Topic: CB750 AHRMA Sportsman 750 Racer

[seanbarney41]

I also found that chart to be in conflict with what everybody else seems to find in the real world...still totally confused on the subject...have just been grabbing the easiest available mcs and if they work? ...use em.  I know there is something more here.

[bwaller]

Don't argue with Mr. Morse, he knows his stuff. The chart offers very predictable results. Originally on my street bikes with dual stock calipers I went the usual route with a modern 5/8" masters and the things are absolutely wooden feeling, it's a good description.

Although I thought the brakes on those bikes were great.....not so. It wasn't until I talked to Morse and bought a brand new 12mm Brembo for $100 (for my race bike) that I knew what he meant. The smaller master offers some lever travel which in turn gives great "feel". Short travel gives very little. I'm a two finger braker and even with small 275mm CB550 rotors never need more.

[scottly]

It appears that an opposed piston caliper should be considered as a single piston for the purposes of the ratio, as each piston is essentially pushing against the other with equal force? The opposed pistons would actually have more "free play" in the lever than a single piston just to move both pistons from the retracted position into pressing the pad against the rotor.
When I first took the Seeley for a test ride, it had a dual 38mm/14mm combo, along with iron rotors and Versa pads of an unknown compound. I pulled out onto a road with a 45 MPH speed limit, and accelerated through the gears briskly, until I realized I was rapidly gaining on the slower traffic ahead of me. I rolled off the throttle and applied the rear brake: it had no affect. I pressed harder on the pedal. Nothing. If you've ever had the experience of a brake failure, you will understand the feeling that the vehicle is actually accelerating.
My reaction was to grab a heaping handful of front brake lever. Mind you, the bike I had at the time was a Yamaha TX750 POS, and a handful of front brake would have been much gentler: I smacked the top of my helmet into the back edge of the windscreen, and I think the rear tire may have come up off the road. I learned to use only one or two fingers for normal braking, and maybe three for panic stops.  

[slikwilli420]

I am leaning toward going with the 12mm master based on the ratio chart, but may have a rebuilt stock master ready to go to play with and see what I like best. RPE recommends either organic or sintered pads with their cast iron rotor, so I will need to do some research there. More to come as that part of the build gets more attention.

[slikwilli420]

After attending the Race Tech seminar at Barber, as well as having a lengthy conversation with a tech at Ohlins, I am trying to decide which shock to choose. Race Tech and Ohlins will run similar pricing, in the $800-1000 range. Both offer a high degree of adjustment, so are really top choices.

When speaking to Ohlins, the tech was confident that one of their shocks could be adapted to the offset clevis of the CB fairly easily, provided I could make offset clevis adapters, which I can.

In the pits this weekend, I saw a lot of Works and Ohlins, but very few bike with Race Tech shocks and am not sure what to make of that.

I am willing to pay for something I can grow with, and most mid-tier shocks are emulsion type which I am looking to stay away from, hence my gravitation toward Race Tech and Ohlins.

[simon#42]

i am slightly biased but if you go for ohlins you do get access to a world of support and information that only showa could possibly rival .
years and years of experience at the highest level of motorsport .

[turboguzzi]

this is how i sorted it out in my 500/4 racer

quite easy to do and gives you total freedom to change height & shock angle

only new 4mm alu triangles needed

[slikwilli420]

this is how i sorted it out in my 500/4 racer

quite easy to do and gives you total freedom to change height & shock angle

only new 4mm alu triangles needed

Thats pretty slick. That would also allow me to run eye/eye shocks without offset clevis mounts, as well as easily adjust shock angle with the stock swingarm arrangement. I'll have to keep that in mind. Any thoughts on Ohlins vs Race Tech?

[turboguzzi]

dont have direct experience with either, but guess it's a bit like asking whats the better car, bmw, mercedes or audi...

all will do a decent job taking you from place to place

here in italy i hardly see any ohlins on twin shockers, race tech's not even sold, some really fast guys on koni/ikons, bitubo, Gazzi, none of them very blingy.

ask yourself if youll know what to do with all that adjustability....

as a minimum, a supplier at this price range should give you free spring exchange so you can find the best rate for you.

unless you are super good, spending that kind of money on track coaching could be more cost effective

[754]

Did you weld on a small bushing for that rear bolt ?

[turboguzzi]

Did you weld on a small bushing for that rear bolt ?

yes, a long M8 nut actually

[slikwilli420]

So after talking with a handful of mid- and high-end shock companies, I have decided to go with a full Race Tech package, front and rear.

There are a few reasons for this. One is that they are made in the stats by a company who is at every AHRMA race event, so service will be a non-issue, but also that they offer front/rear setups which should make any changes easier to discuss with them. They also wrote an excellent suspension theory and setup book, which I will reference throughout my setup. Ease of service was one of my big hangups, since many other companies, while they make nice products, may not be easy to get serviced in the US.

Ohlins proved to be a little more than my budget could bear so I ruled them out, leaving Race Tech and Works as high-end, US based outfits. The lack of information on the Works website threw me off a bit as well, whereas Race Tech has so much information, its almost overwhelming, but in a good way.

Once I scrape the cash together I will get the package ordered from them.

In the meantime, I finalized the design for my rotor carrier. I like designing parts and thought it fitting to have a custom carrier for my new RPE cast iron rotor.



I have also had a set of mockup trees made, in 45mm offset for the spread I need for my application. The cost was minimal and now it will allow me to plug in real numbers from a physical bike rather than calculating fork lengths and wheel diameters, and risking screwing something up. I used a piece of square steel and made a clevis to mimic a rear shock in my intended length, 14". This will allow me to have the frame on its wheels with front suspension in place and a mock rear shock to get very accurate measurements for rake/trail, so I can then finalize a design of the trees, including the offset.



Last is the gussets for the frame, which have come back from the welder. Pretty please with the job he did on these as well as welding the "U" where the downtubes meet.



The tank is being derusted by a local place and should come back squeaky clean inside and out, which will allow me to see how bad the rust was inside. Hoping it isnt too terrible and a quick lining (Caswell's) will work.

Thinking ahead to colors and want to do either a flat orange or blue. I will probably use a duplicor or similar color, but was looking at Eastwood 2K matte clear for the finish to make it gas resistant. What is the finishing after spraying matte clear? Can I cut down the orang peel by wet sanding or will that ruin the matte finish?

[Haybus]

I really enjoy watching your progress. How many AHRMA races do you plan to attend next year and will you campaign any other local series?

Alan

[slikwilli420]

Ideally would run at Gingerman in Michigan,  Road America and Barber. I might try to hit Mid Ohio and Grattan, Michigan with the WERA guys just for more track time. That's an awful lot for the first season so I'll need to play it by ear, and wallet.

Glad you're enjoying the progres. This has become a really fun build so far.

[Haybus]

Barber, sigh...someday. Definitely a bucket list trip. Planning to run Utah next year (formerly Miller). Barber would take running Sonoma or Willows (or both!!) and Utah in order to qualify. Perhaps 2018.

[slikwilli420]

Finally finished machining the mockup trees to accept a stem I had laying around, as well as a spanner and top nut from the original GL trees. Now that I have a front end together, I can add the rear wheel and get some measurements for Race Tech to build the shocks. At the same time I will be able to play with position of the forks in the trees and get an idea of final offset measurements for the real triple trees.

Bike on the bench



Rotor carrier fresh from the waterjet shop


Oil tank mounting






Overall everything is going pretty well and I have not had any hiccups yet, but I can't imagine that will last long.
 
A little bit more work is needed to get perfect alignment of caliper and rotor, which will be done by revising the caliper mount and reducing thickness of the rotor carrier, which will center the rotor in the caliper groove better and give slightly more clearance between the outside of the rotor and caliper groove.

37mm Woodcraft clipons arrived as well. I chose these because of high quality as well as a 2-piece design which allows removal of the clipon without removing the top triple tree. Easily replaceable bars is a nice feature as well, since 7/8" aluminum is readily available and I should be able to make up spares easily in the event I bend one.

Beyond frame setup and geometry, I will focus on mounting the seat and building an electrical system.

[bwaller]

Good work on the triple clamps, that will remove any guesswork. Waterjet?? what's wrong with eyeballing & handtools! 

I switched to 2 piece Woodcraft for this year and they are very good. I still need spare bars so if you're making extras keep me in mind please.

Keep it up and you'll be ready way before you need to be.....something that doesn't always happen!

[slikwilli420]

I love the water jet process. It's much cheaper than CNC milling and the guy I work with had no issue with one off parts or prototypes like the trees. It also let's me be creative but then not have to work so much getting a finished part.

I will get sine 7/8"aluminum tubing to make spare bars. No issue making a few more to send your way.

I will ideally be ready for the home track rave in South Haven, MI in June where I can take the road race class then race that weekend.

[540nova]

May I suggest going with steel for the bars, if you have any plans on drilling them for controls? Much more forgiving.


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[slikwilli420]

May I suggest going with steel for the bars, if you have any plans on drilling them for controls? Much more forgiving.


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Forgiving in what way? I wont be running any stock controls, so locating pins will likely not play a role. I may use roll pins to keep stuff from twisting like the throttle housring. Most guys just drill through both walls of the aluminum tube and drop a roll pin through, flush on one side, protruding on the other for locating controls.

[turboguzzi]

hei slik, what's the swingarm on the bike on the right? stock or custom? need one....

[540nova]

May I suggest going with steel for the bars, if you have any plans on drilling them for controls? Much more forgiving.


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Forgiving in what way? I wont be running any stock controls, so locating pins will likely not play a role. I may use roll pins to keep stuff from twisting like the throttle housring. Most guys just drill through both walls of the aluminum tube and drop a roll pin through, flush on one side, protruding on the other for locating controls.

On my build, the control wires and sheathing required a sizable hole for internal wiring. I wouldn't have felt comfortable drilling such a hole in aluminum. A locating pin hole is pretty small by comparison.


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[slikwilli420]

hei slik, what's the swingarm on the bike on the right? stock or custom? need one....

TG , that is a dresda copy made my member Voxonda. It was set up for the F model as well so it was a natural choice for my project. The fit and finish are excellent. Have to message him to see if he still makes them.

[slikwilli420]

May I suggest going with steel for the bars, if you have any plans on drilling them for controls? Much more forgiving.


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Forgiving in what way? I wont be running any stock controls, so locating pins will likely not play a role. I may use roll pins to keep stuff from twisting like the throttle housring. Most guys just drill through both walls of the aluminum tube and drop a roll pin through, flush on one side, protruding on the other for locating controls.

On my build, the control wires and sheathing required a sizable hole for internal wiring. I wouldn't have felt comfortable drilling such a hole in aluminum. A locating pin hole is pretty small by comparison.


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Since there won't be any wiring at the bars that shouldn't be a concern.

[calj737]

To your question about paint finish and matte clear... If you wet sand the clear to remove the orange peel, you will change the luster of the final finish. I did this on my 550, but still was quite happy with the result as it left it not glossy, but rich in color.

I see no issue with using alloy bars and drilling holes in them. In fact, I use LSL bars in a few of my bikes (aluminum) and run wires (smaller than stock CB controls) with zero ill effects.