Topic: CB750 AHRMA Sportsman 750 Racer

[calj737]

Hey Matt - for the added frame tubes for rigidity, what tubing are you planning to use?

[slikwilli420]

Hey Matt - for the added frame tubes for rigidity, what tubing are you planning to use?

I have 0.75" x 043 wall for the downtube to frame rail and 1" x 065 wall for the others.

[calj737]

In my opinion, that’s overkill. Those tubes are for rigidity, and their length defines their strength in tubing. You can use much thinner walled tubing, and even smaller OD than the frame to save weight. Carbon tubing (1”) is nearly 3#/linear foot. CroMo is about 0.3#/linear foot in equal OD. Talk about weight savings...

You can easily TIG braze or TIG weld them in too for their purposes.

[slikwilli420]

Got any 1" thin wall stuff you would part with (sell)? Its pretty hard to find small pieces. 035 wall as you suggested for the front and one above the swingarm would be awesome.

[calj737]

If not today, then I’ll check tomorrow. I should have some 0.5x0.035 4130 in the rack. If not, I’ll order it tomorrow and ship some off to you. Total lengths of various pieces you’ll need? (I’d rather cut it to ship it for ease).

[slikwilli420]

Cal, it looks like I can get it cheap online, and I will order some more things for my brother's racer. Thank you VERY much for the offer though!

[Kstuhren]

Awesome thread!

I’ve been working for about a year and a half on a heavyweight 750. This is my first post as most that I read are older and this is rather current. I don’t know any of the unwritten rules of forums so if I’m out of place let me know. Is anyone in the Indiana area with connections to a decent machine shop? The cycle x heavyweight bike has a nice setup w/dual piston and large dual rotor. Does anyone know the story of what these components might have originated from?

[slikwilli420]

Awesome thread!

I’ve been working for about a year and a half on a heavyweight 750. This is my first post as most that I read are older and this is rather current. I don’t know any of the unwritten rules of forums so if I’m out of place let me know. Is anyone in the Indiana area with connections to a decent machine shop? The cycle x heavyweight bike has a nice setup w/dual piston and large dual rotor. Does anyone know the story of what these components might have originated from?

Welcome to the forum and AHRMA racing! Not out of line at all. Feel free to ask anything here as this is a great group of very knowledgeable guys.

As for machining, what services are you looking for?

Regarding brakes I would say find out what the rules say and get the very best suspension and brakes you can within the rules.

You should start a build thread in this section to document your progress.

[slikwilli420]

GPS hubs are ordered and will be here in the next few days. I will post detailed pics and weights for weight-loss crowd to enjoy. They will come compete with 25mm ceramic bearings which should keep them spinning happy and free for a long time to come.

I connected with a fellow AHRMA racer on some Borrani rims as well, which are substantially less expensive then from Buchanans, though I will still get spokes from them. They are coming direct from Italy and should be here by January.

Frame bracing as discussed earlier has been updated to 035 wall Chromoly tubing instead for additional weight savings (or is that just less weight ADDED?) vs the DOM tubing I was using. Once the frame is down, all of those will be welded, as well as the new tank mounting tabs I made to get rid of the Rube Goldberg of a mounting system I finished this season with.

Also cranked out a new rear engine mount and caliper mount as well, both rough water jet cut then finished in the mill.

[calj737]

Matt - Whomever is going to weld that CroMo for you, its best to use ER80S-D2 wire. 70S-2 works fine, but 80 has better ductility. A 0.45 gauge would be perfect too. He/you can buy a small lot of it, or if you want, I'll ship you some with the bolts.

[slikwilli420]

Matt - Whomever is going to weld that CroMo for you, its best to use ER80S-D2 wire. 70S-2 works fine, but 80 has better ductility. A 0.45 gauge would be perfect too. He/you can buy a small lot of it, or if you want, I'll ship you some with the bolts.

Cal, brush me up on welding, a .45 gauge?? Im not half bad with a MIG, but TIG is way out of my wheelhouse. I will let him know to use the ER80 instead of ER70 wire as well.

[calj737]

0.045 gauge wire. Mistype'ed that  Definitely want to TIG that thin tubing.

[slikwilli420]

Another big offseason project is a new oil tank. I noticed a lot of air getting into the oil and started to look around to see what I could come up with. I ended up finding the oil tank design from Captain and what he uses on his racer in Australia New Zealand, with a very effective air/oil separator built in. Using pictures he posted and some educated guessing, I have started to build my own. It will come in around 4.3 quarts or so and 3/4 full will get me right at 3 quarts, with another 0.5-0.75 quarts in the oil lines and cooler, I should still be above the stock capacity.

The air/oil separator as it sits now. All it needs is a fitting for the breather cap, an internal perforate tube, and some welding.

Next up is the outer shell, which I am going to flow form the end caps from some 3003 aluminum into a form I am making this weekend. Then I will form a strip around the profile of the end caps and make a provision for the cap and return separator. I will also add the baffle plate as Captain did. I am really looking forward to having this come together.

Here is the link to the original where I pulled my design inspiration:

http://forums.sohc4.net/index.php/topic,155235.0.html

Some pics of my progress

[calj737]

Will that flow-formed baffle get welded? If so, 3003 is practically unweld-able stuff. Just so you know-

[slikwilli420]

Cal, the whole outer tank will be 3003. Im confused why not weldable, since its what almost every aluminum fuel and oil tank for motorcycles is made out of, due to its malleability and weldability. References online indicated good weldability as well. Are you maybe thinking of another alloy? I know a bunch are not good to weld, but think 3003 falls in the good to go column.

[calj737]

Typically, you will see that material only MIG welded and its used in heat exchangers and the what-not. I would use 5000 series personally. It's really durable and well suited for exterior applications.

[754]

Pretty sure guys use 3003 on most aluminum car bodies  , tig welded and gas welded..

[gschuld]

3003 H14(half hard) is a very common material for making custom motorcycle fuel tanks since it forms into compound curves rather well.  Usually tig welded with 4043 rod. 4943 also works and melts a tad sooner. 

George

[slikwilli420]

I wanted to try my hand at gas welding this thing together as a learning experience. I have lot of 3003 I can practice on, just need to get some filler rod, flux and a small tip to give it a try. It will also keep me from going to my welder 10 times to get this whole thing welded. With a $20 minimum it will add up fast vs at least trying on my own.

[turboguzzi]

all you need to know

[slikwilli420]

Great video. I've seen that one a bunch of times. It's the one that always comes up when you search making motorcycle tank.

[bear]

. I ended up finding the oil tank design from Captain and what he uses on his racer in Australia,

Just a word on the quiet, Brent's a Kiwi and Kiwi's can get a bit narky if you tag them as an Ozzy.
Can't understand why.

[slikwilli420]

. I ended up finding the oil tank design from Captain and what he uses on his racer in Australia,

Just a word on the quiet, Brent's a Kiwi and Kiwi's can get a bit narky if you tag them as an Ozzy.
Can't understand why.

Corrected! It would be like being mistaken for a Canadian in America.

[slikwilli420]

Spent the day working on a pattern to do some flow forming for the end caps of my oil tank. The first one cracked since I didn't have all four corners locked down which I corrected with the second try. This took about 15 min or so to shape. I'm using an air chisel with the harbor freight bit I cut off and made a UHMW (hard plastic) tip for. It forms the aluminum so sweet. It only took a couple hours to make the form and get everything set. I'm going to make a smaller tip tomorrow and refine the shape a bit more then do the other side which will have a recess for the oil cap making it a bit more complicated. Overall really easy to do with a little time and planning.

[scottly]

Pictures, please.