Tire Runout

[Lloydo]

Hello again, to all who helped, thanks loads, I think we can put the still leaking post to rest. I got it running today, ran the hoses to the floats between the #2&3 carbs, no kinks, & no leaks, & I feel the bike's ran the best it has since I got it. I noticed something else today when I got it going, I saw a mark on the rear tire, & threw it on the center stand. Seems it rubs, about a 15" swath on the tire, I can spin it by hand, but I hit that area, & it binds, squeaks, etc. It's on the left side, where the clearance is a lot tighter with the shaft drive. ( 79 Special ) Could it be my tire, as I can't see how to adjust the centering of the wheel, like you could with a chain driven bike. I'd hate to have it overheat & blow at freeway speed. Thanks for any thoughts.

[prometheus578]

Put it back up on the centerstand. Get a can of carb cleaner(or something similar) with a straw sticking out of the nozzle. Place the straw next to the edge of the rim and slowly spin the tire. Adjustments to the can must be made, but you'll see if the rim is bent this way.
No use doing that to the tire, as we know already that it's rubbing. Could be a bent rim, or could be the tire.
Check the tire's bead to ensure that it's fully seated all the way around the rim.
If you look at the bead area of the tire(next to the rim), you'll see a thin raised line. This line, depending on the tire, could be anywhere from 1/8 to 1/4 away from the lip of the rim. It should be the same distance from the rim all the way around. If it's radically different, the tire isn't properly seated there and is bulging outward. Makes for a wobbly ride, too.
Yes, there is no adjustment for the centering/alignment of the rear tire.

[mro]

Easy check, with bike on center stand
place a wd40 can with the spay tube on it aimed at the edge of rim (perpindiular to rim) very close but not touching.
Spin wheel by hand and watch space between end of spray tube and rim. If bent will notice space get bigger or smaller.
(Prom mentioned wd40 can idea, I use a steel block and place a thin dowl on it and do same)

Can do same for area where tire is rubbing to see if tire is deformed.

Largest tire size for a special

originally posted by TC
As Mason said, the 140, but with some clarification. This should be a black wall, not raised white lettering. I have a Dunlop 140/90-16 on mine, but it was the RWL, and they rubbed on the left side. I'm still running it, but will be sure to get a regular blackwall next time! Also, different tire brands will have slightly different fitting characteristics, so to be safe, a 130/90 is the stock size listed for the specials....IIRC!
T.C.

While your at it would see if you have any side to side play in the wheel. (like checking front wheel bearings on a car)


mro

[mro]

can of carb cleaner

Not fair........
would a swore you said WD
You sure carb cleaner can will work???


mro

[RUSH]

your using the straw end as a reference point to see if the wheel is bent. dont spray anything on your tire.
if you dont understand how to use the straw on the can method devise your own way to determine if your wheel is bent.

[prometheus578]

Sorry MRO,
I never use WD40. That's fer wimmin! Real men, when they encounter a stubborn rusted nut or bolt, just use a little more force till it either loosens, strips, or snaps off.
Sheez.. and you call yourself a mechanic!
What size tire are you runnin', Lloydo?

[Lloydo]

Well, I looked on my bench, & surprisingly enough (with all the carb work lately), there was not only a can of WD 40 with the straw in it, but a can of carb cleaner, straw & all. I thought about it for a second, & not wanting to hurt anyones feelings, grabbed the can of compressed air with the straw in it! Anyway, the rim seemed perfectly true on each side. Near as I could tell, looking for that fine line, mine was not even 1/16th above the rim, seemed even all the way around. I've got a Dunlop K 491 Elite G/T MU90 HB16 on the rear. Could the tire just start to bulge with age? The previous owner said he had just got new rubber before I bought the bike, about 4 years ago. The tread still looks good.

[Lloydo]

BTW, just checked with the straw right where the mark is on the tire itself, it does definetly rub right when the mark comes around, so it seems to be a deformity or bulge in the tire.

[RUSH]

well, you've discovered the problem. The next step is fixing it.
Get new tires.

[prometheus578]

Is this the first time the bike's been running in four years?
What I suspect is... the bike sat for years on the sidestand.
With the weight on the left side(side stand), the bike wants to scoot to the right, which over time will deform the tire. (the reason the bulge is on the left)
Same as with a new bike sitting in a crate. Tires have flat spots on the bottom. After about a hunnerd miles... heating and cooling, the tire returns to it's original shape. This may be the case here.
Hard to say without actually looking at the tire.

You made a good call in using the can of compressed air. The last thing anyone wants to do is to choose the "wrong" side during a "technique disagreement" between MRO and me.

[pggg]

The wheel sideways about 4mm either side with the bolts inside the pivot points adjustable a case of loosen one side/tighten the other but the rim sounds bent

[Lloydo]

No, the bikes been running pretty much the whole time. According to the spray can/straw test, the rim is perfectly true. I don't see anywhere I can " loosen one side, tighten the other". There's just the nut & cotter pin on the shaft side, & the clamp type bolt around the axle on the right side. I'm supposing I better look for tires.

[prometheus578]

Well, the rear tire is supposed to be a MT90(130/90/16)
You're runnin' a MU90(140/90/16)

Some people have gotten away with it, other's have'nt.
I believe this is what T.C. runs... of course, the raised white lettering has all rubbed off.
But if the bike's been constantly run and hasn't set for a long period, I'd suspect the tire.

[TopCatGr58]

Well,
I haven't gotten away with it completely!

Here's a couple of shots showing the lost raised white letters due to the rub factor!




Pggg, sliding the swingarm left or right won't help, because the tire is inside the swingarm assembly. What I have thought about is that the Spline assembly mounted to the rim, possibly putting a washer between each of the 6 bolts that hold it in place and the rim to slide the rim a few mm's to the right. I realize that this could bring the rear out of true line with the front, but a few mm's, how much would it hurt?
T.C.

[xswilly]

heres what we used to do , back when our family was racing stock cars, they had a width limit on the tires

so we would jack up the car and run it at idle, in gear

we had a wood rasp ( couse file ) bolted to a long piece of 2 x4
we would hold it aganist the tire and rub off some of the corners of the tire

seems that you could do that with a tire
just enough to rub off the lettering
i wouldn't go into the side wall
that could weaken the tire
but that would stop the rubbing on the swing arm which would cause heat to the tire
just my 2 cents worth