Author Topic: CB750 AHRMA Sportsman 750 Racer (Read 171104 times)

slikwilli420 · « **Reply #50 on:** June 16, 2016, 06:40:01 AM »

That's an excellent point. Handling is overlooked more often than not especially by someone new to racing like me. I plan on a strong engine but not insane. The major focus will be weight savings which inherently helps handling. I will also invest in good shocks and options for gearing at each track.

gschuld · « **Reply #51 on:** June 16, 2016, 07:37:13 AM »

The three factors that seem to be the most important starting out are suspension, geometry improvements, and brakes. Unless all these are reasonably good and set up well, no weight savings in the world will overcome the lack of confidence problems the first three will saddle you with.

Most racing cb750s are leaning toward 30 to 45 mm offset trees and raising the rear with a factory length swingarm by using longer rear shocks(or add on extensions for normal length shocks). Rob (Voxonda) favors 45mm trees with a longer swing arm and longer shocks on his endurance racers.

Racetech springs and emulators up front, and good shocks(Works being the most popular)of the ideal length in the rear seems to be the go to setup. Brakes are highly dependent on the class(s) you run in.

It might be worth considering focusing on geometry, suspension, and brakes initially. Starting with even a dead stock motor definitely has it's advantages. Wider power band helps with factory gearing, and the more modest power could deter you from pushing too hard while you learn to be more comfortable at the track.

I'd much rather ride a good handling modest powered bike than a peaky high powered bike with so so handling. And frankly, the latter can be dangerous, especially for someone new to racing.

Adding engine power is easy(not necessary cheap though

)

George

bwaller · « **Reply #52 on:** June 16, 2016, 09:43:17 AM »

I thought it odd my ears were burning!. No hot shot here, just a guy like all you with a lust for racing.

These are all good points.

Definitely focus on a bike that's easy to ride. If it is then the fun factor is increased, and it has got to be fun. In my case it was a 2 or 3 year project. Without being ridiculous my plan was to make every part I touched... weigh less. If I could machine, build a new piece or remove weight from a stock piece or use a different part I had here, that was my goal. I really didn't buy "lightweight" except for alloy rear sprockets. I really enjoyed this part of the process so go for it. In the end though choose the right suspension & brake bits. Something evil handling is no fun to ride and doesn't instill confidence.

As mentioned take a good race school even if you have to rent a bike before yours is ready. Get your feet wet, learn from a pro how to read a track, how to pick out tip in points, brake markers, where the apex is. Again it helps with that "fun factor"

bear · « **Reply #53 on:** June 17, 2016, 06:09:02 PM »

I 'm not about to stick my nose in re; bike setup, I have no idea. ( I'm just a broken down ex sidecar racer)
But I do have one suggestion. Start a logbook now and log everything.

Cheers,
Brian

slikwilli420 · « **Reply #54 on:** June 21, 2016, 08:36:53 AM »

One of the biggest suggestions from everyone is to make suspension a top priority. With that also comes reducing unsprung weight. My focus will be on building the lightest wheels I can, but keep in the spirit of the period, meaning no billet hubs and stuff like that. The rear wheel is my main concern, since the drum is so heavy and even the early F parts are way oversized for the bike.

Can I use a front hub out back without fear of beating the trans up too badly? I was thinking front hub, de-finned, with an adapter on each side for a sprocket and smaller disc. The lighter hub with smaller disc and caliper will help greatly reduce the weight of the assembly and should contribute positively to handling, especially on rougher tracks.

Regarding suspension, it seems like a lot on here will go 1" over on the rear shocks to sharpen up handling a bit. What are suggestions for the rear? I will have a steering damper as well for stability.

754 · « **Reply #55 on:** June 21, 2016, 12:16:42 PM »

Billet hubs for dirttrack have been around for 45 years or more.., period correct stuff, also used on roadracers, hot street, dragbikes..etc

Check out Barnes wheels, A&A, Cheney..etc.. Look for used, save some bux, you can go knockoff or solid mount...

Haybus · « **Reply #56 on:** June 21, 2016, 08:48:01 PM »

Good call on weight and suspension. If you can go straight to the GL1000 forks I would. Just consult the rules carefully first. I will eventually head in that direction for a little more front end rigidity and easy of wheel removal. With only one front brake it won't be as big a deal, but two K calipers sucks for removal and lockwire. I started with stock length Works shocks, then immediately made 1.0", 1.25" and 1.5" extensions to raise the rear and reduce rake. Then swapped in 45mm offset triples from a late model K bike to correct trail a bit. Stiffest springs allowed for the 35mm forks and emulators. It chatters in the corners unless I'm on the gas. The rule is brake or gas, nothing in between. Good rule for an experienced racer, tough when you're learning. I moved up to the 1.25" extensions last time out and I felt pretty comfortable in the corners.

Alan

POPS 911 · « **Reply #57 on:** June 26, 2016, 04:46:52 AM »

Will any of these SOHC 750 be at VINTAGE DAYS at MID-OHIO for the big event this year, we are going to both the Road Race event and the FLAT TRACK race at ASHLAND , OHIO.

slikwilli420 · « **Reply #58 on:** July 03, 2016, 09:20:13 PM »

Well it's official. I have a set of wheels coming from a forum member for the bike. 18" front and rear aluminum hoops with lightened hubs. I guess this will serve as a build thread as well since I got such great encouragement here to give racing a try. It will be a process since money will be tight so now I need to be on the lookout for good used race parts to make every penny count.

gschuld · « **Reply #59 on:** July 04, 2016, 07:31:17 PM »

Good luck friend. Please keep us informed.

George

Bill/BentON Racing · « **Reply #60 on:** July 05, 2016, 04:21:52 AM »

Gluck, interesting build, that crank must spin up real quick! K. Bill

slikwilli420 · « **Reply #61 on:** July 12, 2016, 06:56:52 PM »

Gotta start somewhere and my brother and I have decided on wheels. Courtesy of livefast_dieold is a set of 18/18 rain gutters with lightened hubs. I will eventually ditch the massive cush drive hub and go with something much lighter with a nice tiny disc but for now is a quantum leap forward from stock.

Mid Ohio sent some nice bits our way like a $10 set of GL1000 forks and an aluminum tank that was from a go kart racer that will be flipped upside down and adapted for the oil tank. It is ridiculously light compared to the stock steel unit. I would guess that the tank and oil cooler would be less weight than just the stock tank.

What are thoughts on the oil cooler? I'm looking at Derale since I've heard of issues with Earl's coolers. Can't decide between the 10 row and 16 row unit.

bwaller · « **Reply #62 on:** July 12, 2016, 06:59:22 PM »

Consider a Setrab cooler. I went through two others before the Setrab and the quality is superb.

slikwilli420 · « **Reply #63 on:** July 12, 2016, 07:13:07 PM »

Quote from: bwaller on July 12, 2016, 06:59:22 PM

Consider a Setrab cooler. I went through two others before the Setrab and the quality is superb.

They make a really nice looking unit. What size are you running Brent?

bwaller · « **Reply #64 on:** July 12, 2016, 07:36:50 PM »

I'll have to check & get back to you!

Haybus · « **Reply #65 on:** July 12, 2016, 08:15:38 PM »

Brent is running a Setrab 50-113-7612. Uh, yeah, I stalked his thread and shamelessly copied him.

Alan

bwaller · « **Reply #66 on:** July 13, 2016, 05:54:27 AM »

What Alan said!!

MRieck · « **Reply #67 on:** July 13, 2016, 07:04:37 AM »

Quote from: bwaller on July 12, 2016, 06:59:22 PM

Consider a Setrab cooler. I went through two others before the Setrab and the quality is superb.

I think we talked about that Brent. I've been through some Earl's units myself. Earl's were good prior to foreign manufacturing.

slikwilli420 · « **Reply #68 on:** July 13, 2016, 07:12:13 AM »

Noted and dully noted! Going with known quality and getting the Setrab.

Mike, I might as well get to picking your brain despite a roller being priority one. For the engine, the tentative plan is the Dynoman 12.5:1 760cc kit and a cam that will work well in higher RPMs. What do you suggest for the head? I would like to go full Stage 4 but budget won't allow for that right now. My thought is a fresh set of Cycle X valves with springs/keepers/retainers/etc along with some porting from you to get more oomph from the high compression pistons and good cam. What level of port job would be a good starting point?

slikwilli420 · « **Reply #69 on:** July 13, 2016, 06:08:49 PM »

Got the oil tank that started life as a go kart gas tank. It's 1 gallon and can't weigh more than half a pound. Going to flip it over and hang it from the flange where the stock one went. It needs to have the filler welded up and moved to the other end. There is a nice sight tube on one side and the fitting where the fuel feed is well now serve as the vent. Once mounted I will figure out where the feed and return line bungs go since it will be run in line with the oil cooler.

slikwilli420 · « **Reply #70 on:** July 20, 2016, 11:44:18 AM »

What are thoughts on adjustable offset trees like these? I found these in Europe for sale, and it was stated that they were Spondon trees. I like modern ones but they are pricey compared to my budget and I love the look of vintage race parts. I would think these would be plenty strong enough as long as you had high grade bolts holding the parts together. For that I will probably use ARP fasteners.

These are the trees I found online

And the ones I designed up with 35/40/45mm offset

simon#42 · « **Reply #71 on:** July 20, 2016, 12:16:30 PM »

yes they are spondon yokes . very popular over here from the early 80's onwards . have used them on many bikes without any problem
they are not that light though .

bwaller · « **Reply #72 on:** July 20, 2016, 05:38:49 PM »

Hate to be an old poop, but just be sure you're within the rules before you pull the trigger.

slikwilli420 · « **Reply #73 on:** July 20, 2016, 05:45:40 PM »

Weight was a worry with me on these as well. I will review the rules but ahrma is set up so if it's not specifically forbid its allowed. That's straight from ahrma as well.

slikwilli420 · « **Reply #74 on:** August 09, 2016, 08:41:22 AM »

Still gathering pieces and parts to try to get a roller together. We will be using GL1000 forks will new Race Tech internals. For now, they are getting cleaned up, new seals and fluid just to start figuring out geometry. Once we get closer to a final weight (ours and the bike) springs can be ordered. We will also use the stock triple trees to start mocking up the geometry, as well as a set of struts in the rear to get trail spot on, then I can make the triple trees (adjustable or not) and get shocks ordered.

Fork legs after bead blasting and a once over with a gunsmiths wire wheel.
Front and rear will be getting hollow axles from a CBR600, which had 20mm rear axles. I will adapt the CBR rear to the front since the GL forks have 20mm holes and the wheels we picked up are already upgraded to 20mm bearings.

Regarding the starting system delete, pictures I have seen include a collar that keeps the crank oil spray hole closed off. Is that something that is needed as long as the cover is sealed.

Pic of what others have done (note the collar over the crank snout)

My setup is a plate with a hole and will have a similar crank snout cover.

My thought is as long as I have a gasket, there is no need for the collar on the crank to keep oil in since it would just drain back into the sump in the port at the bottom. Thoughts on this? Without that collar, I can narrow that side of the engine another 1/2" or more.

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Author Topic: CB750 AHRMA Sportsman 750 Racer (Read 171104 times)