Topic: 1970 cb750 frame repair?

[la ca fe]

Picked up this cb750 yesterday and want to repair the cut frame.
Have you ever done repairs to a cut like this?
If so what was the best way to do it?

[denward17]

There are some vendors that make a frame cutout that can be taken out in case you needed to either remove valve cover or head while still in the frame, but not sure of dimensions.

Think cyclex has one, and maybe others.

[bryanj]

For those kits you need a complete frame to modify, you could possible use a kit and make your own tubes to weld in

[rocket johnny]

i have a 78 k frame that has been cut and i've sold some pieces of the frame ,  not sure if the tail section would work for you , but let me know if interested ,,    john

[la ca fe]

Thanks to everyone. I’ll look those frame kits.

[scottly]

Did they leave stubs of the tubing at the front as well as the back? You can use 1" OD tubing to replace the missing pieces.

[la ca fe]

No stubs on the front,

[69cb750]

Have you ever done repairs to a cut like this?
If so what was the best way to do it?

[69cb750]

[la ca fe]

Wow! What a nice job !

[HondaMan]

Yeah, he does beautiful work!

[scottly]

No stubs on the front,

The frame kits splice the upper tubes back together after they have been cut so the head can be removed with the engine in the frame, but without the stubs you would have to replace the tubes like 69cb750 before you could install any frame kit.

[kyle750]

I don't fully understand why people would cut the frame tubes out. Frame stability is destroyed and it makes absolutely no sense to me      Did people cut the frame tubes to remove the engine or to install a modified or different style gas tank??

[scottly]

You have to remove the 750 engine from the frame to do any work on the top end without moving the tubes out of the way. The frame kits are meant to restore the structural integrity of the frame.

[Don R]

 I've welded a section from a newer frame into a 70 frame before. I spliced it internally and butt welded it. I've also done the weld-in splice kit and the bolt in kit. There are weld-in removable connector pieces for 1" tubing on ebay and I think CycleX still sells a weld-in kit.
 Here is my 70 with the old Gordons kit.

[scottly]

The weld-in frame lugs are cheaper on ebay than from Cyclex or Carpy. Someone posted about this a while back, and I think the search terms were roll cage components or something?

[Stev-o]

    Did people cut the frame tubes to remove the engine or to install a modified or different style gas tank??

With the tubes cut out, the cylinder head can be removed w/o removing the entire engine.  Later model Hondas came from the factory with a "frame kit".   My K3 "Park Racer" 750 came with a "shade tree" frame kit, I installed Frank's Kit and it is not visible nor can you tell when riding it. 







BTW - CB500/550's cylinders can be removed w/o a kit.

[kyle750]

BTW - CB500/550's cylinders can be removed w/o a kit.

Is the CB550 frame considered better engineered and an improvement compared to the CB750 frame

[bryanj]

No better no worse just easier to strip engine

[la ca fe]

I found no numbers on the motor, so I’m guessing the chain broke and slapped a hole in the engine case? The mechanic who swapped out the case was lazy and did the cuts to the frame to make his life easier. The bike is a March 1970 KO, and I’m lucky to have found it before it got thrown out. The motor spins with 16k miles on it but it’s going to need a whole lotta love to get it one the road again.  Wow I used Led Zep and Willy in the same sentence. 

[bryanj]

Thats an eary cable operated carb motor and as the ends of the tubes are still there it will be a relatively easy job to replace with a frame kit not forgeting the small braces between the tubes, pictures and measurements would be good, i think i have a very early workshop book with frame dimensions, i will try and look for you

[Don R]

 My friends dragbike was cut, it had an 1124cc stroker motor, rear struts and ran close to the NHRA record at one time. I still choose to put the tubes back in though. It will either get a kit or have the tubes bent upwards to allow removal. Bending them puts the squeeze on the coil area though. My motor will get a magneto so it's cool.
 Here's a mod, not well done but I plan to improve it.

[BenelliSEI]

The weld-in frame lugs are cheaper on ebay than from Cyclex or Carpy. Someone posted about this a while back, and I think the search terms were roll cage components or something?

+1 “roll cage tube connectors”. My favourite solution on most applications. Used one on a diagonal roll cage bar in the Lexus race car, so we can occasionally fit a second seat.

[Don R]

  One more option,
https://andrewsmotorsports.mybigcommerce.com/chassis-products-tube-connectors-honda-cb750-sohc-1969-1978/

[BenelliSEI]

  One more option,
https://andrewsmotorsports.mybigcommerce.com/chassis-products-tube-connectors-honda-cb750-sohc-1969-1978/

Those are exceptional. Nicest solution I’ve seen!