GSX750ET Race Build

[maxwin]

Update time...

So I upsized the forks to 37mm and installed some YSS cartridge emulators, did a bit of maths to work out the spring size, spacer length and oil level and must say I got it pretty close!

Here's the modified guts...

This one shows the tool I made for removing the damper rod, it's an M12 bolt welded to a broken 3/8's extension...

Blanked off the anti dive with an ally plate and removed the pictured ally spacer to allow proper function of the fork compression...

Finished article painted and stickered up

I found the new set up needed a lot more steering damper than before so repositioned the damper rod by making a new bracket...

And a pic of the bike as it stands currently

This is a bit of on board footage of my fastest lap at Donington at the weekend, unfortunately one of the coils popped on lap 4 so ended my race

Hopefully more to come

[Gammaboy]

2 hours ago, maxwin said:

Update time...

So I upsized the forks to 37mm and installed some YSS cartridge emulators, did a bit of maths to work out the spring size, spacer length and oil level and must say I got it pretty close!

Here's the modified guts...

Blanked off the anti dive with an ally plate and removed the pictured ally spacer to allow proper function of the fork compression...

The Alloy "spacer" you removed acts as part of a hydraulic bumpstop at full compression. If you drilled the damper rod above the step and keep the spacer you get the hydraulic bump stop and also the full functionality of the emulators.

[maxwin]

@Gammaboy Thanks for your input, though I may have been a bit blasé about what was involved in the rebuilding of these forks.

If you bore easily please ignore the rest of this post

I decided a while back that I would like to use the 37mm forks as they would be a little more rigid than the 35mm one's I had been using.  Originally all I was going to do was to clean them and renew the oil and remove the anti dive, but after doing all that I realised that the springs were too soft.  I looked at a set of new springs and it was when I was trying to calculate what spring I would need that the project started to snowball, I created the below spreadsheet to calculate spring, preload, and oil level.

I made the springs out of old progressive ones by cutting off the tighter coils and grinding the end flat, couldn't get it to work as a progressive.

The "spacer" is primarily there to direct the fluid through the anti dive mechanism, it may also act as a hydraulic bump stop.  But with this set up I need neither the bump stop nor the anti dive so its to the scrap bin with it!

The YSS PD Valves I have fitted control only the compression damping, as long as they are submerged in oil they work as they should.  They are adjustable but only if you remove them, which is a pain.

Rebound damping is controlled by a shuttle valve in the bottom of the stanchion, changing the oil weight adjusts the rebound.  Through a bit of trial and error and a few tubs of different fork oil I've found that 15w fork oil is about right.  Oil weight also changes the compression so I've had to adjust that several times.

I carefully measured the volume of the assembled fork using distilled water  and found that the oil level i needed to properly submerge the PD valve made the air pocket too small so I had to machine out the top cap to give me the extra volume for the fork to work properly.

Over the last 3 race meetings I have managed to set the forks up to a point I'm pleased with, using around 125mm of the 135mm available travel and the ride isn't particularly harsh.

Only thing I may do is to shorten the rebound springs just to give a little more extension on hard acceleration to cut down head shake.

Edited May 11, 2016 by maxwin

[Gammaboy]

Well, looks like you're all over it

I'm a bit heavier - so i'm running .95 springs and a similar cartridge emulator setup, my antidives are still fitted, but completely bypassed - only running 10w oil which seems to work for me - what fork tops are they?

[Jelly]

The fork modifications look really interesting. I have a set of 35mm forks mounted to a bike now, and have a set of 37mm forks (1100) for spare, which I could build as new. Where did you get the YSS Cartridge emulators? 

[maxwin]

@Gammaboy The fork tops started out life as these...

I cut off the wiggly bit, bored them out and tigged up the top hole. I fitted high pressure schrader valves to the tops as I had looked at pre charging but scrapped that idea.

Almost forgot, I also had to turn a recess into the side for an O ring because I scrapped the original seal.

 

@Jelly I got them on Eblag, here's the link...

http://www.Eblag.co.uk/itm/400838209197?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[Gammaboy]

I used a set of emulators from XS Mike - they're intended for 35mm forks so I had to machine up a stepped adaptor to go from the top of the damper rod to the bottom of the emulator, and one from emulator to the spring.

Interesting set of mods to the fork top - the schrader reminds me of the ones on my old RG500. Had contemplated machining off the wiggle and fitting screw adjusters, or just buying the ohno speed ones from webike. Actually contemplating binning the Kat frontend now - been struggling with a lack of front end feel even though the wear patterns suggest the damping setup is working well.

[Gammaboy]

solution to the rebound issue...

http://sportsvalve.com/sports-valve/

[Pete750ET]

On 1/30/2016 at 6:27 PM, KATANAMANGLER said:

Welcome. @Pete750ET used to race  the 750ET he might be along shortly to share wisdom.

Ask away. Funny that, my bike ran #230 as well

Edited June 8, 2016 by Pete750ET

[niknak750]

Ahh happy days, Is that Mick Bailey your harassing there Pete. You seemed happier on that bike than the 'Runt Racer'

 

[steelelc]

awesome mate how you finding earlystocks I've been thinking of racing a 250lc with them

[maxwin]

@steelelc Earlystocks is a great club to run with, very friendly atmosphere only one LC racing at the moment I think so get in!

Update coming, my Mrs and I had our first child in June so I have had a bit of time off, but racing again at Mallory on Sunday to blow the cobwebs out

[maxwin]

Update time!

For a while I've been threatening to make another more aesthetic seat unit for the bike and I finally got round to it.

Started off with some Cellotex insulation to rough out the shape, made a few last minute changes... 

next up was to lay clay onto the foam and craft the final shape...

Then a couple of day of arsing about with fibre glass and resin and da da!

I must say I feeling quite smug with the result

While I was glassing I also made the bell mouths for the carbs I designed an age ago, I wasn't expecting much but they leaned out the higher rev range enough to put a bigger main in!

The scrutineers have been getting less tolerant of baking trays being used as oil catch trays, at Donnington I was told that they would bounce it at the next meeting.

I purchased a belly pan from Mid Norfolk Mouldings that the racing Bandits use, the frame on the early bandit is similar to the GSX so I figured it would be a good fit.

I welded some tabs onto the frame and used 6 Dzus fasteners to secure it in place, slapped some vinyls on and boom!

Now the bad news );

Last Friday I went to an MSV track day at Cadwell just to get back into the swing ready for Sundays race at Mallory when on the sighting laps the old girl ate yet another big end bearing

Not to be defeated I spent Saturday swapping out for an old running engine I had laying around, despite having a serious perspiration problem it runs pretty well...

Out with the new and in with the old

It was all well worth all the effort and ear ache though as the Mallory meeting was a lot of fun, here are a few shots from the day...

Chillin in the paddock

3rd place at Shaws Hairpin, which I was pretty chuffed with.  James Fishers monster CBX in front.

And for all those who got this far here are the videos of the two races

Race 1, damp and quite slippy around Gerard's

 

Race 2, bone dry!

Thanks for reading, always a work in progress so more to come

[Captain Chaos]

that bike could do with some OSS stickers

[maxwin]

I do have some realestate on the belly pan, how do I get a couple?

 

[vizman]

2 hours ago, maxwin said:

I do have some realestate on the belly pan, how do I get a couple?

 

by continuing to do what you are doing, thrashing an oss and taking time to post it on here.....

 

....oh and by pm'n your address

[Gammaboy]

Hangon - are you running a GSX750 on the track without an oil cooler?

[maxwin]

@Gammaboy you are correct, no oil cooler.  I have been toying with the idae but its not a straight forward bolt on on yhe 750, need to mess about with the filter cover.

I have been checking the engine temp at meetings, never gets over 100 degrees. But when I start increasing compression and have more aggressive timing I think it will be a must.

[Gammaboy]

26 minutes ago, maxwin said:

@Gammaboy you are correct, no oil cooler.  I have been toying with the idae but its not a straight forward bolt on on yhe 750, need to mess about with the filter cover.

I have been checking the engine temp at meetings, never gets over 100 degrees. But when I start increasing compression and have more aggressive timing I think it will be a must.

Odd - the GSX750 motor my Kat had when I bought it had an oil cooler... Why not stick an 11 in it?

[maxwin]

The 750 ES does have an oil cooler if I'm right, but not the ET.  I'll stick with the 750 for now, more power means more tires and the cost of racing is high enough as it is

[maxwin]

@Pete750ET Hi Pete, sorry I missed your post above, you planning on making a return or can I keep the #230

Been getting some tuition from Nigel Lawrence  

Good job getting his bike back btw 

[maxwin]

Mini Update...

So I recieved my stickers, thanks alot btw, however I seem to have managed to stick them on upside down  

though it doesn't seem to matter in this image  getting me knee down at Shaws hairpin!

I have had a few problems with the front end which I've now solved (will go into detail in a later post) that coursed the crank case to ground hard enough to throw me off.

Bike all fixed up and had a full weekend racing at Cadwell with British Historic, managed to beat my personal best with a 1:53.1, still room for improvement.

Here is a video of the second race, speedo overlay was generated from the gps lap timer I have on the bike

more to follow!

[Pete750ET]

On 25/08/2016 at 6:00 PM, maxwin said:

@Pete750ET Hi Pete, sorry I missed your post above, you planning on making a return or can I keep the #230

Been getting some tuition from Nigel Lawrence  

Good job getting his bike back btw 

Only just saw your post.

Won't be making a comeback so you can keep #230 

Nigel will help you out, he knows GSX's inside out.
 

I had ail cooler on mine, still have it somewhere. Was going to put it on the road bike but don't think it needs it.

[Pete750ET]

On 14/06/2016 at 0:11 AM, niknak750 said:

Ahh happy days, Is that Mick Bailey your harassing there Pete. You seemed happier on that bike than the 'Runt Racer'

 

Yes Mick Baillie on the GPZ. We spent three seasons chasing each other, good times and some great racing.

The Runt was great but it was never the same after I destroyed it at Darley. 

Just got the 750 tuned to a point where it could run with the 1100's and got skittled at Pembrey on its first race in full tune state. Loads of damage and got injured again. Realised how much it cost so called it a day. Shame, as the 750 engine never really got to prove what it could do, although no 750 at Pembrey could get near it, so it showed its potential.

Edited November 8, 2016 by Pete750ET

[Pete750ET]

Here's the oil cooler. Uses a special adaptor plate to replace the filter cover.