Topic: CB750 AHRMA Superbike Heavyweight Racer

[scottly]

It will definitely be rubber mounted somehow.

Do a search on McMaster-Carr for "vibration control mounts"; might give you some ideas...

[RAFster122s]

Volvo 240 used a pretty durable utility bushing on the Volvo 240, 740, 940 series that has a metal collar built in with a phlange of rubber on one end to serve as a stop in the mount. They were used on most accessories mounted on the block such as power steering pump, alternators, etc. OD is prob CLO to 19mm with M6 bolt. They could be shortened for your needs.

[MRieck]

Matt....the oil cooler looks good. The only comment I have is can you use rubber bushings etc at the mounting points? I have had the Earl's units crack from vibration.
I also noticed the primary tubes on Hyde's bike. Looks like a variation of Micron's "Serpent" pipes from the late 90's.

It will definitely be rubber mounted somehow. I won't use earls coolers based on reports of cracking. I use Setrab coolers. Competitively priced and made in Sweden. The stepped header on Brent's bike is awesome. Moto gp werks makes them like that for the 550 but won't be doing them for the 750 which is a huge bummer.

I have to post a pic of a 900RR pipe I have that was made by Mark McDade for Erion Racing. This pipe was not available to customers. Team LaBelle also used McDade's pipes.

[Tintop]

Exhaust pipes with the dia. step have been used in Formula Ford for decades.  Don't understand all the science behind it.
http://www.britishracecar.com/MarkWeatherup-Crossle-35F/MarkWeatherup-Crossle-35F-BI.jpg

[gschuld]

That header looks to have both a step up in diameter along with an anti-reversion piece between them as part of the deal.

Fancy😎

George

[MRieck]

Hyde's primary pieces are interesting as the are "flattened" with a larger horizontal cross section. Nothing really new there but I don't see it it to many bikes except MotoGP etc. Like I said Micron marketed pipes like that for the street about 20 years ago right before they went out of business.
 The McDade pipe I have is very tapered  with 4 sections on the primary pipes. 4/2/1 design and that thing worked!

[MRieck]

That header looks to have both a step up in diameter along with an anti-reversion piece between them as part of the deal.

Fancy😎

George

I remember Tintop using some anti reversion pieces in his sidecar. Didn't go so well but there where other things going too.

[slikwilli420]

Just picked up a MotoGP Werks 4-1 from a member. I didnt need to spend the money, but the perceived scarcity of their items for the CB's made me pop on it. Ill get back the base price if I decide to sell.

Thinking forward to the rear (haha) and while I was planning on using my Calfab from my Sportsman 750 bike, I want something different. I will use the Calfab on a street project so it wont go to waste, but only if I can find something that will work here.

I really like what Jim Sawtell from JESBuilt is doing with braced arms for the DOHC bikes. I know those bikes have longer arms so its easier to find donors, which brings me to the issue at hand, finding an aluminum arm that is the same length as a stock CB750 arm.

I see monoshock conversions using CBR and ZX arms, but those are 3-4" longer than stock, so no good for a bike I need to handle properly.

Is there anything out there in aluminum that I could start with? Used crotch rocket arms are $50-75 all day long, and with some well planned mods, I will be in a few hundred for a complete and updated arm.

[calj737]

Is there a reason you don't use the 550 arm which is 1" longer? Or an ally arm based off the 550 length?

[slikwilli420]

Is there a reason you don't use the 550 arm which is 1" longer? Or an ally arm based off the 550 length?

Didnt want to go any longer than what I already had. Is there an alloy arm that is 550 length? 1" probably wont kill me, but longer than that is out of the question.

[gschuld]

Matt,

I’m curious as to what you are after swingarm wise.  Weight savings?  Better axle bearing as opposed to factory style bushings? Tire clearance for wider tires?  For a reference, the pic below is of 3 swingarms without axles or adjusters.



Factory K model on the bottom, a vintage 70s Dennis Curtis (CMR) custom cb750 arm, and a mild steel Carpy Dresda “copy” arm.

As you can see the factory arm is lighter than both of them.

Aluminum arms are generally comparable weight and stiffness wise to high quality 4130 or similar steel arms.  Aluminum is lighter, of course, but requires more material to make up the needed strength.  Basically it is a wash.

I’d hate to see you spend untold hours modifying a modern aluminum arm to end up the same weight and stiffness as a quality steel arm made for a cb750.🤔

Id think an arm like CMR makes would be about perfect for you.  Like the one he made for Brent Waller.

George

[gschuld]

Brent’s CMR (Dennis Curtis) arm, FWIW

George

[RAZZ]

Hi

I have an old JMC braced superbike swingarm (not for sale) i was trying to find one for you online, but no lock, but i found Thise from germany : http://www.krueger-junginger.de/html/exzenterschwingen.html

Maybe some thing to look in to?

Here a pic of a JMC swingarm i found online



Sent from my iPhone using Tapatalk

[slikwilli420]

Partly because I want something that looks the part, but not sacrificing function, I hate stock parts, and I like unique. The CMR arms are awesome, but I would never spend what he charges for them, no matter how good the work is. I can get a Calfab from MotoGP Werks for less and there is a lot more process in one of those.

The ones Jim Sawtell does check all my boxes. It does need to be similar length though unless moving the pivot isnt that big of a deal.

[754]

 Moving pivot on an aluminum arm is a big deal. Heat treating is pricey..

[slikwilli420]

Moving pivot on an aluminum arm is a big deal. Heat treating is pricey..

But adding to it isnt a big deal? Were all these OEM arms heat treated?

[livefast_dieold]

I would stay away from the eccentric chain register. There are a few people here using the Bimota replica swingarm that complain that under power it turns around... And I guess you will be in the same power range to have to deal with it.

There's a late 70s/early 80s suzuki 1000 model that has an aluminium swingarm, a guy in my class is using it with a 150 wide tyre, but he's racing a big bored (to 770cc) cb650 so having a longer swingarm is not an issue

[slikwilli420]

I would stay away from the eccentric chain register. There are a few people here using the Bimota replica swingarm that complain that under power it turns around... And I guess you will be in the same power range to have to deal with it.

There's a late 70s/early 80s suzuki 1000 model that has an aluminium swingarm, a guy in my class is using it with a 150 wide tyre, but he's racing a big bored (to 770cc) cb650 so having a longer swingarm is not an issue

Yeah the eccentric adjusters look cool, but can change the geometry of your bike. Someone at my skill level wouldn't notice, but never felt great about that style. GSXR1100 arms seem to have a long parallel section out back where you could move the axle adjusters up to get the proper length arm and restore geometry/handling. Still unsure if OEM aluminum arms were heat treated. I have a hard time believing OEM's would have gone to all that extra trouble in that era, but maybe Im wrong. If I am right, then modifications to such things would be much easier.

Here is one on eBay that would be awesome braced up:

https://www.ebay.com/itm/Suzuki-1991-GSXR1100-GSXR-1100-5-22-SWING-ARM-SWINGARM/132674079618?hash=item1ee3fdcb82%3Ag%3ABP4AAOSwgTJbJBaR&_sop=15&_sacat=0&_nkw=gsxr1100+swingarm&LH_ItemCondition=4&_from=R40&rt=nc&LH_TitleDesc=0%7C0

Move adjuster blocks and space/shorten pivot if needed, and add bracing.

[livefast_dieold]

It's from a Suzuki GS1000E (1978), check this thread: http://www.xs650.com/threads/gs1000-aluminum-swingarm.16593/

[slikwilli420]

My brother is running one on his GS750. They are a fair bit longer than a CB750 arm, but if you could move the axle adjusters forward some that would really help. Still need to know about heat treating.

[754]

The Suzuki ones with twin shock mounts are often used. I think Kawi Zephyr used twin shock with eccentrics.
 One advantage of the eccentrics is height adjustment,

 Stock aluminum arms  should be heat treated, it's about 50 per cent stronger.   Should be done before machining certain features.  Modding them, some stuff you can get away with.

[livefast_dieold]

I think Kawi Zephyr used twin shock with eccentrics.

Got one of those from ebay a couple of years ago, I sent it back, it was massively heavy

[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?

[slikwilli420]

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.

[Tintop]

The Calfab arm without bottom bracing was available pre 82, I had one on my 81 CB750F DOHC.  That said, Brent has had a lot of success with a CMR arm, and Denis has made an RCS 1000 replica arm.