Topic: Just picked up a Planet Blue Cb750 project, need some advice/guidance on frames.

[TheArchitect]

So, I am somewhat new to the site, have been lurking for a while and working on getting a cb550 back on the road, and along came a real nice looking planet blue metallic cb750 that i could not say no to! Now i have two non running bikes 

I got it, everything is in decent shape but the p/o did some things...

He swapped out the front forks, front wheel, rear wheel, and swingarm to put 77 750f parts on it. Yes it has the dual brakes in front, and disc in the back on comstar wheels.

The real bummer is he hacked off the rear foot peg frame supports, the whole triangle portion.

I want to get it back to stock, drum brake in the rear, spoked wheels all around, and correct fork.

There is a frame near me for a very good price, but it is from a 73 cb750. I read somewhere here that the seat mounting is slightly different? Hondaman stated it here

http://forums.sohc4.net/index.php?topic=82296.0.

I was hoping to get some more info. I have stock k5 seat that is nice and want to keep it. Planet metallic is k5 right? even though 74 build date? Is the seat going to sit funny?

Then the other question, anyone have a 75 frame if the 73 is going to fit the seat funny? and forks, and wheels? Trying to get this back to where it should be!

Currently running the vinegar soak in tank, Ill start a project thread once it gets going...

Thanks! 

[HondaMan]

The seat hinge changes included some height differences on the hinge arms, but you may be able to swap your old ones to fit things better. Also, during the K5 the seat hinges swapped sides(!) as well. On the earlier bikes the hinges are on the right side. The K2-K5 (before the swap) will usually fit, aside from some slight height differences.

For one example, take a look at my book's cover: that bike is a late K3 frame (possibly titled as K4) with a K5 seat aboard. You can see how it sits slightly up off the tank's lower line. That's where the difference shows up. The bottom of the later seat is higher and the hinges are slightly taller, as are the rubber blocks.

[TheArchitect]

Hondaman, Thanks for the reply!

So, when you refer to "hinge arms" those are the ones on the seat pan itself? not the receivers for the seat pin on the frame itself? So it could be that the frames are the same? I have been scouring trying to find good pictures of each year, but cant find decent ones that show the hinge portion on the frame.

But, that would be hard to "swap" out, the frame portion of the hinge. So if i am not mistaken, you are saying that the hinge arms on the seat pan and associated rubber blocks are taller on the k5 than k3, but the location on the frame is the same... ha, sorry, trying to cross my t's and dot my I's.

My hinges are on the right hand side.

[Stev-o]

Planet Blue is a K5, nice color, I had one.  Too bad the PO chopped it up.

Personally, I would get it running and sell it if you want a stock bike.  Buy another body kit and save the PB body for the next bike you buy.

[Retro Rocket]

The seat hinge changes included some height differences on the hinge arms, but you may be able to swap your old ones to fit things better. Also, during the K5 the seat hinges swapped sides(!) as well. On the earlier bikes the hinges are on the right side. The K2-K5 (before the swap) will usually fit, aside from some slight height differences.

For one example, take a look at my book's cover: that bike is a late K3 frame (possibly titled as K4) with a K5 seat aboard. You can see how it sits slightly up off the tank's lower line. That's where the difference shows up. The bottom of the later seat is higher and the hinges are slightly taller, as are the rubber blocks.

Thats interesting, I have a K6 frame cb750 268 **** that has right side hinges, actually i've never seen left side hinges on any Aussie model K0 to K6..

[DH]

1975 K5,   mfr. date 11/74.....I can take pics of things and measure if it'll help you for whatever reason.

[TheArchitect]

DH,

One day, mine will look like that. Thanks! I have the 75 frame, would love some pictures of a 73 at the seat hinges...

Stev-o

I like a good project, especially one I can ride while making a nice rolling chassis to eventually swap the stuff into, at least that was my thought, maybe it doesnt make sense in the long run... I have seen so many threads where one thing leads to the next...and I know that will happen to me hahahahha.

But, as much info as i can get by looking at pictures, I think the differences in the seat Hondaman is referring to is only in the hardware of the seat pan, don't take my word for it though.

So, unless anyone thinks it might not work, I am going to pull the trigger on the 73 frame, and swap all the 75 stuff onto it at some point. Ill post the thing in projects once i take pictures etc...

I hope to be able contribute as much as possible to the site, this forums is a amazing place, gives the internet a real good reason to exist.

First word to the wise, don't do the vinegar soak if you live in an apartment where the floors shake and your gas tank lid seal is shot...

[Old Scrambler]

Most of these bikes, especially on the west coast, are titled to the frame. On resale, original motor and frame usually sell for more.  Its not too hard to weld the foot-peg brackets onto the frame............especially if you have a set of original pipes to get the position 'just right'   Several of us have scrap frames to supply the material.

[TheArchitect]

Well guess ill just have to find some original pipes to rig the weld up then!

I am in maine, so all i need is a bill of sale and can register anything, figured i would just swap the original 75' vin plate, or just get a bill of sale with the replacement frame and register that. Interesting enough, the frame I am looking at is actually two frames, on cut (just for a cafe hoop), the other original, so I could end up with a 73 frame, and a fixed 75 if I work on my welding skills, really only comes down to the $$, and I need a garage that isn't an hour and a half away.

[Stev-o]

Well guess ill just have to find some original pipes to rig the weld up then!

...figured i would just swap the original 75' vin plate

Not so fast, the VIN is stamped on the left side of the head. 

[Retro Rocket]

Well guess ill just have to find some original pipes to rig the weld up then!

...figured i would just swap the original 75' vin plate

Not so fast, the VIN is stamped on the left side of the head.

And it has to match the VIN plate...

[Don R]

 I'd do some serious swapping of parts with you if I had a 75 frame and was closer. I wouldn't mind a hybrid I actually prefer one with triple disc brakes. It's on my agenda to own one again, I have the F0 back half already.

[TheArchitect]

I was thinking of a little bondo over the stamped numbers and repainting the donor frame and relying on just the vin tag for registration purposes...is that 100% illegal? 

Again, if i get a bill of sale with a frame in this state i can register a frame as a working motorcycle.

Don R, The parts will be available, so if you find a 75 frame in your neck of the woods let me know!

Thanks for the advice and comments, it is never as easy as it initially seems, but I think that might be what we all like about these projects.

[seanbarney41]

yeah, that's pretty much totally illegal, but it's unlikely that you would get caught...until you want to sell

[Stev-o]

Forget the bondo, break out the grinder!

[Retro Rocket]

Anyone know if the Honda replacement frames were stamped...?   

[TheArchitect]

Grinders are more fun than bondo thats for sure.

And I am going to go with, yes, replacement frames were not stamped, at least that is what I will tell the dmv.

I have no idea if that is a fact.

However, to close this out, I downloaded the parts lists from this site here, and the list carries the k3,k4,and k5 and list the frame as the same part. So, I am concluding that there is no difference in the frame itself and is interchangeable.

Thanks for all the help everyone!

[Don R]

Rock on then,