CB750 DOHC Fork Interval Question(New problem updated)

E

enterlance

Active Member
Hi, on my way putting up the CB750 I started last year, after installing the triple tree and fork legs, I found that the fork interval is not equal - they are not parallel. The top interval is as much as 1' wider than the bottom(5.8' vs 4.8').
Is this a problem? If so, how should I fix it before putting on the front wheel?

New problems updated below:
The tarozzi fork tubes arrived today. They absolutely made mounting process a lot easier.
However, after fitting the lower fork legs onto the front wheel, it seems that the fork is not sitting properly (as seen in the attachment), the other side seems fine.
The left fork only has little clearance against the brake disc, what could be the problem? Is my lower legs messed up?
 

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Re: CB750 DOHC Fork Interval Question

You are not measuring fork parallelism as you are measuring different diameter points. You need to measure distance between the tubes at the top and where they enter the lowers. And it must be a very accurate measurement. But, yes, they MUST be parallel. If the tubes are straight and the tripples are matched, there should be no problem - they will be parallel.
 
Re: CB750 DOHC Fork Interval Question

pidjones said:
You are not measuring fork parallelism as you are measuring different diameter points. You need to measure distance between the tubes at the top and where they enter the lowers. And it must be a very accurate measurement. But, yes, they MUST be parallel. If the tubes are straight and the tripples are matched, there should be no problem - they will be parallel.
Click to expand...

Man, how could I be this stupid! Must be the Marlboro messed me up last night...
Anyway, thanks for the advice! My guess is that the powder coating guy coated the inner triples, so I have to strip the powder coating before install the forks... I will try to work on it today.
 
Re: CB750 DOHC Fork Interval Question

Tried to get rid of the powder coating in the triple trees, they are still not parallel. I suspect that at least one of the fork is bent...
 
Re: CB750 DOHC Fork Interval Question

Ok, did a quick check. The fork tubes are bent in a bad way. Now my mission is to find a pair of replacement. Man, aren't they expensive and hard to find!
 
Re: CB750 DOHC Fork Interval Question

I've heard this place mentioned many times: http://franksforks.com BTW, a '78 or '79 GL1000 front end, triples and all dropped right in my '79 F.
 
Re: CB750 DOHC Fork Interval Question

I'd opt for a set of CBR F2 forks if they have to be changed out.
 
Re: CB750 DOHC Fork Interval Question

pidjones said:
I've heard this place mentioned many times: http://franksforks.com BTW, a '78 or '79 GL1000 front end, triples and all dropped right in my '79 F.
Click to expand...

They quoted me over $500 for the fork tubes, ends up buying Tarozzi fork tubes from ebay for $400. I'm kinda nervous about buying used forks as they could be bent too so as well just buy new ones.
 
Re: CB750 DOHC Fork Interval Question

J-Rod10 said:
I'd opt for a set of CBR F2 forks if they have to be changed out.
Click to expand...

If only I saw your post earlier lmao. But it's OK. I'd prefer original ones.
 
Re: CB750 DOHC Fork Interval Question

The tarozzi fork tubes arrived today. They absolutely made mounting process a lot easier.
However, after fitting the lower fork legs onto the front wheel, it seems that the fork is not sitting properly (as seen in the attachment), the other side seems fine.
The left fork only has little clearance against the brake disc, what could be the problem? Is my lower legs messed up?
 

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Remove the wheel and put the axle into place. It looks like the left leg (right in picture) is longer than the other.

You need to find out why. Is the leg a different length or was assembly incorrect? You should be able to loosen the upper and lower triple clamp on that side and let the get slide higher or lower until the axle fits properly and then see how much different they are side to side.
 
teazer said:
Remove the wheel and put the axle into place. It looks like the left leg (right in picture) is longer than the other.

You need to find out why. Is the leg a different length or was assembly incorrect? You should be able to loosen the upper and lower triple clamp on that side and let the get slide higher or lower until the axle fits properly and then see how much different they are side to side.
Click to expand...

Given the fork tubes are new and the lower legs are unlikely easy to be bent, I suspect the powder coating inside the triples is messing up the fork set up. I will double check tomorrow, maybe take the whole front end off and go from there
 
More likely to be one leg assembled wrongly. Check the damper rods and spacers/springs.
 
First, tighten the nut onto the axle. Then the Right leg (in this case) should have the clamp tightened centered up on the nut (first the front, then the back - usually ~13 ft lbs). then compress and release the forks to center the left leg in the sliders and tighten the left clamp (front first). With the calipers installed, there should be ~.7mm clearance between the rear caliper (not the pad) and the disk. If way off, you have some serious problems. If close, you can loosen the left clamp and nudge it a bit. If the right caliper doesn't fit then you definitely have things out of position or are not using all of the correct parts.
 
The key to what PID said is not to force anything. Your issue does not appear to be the calipers, it's that one leg as fitted is longer than the other and that is what needs to be investigated. It could be parts assembled in the wrong order or one leg missing a rebound spring or a damper rod hanging up inside the leg or a missing lower hydraulic lock or numerous other possibilities. It could also be as simple as one leg bolted into the triple clamps lower than the other.
 
Disassembled the forks and checked. I forgot to mention that I did not put fork spacers in as I still don't know the length that I need to cut them (they are PVC tubes along with the Progressive Spring), so the spring is not forcing against the damper rod and thus the front wheel mounting is having trouble? I don't know. Maybe I should torque everything down to spec and try it again? Right now I'm kinda stuck.
 
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