Topic: Long time gone.................

[gschuld]

No please ....go on for hours....   l loving the info and I promise to pay attention..  I do recall you having used a longer swingarm.  I have a 1979 set of 45mm offset 35mm fork triples on their way already as they seem a popular option to have.

All balls bearings all around, including swingarm is in the plan.  Do you prefer the late cb750 fork sliders for the extra length or did you use something else?

Yeah I'm pretty sure the yoshi copy is a no frills carpy.  I'd consider making a hand bent yoshi exhaust at some point as I love that sweeping shape and I enjoy challenges.

What do you recommend regarding frame bracing?  I will likely be using the Avon Am22/23 club race tires in 130 rear 110 front on Borrani  shouldered 18" rims front and rear.  Should provide plenty of grip to expose other handling deficiencies.  I'd like to hear more about your improved motor mount system. 

I didn't know the front axle made such a difference.  Interesting.

George

[voxonda]

This is the frame I am using, the 1st gen sadly without framekit, do not want to destroy the powdercoating. You can see there is some bracing but nothing major. There is nothing wrong with these frames. Make sure the engine is mounted correctly.


The longer swingarm, in the other F2 frame whch I think is less desirable than a K frame.


The build of the swingarm.


Set of motormounts I used to make.

Rob

[gschuld]

Great stuff.  Thanks.  I assume that you would use a top frame kit to allow top end of the engine removal if starting over?  I wonder if the frame kit would have any effect on the upper frame stiffness.  I was hoping to talk Jaguar out of his Seeley frame but he is rather attached to it .  Starting with a k0 frame is just fine though and will help keep me from going too overboard on this bike.

George

[gschuld]

Hi George,


...I am giving my opinion based on my experience and expertise. There will never be a concensus about this. When racing a CB 750 K0-K6 a few things a bound to happen. You'll be weaving all over the place and when coming out of corner at considerable speed expect a terrifying speed wobble. Make sure all bearings are setup well, swingarm pivot and headstock. Tyres, the better they are the worse the bike tends to behave. Adjust spring loads, check alignment etc. Next step loose that swingarm, never found one to my liking and decided to build my own after the Dresda swings but stronger and longer. Mine is 40 m/m longer than stock. I use longer (360m/m)shocks (Koni). Trail on the 750 is too short, hence the prob's with wobbling and shaking. I use 45 m/m off-set. I use 18"front and rear. Use 35 m/m front from 1st gen DOHC 900. Much longer lowers which give more overlap. Added a stabilizer, but biggest improvement is a 20 m/m front axle. Makes the front much stiffer and the fork's tendency todeform under braking is next to zero. Another point for improvement is the way the engine is mounted in the frame, not good and under acceleration tends to move about in frame. Solve that and you'll have a safe and predictable bike. Could go on for hours but you have some to think about. Rob

Some questions.  Your mention of the terrible speed wobble coming out of a corner, this was referencing an unmodified factory cb750 setup correct?  I'd like to explore my options regarding the use of pre 1972 vintage parts.  Like the 970 kit cr750s were set up.  Twin factory disc/calipers, cr style fork brace/front fender, possibly CR style trees on 35mm forks.  I know better options evolved as time went on but I'm a bit stuck with an early vintage style I'd like to explore.  Do you see a reason why the early fork ends couldn't be machined to accept a 20 mm front axle? 
Does anyone know the offset on the cr750 trees offhand?

George

[bwaller]

The fork legs accept 20mm George, just need to change wheel brgs. to 20mm ID. It's a good point Rob and four stud fork caps would help too. Use a hollow axle while you're at it, stronger & less weight to boot.  I know you want to follow the early style, & that's fine, but you will give up some stability with the shorter fork legs. A quality fork brace is a must.

Trust Rob's logic, this is a guy who works methodically and it shows.

[gschuld]

Brent,

Thanks.  Good info on the front axle.  I am trying to learn all I can so I can evaluate what set of compromises I am prepared to make starting off.  Everything is a compromise compared to a full on custom framed, custom or super rare everything else race bike.  If I can put together something that could handle/brake well/safely regardless of overall speed in the early style/ early parts, I'd be thrilled.  FWIW, I have no problem custom making a very stiff fork brace for the early forks.  The reduced fork/slider overlap will still be a disadvantage in itself, I get that.  Early dual brakes will be less than ideal, even with custom brake pads with a race compound.

There is no way I will be competitive with the wide open USCRA heavyweight supervintage class without going ballistic on a build.  I feel that this would not likely be the bike to learn to road race on anyway.  So if I need to run in this class and not be competitive with the big dogs, running slower with a really vintage style racer tgat appeals to me aesthetically would give me some extra enjoyment.  Not set on this path yet mind you, but I'd like to explore what I prefer to do and work my way back to reality if necessary with an open mind.

I am stubborn, but a realist.

George

[johno]

George  ( and others)
I Started making some new pipes for my salt bike last week , wanted some smaller primary diameters, this presenting me with some challenges as I wanted mandril  bends but the pipe diameter I am using is 35mm OD  ( 32mm ID) which is a very rare tube in OZ and I combed the country looking for someone to do mandril bends to no avail.    So frustrated on the weekend I used the normal exhaust shop pipe bender which draws the tube and reduces one way about 1.5mm  and compared it on a flow bench at 10 inchs with a straight piece of tube......... guess what didnt make any difference to the flow numbers   so now I'm not stressed about it and will use the drawn machine     its for racing only so not worried about the appearance only performance  Plus if someone says anything I'll just tell em it steamboat punk retro man , totally hip cool , just like the new trend to not passivate or polish the welds on exhaust primary bends 
I'll post something when finish just to show you ,  hopefully they work better.......oh must sound horny as well.
ciao johno

[voxonda]

This weekend we did very well during the annual 3-hour race. What a cracking team!

[Old Scrambler]

Beautiful

2-Riders............slightly different style

I notice the vents on the front............any ram-air?

[gschuld]

Oil cooler inlet I think.

George

[voxonda]

George is right, oilcooler air inlet. Yep two riders, one 70 yrs old and one 24 yrs of age. Guess who is fastest..... But both lovely to work with, Tonny the older one has a wealth of experience and raced Honda's RCB Endurance racers and all. Multiple Dutch champ.

[bwaller]

Congratulations Rob, bet you're proud about now. How do the boys like the bike?

I'm not going to guess who's fastest because I know some 70yr. old very fast guys. 

[Tintop]

congrats Rob, bike looks great.

[Retro Rocket]

Excellent Rob..