Looking for a front end for a 750SF2 racer

G

Grunbay

New member
Location
Maine, USA
I have a track bike that has a Grimeca 4LS brake. I am interested in sourcing a replacement front end for this bike as I need disc brakes for racing. The track I race at rewards late braking! My current forks are from an unknown Suzuki model and have been modified to not accept a disc anymore. Thus, I am looking for information that would help me find a different front end.

The vintage class I race in prohibits fork tube diameters above 38mm, and no male slider forks. That narrows my search down somewhat. I can use a cast wheel as the SF3 had cast wheels.

Does anyone have any experience in adapting a different front end onto an SF? I assume that, given the class restrictions, I will be looking at a '80s vintage Japanese sport bike. I'm not afraid of a bit of modification to make it work.

My current yokes are Ceriani 38mm. I could use them in concert with replacement fork tubes. I don't really have a preference.

I could convert it back to a Ceriani front end, but would need to upgrade the calipers and discs. Also, Ceriani set ups are pretty expensive!

So, what works on the front of an SF???
 
Good news another SF to see the track.
For front ends, absolutely anything can be used. As you say you are able to do modifications yourself, find anything long enough that is for a similar weight bike. Modern front ends use bigger stanchions, anything 38 or less is generally for lightweight bikes. Go for one with teflon bushes to avoid the stiction inherent in earlier forks. That means probably?80s. Japanese bikes. Jap bikes of that era all used sliding calipers, so you will be looking at adapters to use twin pistons. If you have original SF 38mm triple clamps, be aware that they have offset angle, and so not neutral steering. Your biggest challenge will be setting up your dampers. That age conventional forks are most likely basic damper rod type, not cartridge. Either way people like RaceTech have cartridge emulators to vastly improve things, and if you do score a cartridge system they can supply replacement valving tailor made to your usage.
There are a couple of people on the forum with altered front ends who might share their experiences.
 
I guess I should have said, "Effective late braking"!!

I took the Grimeca apart and found some oil soiling on the shoes. I'm gonna get some race lining material and try the Grimeca again.

Meanwhile, I am still looking to graft on a different front end. The 38mm limitation seems to be problematic as this size was mostly used on dirt bikes and the length is wrong. Also, most dirt bikes don't have accommodation for two disks.

I see that the GPz900 from the early 80s used a 38mm fork tube, but it looks like they may be air forks - anyone out there have any knowledge of GPz900 forks?
 
Forget the Grimeca drum - you won't even brake late on the road with one, let alone on the track. I raced my SF1 in the latish seventies with a Yamaha 4 leading shoe monster from an old air cooled TZ racer. Very powerful but fragile (the cast iron drum warps and separates from the alloy casting). Even that faded on a street circuit with mostly right angled corners. They
re also worth a small fortune these days.

I've since had Ceriani 35mm disc brake sliders and Brembos, then an assotment of Japanese front ends with Brembo adaptprs and later Tokico 4-spots with adaptors. As you can see you can do pretty much anything.

If the GPZ is 38mm I'd think seriously about that. The 'air' will be air assist and those bikes handled very well, so they will function fine for your purposes. Again, make up adaptors and fit whatever brakes you want. You might find there is compatibility with Brembo discs (either the whole disc, or the cast iron outers that bolt on/off.
 
I used to have a GPZ900R. I don't remember whether it had 38mm forks but according to the attached PDF list it probably did (search for "Ninja"). The list will gove ypu a range of options for 38mm forks.

The GPZ wasn't known for front end problems so I guess the forks worked well enough. It had an anti-dive valve I think.

38mm Marzocchi or Ceriani disk brakes front ends are easy enough to find, and would be a simple bolt-on conversion on your SF2.

Grafting a front end from a Japanese or other bike might change your geometry (possibly different trail measurement) which will affect your handling for better or worse, and may require some machining of spacers or disk carriers, or both, depending what triple clamps and wheel you use.

Cam
 

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They won the Castrol 6 hour Production race the year they came out. Supost to be one of the first good handling Jap bikes.
 
Forget the Grimeca drum - you won't even brake late on the road with one, let alone on the track.
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Wouldn't entirely agree with that Quentin. We had to have drum brakes on our Sf's in the proddy class - I used a Grimeca 2x2LS front brake, but had it set up by a drum brake expert who fitted softer tips both ends of shoe, separated from a harder middle lining, then  the whole assembly skimmed to an exact fit in a lathe. It still faded - think Pembrey hairpin was the worst - but as the British bikes only had single discs it still was good enough for some good results. - Regards - Phil

 

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Piet set up my 750 drums and new shoes on his lathe.
I think we ended up with around 90 to 95% contact between shoes and drum.
 
phil37 said:
Wouldn't entirely agree with that Quentin. We had to have drum brakes on our Sf's in the proddy class - I used a Grimeca 2x2LS front brake, but had it set up by a drum brake expert who fitted softer tips both ends of shoe, separated from a harder middle lining, then  the whole assembly skimmed to an exact fit in a lathe. It still faded - think Pembrey hairpin was the worst - but as the British bikes only had single discs it still was good enough for some good results. - Regards - Phil
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Apologies ... I missed the 4LS preceding 'Grimeca'. I was thinking 2LS a la SF and SF1. I hated my front brake with a vengeance, especially once brother Lee had an SF2 with two-finger tyre screeching Brembos!

Phil, that setup would certainly get the very best out of the 2 x 2 and no doubt as good as you would get for that period. My Yamaha 4LS was a treat, but as I say, too fragile. Always depends on the track too.

I had a guy on a GPZ900R behind me on a very bumpy rural road that I know like the back of my hand and I was cranking - he must have had pretty reassuring handling to stay there. When we arrived at a T and pulled alongside he was probably a little shocked to see an early 70s Laverda 750 twin  :o But yes, those bikes were given well-deserved credit for their capable handling.

Grant, I think he already has 'stock' triple clamps so rake, trail etc should be no change if the fork length is close.
 
I was thinking 2LS a la SF and SF1. I hated my front brake with a vengeance, 
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Me too - I used it once at Mallory and nearly wiped myself and a bunch of others out at the hairpin - no stopping power at all by lap two  :o :o
 
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