Suspension

So, I just got 3LN bike and even without riding it much, it's crystal clear that I will have to do something with both ends. I've done some searching here and all I found was recommendation to try to do a swap for either ZXR250 or TZ250. Now, either one of those are very very rare around where I live so unless someone drops them miraculously to my back yard, I have to work with the stock as a start.

First of all, does anyone know the spring rates for front and rear (3LN)? Are the front forks and the rear shock by any chance identical to FZR400? If so then I know what the spring rates are ....

Has anyone by any chance used springs and cartridges from racetech.com to refresh their FZR forks?


Thanks

 

Thanks, but this is one of the biggest mistakes people do, thinking that by changing the pre-load of the spring it makes the spring harder. All you would achieve is to change a static sag. I will run the bike hard at a track so it needs to be done correctly.

 

Thanks Dave. I'd like to throw a set of GVEs in as well and spring it correctly. I've used the racetech stuff before so I am familiar with the calculator. Considering that the bikes have almost identical geometry I think I can use the FZR400 to get the spring rate and hope they will have the correct spring in the diameter and size I need will need. Looking at the results, no wonder the stock stuff is so sooooft.

Rider Weight: 140 lbs.
Bike Weight: 350 lbs.

FRONT FORK SPRINGS
Recommended Fork Spring Rate for Racing: 0.753 kg/mm (use closest available)
Stock Fork Spring Rate: .464 kg/mm (stock)

 

I mean to be serious, but within certain budget. It's a 20 years old bike used for ocassional track day or a street ride ....

I haven't look into the GVEs closely yet, but correct me if I am wrong, they will pretty much fit any damping rod based forks, correct? Or do they sell them per bike as well?

BTW, can you pls confirm for me .... I know the springs are not the same as in FZR400, but is the size of the forks the same (like diameter ...)? 400 is using Kyaba 38mm if I am not mistaken, right?

 

It's fine to mix weights. For example people frequently used to mix 10 and 5W to get 7.5 when nobody was really making 7.5W. Now Motul makes it and probably others as well, so it's not necessary. But there's nothing wrong with it in general, just don't do it by eye, use a scale marked container.

 

So, I finally found a rear shock replacement (based on Don's recommendation). I will follow with pics and little guide, in case someone will decide to follow the same mod (I am thinking there must be tons of these bikes with original shock with no left rebound damping). Stay tuned ...

 

I just finished putting the new shock in (literally 10 mins ago ...) . Few more images and I will be ready to write it up. Couple more days probably (I am in the middle of renovating a kitchen, so I have to keep things in balance ... wife LOL).

Just a few push downs on the seat and the feeling of having a nice rebound damping back .... yupeee <!-- s:roll: --><img src="{SMILIES_PATH}/icon_roll.gif" alt=":roll:" title="Rolling LoL" /><!-- s:roll: -->

 

It's been more then a couple of days, but I finally have found some time to recap what I have done ....

1) Get hold of an R6R (stay away from S) OEM shock from 06-09 model. Normally they are easy to find around people who locally race. Most people end up upgrading to Fox, Ohlins etc, so they let it go cheap. I paid 50 bucks for mine .....

2) You will need to take a load off the rear end, by either hanging the subframe on a ceiling joist or you can ask buddy to lift up the rear end and stick 2x4 between the rear tire and the subframe which is what I did, after I initially put a small lift jack by the rear wheel to lift the subframe a bit up. You will need to do that only if you don't have an extra pair of hands around ...

3) Next is to see what we have to do to accommodate the new shock. Well, the top mount uses the same diameter bolt (12mm) it's just narrower by 5mm on each side. Easily can be dealt with by buying two washers which together have 5mm thickness. I took my calipers to a local hardware store and was going through the bins until I was close enough. The bottom fork mount is a direct bolt in and no fabrication is required there. The last thin which need to be considered is the length of the shock. Unfortunately, it's about 10mm shorter than 1991 3LN stock shock. Too much of a difference to leave alone and deal with by adjusting ride height in the front. The handling would be handful to deal with which I didn't want to take a chance on. So, will have to figure out how to make a new dog bones linkage (one for each side) and how long they should be. The material to be used can be nothing special steel plate, the most important is the distance between the holes which has to be certain distance and both dog bones need to be as close to identical as possible. If you have an access to a machining shop this becomes an easy exercise. According to my measurements and I will explain how I did that, the new distance between holes should be 132 mm which is about 8 mm shorter then stock. Remember, the shock is about 10 mm shorter, but there's an x factor the linkage adds to the pivoting action. How did I come up with 132? Well remember the 2x4 which basically lock the rear end. I took the old shock out after that and put the new shock in. Then I moved the L element of the linkage until I was able to stick a bolt through the bottom fork mount. this basically brought the holes to the position where they need to be. Then I simply just measured the distance from center to center.

Her's a few pictures which might make it easier to envision ...

New shock


The top of the new shock will need to be lightly filed so there's no protrusion from casting as it will be pushing into the bracket which supports the battery.


Old shock just for a comparison ...


Old dog bone linkage and new ones for a comparison


4) You have shock, spacers for the top and new dog bone linkage, all you need to modify last is the bracket holding the battery. Once you dry fit the shock in it becomes very clear what needs to be done. 15mins with Dremel and it should be all good.

The bracket supporting a battery. It needs to be adjusted a bit so it can freely receive the shock. It becomes obvious once you start looking into it ...


5) Now the shock can come in. Here you will need to exercise a little bit of patience, especially with with washers functioning as top spacers. I ended up putting two washers on each side. You might ask why didn't I have two spacers machined each 5mm thick? Yep I could have, but I considered it to be easier just to buy nicely zinc plated washers, but the downside is that you will not find one 5mm thick so you end up with two on each side and that means a bit more work to put them in. The problem is the bracket restricts access to the space between the frame mounts and the shock. But after 15 mins doodling around you will find a way.

6) Mount the dog bones and bolt everything up according to the specs.

7) Not done yet ..... check the plastic chain guard. It's getting too close, when the swingarm pivots to, the shock reservoir. So just trim the corner a tine bit, takes two seconds. On my bike the chain is getting very close to the reservoir, but not close enough to be a concern. Lets call it a luck day, because if it was the shock would have to be offset to the right, which would I guess work as 5 mm would be all it would need.

Few pics with the shock mounted ..






8) Lastly, do yourself a favour and set the shock up. I mean measure sag and make sure it's within a range it should be in. I was lucky because the red spring it came with is just about right for myself which is 155lbs with gear and I still have a lot of preload adjustment left, so it copuld be OK for another 20 lbs. Heavier than that and you will have to change the red stock spring otherwise you will not be able to set the sag properly as the string will be just too soft. Or better yet, look for a shock with already changed spring for heavier rider. As far as the clickers, they do work (lots of OEM shocks have clickers but they make a little difference ...), but I had to turn them almost all the way to end. For example, rebound damping is on third last point ....

All in all, I consider it a great upgrade as I can finally push the bike the way I want. Should be a great fun at the track ....

I have to thank here a great deal to Don (Dontz125) who basically pointed me in the right direction as far as what shock to get and what to expect Thanks again Don.

If anyone has a question pls fire away, I'll do my best to answer them all.

 

Hmmm .... I still I have obviously the stock dog bone. So perhaps I can trace that and just move one of the holes accordingly so it can be re-traced. Let me think about it and I'll see what I can do. Might take a day or two ...