Gs450 Race Bike

[Guest]

Hello, I am building an 81 gs450 to race AHRMA Vintage Superbike Light Weight. I have built other vintage race bikes but not a GS. At this point I am thinking of doing just the min. to get it on the track. Low milage motor(10,000) Check valves check for leaks head gasket etc. I have a Dyna S ignition I think can be modified to fit, 34mm Mikuni's and race exhaust.18in front wheel from a GS450s, better rear shocks, rearsets from a cbr929 which are amazingly almost bolt-on once the old brackets are removed. Stripped down frame, rotor, stator and starter removed. This build is pretty low budget, but I know the forks will need work or upgrading at some point(41mm max.)and maybe the swingarm. Any and all info concerning weak points, reliability issues, frame bracing etc. would be GREATLY appreciated Thanks!

[pete]

If you want the Dyna ignition on there, get the kit for the GS400 twins, but tell the guys at Dynatek you're putting it on a 450 and need the rotor spacer they provide with the kit for the larger inline 4's. Then it really will be a bolt on.

Can you shoot photos of the how the rearsets go on? And what year 929? In the back of my mind is thoughts of redoing my 450 once I get my Katana on the road and I'm still contemplating the idea of rear sets for it.

Sounds like a bit of fun to me!

[GregT]

If you're as cheap as me, you can make any Dyna fit with some work.

In my experience racing 450's they don't need frame bracing. Decent shocks, yes, fork work, yes. Just get your weight lower and up forward.
When you check the valves, I'd recommend going to around .004in inlet and .005in exhaust clearance. A bit more than stock doesn't hurt - and it will get hotter racing.

[herm744]

Very helpful info Thanks guys! I will post some pics as the build progresses. Not 100% positive till I double check, but the rearsets are 00-01 cbr929. I will post a pic once I have them mounted. Again Thanks!

[RichDesmond]

I'd at least though some good fork springs and oil in the forks, it will make a big difference.
We don't have any that will fit, but Race-Tech makes a 22mm OD spring that should work.

[herm744]

gadoots.jpg Getting stripped down for race prep. replaced swingarm needle bearings greased and adjusted steering head. Looking for a used pair of 34mm Mikuni round slides. Vintage Superbike are production classes that requires you use tank, side covers, fenders(can be trimmed or replicas), Seat pan(can modify and recover), headlight shell, instrument pods(speedo can be replaced with just a shell) from the original production bike. No handle bars lower then the top fork crown. No fairings unless original equipment. Year cutoff is 82' or "like design"

[herm744]

craigs suzuki.jpgHere is an example of one my friend just happens to be selling. I think this bike is still streetable where mine won't be.

[dorkburger]

Your friend's bike is cool! Good luck with your build, and welcome to site.
Where will you be racing?

[Steve]

[ATTACH=CONFIG]49314[/ATTACH]
I think this bike is still streetable ...

Yeah, you might still be able to ride it on the street, but you are limited to how far you can go by just one tankful of gas, because you can not stop the bike and get off anywhere except where you left your paddock stand.

.

[herm744]

Haha good point, yes you would have to put the side stand back on, tail light and headlight, and maybe the charging system and starter if it was removed.

[Buffalo Bill]

Nice and clean!
I would want lower handlebars, those are rather high and pulled back. I would only use those if I were riding la-di-da around town.
According to the rule, straight drag bars are legal and they would get your shoulders, arms down a few more inches and forward.
Best of luck!

[herm744]

Stripped down, frame still needs some tabs cut off I have a box of parts now of what was removed, must weigh 50 or 60 lbs. I should be able to save another 10lbs. with the exhaust changed. Plan is to cut 1.5" off the fork springs and make a spacer out of 1" pvc pipe to stiffen the forks and run some 15wt. fork oil. These forks take 150cc. I have changed the front rim to an 18in. They steer to slow with the 19. Swapping out the rear rim for an aluminum 3.00x17. Stock rear sprocket replaced with an aluminum one. I will need a toe guard for that buzz saw yikes. Cut the rear fender. Lightening the rear brake plate next. Redwing shocks for now, I have a pair of mulhollands that I am rebuilding I put them on everything pretty much, but you can run piggyback shocks in the class. Rearsets fit good, but still have to check clearance for the exhaust. The seat will be cutdown 1" still trying to figure the best way to do it. I have a ratty seat to try on. Stock ignition is shot still have to adapt the Dyna S. Found some cheap 34mm snowmobile carbs to try. and Got the drag bars .It will run total loss ignition, and the starter flywheel rotor and starter clutch and gears will be removed soon as I know it will start! Finally I need help getting the nerve to cut up a perfectly good front fender!suzuki2.jpg

[herm744]

race bike

suzuki1.jpgand the back

[RichDesmond]

...Plan is to cut 1.5" off the fork springs and make a spacer out of 1" pvc pipe to stiffen the forks and run some 15wt. fork oil. These forks take 150cc...

That will help a little, but the stock springs are so soft that cutting them down won't help much. If there's enough room in the budget a good set of springs (Race-Tech has the size you need) will help a tremendous amount.
If you stick with the cut down stock springs you'll need 1/2" schedule 40 PVC. Rather than use the stock volume, set the level to 100mm (stock springs) or 120mm (aftermarket). "Level" is actually the air gap, it's measured from the top of the tube down to the surface of the oil, with the spring and spacer removed and the fork leg fully compressed. Bigger number means less oil.
Ping me if you have any questions.

[herm744]

The only reason I did not want to spend much on these forks is because the class allows up to 41mm tubes. The plan is at some point to upgrade the whole front end with later model forks. However, when I pulled those stock springs out I didn't know they where so long and so many coils. There is no way to stiffen them enough without them binding up. I was wondering if there is a gold valve upgrade for these forks. Will check that out .Thanks for the info!