Topic: CB750F Rear wheel wobble

[Helo229]

Hi all - Like the subject says, I have some pretty bad wobble on the rear wheel of my CB750F. I more or less just got the bike up and running strong, and aside from the wobble the bike is best as can be.

Here's the symptoms:

With the bike on centerstand in 1st gear the wheel is wobbling left > right by about 10-15mm. The rotor, as best as I can eyeball, is dead straight, which rules out alignment. There is, however, a bit of popping coming from the chain, which I can hear/feel when I'm riding, which I think may be related, seeing as the chain is in good condition as are the gears. It's almost as if the chain is rubbing on it's guard.

I just purchased a new set of tires/wheel bearings which I was hoping to change this week. The wheel itself is 130/90 16, which leads me to believe that at some point a harley rim was put on? I haven't had the wheel off to look at production stamps, and haven't been able to ascertain OEM wheel size on 750F's. I know with it having the disc installed it's not nearly as common as the K models.

In anycase, if replacement wheel bearings don't do the trick, what are my options as far as re-lacing? Would I be better off to purchase a new rim being as this one is perhaps non-standard and I don't know what spokes it takes, buy a new wheel and use the Harley Rim/Honda Hub spokes available on eBay, or could this wheel be Honda OEM (wear and style compared to the front are exactly the same) and could there be a spoke set out there for it? Or just blow the whole thing off and steal the comstars off the next 750 I see parked in town?

[scondon]

    With that much rim distortion and a 130 tire fitted I imagine the tire might be hitting the chain when riding. I don't know much about spoked wheels, but I thought they could be "trued" by loosening/tightening the spokes.

[KB02]

    With that much rim distortion and a 130 tire fitted I imagine the tire might be hitting the chain when riding. I don't know much about spoked wheels, but I thought they could be "trued" by loosening/tightening the spokes.

That would be my thought as well. Esspecially if the disk is running true, than I would this that the hub and bearings are set as well.

Perhaps when someone put the smaller rim on they didn't get it lined up and alligned properly, thus causing your wobble. That's where I would check. Also, double check to make sure all your spokes are tight. Could a loose one or few that are causing the issue.

[m00ntan]

I had this problem.  I found eight spokes just cut off on a 16 inch wheel.  I found a straight 18" wheel off ebay and had some good luck.  Just be sure they can tell you the runout before you bid.

[steam-powered man]

if there's no runout/wobble on the disc, that may mean your wheel bearings are OK.     

i'd first check the trueness of the rim.  after a search here for some pointers, i trued my spoked wheels to +/- 1.5mm in both directions (hor/vert). 

if the wheel bearings are OK and the rim is true, then it may mean your tire is mounted incorrectly.

if the chain is rubbing on the guard, make sure the front sprocket is mounted correctly.  PO on my bike had it flipped wrongside out.
good luck!
bobp 

[RSV12K]

Maybe this is a dumb question, but are you dead certain that the wheel adjusters are equal on both sides of the swing arm? That will cause wobble, but most people already know to check something that (hence, the dumb question). You can check alignment using a long string. Like this: http://www.uponone.com/howtos/31.pdf.

[upperlake04]

are you dead certain that the wheel adjusters are equal on both sides of the swing arm? That will cause wobble..

 

[RSV12K]

are you dead certain that the wheel adjusters are equal on both sides of the swing arm? That will cause wobble..

 

I guess I should have been more precise. If the adjusters are not set equally on both sides, the wheel may wobble. Happy?

[upperlake04]

 Not yet. I would think that the adjusters allow movement of the rear wheel to tension the chain and to line up the wheels. If the adjustment  is off and the fr/back wheels aren't on the same plane, the bike would dogtrack, but I don't see a wobble problem when "With the bike on centerstand in 1st gear the wheel is wobbling left > right by about 10-15mm"  as the original poster described. 

[spitfire]

You have probably checked this one already, is the tire on the rim correctly, centred, mine wasn't and wobbled, took it off deflated it, bounced and adjusted it until the it was central and away we went.

Cheers

Den

[Helo229]

Alright, I went ahead and double checked the alignment with the string test, and used my digital calipers to check for equal spacing on the alignment screws, and it's tip-top. It's good to know that with the rotor being straight I don't have to worry about the wheel bearings, but in any case I've already bought replacements for front/rear.

I also did the poor-man's runnout test with a spray can/straw at a few different spots on the rim/tire. It looks to be on the rim in one spot there was a gap of about 3mm in.

The bike did sit from some time. If I had to guess it would be in the area of 2-5 years, being as Dunlop 501's are mounted. I'm going to let the bike sit for the time being just to avoid any further damage to the wheel if it's out of true, which seems to be the case.

So, being as the wheel needs trued, anyone have input as far as relacing it? The spokes are fairly rusted, and while part of me wants to replace them, the other half of my head is saying "just take the dremel to them." If I do some light sanding to the spokes to clean them up will they still be safe?

I know that there are the Harley wheel spokes for 16" rim conversions, but will this work with F models? I'm assuming that there's some difference between the diameter of the hubs from K>F with the different brake systems.

And one final question (sorry I'm making you all read so much): I tried checking runnout on the cush drive of the sprocket, and while I'm not entirely sure, I think that it may have been slightly off. It's hard to tell because of the chain bouncing a little with no weight on the rear wheel.

Once again, thanks all, I'll keep ya updated.

[eurban]

Certainly sounds like you have issues with rim trueness and or tire seating. . . . As a result, any string tests for alignment will tell very little as you are referencing off of the tire with the strings. If you are worried about precise alignment you will need to start with a properly trued rim with a properly seated and undistorted tire. The alignment marks on the swingarm will get you in the ball park but they were not particularly accurate on my 78K.  . . . . Have you actually taken a good grip on the rear wheel and checked for play? There should be none.  Does the rim/tire flex while the hub etc stays put? If so check for broken, missing and loose spokes.  Do you feel some play in the hub to axle mating? If so check for axle bolt torque, bearing wear and axel runout. Does the entire swingarm have side to side play? If so check your swing arm bushings.  In all you might have a few issues going on at once.  The chain should not cause the rear wheel to visibly wobble. If the chain is able to affect the wheel in such a way then something is loose at the wheel. This of course does not mean that you shouldn't change your chain/sprockets if it is not operating smoothly. If you suspect your cush drive, pull the wheel and examine the rubbers.  However, this alone should not cause the tire/rim to wobble as you spin things on the center stand. . . Although I am not absolutely certain, I do believe that inspite of the early Fs rear disc hub, they should take the same spokes as the 750s with drums.  Honda did not do a 16" rear rim on the spoked sohc 750s.  Up till 76, they used an 18" rim and then followed this with  17".  It sounds like you have the typicial Harley rim conversion and I would be very suprised if a new set of spokes designed for a 16" Harley rim conversion didn't fit your application.  Badly rusted spokes are not worth the effort of cleaning up but mild rust shouldn't cause much structural issues.  If you have any broken spokes I would replace them all.  If you want your spokes to look nice for a good while then you will need to replace them.  If you want to ditch the the harley rim for a 18" or 17" 750 one (or even better an alloy 17" rim from a spoked GL1000 or Hondamatic) then consider that before you buy your spokes.  The 17" rims in particular have a nice selection of tires available and do well with the 130 width tire size.  Of course the tire you bought for your 16" rim would not fit.  Also the 130/90/16 size tire is smaller diameter setup than stock so if you went back to a stock size, the rear of your bike will be a a bit higher up and the gearing will be changed somewhat.  Hope this helps!

[Helo229]

Wow, thanks Eurban - you pretty much covered everything. I've written the whole wobble off as being the rim/wheel. As for the chain, I've yet to check the sprocket tranny side. I've been putting off any work on the bike being as I have tires being delived soon, and will be tearing it all apart then. I've parked the bike for now, I just got off a quick run to town, first ride since saturday morning, and it's at the point I'm no longer comfortable riding it, waiting for some part of the drive to pop off in a corner. I doubt that it would happen, but with my luck, I'd rather not risk it. (just hearing the chain rubbing while I'm moving is causing my spidey-sense to tingle)

For right now, I'm going to look into getting new spokes for the wheel I already have (since that 16" tire is already paid for). Perhaps I'll swap it back to original 17/18" down the road, or just get mags. So, new spokes, new rubber, new bearings, and I ought to be set for a while. Hopefully...

While I have it apart I'll double-check the cush disk for excessive wear, and as Shoemanii suggested, check the orientation of the front sprocket. I knew the PO, but he only ran it .4 miles, and there's no telling what the guy before him did.

Thanks again everyone! Much appreciated!

[dusterdude]

dont know if this has been done yet,have you taken the chain off the wheel and checked it that way?good luck.

[blacknblue_cafe]

I know this is an Old Thread, but I've desperate to swap out my rear rim....

It was said in this thread that the 'spoke conversion' sets for a Harley 16" will most likely work on the CB750F disc brake hub....it seems like the OP could have had some issues.  Has anyone else done this.  The conversion packages are w/in my price range, but if I can't lace the 16" rim upto my hub then there's no point

ANY HELP/COMMENTS???