FJ in MI here

[swiftnick]

So I found a killer deal locally on a Thundercat rear wheel, sprocket carrier, cush rubbers, axle and spacers etc. I'm thinking 170/60-17 rear tire. Does that sound right?

[Millietant]

Yes, 170/60-17 is  perfect 

Just make sure you get the caliper carrier/mount as well.

[gdfj12]

Nick,

I may be able to help with getting it all to fit. I've got my '89 with the YZF rear and front setup and the '86 in the middle of being disassembled has the YZF rear wheel also.

George D

[swiftnick]

Nick,

I may be able to help with getting it all to fit. I've got my '89 with the YZF rear and front setup and the '86 in the middle of being disassembled has the YZF rear wheel also.

George D

Thanks George. I did a trial fit up last night and found that the overall width of the wheel, sprocket carrier, calliper bracket and spacers is bigger than the FJ swingarm. It looks like I need to make the left side spacer 9mm narrower and that gets the sprocket and wheel centrelines where they need to be (+/- 1 mm). I'm going to need to thin the calliper bracket some as well, still need to get a measurement for that. YZF rear brake rotors seem to be in short supply, I may need to buy a new one. Seeing as I'm only $70 into this so far that wont be too much of a hardship.   

[gdfj12]

8mm off of the left spacer and 8mm off of the outside of the caliper bracket. I may have one already machined. I am still going thru all of my parts bins as I'm in the middle of the rebuild on the '86.

George D

[Millietant]

No need to machine the left spacer Nick/George, just use the right side FJ spacer in place of the left with the YZF wheel, so all you have to do is take the 8mm (or 9mm) off the caliper mount where it sits in contact with the swinging arm

You can get an Arashi rear disc for not a lot of money (£40/$50 here in the UK).

The manufacturing tolerances on the FJ swinging arms don't seem to be "mm" accurate at the wheel spindle end. I took 8mm off my YZF Caliper mount and did the spacer swap and my wheel alignment has been checked a few times and it's spot on. Another guy I know who has just recently done the swap had to take just over 9mm off the caliper mount (his swinging arm gap at the spindle was 1.5mm less than mine).

[gdfj12]

Thanks for the info, Dean.

[swiftnick]

Hey Dean, I was excited to read your post above about using the right spacer of my FJ wheel on the left side of the Thundercat wheel, however I guess its different on my 91 FJ. That spacer is a little too wide and is too small a diameter to engage with the seal  Back to machining I guess. At least the weather has turned cold for a week or two so I'm not yearning to ride.

[Millietant]

Yeah, I'm very surprised that it's the wrong outside diameter size on your bike, there are a few people who have used the spacer swap, but it's only a 5 minute job to machine down the left side YZF spacer, so no big issue.

I must admit I'm not that surprised that the width might not be playing ball, as from conversations I've had with others, it does seem as though the gap in the arms varies a little bit - seems to be +/- at least a mm or two.

Hope it all goes well for the rest of the swap over. 

[swiftnick]

I figured out the dimensions by measuring the original FJ sprocket and wheel centerline from the left side spacer surface, with the axle in place and cinched up to ensure the sprocket hub was fully in. Then compared these dims to the Thundercat dimensions, that told me how much I needed to take off the Thundercat left side spacer. Once I had that I worked out how much to take off the brake carrier arm to make the whole assembly a tight fit into the swing arm. I actually need to spring the swing arm out by maybe .5mm to assemble now. Anyhow, I have the parts machined, assembled and new tires fitted front and rear. Still waiting on a brake rotor which is 2 or 3 days away so cant ride it yet. However the set up looks really nice and `correct' like that's how the FJ was always supposed to be. Great mod, glad I found this forum, thanks for the all the help. Any advice on tire pressures? My ST1300 runs the same size rear and 18 inch front radial rubber and is 42psi front and rear. Figured I would go with that for starters. 

[Millietant]

Just checking Nick, did you put the FJ sprocket on the Cat cush/carrier with the shoulder to the inside of the wheel ?

[Millietant]

I know what you mean about it looking "correct" - I like the fact that it looks just like Yamaha would/should have done it.

I measured everything from the centre line of the FJ Wheel outwards on each side and lined everything on the Cat set up up to the original FJ dimensions. Funnily though, a couple of guys had to take a bit more material (1mm extra) off the caliper mount than the 8mm I measured, for everything to fit easily between the 2 arms.

My front and rear wheels aligned perfectly and with the FJ sprocket reversed on the Cat cush drive, there was about a 1mm miss-alignment between the FJ wheel mounted and Cat wheel mounted rear sprockets - I don't think they were actually ever any more accurate than that from the factory, bike for bike  .

Great to hear all is going well 

[Millietant]

I figured out the dimensions by measuring the original FJ sprocket and wheel centerline from the left side spacer surface, with the axle in place and cinched up to ensure the sprocket hub was fully in. Then compared these dims to the Thundercat dimensions, that told me how much I needed to take off the Thundercat left side spacer. Once I had that I worked out how much to take off the brake carrier arm to make the whole assembly a tight fit into the swing arm. I actually need to spring the swing arm out by maybe .5mm to assemble now. Anyhow, I have the parts machined, assembled and new tires fitted front and rear. Still waiting on a brake rotor which is 2 or 3 days away so cant ride it yet. However the set up looks really nice and `correct' like that's how the FJ was always supposed to be. Great mod, glad I found this forum, thanks for the all the help. Any advice on tire pressures? My ST1300 runs the same size rear and 18 inch front radial rubber and is 42psi front and rear. Figured I would go with that for starters. 

I'm running Bridgestone BT023's and tend to use 36psi in the 170/60x17 rear for everyday blatting about solo and 38psi with a bit of luggage or a passenger, on tour - but, we all know how accurate gas/petrol station tyre pressure gauges are 

[swiftnick]

Yes I flipped the sprocket over so the recessed face is towards the cush drive. That got the sprocket within a millimetre of the original FJ dimensions. I ended up with the brake carrier bracket at 20.4mm thick and the left side spacer at 11.0mm thick and its a snug fit in the swing arm. Thanks for the tire pressure suggestions I will start at 36 and experiment from there.