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Wheel Offsets and Chain Slack

Started by Power2Go, August 11, 2017, 01:02:33 PM

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Power2Go

Greetings All,

I have been fussing with the chain slack on my '91 FJ1200 and along the way I've had to get involved with rear wheel alignment. I affixed two long straight boards to the rear wheel and discovered that the rear wheel center line is offset to the right about 7/8" compared to the front.

The wheels are parallel and the bike rides very nicely but I don't push it hard enough in the corners yet to be able to tell if it's different in right vs left corners.

The PO put on a GSXR rear wheel and Michelin tire (170/60-ZR17) which is, according to the numbers, about 0.8" wider than stock (150/80-V16). So that may account for the offset but the question is: Would that offset make the bike handle differently or is it a problem in any way? Would it  be noticeable to a more experienced FJ rider? As close as I can determine, the sprockets are in line.

BTW, why does the manual (and many video makers) recommend to adjust the chain (to mfr's specs) with the wheel down? This makes for a very tight chain under load. I worked through the geometry and determined that slack at full down position due to geometry alone should be about 0.75", then with about 0.25"-0.5" of slack at full load, that would allow me about 1" min at full drop. I found some other numbers for any generic sport bike suggesting 1.2"-1.5" at full drop. What have you guys found?

Thanks,
Cliff
'91 FJ1200
'89 R100RT

FJmonkey

Offset wheels will cause the bike to try and turn. The more offset the more it tries to turn. So any offset should be avoided. I have a GSXR rear with a Conti Motion 180/55-17 rear wheel. The tire just clears the chain. A Dunlop Q2 in the same size does not clear the chain but a 170 will. To get the wheel centered I machined a spacer, others have just used a stack of washers.
The glass is not half full, it was engineered with a 2X safety factor.

'86 Ambulance - Bent frame, cracked case, due for an overhaul
'89 Stormy Blue - Suits my Dark Side

Pat Conlon

Quote from: FJmonkey on August 11, 2017, 02:06:01 PM
Offset wheels will cause the bike to try and turn. The more offset the more it tries to turn. So any offset should be avoided......

^^^ Yes, yes, yes.

Cliff, 7/8" rear tire offset is too much. Something's wrong.

To demonstrate, measure and mark the centerline of your 170/60 tire. With a right offset, now measure to the left 7/8' over from the center line mark. See the mark in relation to left shoulder? This is why your bike will fall quickly into left turns and turn slower on right handers. Dancing my heavy FJ thru quick right left right left transitions is all about a smooth rhythm, something I see would be a problem with an offset like this.

Something to check: Are you sure your boards dead nuts straight? Wood boards are seldom straight. I use 1.5"x 1.5" square steel tubes 84" long.
Are you clamping the boards at the same spot on the right and left side of the back tire?
Is your front wheel straight? (equal measurements)

You should consider fixing this issue, by narrowing the left spacer to move your wheel to the left, then getting an offset back sprocket and machining the rest off of the sprocket face of the cush hub, to keep your chain alignment.
Machining the cush hub is no big deal. Folks have done it for years on the YZF600 back tire mod: http://www.fjowners.com/index.php?topic=2511.0
Come as close to your tire with your chain as you can. You should have plenty of room with a 170/60 tire.  Make a custom wider spacer for the right side as needed.

Re: Chain slack: Rule #1) A loose chain is a happy chain.
I measure the chain slack with the bike on the ground.
If you have altered your rear end (raising) you need a slightly looser chain than normal due to the different angle of the swing arm.
Get a top quality chain and adjust it on the loose side. The chain will stretch very little (if any) over it's life.
With top of the line chains, gone are the old days when chains would stretch.

Hope this helps.  Pat

Open question to all FJ'ers with the GSXR rear wheel mod: Have you guys checked (actually measured) to see if you also have a back tire offset like Cliff? Chain alignment is one thing, the back tire is something else.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

movenon

I measured mine using the string method and later with some steel.  From memory it took some minor adjusting of shims but when done it was as in track as far as I could measure.  I assembled my wheel with the shortest combo of spacers I could find so I could add shims on purpose for adjustment.  Again from memory I used a Honda front sprocket and did some milling to get the chain where I wanted it.  My rear tire clears the chain by slightly less than a eye ball 1/4 inch.  
George

Life isn't about having the best, but about making the best of what you have...

1990 FJ 1200

Power2Go

Thanks a bunch all,

I was thinking of doing the string method but the errors seemed too small to be differentiable. And with no way to fix it in position.

Pat, I put a cross piece between the boards at the front the same width as the spacing (tire width) in the back and though the boards are not as good as a piece of steel they are very straight and usable for a first look. I had very usable measurements to all four corners of the front tire. And the measurements all added up perfectly side to side for the front and back of the front wheel so I know at least that the wheels are parallel.

When I get to doing the spacing adjustment as you suggest, I will find some more respectable reference sticks.

I kind of figured that offset was a bit much and I don't think the PO spent enough time thinking about that particular result. I don't know exactly how much space I've got left between tire and chain but it doesn't look like much - certainly not 0.75". But I guess the closer I can get it the better. (Maybe I should shave the edge of the tire...haha)

Is there some easy way to determine whether the sprockets are exactly in line? Can the inside surface of the left swingarm be used as a reference point?

Now, lastly, is this tire and wheel change really worth the extra trouble it entails? I had an '84 FJ1100 and it ran just fine with stock rims and tires though I have to tell you that I've never considered myself a push-to-the-limit kind of cyclist. Does it improve a design that may be considered slightly deficient? Or is this something that is done mainly by a road racer looking for vastly better handling performance? And how much does the performance actually change?

Thanks again,
Cliff
1st bike: 1964 Honda 150 Dream

Pat Conlon

I do sprocket alignment with a laser fixed on the back sprocket pointing to the front sprocket.
I find that the easiest.

Yea, I suspect you don't have a lot of width on the left side spacer to work with. When you get that rear rim close to the inside edge of the swing arm the first contact point will be the studs then nuts that hold the chain sprocket.
To get additional ~1/2" clearance I've seen bikes where the sprocket studs are removed from the cush hub and counter sunk machine head bolts are threaded into the cush hub, meaning the heads are counter sunk into the steel sprocket so the face of the sprocket is smooth.

The proper order of rear wheel modifications is always align the center line of the front and back tires first, only then do you figure out what you need to do to for spacers to hold that alignment, then finally, what you need to do to align the chain. Never prioritize chain alignment over tire alignment.

I don't have a GSXR rear wheel mod and I have never done one so I can't help with the specifics.
My experience is with (2) YZF600 mods and (2) YZF1000 Thunder Ace mods.

I do know a lot of our FJ brothers have done the GSXR mod and they seem very happy with the results.
I "assumed" they checked the center line front/rear tire alignment...someone had to, I just know it.
It's fundamental.

If you would have asked me 2 years ago if the 17" back wheel mod was worth it, I would have said "absolutely". The oem 150/80-16 tire sucks, bla, bla, bla...
However since then, Avon has come out with that bitchen 3D Storm radial tire in the 150/80-16 size.
That is a great tire!
How long will Avon continue to make 150/80-16 size? Who knows? Many tire companies have discontinued that size. I know I am safe with the 170/60 and 180/55 tire sizes. There are plenty of really really good tires out there. Modern tires rock. That modern Avon 150/80-16 3D Storm radial rocks.

Before you freak out, get some 7' steel tubes and clamp them to each side of your back tire and double check your measurements.
If the PO followed the instructions for the GSXR mod, there is no way there could be a offset that much. Others would have reported it.
Live with a 1/4"offset? Well ok maybe, If I'm in a hurry and the rally is days away, but a 7/8" offset? No way.

Cheers. Pat

1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

Sparky84

Quote from: Pat Conlon on August 12, 2017, 03:47:14 AM
I do sprocket alignment with a laser fixed on the back sprocket pointing to the front sprocket.

That modern Avon 150/80-16 3D Storm radial rocks.

I do the laser also, nice and easy .

I wish Avon had a 120/80-16 Storm for the front, it would be easier than changing both rims

Cheers Alan
1984 FJ1100
1979 Kawasaki Z1300
1972 Honda CB750/4 K2

Pat Conlon

Quote from: Sparky84 on August 12, 2017, 04:43:08 AM
I wish Avon had a 120/80-16 Storm for the front, it would be easier than changing both rims


On that point, I still firmly believe a mod to a 17" x 3.5" front rim is the only way to go, no question.
Modern tires are amazing and the selection in the oem 120/80-16 size is slim to none.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

ZOA NOM

Quote from: Pat Conlon on August 12, 2017, 11:30:16 AM
Quote from: Sparky84 on August 12, 2017, 04:43:08 AM
I wish Avon had a 120/80-16 Storm for the front, it would be easier than changing both rims


On that point, I still firmly believe a mod to a 17" x 3.5" front rim is the only way to go, no question.
Modern tires are amazing and the selection in the oem 120/80-16 size is slim to none.

Also, don't bother looking for the 87-88 FZR wheel, just get the 89-up (easier to find), and drill the forks for the 17mm axle. Easy-peasy.
Rick

Current:
2010 Honda VFR1200 DCT (Full Auto!)
1993 FJ/GSXR 1200 (-ABS)
1987 Porsche 911 Carrera (Race)
1988 Porsche Carrera (Street)
Previous:
1993 FJ1200 (FIREBALL)
1993 FJ1200ABS (RIP my collar bone)
1986 FZ750
1984 FJ600
1982 Seca

markmartin

Power2Go,

This is a post I wrote in 2012 when doing the GSXR mod, dealing with centering the rear wheel to the swingarm, or as I found out, at least putting it back where Yamaha had placed the stock wheel in the swing arm. 

I hope it helps more than confuses the issue!  FWIW, I never experienced any funky handling in turns or on the straight - I can also let go of the bars with no wobbles or weirdness.

I'd be interested to see what a laser like the one Pat describes would give me for alignment to the front.

I measured the stock FJ wheel as it sat in the swing arm (to my knowledge, I had a stock set up) and this is what I got:

The stock wheel set up has the FJ wheel off center of the swing arm by 3/64ths of an inch to the right of center.  I was measuring this with a combination square, squared off to the outside of the swing arm, measuring to the wheel closer at the front side (motor side) of the wheel. Also, the stock FJ distance from the outside of the swing arm to the teeth on the sprocket was an even 2.100 " ,(measured with a vernier caliper). 

On the GSXR, I used (off the shelf washers)  .258" spacers on the brake side and .075 spacer on the sprocket side. This put my GSXR wheel a weak 1/32nd  to the right of dead center, and a distance of  2.055" to the sprocket. Incidentally, I used an JT 38tooth sprocket, and flipped it to get the teeth further from the swingarm.

Now, I could get custom spacers to tweak the wheel off center to the right another .0312" or so to more to mimic the original FJ measurement and consequently move my sprocket closer to the original measurement.  I don't know if this is spitting hairs .  Also, I was perplexed by the original wheel being off of center of the swingarm.  Granted it may be this way by design to have the wheel centered to the bike frame.

Pat Conlon

Thanks Mark

Being off center of the swing arm is not a concern as much as being off center of the front tire.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

Power2Go

Mark, Pat,

I've made some more measurements and I think I am getting deeper in the hole. I strapped a laser level to the rear wheel and my offset numbers have gotten worse.

I give these measurements here for reference and hope it doesn't confuse the issue further.

Rear tire max width is 6.97".
Rear wheel width is 6.2".
Clearance between swingarm and outermost tire surface at the front of the tire is 1.0" on the left side and 0.5" on the right side. (Swingarm is curving in at this point. Chain slack is set and wheels are parallel.)
Clearance between tire and chain is 0.35".
Clearance between the swingarm and sprocket nuts is 0.3".
Chain width is 0.9375".
Clearance between sprocket and swingarm is 0.625".

The total possibly usable clearance on the left side amounts to the 1" - tire to swingarm. I would need almost the entire amount for corrective offset (according to the laser measurements) to the left so this could conceivably be done. Moving the chain closer to the tire would require countersinking the sprocket for flat head bolts and sounds like a real chore. There must be spacers between the cush hub and swingarm but I won't know until I drop the wheel. The cush hub is probably the main impediment in reducing the distance.

Is it possible to view the original instructions for converting to the GSXR rim? Maybe that would give me some more insight.
The notation on my rim reads: J17XMT5.50 SUZUKI. This suggests it's 5.5" wide, I think, but it's actually 6.2" wide. I think the 5.5" refers to the bead seat width or some other internal spec. My tire is wider than spec but only by 0.25".

I don't quite understand how you put on this same wheel (is it the same?) and it came out centered. And you did nothing else other than use different spacers?

According to Pat, zero tire offset is more important than chain alignment. Don't the chain and sprockets wear unreasonably with misalignment?

I'm almost thinking when it's time to change the rubber, it may be easier to find a 5"x17" rim and go with a 150 or 160 tire.

Thanks again for all the response.

Cliff
'84 FJ1100 1st Yamaha

Pat Conlon

You misunderstood me, both sprocket alignment and wheel alignment are important, and necessary.

You align the wheels first. Once the rear wheel is locked into alignment with proper spacers, then you work on doing whatever you need to do, to align the sprockets. There are several options available to you for chain alignment, e.g. longer XJR countershaft, offset front and/or back sprockets, machining the cush hub or any combination thereof.

Re: Rim width, that is measured at the bead, not the outside face of the rim.

It sounds like you are driving yourself crazy.
I use the laser to measure the sprocket alignment, not wheel alignment.

Again, take 2 straight tubes and clamp them to the outside face of your back tire.
With your front wheel turned straight, it is very easy to measure the wheel offset.

Visiting our Suspension Files section will show you this:
http://www.fjowners.com/index.php?topic=3380.0

Hope this helps.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

Power2Go

Hi Pat,

Thanks again for the excellent pointers.

I dropped my wheel today (this is starting to sound like a saga) and found some motley assortment of spacers and washers. Then I cleaned the chain and rear sprocket and wheel and hub. Then I took off the left crankcase cover, discovered the locating dowel and lower bolt missing and lots of greasy gunk and a BADLY worn drive sprocket. Oddly enough, the chain seems new as well as the rear sprocket. So now on to other issues before I can get back to the one that started all this. Typical, right?

I almost ought to start a new thread but I think I'd go crazy keeping track of it all.

Anyway, do you have dimensions for the lower bolt and locating dowel? I'd want to put it in but maybe it's not critical. I can probably make a spacer but the length would be guess and trial and error. Also, it appears that there is gasket material at the top and gasket type washers on the other posts? Is this the case?

The wheel mod seems straightforward and simple enough. Thanks for the link. I'll install a new sprocket, clean everything up really well and see how everything goes back together.

In your opinion, could the measurements APPEAR to be the same at the front and back of the front wheel on both the left and right sides yet have different measurements side to side?
It looked to me like the wheels were parallel but maybe the error in the difference between front and back measurements of the front wheel is too small to determine parallelness. I'm having this growing feeling that what I was really seeing was the misalignment of the rear wheel rather than a centerline offset.

After reading through the GSXR mod, the setup should be fine on my bike. I DID notice running down some flat straight road today that the bike DOES want to turn left...most likely because the back wheel is turned to the right. OK, steel tubing.

Well, if I hadn't taken everything apart, I'd have never discovered the worn drive sprocket - looks like it's ready to lose its teeth!

Thanks,
Cliff
'70 BMW R60/5 1st Beemer - from a yard sale - ran fine - ugly windjammer

Pat Conlon

Yes, what can appear to be a center line offset could really just be a crooked back wheel i.e. Not matching the left side swing arm index marks to the right side index marks.
The tubes will show if the back wheel is crooked in the swing arm or if the back wheel center line is offset.

Sorry, I'm away from home now, perhaps others can help with your measurement question.

Good catch on the worn countershaft (c/s) sprocket.
While the rear sprocket is visible, the countershaft sprocket is hidden and can get overlooked.
Your stock c/s sprocket is 17 tooth, I recommend an 18 tooth c/s sprocket.
It's easier on the chain and gives you slightly lower RPM's on the highway.

RPM offers a straight c/s sprocket: http://rpmracingca.com/proddetail.asp?prod=M%2FC%3AFDS

.....and if you need it (yes, the tubes will tell) a 1/4" (.25") offset c/s sprocket.
http://rpmracingca.com/proddetail.asp?prod=M%2FC%3AOFFSETFDS

If you need custom offsets on your c/s sprocket or rear sprocket, contact Randy at RPM and he can order you what you need.
Sprocket Specialists and PBI Sprockets do orders for custom offsets.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3