Topic: CB750 AHRMA Sportsman 750 Racer

[Sam Green Racing]

What year motor and frame are you running at the moment ?

Sam.

[slikwilli420]

76 motor out of my F street bike. Frame is a 77k. I looked at my tank and don't have enough room to move the rails anyway but it would have been nice.

[Sam Green Racing]

76 motor out of my F street bike. Frame is a 77k. I looked at my tank and don't have enough room to move the rails anyway but it would have been nice.

I think you might be able to use the Auto frame like Dennis said but without having to do the alterations he mentioned.
I found all this out when I fitted an early K extended swingarm into my Automatic drag bike frame.
Mixing and matching is ok as all engines will fit into any frame as will all swingarms but that's where it can all go wrong.
The problems being, chain alignment and the left side shock mounts.
The later Fs and the Auto had a longer final drive shaft which required a cranked out left side swingarm arm and a longer spigot where the left shock mounts onto the frame.
I think you might be ok with the later K frame but I'm unsure about the early F motor. It's just a matter of measuring the spigot where the left shock mounts and the distance that the gearbox sprocket is out from the casing.
Tank fitment is then up to you.

Sam.

[Sam Green Racing]

My Auto.

[bwaller]

Hey Matt, hope you're over the long drive home. Tyler left Sunday just before noon and said the first hour or so was pretty sketchy on the highway.

Do you mind sharing what front caliper you're using?

[slikwilli420]

My Auto.

Killer auto Sam. If I had access to a frame I might consider it but for now I'll pursue the frame kit and see what I can get done.

[slikwilli420]

Hey Matt, hope you're over the long drive home. Tyler left Sunday just before noon and said the first hour or so was pretty sketchy on the highway.

Do you mind sharing what front caliper you're using?

Brent, the drive was a long one through the night but no major weather issues. Home safe and already itching for next year.

Front brake setup is a Grimeca caliper with SS brake line and the 12mm Brembo master. Cast iron rotor from RPE in Australia on a custom carrier. It works extremely well with the Ferodo race compound pads.

[Haybus]

If you need to adjust the valves don't you pull the motor and put in another one? Maybe I've been doing it wrong. 

[gschuld]

If you need to adjust the valves don't you pull the motor and put in another one? Maybe I've been doing it wrong. 

Spoken like a true masochist.

George

[slikwilli420]

Alright, so its the off season now but that doesn't mean its time for rest. I have been scouring the internet and researching all sorts of ideas on shedding weight from the bike (and myself) though I must admit that while the bike is dropping weight, I have not (yet).

I am taking unsprung weight very seriously this year and plan to check that box for good. I have taken some weight off the front rotor via some larger holes in the non-swept are of the brake pad and lightening between the mount holes. I have also removed the caliper mount lugs from the right fork since I can only have one caliper, its unnecessary weight (good for 4oz). My 7075 aluminum damper rods are also complete and good for almost 6oz of weight lost. The last piece up front is the hub itself, which is getting replaced with a GPS racing billet Barnes style hub with larger bearings.

Out back is where the real magic is going to happen. The massive rear drum is going bye bye in favor of a GPS racing quick change hub with 25mm bearings, a Ducati Monster rotor (going to get Swiss cheesed), Brembo P32 caliper on custom hanger, and a Brembo 11mm master cylinder with remote reservoir. I am really hoping to lose 10lbs or more with the new rear hub, which will make the suspension work substantially better.

I have also finished moving the belly pan up and out of harms way (dragged a mounting screw at Barber) and with the additional trimming needed and the loss of my steel extender plates, is now appreciably lighter.

On the adding weight front, I am putting tubing between the down tubes and frame rails as well as a tube between the front engine mounts and one with gussets over the swingarm pivot, which is getting some lightening thanks to a grade 5 titanium replacement.

All of the engine hanger bolts will be replaced with 7075 aluminum and Ti nuts as well, good for almost a pound in savings.

Any of my faithful readers will remember the engine I bought to run in 2017 that locked itself up before my first race. That engine is getting a full and detailed tear down and inspection, and will be getting a 4th over stock compression piston kit and cam from Cycle X as well as a ported head I picked up at Mid Ohio this year, which is complete with oversized Manley SS valves, which still needs to be checked out by Mike Rieck upon his recovery.

[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.

[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.

[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.

[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.

[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

[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.

[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.