|Lemans IV GSXR Front End Conversion
The biggest GSXR-Showa conversion problem is in the steering stem area. The GSXR forks and Guzzi LM IV forks are approximately the same uncompressed length. This is good...minimal steering geometry changes, etc. .
The steering stems are incompatible, though. This is the pain in the butt. You have to press both steering stems out of their respective triple clamps. This is no small task, as they're both shrink fits with about 8 thousandths of an inch interference. This requires a lot of force to dislodge, and it makes a big bang when the 10-ton press finally pops them apart. Be veddy veddy careful at this point. I take no responsibility for you lodging a steering stem through your skull.
I then substituted the Guzzi steering stem for the GSXR steering stem in the GSXR front-end assembly, and bolted the whole thing on the Guzzi. This required machining a small spacer to fit the smaller Guzzi shaft in the larger GSXR lower triple clamp hole. This was the easiest way to accomplish the conversion, as no suitable bearing was identified to make the GSXR stem work in the Guzzi steering head.
The Nissin 4-pots are de-linked. The stock Brembo front master cylinder wasn't driving the huge pistons in the Nissins too well, so I'm using a little bit larger Macgura master cylinder. It's originally for a '79 BMW R65. This works pretty well, and provides useable braking. I did this again, I'd try to find a littler larger (~16 mm) master cylinder that bolts right onto the LM IV controls like the Macgura did.
The GSXR front wheel is wider, and lighter than the stock Guzzi wheel. It worked very well with this conversion. It’s also about $600 less than an aftermarket Dymag. Be prepared to have to make wheel spacers on the lathe, though. Approximate cost (doing all labor myself, and using mostly used parts) was around $1400 for brakes, wheel/rotors, clip-ons, master cylinder and miscellaneous parts.
1)'92-94 GSXR 750 parts are what I used- The only thing that I'd really worry about is that the fork tubes' uncompressed length is the same between the Guzzi and GSXR. This maintains close to factory steering geometry, except for the 17” wheel and fork tube spacing. Spring rate differences? Who knows? I did zero testing on spring rate compatibility. The GSXR spring rates seem to work fine in the Guzzi, though.
2) I used the Guzzi steering stem, so the steering head bearings were the same as stock- I replaced the stock ones with common Timkens-they cost about $10 each from a local bearing distributor, and were cross-referenced by dimension with the Guzzi parts. This is much cheaper than through a Guzzi dealer. Again, I machined a spacer so that the Guzzi stem could be pressed into the GSXR bottom triple. I used about an .005" interference fit between the stem and bottom triple clamp. Keep in mind that I did this mod to a LM IV, which had a longer steering stem than other Tonti frame bikes. This shouldn't change much if you're using the stock 850T (short) stem- the head bearings are probably the same as mine.
3)I used GSXR triple clamps, clip-ons, front wheel, 4 piston Nissin brakes. All from the GSXR model. I used the Lm IV controls. The fork tubes are about ~54mm where clip-ons attach. if I were to do it again, I'd get GSXR Heli bars. They’re not that much more $$ than GSXR clip-ons, and seem to have more adjustment. Side note- one obviously racing-fuel-fume-addicted Japbike scrapyard salesman wanted to charge me $100 each for used GSXR clipons. “They list for $200 each”, he sez, “so I’ll take half of that”. Yeah, right- Caveat Emptor! The clip-ons are a bit much on long rides, unfortunately for my back and wrists. Also, I needed to bore the top triple clamp out a bit to stick the steering stem though it. No big deal.
4) I used a Macgura master cylinder from a R65LS because it bolted into the LM IV controls pretty nicely, and I wan't sure if I could clear the controls with a stand-alone Jap master cylinder assembly. Yes, brakes are de-linked, too. UPDATE: I’ve since hacked the hell outta the stock LM IV right hand control (for clearance) and added an 18mm master cylinder which is also a Macgura. The difference? I can now perform stoppies. Braking control is much improved with the 4-pot Nissins.
5) I was able to use the stock steering damper from the LM IV. It's cranked up so that its influence is significant. The handling on the GSXR-equipped LM IV is unmatched! Wider GSXR 120/70 R17 front wheel = *very* smooth steering transitions and lower profile 120/70 tires with stiffer sidewalls. If you're going to do the forks, I'd recommend the front wheel as well! I got a bit of a wobble with no steering damper during high speed and extreme maneuvers, so the steering damper is good insurance.
My costs: $200 for front wheel and discs. $450 or so for '92 GSXR 750 forks, triples, and axle. $20 to replace the axle that was bent when I received it (…and I don't *wanna* know how). Try the Rice Paddy in Columbus, OH as well. Tom is familiar with my bike, and helped me with parts. I know that they have wheels and they might have other stuff... Measure the uncompressed length of your fork legs- that's the only spec that I'd want to match between the Guzzi and jap forks. You can always move the forks up in the triples if they're an inch too long, too. Check Erico Motorsports.com - they might have a front end lying around, and they’ve always provided me good prices/service. I've seen GSXR stuff on Ebay as well. Just be careful that what you're buying hasn't been wrecked, as is the case with some (most?) Japanese sport bike parts...
The results: wider, lighter front wheel; better brakes; fully adjustable front suspension- compression and rebound damping and preload; stiffer front end, and it looks BAD ASSED. I also managed to decrease the ergonomics of the Lemans IV by using the GSXR clip-ons, but I got used to it.
It’s been over a year and a half and 10k miles on the bike since I did the conversion, and it’s stood up to the test of time. I’ve also moved to Los Angeles since the conversion, so my new test track is A.K.A. the Angeles Crest Highway. I needed to adjust steering head bearings at about 2000 miles, after everything bedded in. This took care of a slight weave that I was feeling at speed. If I were to do this again, I might hold out for a later GSXR (or Hayabusa!) front end with 320mm rotors, and 6-piston Tokico calipers. The later forks may have hardened sliders too. I dunno. Then again, I have to keep telling myself that I want to maximize my bang/buck ratio, which means forgetting about the cutting edge late model stuff and going with the 5 year old performance parts that are almost as good. Hell, I’m not trying to trim tenths off of my lap times or anything.
In all, I started out with a bike that the insurance company wanted to total after I got hit by that left-turning driver (thus necessitating a new front end). I made a little investment of time and money and ended up with a 15 year-old Guzzi that is a sheer joy to ride and passes many a modern sportbike in the twisties. Not bad.
OK. I’m getting sick of getting hit by left turning vehicles. It happened again. After two 40mph frontal impacts, my stock IV frame has had it. It’s bent, bowed, and broken. It now sits in eternal rest in the back yard of Moto Guzzi Classics in Long Beach. I replaced the frame with a later model EV frame. The later Tontis, like my ’99 EV frame, have an extra brace to the transmission, so they’re marginally stiffer. They also use larger swingarm pivot bolts, for whatever reason.
I used a 2001 GSXR front end with Titanium-nitrided fork sliders for the rebuild. I also used 6 piston Tokicos from the same year bike. The master cylinder is a 20mm Magura from a BMW K1100. I’ve used three of these master cylinders so far, and they all leaked. I had to order replacement pistons from Eurotech motor sports. It’s hard to find cheap master cylinders as large as these, though, so with about $100 into each including the rebuild, they’re worth it. Braking is effortless and brake feel is excellent.
There is little difference between the earlier GSXR forks and the TiNi deals. The later forks exhibit a bit less stiction. You also have to compete with riders of earlier GSXRs on ebay to get the TiNi deals as those guys all want to upgrade their front ends to the TiNi forks.
So, anyway, after mondo rebuilding, and a fresh paint job (courtesy of Mark Etheridge @ Moto Guzzi Classics), here’s what the mighty LM IV looks like. Also, here’s a drawing of the spacer that I used to fit the Guzzi steering stem in the GSXR triple clamps.
I really hope that this is the last rebuild on this bike (understatement of the year).