CB750 bobber build... gonna need help!

fro_daddy121

www.bclongboards.com
Whats up everyone! Fro_daddy here! I'm new to the forum and to the world of street bikes. Grew up racing dirt bikes, quit riding altogether for a few years, then recently stumbled upon my love for bikes again. My buddy recently got a yamaha xs650 he is turning into a cafe racer, and I picked up 1981 cb750c that I hope to turn into a japanese style bobber.

1-2.jpg

4-1.jpg


Believe it or not I picked this up for $50 big ones. I think its been sitting in ole boys garage since '91. My plan is to tear it down, clean the engine thoroughly, and fix up the body a bit. Probably just rat style with existing parts that are modified to fit my needs. I only havea bout $700 to spend on fixing it up. Tires and throttle assembly are a must on the to-buy list as well.

After 5 days of slow work and tinkering this is where Im at:
mybike.jpg


OK now first things first. I'm looking for a way to lower the rear end of the bike. I want it to remain a softail so my idea was to shorten the rear suspension. Does anyone have any ideas on how to shorten the shocks? Or any locations where I can purchase shorter shocks? These are at 13". Any help would be greatly appreciated.

Thanks
Fro
 
lowering blocks or shocks off a smaller bike, 550 or so... a few companys make short shocks, but they probably arent in your price range...
 
I read in another forum of a guy just cutting the springs shorter on the stock shocks. Is this right or wrong? good or bad?
 
You can do it that way but if you bottom out you will at the least destroy your shocks. The stiffer springs tend to damage the shock mounts.

Best options are: shorter shocks from a donor bike, air shocks (getting harder to find) that let you set the ride height, or shock lowering blocks (you can find them online, should run $15-20).

Don't cheap out on your new tires. If it was mine I'd run nothing but Dunlops. Tread lasts at least twice as long as Kendas, they hold air pressure better than the softer cheapies, and they don't get stuck in grooves as readily. Bridgestone are okay, Avon is a nice tire but wears down fairly quickly. Metzeler tires are great, but pricey.

If you change bars, do not buy Emgo, MotoAsia or other Chinese crap. Hit a pothole and they can bend or break. Flanders and K&N are the only 7/8" bars I buy anymore, Biltwell makes 7/8" bars as well but without personal experience I can't say whether they are good or bad.

I have access to literally thousands of new old stock 1970s metric chopper/bobber/custom/cafe parts where I used to work. It takes some time and digging, and I can only run up their occasionally, but if you need something I can try to find it for you. They do have an attached bike junkyard as well as a few thousand inside bins of used parts.
 
just cutting the springs, wrong imo... the damper is still going to have the same amount of travel, so you hit a pot hole and the rear tire leaves the ground and all the sudden that spring is just flopping around... that and it will be so stiff you might think its a hard tail... much easier to find some 500/550 shocks, dime a dozen. check out the sohc4 boards too....
 
Yeah your probably right, just thought i'd check. How long are 500 springs? I believe the one's I have are 12" or 13". Im not sure how they measure it but mines a 750c so I think its already a touch lower than say an F. Correct?

I think I would prefer to have 10" shocks? any advice?

Also, the tank has been sitting with some gas in it since '91. The tank is in excellent condition so I hate to scrap it, but the inside is lined with goo. Not rust, but goo....lol Does anyone know of a good way to clean out a tank and reseal it?
 
fro_daddy121 said:
Yeah your probably right, just thought i'd check. How long are 500 springs? I believe the one's I have are 12" or 13". Im not sure how they measure it but mines a 750c so I think its already a touch lower than say an F. Correct?

Shocks are measured from mounting point to mounting point. I just measured my (900) F shocks at 350mm if that helps?

Ronin has a nice bobber thread going at the moment: also a 900F, and you will see that he has relocated the top shock mount to lower the rear. He has actually done a fair bit of modifying to the rear frame section, and that might not be the way you wan't to go, but it would still be would be worth a read.

Also, the tank has been sitting with some gas in it since '91. The tank is in excellent condition so I hate to scrap it, but the inside is lined with goo. Not rust, but goo....lol Does anyone know of a good way to clean out a tank and reseal it?

There's quite a few different ways to clean and seal tanks. Perhaps run a search query and pick something that takes your fancy.

Tyres are also something you'll get lots of opinions on. On my bike, the best cross-plies I've come across are Bridgestone BT45s.

Nice to see another DOHC honda here, and that sure was a sweet deal.

keep us posted.

cheers
ian
 
keep in mind clearance between the rear tire and the frame, dont want to rip the rear tread off at 65mph! most "short" shocks are 11". any lower than that, just hardtail the sucker... imo
 
OK OK... this is all good info for a newb like myself. Thanks alot guys.

Now after some more tinkering last night, I'm ready to drop the motor.
Although I had this come to mind last night to get more rake in the bike. What do you think if i were to lower this bracket about .5" to get rid of this hump for my new seat. Is there a reason why the gas tank has an 1" of clearance on the frame? Will it cause problems if it touches the frame?
bracket.jpg

room.jpg


Some more of the hump in the front fo the seat I'm trying to eliminate.
myseat.jpg


And then raise the rubber stop mounts in the front of the tank about .25" to give the tank a more sloped look like below:
Low tank:
lowtank.jpg

High Tank:
hightank.jpg


I like how the higher tank opens up the engine more as well as the extra slope to it. And then with the 11" shocks (not pictured) I think I will have the overall rake perfect for my taste. Does anyone forsee any problems I am overlooking?
 
domer said:
keep in mind clearance between the rear tire and the frame, dont want to rip the rear tread off at 65mph! most "short" shocks are 11". any lower than that, just hardtail the sucker... imo

I have never had a chance to ride a hardtail is it as rough as they say.... jerk's your spine??
 
that depends on a lot of things, here in sf a hardtail is hell as the roads suck..l. but if set up right its not too bad, a nice springer seat with a gel pad will make things a little better but to each his own! if it was really that bad nobody would do it!
 
So I bobbed the bike.... rough cut the seat and frame to get a general idea of how it will look. Let me know what you think.

bobbedseat2.jpg

Bobbedseat.jpg
 
People only hardtail a bike to get that old look. It really doe'snt matter where you live. A hard tail will jam you're spine. It's not good for handling, ride, performance, just that look. With the oem shocks check you travel. See just what would happen if you go all the way. With the swing arm bottemed out check the length of shock in that position, add three inches of lift. Try to find shocks that long. As for you're tank, POR-15...
 
Yeah Im certainly going to leave it a soft tail. Found this sweet salvage yard over the weekend that is full of old bikes. Got some tread while I was there but def. going to go back for more parts.

I need to wrap the seat, attach the fender, then i'll be ready to strip and paint everything. Its getting exciting ;D

Triumphrider... do you think we could just get the mods to move my current thread to the "Big Arse Projects" area?
 
fro_daddy121 said:
Yeah Im certainly going to leave it a soft tail. Found this sweet salvage yard over the weekend that is full of old bikes. Got some tread while I was there but def. going to go back for more parts.

I need to wrap the seat, attach the fender, then i'll be ready to strip and paint everything. Its getting exciting ;D

Triumphrider... do you think we could just get the mods to move my current thread to the "Big Arse Projects" area?

Which salvage? A&A?
 
Yes A&A! I was blown away by all the "junk" he has. Probably at least 100 bikes, tons of wheels, tires, forks, pipes, etc... The only we couldnt find alot of were seats. Every seat had already been snatched up. Alot of different components like brakes, mirrors, shocks, pegs, etc... Engine parts.... You name it he has it somewhere in there. You should really check it out if your ever in the area. Hell you could build a bike outta there.
 
Bike Exif just posted a bobber CB750. It was a hardtail, but looked killer. Thought you might like the inspiration.

honda-cb750-custom.jpg
 
Back
Top Bottom