Author Topic: 78 CB750f3 shock mount offset????  (Read 1756 times)

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Offline colvinry

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78 CB750f3 shock mount offset????
« on: June 16, 2020, 08:54:11 PM »
Hello gents,

Turning a 78 CB 750 f3 into a flat tracker to try and take on the hooligan class turning left, hooligan is stock frame, 750cc and up, over 400lbs. I am mounting some works performance shocks which are eye to eye style. I noticed the stock shock mounts have an uneven offset. What is the deal with this? Eyeballing it, the frame looks even but I don’t trust my eyes anymore, had to redo too many things.

Picture of the concept bike. R6 forks. 19” wheels and some rubber with some decent rear shocks. Gonna see what she can do.

Shock mounts pictured as well.

Ryan

Offline dragracer

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Re: 78 CB750f3 shock mount offset????
« Reply #1 on: June 16, 2020, 09:01:26 PM »
Without looking at my F3, I'd venture to say the longer spacer was for the left side of the bike. Odds are that is done to give clearance for the chain. I need to look at my bike to verify.

Offline colvinry

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Re: 78 CB750f3 shock mount offset????
« Reply #2 on: June 16, 2020, 09:05:08 PM »
The longer side is on the right side. 100% certain.

Riders right
« Last Edit: June 16, 2020, 09:08:21 PM by colvinry »

Offline scunny

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Re: 78 CB750f3 shock mount offset????
« Reply #3 on: June 16, 2020, 09:12:34 PM »
Can't help with anything 750, but, look forward to a report on the hooligan racing.
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Offline colvinry

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Re: 78 CB750f3 shock mount offset????
« Reply #4 on: June 16, 2020, 09:20:02 PM »
Trying to do what Ricky Graham said “#$%* that” to. Which lead to the development of the RS750. We shall see if the Honda can take on the 1200 S&S bikes. Will be fun win or lose. I will have a GoPro on so I will post the footage for all to see.

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 78 CB750f3 shock mount offset????
« Reply #5 on: June 16, 2020, 09:57:26 PM »
The 77/78 F and K engine output shaft is offset 10mm to accomodate a double row bearing. Therefore everything behind it has to also be offset 10mm. Swingarm left side, rear sprocket carrier, left shock upper mount. Axle spacers are the same 77/78 and pre 77/78. 
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline scottly

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Re: 78 CB750f3 shock mount offset????
« Reply #6 on: June 16, 2020, 10:07:11 PM »
The late swing-arm is wider, and has an off-set shock mount to match the off-set in the frame mount. Do you have an early arm?
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Offline colvinry

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Re: 78 CB750f3 shock mount offset????
« Reply #7 on: June 16, 2020, 10:48:17 PM »
No stock. So I should keep the offset?

Offline scottly

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Re: 78 CB750f3 shock mount offset????
« Reply #8 on: June 16, 2020, 10:58:24 PM »
You are now in the world of customization. ;) You need to make the shock mounts line up. Normally, for a shock with a lower eye type mount, it's done with "ears" on the arm, with a bolt through the ears and shock eye, not with a stud like at the upper mount.
Don't fix it if it ain't broke!
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Offline johno

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Re: 78 CB750f3 shock mount offset????
« Reply #9 on: June 17, 2020, 04:49:06 AM »
Jerry and Scottly are spot on re the 10mm wider left hand shock mount.
If you have the original motor, frame and swing arm no probs just weld em all back on, if not, or if your not sure always start with the identifying motor ( sprocket mount shaft) then work back from there ie left hand upper shock mount, sprocket holder width ( go on cycle x web site as they have measurements and pictures of the two types sprocket holders for you to compare.)
There have been so many engine , frame , swing arm swaps over the years I wouldn't mind betting there are hundreds out there with the chain not aligned by 10mm, much worse than the shock mount 10mm out :o

Good luck with the bike project, its a journey  :)
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Offline Alan F.

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Re: 78 CB750f3 shock mount offset????
« Reply #10 on: June 17, 2020, 05:23:14 AM »
For visual reference:


Offline turboguzzi

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Re: 78 CB750f3 shock mount offset????
« Reply #11 on: June 17, 2020, 08:03:29 AM »
i know its not a good picture, but had the same problem adapting eye/eye koni to the stock swingarm.

simply built this alu plate triangles, one bolt through the swingarm shock eye, another through a spacer welded to the arm, third through shock

lets you change geometry/ride height easily by making different plates

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 78 CB750f3 shock mount offset????
« Reply #12 on: June 17, 2020, 09:54:32 AM »
You can see the frame pieces offset in your picture. Now you need a 77 or 78 engine or a 10mm offset front sprocket. Gotta keep the chain aligned front to back.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Alan F.

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Re: 78 CB750f3 shock mount offset????
« Reply #13 on: June 17, 2020, 11:38:31 AM »
You can see the frame pieces offset in your picture. Now you need a 77 or 78 engine or a 10mm offset front sprocket. Gotta keep the chain aligned front to back.

Or a k7-k8 sprocket carrier?

Offline colvinry

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Re: 78 CB750f3 shock mount offset????
« Reply #14 on: June 17, 2020, 12:57:57 PM »
Thanks gents,

All is stock 78 f’r parts. I have a 19” wheel laced up. I will need to get that sprocket aligned. Going to shorten the swing arm to achieve a 55” wheelbase and will get the shocks mounted to achieve a 4deg swingarm angle and that will be about all I can do without getting crazy. Need some axel spacers as well.

Offline Alan F.

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Re: 78 CB750f3 shock mount offset????
« Reply #15 on: June 17, 2020, 02:28:51 PM »
I dunno about F's but K7-K8 rear spacers are 25 & 35mm

Offline colvinry

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Re: 78 CB750f3 shock mount offset????
« Reply #16 on: June 18, 2020, 05:09:23 PM »
One more question. Off topic, just looking for keywords and a point in the right direction. I think I would benefit by lowering the power curve in the rpm. Do I advance or retard the cam. And who has decent adjustable sprockets.

Offline 754

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Re: 78 CB750f3 shock mount offset????
« Reply #17 on: June 18, 2020, 05:50:13 PM »
 I think APE has them..
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Offline johno

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Re: 78 CB750f3 shock mount offset????
« Reply #18 on: June 19, 2020, 05:25:10 AM »
advancing the camshaft makes more torque acceleration, retarding the cam makes more top end HP.....supposedly.
One thing for sure Ive never had any success with retarding the cam timing and would avoid it like the plague.
With such a long cam chain connecting the crank to the camshaft,  centrifical force makes the chain rollers move up higher on the sprocket teeth which retards the valve timing greatly.
I used to think the cam manufacturer would have built some compensation into the grind but I have spoken to two cam grinders in OZ about it and they both said " the chain is your problem not ours"
So the good oil for the hi revving, long chained overhead cams is always advance the the camshaft , running them straight up or retarding makes them accelerate like old dogs and even though the retarded theory is more top speed any experiments I done on any Honda engine retarding made them slower both access and
top end.

I once had a play with cam timing on a little Honda Z50, put in a hot cam and tried the cam position from 10 deg adv, 5 deg adv, 2 deg adv, 0. then 5 deg retard, 10 retard.
Result was advancing made it easy starting, good accell, Evan a wheel stand  ;D
Retarding , hard starting, slow accell and slow top speed, at 10 deg retard I had to run along side and push like #$%* to get the bike to Evan go.

Eventually the cam placement becomes a big player in racing engines and can be used to compensate for gear ratios, track condition,  average corner radius, fuel consumption, tyre compounds and stuff like that.
In my world If your sealing up the HP motor for a while ie road bike I always go 1 to 3 deg advanced, stock  I would go 3 deg cos the chain wears like #$%* with milage.

 
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Offline colvinry

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Re: 78 CB750f3 shock mount offset????
« Reply #19 on: June 19, 2020, 09:06:16 AM »
Thank you very much for the info. I will need to try it out. I will start with advancing and see how it feels. Motor does feel a bit sluggish.