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Discussion Starter #1
ok guys - I am going to try to put my cb750F on a diet. So far she has a fiberglass tank and seat, stripped most of the useless lights off. Now I want to get rid of some reciprocating weight.

so which is the lightest:

Mags - stock comstars?
Mags - Lesters or Morris
Mags - Billet Harley style rims from the 90's (like PM)

Spokes - Stock 75-76 cb750F
Spokes - SS spokes laced to a DID aluminum rim

I have some of these so I can weigh them and post but if anybody has any of the above mentioned rims maybe they can weigh them and post the weight?

any other suggestions? I am going to convert the heavy calipers to the lighter and much improved twin piston jobbies off the 80-82 cb750F.

Any other suggestions for weight savings?



Edited by - Geeto67 on Oct 04 2006 10:56:33 AM
 

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Probably can't tell you much that you don't already know. The steel fenders, bin 'em. If you're really nuts, remove the wires from the harness that don't serve a purpose anymore. Go to a battery-less ignition.
One thing I've found over the years, if you're going with tube type tires, spend the money on good quality tubes. They're heavier, 'cause they're actually thicker rubber, and do improve handling, less tire flex etcetera, so you may not save as many ounces vs tubeless...


FR
 

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Discussion Starter #3
Bike is a 1978 Supersport Cb750.

Mods done by previous owner:

dunstall tank
Fiberglass seat
drag bars
ditch stock signals and taillights

The bike currently has comstars, which means I am running tubless tires already. Not really looking to go back to spokes unless there is a noticable weightloss (must be 1 lbs or more).

When I was at the e-town swapmeet I found scores of those old harley mags from the 90's in billet aluminum. They felt pretty light as compared with a stock cast aluminum harley fatboy rims sitting next to them. Didn't have any stock wheels with me or nearby to compare them to. Since most of them are out of style now on choppers you can pick them up pretty cheap.

I have a friend that does a lot of business with Performance Machine. He tells me he can get rim blanks from them and then I have to machine it to fit my bike. I might just look into that, depending on the cost it might be worth it, some of those PM wheels are hella strong and super light.

What size rim would I need for a stock cb750? wm3? WM4.5?

You can't run a cb750 without a battery, period. I mean it is possible but you have to GP start it at every light because the engine will need to turn 2000rpm to start sans battery. Joking aside, a cb750 is one of those bikes you can;t run without at least a small battery.

Other mods I am planning to do to take weight off this pig:

- Headlight: probably going to go with a car fog light since they seem to be pretty light - two PIAA lamps weigh less than my stock cb750 bucket, rim, and glass. I was kicking around the idea of using two small streetfighter style lamps and mounting minigauges into the backs of them for the tach and speedo, thus deleting the heavy gauge cluster too

- headlight ears: heavy pressed steel, getting replaced with cheapie JC whitney brackets because they are cheap

- Front fender: still running the stock one right now. This is hard because I can't just bolt on a fiberglass one and go. The cb750 front end is required to have some kind of fork brace. I think what I am going to do is drill out the brace/mount from a stock fender and then mount a fiberglass blade fender. There is too much crap on a NYC street for me to run fenderless with just a brace.

- Taillight: Previous owner used two early cb750 turn signals as the taillights. Not very heavy but an LED is way brighter, has a cleaner mount, and is lighter.

- Clipons: I have a really nice set of cast aluminum clipons that are light as hell. They have a little bit of a rise so riding position won't change that much.

- Drill the shit out of everything: Breaking out the hole saw to the chainguard and anything else I find that doesn't need a smooth surface to do its job.

- Rearsets: stock levers and footpegs are heavy, this should take some weight off.

Any other suggestions?
 

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Once again, you probably know this but...does this bike run the 530 size chain? If so, can you go down to 520 chain and aluminum sprockets?
Speaking of chains, for just occasional use as a fair weather bike, I'd run a non O-ring chain. Not that they're that much lighter, but they do increase the drag perceptably, and for a "vintage" bike, that's a drag.


FR
 

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Geeto,
Here are a few suggestions:

Aluminum swingarm?
Rear caliper, replace it with one off a CR80. E gay is full of them
Plastic chain guard
Lose the center stand
Aluminum oil tank - looks trick and can be relocated
530 chain and alloy sprockets. Stock is 630 and I don't know if you can go to 520. Maybe 525?
Alloy lower triple clamp?
Lighter brake disks


I think spoked wheels with alloy rims are lighter than any mag type wheel unless it is real magnesium i.e. Morris or Dymag

Ken


AHRMA 412
Vintage racing - old guys on old bikes
 

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Discussion Starter #6
quote:
Geeto,
Here are a few suggestions:

Aluminum swingarm?
Rear caliper, replace it with one off a CR80. E gay is full of them
Plastic chain guard
Lose the center stand
Aluminum oil tank - looks trick and can be relocated
530 chain and alloy sprockets. Stock is 630 and I don't know if you can go to 520. Maybe 525?
Alloy lower triple clamp?
Lighter brake disks


I think spoked wheels with alloy rims are lighter than any mag type wheel unless it is real magnesium i.e. Morris or Dymag

Ken


AHRMA 412
Vintage racing - old guys on old bikes
I'd love to hear more about this cr80 conversion for the rear caliper.
 

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Geeto, I dont have a real planned conversion. I have just seen lots of CR80 calipers on Egay and they are really small and go cheap. It looks like a cool setup. I am going do do it on my Seca550 rear brake before next race season. Another good way to lose weight is to go with a Rickman frame. Other than the fact that they are really hard to find and really expensive, they would be cool.

Ken

AHRMA 412
Vintage racing - old guys on old bikes
 

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Discussion Starter #8
quote:
Geeto, I dont have a real planned conversion. I have just seen lots of CR80 calipers on Egay and they are really small and go cheap. It looks like a cool setup. I am going do do it on my Seca550 rear brake before next race season. Another good way to lose weight is to go with a Rickman frame. Other than the fact that they are really hard to find and really expensive, they would be cool.

Ken

AHRMA 412
Vintage racing - old guys on old bikes
I Have a rickman frame - but that is for another build (I'm working on it).

I know that there is a way to adapt ex500 zx6 calipers to old bike front ends (you have to make a bracket and mill your rotors to 5.5). Harley rears use a disc that is close in size to the cb750 rotor so I wonder if it is possible to adapt one to a cb750. If not Performance Machine makes a badass 6 psiton caliper and I will just have to have a mount made (fabricator kevin does this - http://www.fabkevin.com/).
 
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