Topic: CB750 AHRMA Superbike Heavyweight Racer

[SOHC4 Cafe Racer Fan]

I can get a Calfab from MotoGP Werks for less and there is a lot more process in one of those.

Why not get one of them and call it a day?

Doesn't make a braced on, and the standard ones are $950, though considering the processing that goes into making one its still a good deal.

Turns out that the arm needs to be pre-82 or new construction, so that leaves all the 90's aluminum ones out of the mix. I may end up with a box section with some bracing and that would be fine by me.

With the Canadian exchange rate, I got my CMR swingarm for less than that.

[gschuld]

Regarding a braced swingarm, is this interest more for a perceived need for extra stiffness over a non braced arm?

FWIW, Kenny’s VERY fast heavyweight super vintage racer used what looks like a dead stock factory cb750 stamped arm other than a few tabs removed.

George

[slikwilli420]

Im going to continue to explore building a swing arm. A jig does not need to be anything fancy and I can use a stock arm for the pivot and axle points. The 4130 chromoly material is around $120 and I have a few places that can weld something up. Again, just too hard to justify the price for a box section arm that is as simple to construct as that. Then I can also do some additional bracing.

As to a stock arm, they may be plenty strong, but they are ugly as sin and don't meet the need for this build. Stock parts aren't special and with this build, every piece will get attention, just as the other build did.

[Eddie747]

Awesome to hear someone is trying to run a sohc honda in heavyweight. I bought a 78 supersport to run in novice production next year with the plan to build it for heavyweight superbike over the following winter but I am getting the itch to just jump all in for next year. Sounds like you have a lot of the same ideas I do as far as chassis and suspension goes. Very interested to see what you come up with for a swingarm, I too have been exploring this and plan on using 1x2x.065 wall rectangle tube along with bracing where needed.

[slikwilli420]

Awesome to hear someone is trying to run a sohc honda in heavyweight. I bought a 78 supersport to run in novice production next year with the plan to build it for heavyweight superbike over the following winter but I am getting the itch to just jump all in for next year. Sounds like you have a lot of the same ideas I do as far as chassis and suspension goes. Very interested to see what you come up with for a swingarm, I too have been exploring this and plan on using 1x2x.065 wall rectangle tube along with bracing where needed.

Single cam Honda's unite! Glad to hear you are coming out to play. I was told the Honda couldn't play with the big boys in my class in sportsman and so far I think I've raised more than a few eyebrows. I thought about production as well but hate stock bikes do it would never have gone over for me. Even after going full tilt in sportsman with my build in gearing up for even more work here. I need to refine my skills but I build bikes to win and I fully intend to build such a machine for heavyweight. Better go start a project thread so we can follow along.

[slikwilli420]

Finally some pictures!! I know, I know, its only good with pics. Since I am starting at the front and working backwards, the front end has been the focus. The fork let with smaller axle hole is bored out and once I get the other broken down (needed to drill the damper rod bolt) I will get the legs off to vapor blast then they can go back together. Still trying to source some aluminum fork caps but so far Im getting nowhere. I tried the 41mm cap from my Thruxton but to no avail. I may need to have them made custom.

The big focus has been getting bearing adapters made for my Astralites to hold big 20mm bearings and rotor carriers that will mate with custom 13" ductile iron rotors.





Forgive the crappy paint as they were painted over that gorgeous hard anodizing, but its pretty bad, so it may just power wash off.

Im still looking for places to get custom rotors made. I found a race car outfit here in Michigan that can do them, but I am also exploring having ductile iron slices sourced and then cut out on the water jet. Going that route would mean needing to get them blanchard ground afterwards so we will see.

Waiting on MotoGP Werks to get the Spondon replica calipers done so I can figure out where the will mount given the size of the rotors and spacing to the fork/wheel. Once that is complete I can get the AHM-style triples water jet and can start finishing them at the shop. Here is a pic from Jim Sawtell of the ones he is having made. Too much coin for my blood but they give a great pattern to follow.



I also picked up a cut down SS seat from a forum member that I will be using:



I have also sourced an Auto frame and am having some special mods being done to that including having a supersport tank fitted to the frame rails. That should give clearance to get the valve cover off and at least to cam changes/adjustments. The frame will get a number of braces just as my other bike had, as well as relocated shock mounts as it seemed a very period mod in the day to get a more progressive feeling from the rear suspension. With custom shocks from Race Tech, there really isnt a way to go wrong here, so what the hell.

The oil cooler mount will also be pretty unique and of the period, being out front. I ordered a 10 row Setrab series 6 oil cooler to run up front. I should be able to get it mounted right under the number plate which will have the headlight bucket attached to it and have a nice clean package up front. Lines will run down the backbone with one returning to the tank and the other going down to the engine. This is one aspect of the bike I am really looking forward to. I have never seen a bike quite like what I am building.

[seanbarney41]

Nice snag on that seat.  I would have snatched that up if I had seen it!

[slikwilli420]

Still making small progress. The fork legs have been modified (one got bored out, other got a thin spacer) to accommodate the 20mm CBR rear axle. Spacers are made and ready. I had ordered 42mm OD bearings and went to bore the holes in my bearing adapters and guess what!? Hole was too big. So sending the 42mm OD bearings back to Microblue for some 47mm OD bearings (20mm OD, 14mm width) to get fitted to the adapters. Aside from that they are done and looking sweet!

I had a mock rotor made up in 13" diameter and while it fits and looks killer, may be a bit much. A pair of 12" iron rotors should be plenty of stopping power as I plan on getting really light with this one too. Here is the mockup with 13" rotor and the AP caliper Ill be using on the rear:



There is quite a bit of offset between the caliper mounts and where the caliper will actually live so caliper mounts will take some extra work over what I planned and will mount to the outside of the caliper instead of inside, which is no big deal. Hoping MotoGP Werks gets the Spondon replicas done soon so I can get them in my hands. They will look the part and provide the ultimate in 2-piston period correct stopping power.

Also picked up my oil cooler, choosing a Setrab again. This will have the mount tabs cut off the ends and fit into a bracket that will be rubber mounted under the number plate. Without tabs its the same width as a number plate and is in the perfect spot to grab a ton of air. I also went with their banjo fittings with -10AN threads.

Up next: bore bearing retainers for bearings, vapor blast them and fork legs, get bearings installed and figure center distance between forks, then I can get triples rough cut, as well as begin building the AHM fender mount to go with the integral fork brace. I am looking at the CB1100F fender from Air-Tech. Has a great superbike look and should look even cooled mounted up with the AHM fender stay, like this:

[simon#42]

the spondon calipers where not considered much good back in the day , most people swapped them for brembo´s which are lighter and work better .
if you have a look at some pictures of privateer gp bikes of the 70´s and early 80´s you will see lots of brembo´s and very very few spondons .

[slikwilli420]

the spondon calipers where not considered much good back in the day , most people swapped them for brembo´s which are lighter and work better .
if you have a look at some pictures of privateer gp bikes of the 70´s and early 80´s you will see lots of brembo´s and very very few spondons .

Was that more due to price? Brembos are about 1/3 or so of the Spondon calipers, and half of AP. What about them was no good? They are essentially an AP copy, but monobloc design. That design feature alone should bring a lot to the table over 2-piece designs.

[simon#42]

the originals were a monoblock design , but for some reason they didnt work well . i rode plenty of spondon bikes which i loved but the first things i took off them was the brakes ........then the forks which also looked great but were crap .

[slikwilli420]

the originals were a monoblock design , but for some reason they didnt work well . i rode plenty of spondon bikes which i loved but the first things i took off them was the brakes ........then the forks which also looked great but were crap .

Interesting...

[scottly]

What does the AP caliper weigh?

[slikwilli420]

I need to weigh one. I was going to compare to a Grimeca as well. The AP has 2 bolts holding the halves together, while the Grimeca as 2 m8 and 2 m10 bolts. With the Spondon being monobloc, Im guessing at least a bit less, though with its monobloc design, the front of the caliper is larger to accommodate the cap that seals the outside piston. The piston is where there can be strides made. Modern replacements for the AP are anodized aluminum, while the MotoGP werks Spondon replicas have SS pistons according to him. Would be nice to have an anodized aluminum version offered.

[scottly]

I weighed my rear Grimeca years ago at 1375 grams, but it may not be an accurate weight, as the brake line was still attached to the MC.

[slikwilli420]

I weighed my rear Grimeca years ago at 1375 grams, but it may not be an accurate weight, as the brake line was still attached to the MC.

I have a loose Grimeca and an original 3 rib AP caliper that I can weigh tonight.

[simon#42]

i will dig out a spondon caliper at the weekend and weigh that for you , from memory they were about 3/4 of a pound heavier than a brembo and similar to a lockheed

[slikwilli420]

i will dig out a spondon caliper at the weekend and weigh that for you , from memory they were about 3/4 of a pound heavier than a brembo and similar to a lockheed

I wonder whey the difference to the Brembos? Never been a fan of those, they look gaudy to me with the weird sideways mounting bracket.

[Tintop]

While I applaud your commitment to using unique, period 'type' pieces I'm not sure the 'Spondon' calipers are a better choice than Brembos (or AP for that matter).  Reason, your building a race bike, not a show bike and replacement parts need to be readily available.  Brembos tick all the boxes (multiple pad choices too), how easy, & who's pads & seals do the Spondons use?  I'd also stay away from the Grimeca if it is the one that looks like a Brembo F08 copy, seal kits are NA, although I have done them using pieces from different kits ($'s).  Just finished doing some Brembo P108's, & BIT P108 copies.  Parts in 24 hours from my local bike shop.  My .02

[scottly]

While you guys are weighing the calipers, break out the calipers and check the piston diameters. Pad shape and area may also provide clues as to performance variations.

[RAFster122s]

Was it understood in the 70s the MC ratios that Vintage Brakes recommends for various caliper piston and piston sizes? I imagine it was but there may not have been enough choice in MC to overcome or assist the caliper doing its job well. ??

[bwaller]

Lot of truth here David, there wasn't a huge selection of options in m/c's. It was trial and error.

[slikwilli420]

I agree with you Tintop in that spares are going to be of importance. The AP calipers have a robust spares list and are fairly widely available. The Spondon replicas from MotoGP Werks will probably be harder to get spares for, so I will get some with my initial order. Chris's reputation precedes him and I have no doubt about his claims of the capabilities of his replicas. To take on a project such as replicating a caliper like this is monumental, and I believe he would not have done it without the confidence that he can build a superior product.

As to MC choice, I agree things have come lightyears from the 70's. I have to believe that the adjustable ratio master from AP is the zenith of technology for the period and even today in terms of period parts, which is why I am using that very master on my build.

I definitely need to get more information regarding the spares list from Chris, as well as pad choices. Given the wide range of choices for the AP units, I will have to at least be able to get the Ferodo race pads on the open market to make it really worth while.

[RAFster122s]

Vintage Brake(s) carries Ferodo in lots of race spec compounds and are a go to source I think you should look at... It would behoove you to not at least talk with him to see if you can find a near optimum solution in compound since you are spinning your own combo of discs, caliper and MC with vintage and modern repro solutions in keeping period correctness.  It is fun following along watching and hearing your plans and stuff you are gathering for the bike.
David

[RAFster122s]

BTW, anyone ever take a modern rotor's disc and build their own carrier? Maybe converting a floating design to rigid give floating wasn't on the scene in the 70s , (was it?) ??  Maybe even buying the rotor from EBC, etc directly without the carrier. Might be less expensive than having your own made if you can come up with a solution that way?  Or, is a floating disc not going to play nice if trying to make it a rigid disc?  I don't know, just thinking out loud and pondering the expense and effort involved in custom rotors.
But, you may need a custom solution for your Astrolites.