stayed away from anything from the earlier years although as the other posters have said, some of the parts are interchangeable.
I figured that it was the last years that they built the SOHC, so they'd probably figured it out.
Besides, the engineers were busy with the DOHC...

And you are right about this site - the people here and their willingness to share their experience is amazing. I could not have finished my project without sohc4.net! 

[solo 2]

Thanks for the info so far, how about frame geometry. Is most of the length dif in the swing arm and are swing arms interchangable. I'm mostly concerned about handling characteristics, on such a large top heavy machine longer usually means slower handling. BTW, I realize this thing will never handle like a modern sportbike, I just want the best I can start with and buy at a reasonable cost. As I said this bike is going to be heavily modified, if I was doing a resto I'd go older, better and not worry so much about initial cost.

I'm also considering doing a 550, my only worry there is resale value as the 750's seem to bring more $$ as there more desireable in any form it seems. I never plan on selling any bikes I buy, I have 9, but things/projects change all the time. I enjoy working on them but when they're done I have to decide to keep or sell. Any input on this.

[Retro Rocket]

Triple tree offset changed with the "F" models i think it was 10mm shorter on the "F" bikes. A longer swingarm will slow the steering a little but it also makes the bikes more stable, these old Honda's had fairly twitchy handling for an older bike and when set up right handle surprisingly well, you can always raise the rear with longer shocks to get the bike to steer a little quicker but i doubt you'll need it. I always fit a steering damper on my bikes, makes them behave better, no tank slappers.

Mick

[ZanVooden]

My 78 had the roller bearings in the triple tree, the 77 had lots of balls.

78 stock came with balls and races. Roller bearings must have been added by a PO.

77/78 parts are what you'll need to look for. the eariler parts wont always fit.

[brianmac]

anyone know if i can use  81 750c triple trees with roller bearings on a 78 750k?
im trying to go with dual discs and comstars(already on frankenbike)