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Fzr Suspension Expertise?


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I chatted with my friend Jeff about this and he suggested posting the question here for some ideas.

 

One of my track bikes is a 1989 Yamaha FZR400/600 hybrid. At around 100mph I get some pretty constant vibration / shaking in the front end that gets progressively worse as you increase speed. I also have some interesting uneven wear patterns on the rear tire. The rain grooves in the tire are becoming raised on one side and lower on the the other side almost like a car tire that desperately needs rotation.

 

The problem that I have is this bike is a bit of a oddball and I'm not sure how well many of the suspension places can deal with it. Here's what I have done so far. The 600 front end swap is pretty common for the FZR400/600 hybrids and has been done by many other owners. All of this work was done before the bike was taken to the track so I have no idea how well my original parts performed at speed other than some road riding.

 

- Rebuilt FZR600 forks with the sag shims correctly cut for my weight. These are the old school style. No external adjustments. The rebuild is about a year old.

- FZR600 Calipers.

- FZR600 Rotors. (originals warped on my first dry track day and they were replaced with EBC contours)

- Rebuilt Fox Twin clicker set to track defaults listed in the manual with sag set correctly. I did make some adjustments to stiffen it up slightly as I was having a rear end "squat" issue under heavy throttle. Rebuild is about 6 months old at this point.

 

I did most of the front end work myself and it's all been checked and double checked and there's no bolts or parts that are loose in the front end. Jeff suggested looking at the steering head bearings which I plan to do but I was wondering if anybody else had any ideas? I'm planning a rather extensive winter overhaul and have to do some repair work to do after breaking something in the drive train at Barber. While I have the bike down I might as well try to figure out whats going on.

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Im no expert but it looks like the winter weather has cause your oil to become too "sticky"

 

what weather did you ride in while experiencing such headshake/vibrations?

 

pics help alot

 

also, steering bearings

 

Thanks for the response. Weather does not seem to matter much. Warm, Cold it's about the same.

 

I'll work on getting some photos of the tires. :)

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Stock wheels? Are they true?

Any idea on the service history of the steering head bearings-the swingarm bearings-the wheel bearings?

Do the front forks have emulators in them or still just damper rod forks?

What weight fork oil? (not all fork oils that say 5w or the same, same goes for all weights- pick a brand and stick with it for all changes)

Any idea of fork oil level?

Steering damper installed?

Could it be the tire wear that is causing the problem, not the problem that caused the tire wear?

Any hard crashes that could have the frame tweeked or swingarm-wheel alignment?

 

I have 1990 FZR400 with ohlins front and rear and a steering damper that has no problems upto its max top speed. It has a 17" rear wheel conversion (86 GSXR750) and about 22,000 miles, 15w Maxima blue bottle fork oil, but I did strip it down to a bare frame and clean and make sure everything was straight and properly functioning, all new wheel, steering head and swingarm bearings were installed.

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Stock wheels? Are they true?

Any idea on the service history of the steering head bearings-the swingarm bearings-the wheel bearings?

Do the front forks have emulators in them or still just damper rod forks?

What weight fork oil? (not all fork oils that say 5w or the same, same goes for all weights- pick a brand and stick with it for all changes)

Any idea of fork oil level?

Steering damper installed?

Could it be the tire wear that is causing the problem, not the problem that caused the tire wear?

Any hard crashes that could have the frame tweeked or swingarm-wheel alignment?

 

I have 1990 FZR400 with ohlins front and rear and a steering damper that has no problems upto its max top speed. It has a 17" rear wheel conversion (86 GSXR750) and about 22,000 miles, 15w Maxima blue bottle fork oil, but I did strip it down to a bare frame and clean and make sure everything was straight and properly functioning, all new wheel, steering head and swingarm bearings were installed.

 

Hey. Thanks for the suggestions on stuff to check! I'm compiling a big list. :)

 

The wheels i suspect are ok because I have two sets and the vibration persists between both sets. I have stripped the paint off of them down to bare aluminum and they appear to not have any damage.

 

As for the forks I'm not sure. I bought these from a friend that upgraded the front end on his FZR to more modern forks. He recently serviced them and weighed the same that I do. I'm not sure if his bike vibrated at 100 because it was a street bike and I'm a goodie two shoes on the road especially on a friend's bike. :) I'm planning on doing the emulators as an upgrade so it might be worthwhile to talk to the suspension guys when I have that done.

 

I'm far from a purist but I would like to retain the original geometry with the funky 18 inch tire. For me that 18 inch rear wheel is what makes this bike so unique. A lot of people have made improvements with the 17 inch wheels though and have a much easier time finding superior tires as a side benefit.

 

The original owner that raced the bike had a steering damper in place but it was removed before I bought the bike. I still have the damper and that's an idea to try it installed just to see if that improves things. I have some videos of this bike taking some pretty hard hits on the track so I know it's been down. Frame seems fine though other than some gravel trap pecks. If I get desperate I may head out to GMD computrac and at least have it measured and see if it's terribly misaligned.

 

For entertainment value. My FZR getting crashed by it's former owner.

 

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Well the problem with the 18" rear is this;

Bridgestone was the last producer of any decent track quality rubber in that size and they stopped making it about 5 years ago.

So while you can still find some very old "new" tires around for the rear of the bike at about $180 a pop, the supply is very limited and at some point your only choice will be to go with a 17" rear wheel swap or ride on inferior rubber.

I already consider 5 year old rubber about the end of the tires useful life, most manufacturers state that the preservative/mold release they put on the tires is good for 5 years, so take it for what it is worth.

 

I have seen several of these as race only bikes with the conversion and suspension upgrades and some other goodies go for under $1000.

 

I would start with cleaning, inpsecting and servicing the wear out items.

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Well the problem with the 18" rear is this;

Bridgestone was the last producer of any decent track quality rubber in that size and they stopped making it about 5 years ago.

So while you can still find some very old "new" tires around for the rear of the bike at about $180 a pop, the supply is very limited and at some point your only choice will be to go with a 17" rear wheel swap or ride on inferior rubber.

I already consider 5 year old rubber about the end of the tires useful life, most manufacturers state that the preservative/mold release they put on the tires is good for 5 years, so take it for what it is worth.

 

I have seen several of these as race only bikes with the conversion and suspension upgrades and some other goodies go for under $1000.

 

I would start with cleaning, inpsecting and servicing the wear out items.

 

Appreciate the info. Last time I bought tires I had to go with the BT090 because I could no longer get the tires that I used previously. I was unaware that the tire situation had become that bad already. I may go ahead and buy a small stash of these tires "just in case". There's also the option I have not yet explored yet of European market and Japanese market non DOT certified tires.

 

I do realize one day keeping the 18 inch rear will probably mean the end of being able use this bike on the track but I am completely ok with that. It's still a an absolute joy to ride on the street and still has valid plates and street registration.

 

Regardless of where I enjoy this bike I do want to get rid of the shake. I really appreciate all of the suggestions. I'll be tearing into it within the next few weeks to get started. :)

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For entertainment value. My FZR getting crashed by it's former owner.

 

 

 

 

What happened in this crash, do you know? Seems like weird place to crash, did someone hit him from behind?

 

 

I have wondered the same thing myself.

 

My theory is that since he was in the braking zone before the Barber hairpin he locked up the front brakes.

 

When I first got the bike it had the original FZR400 rotors and two piston calipers on it and the original master cylinder was in desperate need of replacement. It had a tendency to resist you when you put on the brakes and then when you put more lever pressure on it occasionally gave you way more brakes than you intended. It may have just started that behavior and surprised him as it had surprised me a few times riding it on the street. Under normal braking it would not lock up the brakes but it was quite unsettling to say the least.

 

Since then I have installed an FZR600 master cylinder, new brake lines, 4 piston FZR600 calipers and EBC Contour Rotors. Now it stops just like a more modern machine does.

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