Topic: First Bike and First Build - 1978 CB750

[robotdoc15]

I recently bought my first bike, a Craigslist-find project bike. The seller had begun to re-build it as a cafe racer and I am finishing the job. The bike came with a professionally painted fuel tank and a sharp-looking cafe-style seat, but some essentials were missing (no turn signals, broken headlight), and some other essentials came uninstalled (front brake, speedometer).

This is the only "before" photo I have, taken after a 10-hour drive there-and-back to buy the bike.


Phase 1 of my build is to strip and re-paint the frame, after I de-tab it and weld on mounts for the seat, custom oil tank, and modern electronics (AGM battery, SS reg/rec, etc.). Before I began disassembly, the engine was in decent running shape. Pulling the engine was an adventure, but I got it out on the second attempt, after strapping on a length of 2x4 to assist in controlled maneuvering.


I purchased a cheap engine stand from Harbor Freight. I made four brackets out of iron angle and then mounted the engine with two lengths of threaded rod.


I plugged up all ports on the engine and began scraping away 40 years of crud using Castrol SuperClean and a plethora of scrub brushes. Small components safe to blast with sand have been cleaning up nice and easy. I am considering fashioning a large enclosure to sand blast the entire frame and soda blast the engine.




Today I removed the rear shocks and staged what the main line of the bike will look like with a raised tail and seat. The bike came with shorter 11.5" shocks and I plan to restore it to somewhere in the ballpark of 13". As for the seat interface, I plan to cut another 1.5" off the tail of the frame and weld capped brackets for turn signal mounts, below the seat cowl. Weld a shelf to hide electronics beneath the cowl. Relocate the oil tank to mostly clear up the back triangle.


I will try to post my progress as the build continues. I can't wait to be finished with cleaning and get on with building the new!

[SOHC4 Cafe Racer Fan]

Make sure to weld in a new cross-member where you or the prior owner (PO) cut off the fender mount.  That cross-member helps stabilize the rear frame and prevent twist.

[calj737]

This will make a nice looking project when you're done.

A couple of "food for thought" things:
 - Definitely restore the seat rail cross brace without conflicting with your tire/shock travel
 - Soda blasting an assembled engine is doable, but be Damn Skippy Certain that your purge all the media from the oiling system afterwards. Oil/Soda media coagulates... 
 - The exhaust flanges will rust pronto without some type of protective coating.
- I'd encourage you to service the front forks (if their status is unknown).
- Definitely return to a stock length on your shocks, and slide the front trees back up to match the stock geometry. Or drop to an 18" front wheel/tire. A fender or fork brace will be a good addition for handling too.

I dig the paint scheme on that bike!

[robotdoc15]

Thanks for the compliments and the advice! Much appreciated. I do plan to restore the triple tree to stock height after I service the forks. They're coming off the frame along with everything else before the frame gets a weld and paint job. Tail hoop and cross brace are certainly included with the welding.

I tried to remove the swing arm and the bolt would only budge about 3/4" and is seized up. Any suggestions on how to free it? It rotates freely but is not sliding out. I was thinking about taking a torch and heating up the swing arm to loosen things up. My concern there is that it might anneal and weaken the steel. I'd like to turn new Oilite bushings on the lathe and cut grease lubrication grooves on the collar per Hondaman's prescription. So I'd like to remove the swing arm for more than the paint job.

[calj737]

Typically a stuck pivot bolt is due to hardened grease and corrosion with the tube, against the bolt. You can try to first add some new grease and hope to purge the hardened goop, as well it might just force the rod loose enough to pull out. Also, you can drive it out carefully from one side.

Heating it isn't the end of the world, but you're heating the swing arm, not the tube/rod where the corrosion is, so you'll really need to cook it before it makes much difference. If you distort the rod with force, you'll be searching for a replacement.

Another option is to dunk the tube end of the swing arm in Diesel, or Kerosene (find a container large enough to do so) and let it soak. That can release the goopy-stuck on, stubborn bits and then let you really keep spinning the bolt to free it up. Smashing it out is the last resort.