Thunder Ace swingarm on an '89

[jamesearthdrum]

This mod was done last year and I have since put about 4000 miles on it. I rode out to the MotoGP races at Indy then down to the ECFR. I am a novice rider at best, but felt much more confident staying with the group than I did at my first Rally in '06. The mod has made a huge difference in how the bike handles. I thought I would post this so some of you '89 owners will know what to expect. I did post it to the Yahoo list some time ago. Enjoy!

I thought would write up my discoveries while undertaking the Thunder Ace swing arm mod to my 1989 FJ. What follows should only be applied to the 1989 model.
After obtaining the pre machined parts from Marc Rittner I followed the instructions for modifying a 1993 FJ1200 written up by Marc on Barry Edwards's excellent FJ Mod's site http://www.fjmods.btinternet.co.uk/MarcRittner.htm. Marc does say that the procedure may vary for other models, but his parts all worked as indicated with my '89 with one exception, the dog bones.

Where I began to have to improvise from the directions was once I had the Ace swing arm installed. It fit the frame exactly right and I proceeded to reconnect the shock/relay arm/dog bones. I was reusing my stock shock, but had fabricated new dog bones with the indicated 3 7/8" centers. Once I had all the connections made, my first indication that something was awry was when I moved the swing arm through it's range of motion it would contact the rear brake light switch near the rear master cylinder. It also looked as if it wasn't going to clear the rear master cylinder if I moved the switch. I relocated the brake light switch and swapped the OEM master to the R1 master I had. Oh, I'm also installing the R1 rear brake caliper at the same time. It looked as if the swing arm would clear now. It still seemed awfully high though. I spooned on my new tire and mounted the rear wheel. The new dog bones were to place the tire about ¾" off the floor. Mine however was several inches above the floor and the swing arm was almost parallel to the floor. Well okay, I guess I need to make different dog bones to bring the swing arm down. When I disconnected the dog bones from the relay arm the wheel did drop but only about a half inch. The swing arm brace was now resting against the shock spring. So shorter dog bones would not work. After reattaching the swing arm to the relay arm I observed that there was only about a 1/8th of an inch clearance between the relieved swing arm brace and the shock spring.

Hmm..... After pondering my situation and getting some information from the group I determined that by lengthening the shock, it would bring the relay arm down and back slightly so the swing arm would move down and I would gain some clearance for the shock spring. I dropped the swing arm and wheel down onto a piece of 1/4" plywood and used a double eye turnbuckle in place of the shock to line up the relay arm and dog bones and give me the length the shock needed to be. I lengthened the clevis on the shock by welding a couple pieces of 1" x ¼" flat bar to the outside of the clevis. These had a spacer welded to them to bring the gap back to the right size where it attached to the relay arm. I welded and drilled the flat bar pieces before welding them to the clevis. Of course, I had some reservations about welding on a Nitrogen pressurized cylinder, but hey, what's the worst that could happen..... After a bit of grinding I had a rather crude but functional clevis that was 1 3/8" longer than stock. This time when I mounted the lengthened shock to the relay arm with some longer shoulder bolts acquired from McMaster Carr, I discovered that the dog bones were now to short. So I made up another set at 4 5/8" centers. The tire now just skims the floor when on the center stand and the shock is centered in the swing arm. I wanted to make sure the swing arm would move through its range of motion without contacting the shock spring so I dropped the bike down off the center stand. Well the relay arm is now low enough that the center stand will not go up all the way, so I guess I will need to remove it. The relay arm is not any lower than the chin fairing and exhaust so it shouldn't be a problem. The swing arm moves without interference from the shock so all seems good.

   I will order a Penske Sport shock made in the corrected length to work with this mod. I inquired about the spring diameter on the Penske and it is the same as the OEM spring, 88mm, so my clearances should be fine. I will also be changing to a 41 tooth rear sprocket to lessen the contact wear, where the chain passes over the swing arm.

   The difference in the geometry of the shock/relay arm/dog bones/swing arm between the 1993 FJ that Marc modified and my 1989 FJ must be enough that I needed to make the adaptations outlined. I cannot see any other cause for the results. My hope is to compare my '89 to a modded '91+ sometime at a rally to draw real conclusions. For now here are my observations as I discovered them, as always, YMMV.

1)   Modification to the OEM shock, if used, is necessary.
2)   An alternative to 1) is an aftermarket custom length shock.
3)   The OEM shock spring is the same diameter as a 1400lb. Penske shock spring.
4)   The Thunder ace swing arm brace must be relieved according to Marc's instructions for use of an aftermarket shock.
5)   Custom dog bones will need to be made. The length should be determined after the swing arm and shock are attached in accordance with how low you want the rear tire.
6)   The loss of the center stand is inevitable. *NOTE* the Ace swing arm can have spools attached for a swing arm stand. It also has a hollow axel.
7)   Relocation of the rear brake light switch is advised.
   A 4" right angle grinder is an amateur welder's best friend.

MOD ON!!!

James
'89Ace and '86 in MA

PART II

   Well it has been several months since the first installment of this modification. When I finally had time to get to remount the exhaust on my '89 I discovered that the stock exhaust could not be used. The Ace swing arm is a good bit wider than stock. I explored the possibility of getting an aftermarket system, but was concerned that it would still not fit as they are designed to work with the bike in stock form. The next option was to get a pair of universal cans of some sort and have custom mid-pipes made up. I soon discovered after some shopping that needing a pair of cans was going to send the cost well past what I felt I could live with. Once again I turned too the list for recommendations. It was discussed that any can from a similar displacement machine should work. I remembered reading about someone using OEM Hayabusa cans on their FJ. Sure enough they were plenty to be found on EBay and cheap too. I had a pair of custom mid-pipes made up at "Lou's Custom Exhaust". The stock Hayabusa cans are a bolt on type with a flange being welded to the stock mid pipe. Lou's cut the flange from the mid pipe and welded the new custom pipe to it. A bit of swagging on the other end and it slipped right over the stock collector. I needed to slot the swaged end, to allow the modified clamps I acquired from the Hayabusa mid-pipes, to squeeze the connection tight and viola, I had an exhaust that fit. Slotting was done with that favorite friend of the amateur welder, the right angle grinder, using a cut off wheel.
   I have also installed a set of 1kg Sonic springs in the forks with new seals, the right way up this time, and Uni Dual Pods, The intake sound almost drowns out the exhaust when accelerating. I do not mind the bike being quite as I commute to work each morning and have to start it right outside my neighbors bedroom window. I have only ridden the bike once since the mod has been completed, since it is currently monsoon season here in New England, but during that first ride I have noticed that the bike seems lighter handling and surer footed when turning. All in, for this novice rider, it is has been the journey doing the modifications, not so much the results, though I think I am going to be very pleased with the results. I would like to send out a huge thanks to the FJ list for your inspiration and assistance is getting this done.

MOD ON!!!

James
'89Ace and '86 in MA

[Marsh White]

James, great write up...thanks for posting it!  My Penske 8981 rear shock has adjustable length...really nice for fine tuning the handling of the bike.  I don't know if it does; but it would be nice if the Penske Sport shock that you are interested in has this feature as well...then you wouldn't have to worry about the length or dog bones anymore.  It is a MUST HAVE feature if you ask me for future moditis.

For example, when I swapped the stock forks on my 89 to YZF-600 forks - it upset the finely tuned balance I had had for years.  The length and angle of the new forks was supposed to be the same as the old 89...but I'm certain that the angle was a bit steeper.  I ended up having to raise my rear wheel (shorten the shock) to compensate - to dial everything in just right.  This took four or five 50+ mile runs to sort it out.  For example...just when I thought I had everything PERFECT, I happened to take the bike up to 110-120 mph real quick to check the stability...front end started shaking badly...back to adjusting the ride height.

Anyway, my point is - when doing mods - I find it highly unlikely you can get the perfect handling and balance of your bike by just taking measurements and going off what people say.  You can get CLOSE, but in the end, the critical fine tuning is most easily accomplished by a height adjustable rear shock and test rides.  FWIW...

[rktmanfj]

<snip>
For example, when I swapped the stock forks on my 89 to YZF-600 forks - it upset the finely tuned balance I had had for years.  The length and angle of the new forks was supposed to be the same as the old 89...but I'm certain that the angle was a bit steeper.  I ended up having to raise my rear wheel (shorten the shock) to compensate - to dial everything in just right.
<snip>

Marsh, did you use the stock T/Cs with the YZF600 fork, or the FZR1000?

Randy T
Indy

[Marsh White]

Randy,

I ended up buying a pre made mod that Marc Rittner had made for himself before he put on his USD forks.  It uses the FZR 1000 triple clamps with Jon Cain adapters to run the stock handlebars.  The forks were setup by Stig Pettersson - world renowned suspension guru ( http://www.ppsracing.com/ )...who also happens to have his shop about 15 minutes from my house.  I really need to get him my rear shock for a rebuild...it is way overdue.

[rktmanfj]

That's pretty much the front end that I have on mine, except that mine was built by the somewhat less renowned (but still pretty damned good) suspension guru Buff Bill Prodoehl, and Dalmatian Engineering (my workbench) bar adapters.  The Jon Cain adapters were on backorder.

My stock shock will be retired in a few weeks with a new Penske.

Randy T
Indy

[jamesearthdrum]

Thanks Marsh,
              This mod was done last winter and I have the Penske Sport Shock installed. Sorry about the confusion. Given the amount of extra length required to make the swingarm function, I ordered the Penske longer than stock, one of the great things about Traxxion. I can now use the height adjustability to fine tune things. That is of course once my riding skills advance to the point where I can feel the difference.
              Also if I keep reading about these front end mods the DT's are going to set in and I'll be looking for an USD set of forks!!!