Author Topic: strange bounce (Read 50407 times)

i-man · « **Reply #25 on:** November 04, 2014, 01:24:23 PM »

I'll post here, but i should probably start a new thread.

Does anyone know if Ride-on ATV is different then Ride-on MC? The ATV ride-on is half the price.

i-man · « **Reply #26 on:** November 04, 2014, 07:29:26 PM »

sorry for that last post. that just muddies the water.

Anyway, I just pushed down on the rear of the bike in an attempt to test the rear shock. it didn't bounce. In fact it seemed quite stiff. Don't know if that's a good thing or not.

Novafrk · « **Reply #27 on:** November 05, 2014, 04:43:23 PM »

It sounds better than mine. Mine is so soft/weak that I almost get the rear tire to come up off the ground... :nono

Motorhobo · « **Reply #28 on:** November 06, 2014, 09:59:48 AM »

How still is stiff? No compression at all? I had no compression on my old Progressive and the shock was kaput, I was basically riding a hard tail. That's not supposed to be good for your final drive among other things.

i-man · « **Reply #29 on:** November 06, 2014, 10:50:01 AM »

I did't jump up and down on it 'cuz the front wheel is off, but there was some give. It was pretty stiff though.

If this is a sign that something is off, is there any other ways to check it?

i-man · « **Reply #30 on:** November 22, 2014, 03:34:04 PM »

since I last posted, I've balanced the front tire with 8 oz of Ride On and read up on adjusting the front forks and did a little of that , to the best of my abilities. I took it for a test ride and the bounce seems about the same. I can stand on the pegs and lean over the handle bars while going down the road and the front wheel looks off, as in there looks to be a slight wobble.

It doesn't really seem unstable and it handles fine, but I'd like to figure this out.

Any ideas?

hector planter · « **Reply #31 on:** November 23, 2014, 03:02:33 AM »

I ve just read through this thread and I belive nobody has mention something called " sticktion", and your gonna love this. Assumming your tyres is fitted correctly, wheel not buckled, bearing , tyre pressures, fork oil and the head bearings are fine it only leaves sticktion. Still none the wiser then i will explain. Back in the day, when moto bins still had a forum, and folk still rode 2 valve twins sticktion was a big thing and there was quite an impressive thread on it ( airheads too). In a nut shell Bmw forks are made to very fine tolerances and a slight misalignment would cause stickion, that is the forks stick in certain position due to the friction caused by miss alignment, they dont lock fast it just takes a little jolt to get them going. Try this, you've stopped your bike and the forks have depressed during breaking your are idling waiting for the lights say, you let go of the front brake or roll the bike backwards and the for pop back up a little, that is sticktion.

The cure is quite a pain, I did to my R80. What you need is a dial gauge and a sheet off glass, you then put the bike on the centre stand with the front wheel in the air, difficult enough I know, the bike has too be firmly pinned down so it cant fall. remove the fairing ,front wheel mud guards and fork sliders. you now have just the fork stantions comming out of head brace, so with the dial gauge measure between the forks from top to bottom to make sure they are parallel, looking for very low tolerance here. Next your get a sheet off glass lay it across the fork stantions and it should touch in four places, you should not be able to wobble it, feeler gauges are good here as we are talking thousands of an inch. This of course assumes you stantions are strait in the first place, you can check these by removing them and rolling them on a flat surface.
Once you've decide that you have a misalignment the pain really begins as you are going to try to correct it by applying force to the fork stations over night to correct the misalignment, remeasure and repeat the process. To be clear it is the fork head stock which you are trying to realign so all clamps have to be tight on the head stock and if the head stock is ever disturbed the process has to be repeated. It took me atleast ta week to do this but was worth it in the end.

hector planter · « **Reply #32 on:** November 23, 2014, 03:12:32 AM »

Sorry what I ment to say was read K75 fork tuning in the lieberry.

i-man · « **Reply #33 on:** November 23, 2014, 08:55:48 AM »

Yeah, i've been reading about that for a week or so. The sad thing is I kinda' know that's the problem. crap. Sounds like a real PITA to figure out.

i-man · « **Reply #34 on:** November 23, 2014, 10:47:33 AM »

I tried this fix http://forums.bmwmoa.org/archive/index.php?t-64101.html
No dice.

i wonder if Japanese of 'merican forks would have the same problem?

hector planter · « **Reply #35 on:** November 23, 2014, 11:25:07 AM »

The first time is always the hardest, I bought a cheap dial gauge on ebay and made a bracket for it, the glass from the kitchen top came in handy too. Ratchet straps and some big bits of wood are pretty useful when it comes to stressing things into place.

i-man · « **Reply #36 on:** November 23, 2014, 12:12:59 PM »

the thing that bugs me about that whole procedure is having to use very imprecise means to achieve very precise results! Straps and blocks of wood?! tensioning over night!?! Really BMW?! (that isn't directed at you Hector, I read about the same procedure on line)

Goldwing forks are 41mm and they're cheap and plentiful, are they subject to the same absurd need for precision? i'm going to see what I can find.

johnny · « **Reply #37 on:** November 23, 2014, 01:55:14 PM »

im betting there is either nothing worng... or if there is its the rear tior or the rear shock...

assuming the tior aints whack...

1... remove wheel... drain both forks... refill to proper levels with honda ss8-10 suspension fluid...
2... make sure front brake pads have even wear... reinstall the front wheel butts donts tighten it down yet...
3... with front axle installed with spacers and all... with loose pinch bolts... on center strand...
4... cycle front brake lever till you gotts the brake pads tight on the rotors...
5... hold in the brake lever and bounce the front tire on the ground about 10 times...
6... keep a hold of the brake lever and tighten the pinch bolts...
7... now you know your front tior is centered...
8... spin the wheel taking note to the rims relationship to the fork... both sides should be true...
9... if you gotts whackness it could be the wheel... if the wheel is true... yeeeehaaaa...
10... ride it... if the bounce is still there it could be the front tior...
11... now go to the back tior... spin it... note the rims relationship to the swing arm... both sides should be true...
12... if you gotts whackness it could be the wheel... if the wheel is true... yeeeehaaaa...
13... now... the rear shock...

i had a front end wobble once... the tior was about 5mm from the swing arm... until it got hot... then it would widen out and barely rub the swing arm making the front end wobble... an old german k man named mathais in long beach ca showed me the rub... would not see it on a pre race inspection cause the tior was cold... butts sure enough it was rubbing when it was hot...

j o

i-man · « **Reply #38 on:** November 23, 2014, 03:12:15 PM »

thanks Johnny. I'll give that a shot.

one thing that makes me think that it is stiction is the axle is very hard to take off and on. I've read that it should be easy and that if it's not easy to take on and off then it's likely forks out of line.

Anyone have the same experience with difficult axle removal?

i-man · « **Reply #39 on:** November 25, 2014, 05:23:53 PM »

Spun the front wheel and there is a definite wobble. Doesn't seem like that could be the forks, cuz there would need to be load on the forks for it to have that effect? Anyone agree or disagree with this?

couldn't tell if it was the rim or tire that looked wobbly. The wobble was very localized, like a bicycle rim the has a couple of spokes too loose or too tight.

time to add a bit I probably should have from the beginning, but I didn't think it was relevant. I rode the bike for several, not sure how many, a but more then 20 and less then 100 miles, with the pinch bolts, all four, loose. When I first noticed the 'bounce' i rode home and examined the front to see if anything was amiss, and discovered that the pinch bolts were so loose as to be close to falling out.

Did I likely damage something, and what?

hector planter · « **Reply #40 on:** November 29, 2014, 03:52:27 AM »

I think you have found the cause to your problem, for as I understand it every time you disturb the forks you have to recheck for fork alignment. Also a point to consider, you may or may not of heard off it but on the BBC in the seventies there was a program called tomorrows world, it ran for years and was about technical innovation. Anywho, they did an article about Bmw motor cycle forks and how due to extremely fine tolerances to which they made them they had eliminated tank slappers, now I suspect they did something pretty unusual or they would never have gotten a feature on the program. BMW also used to have a policy of almost never changing anything from year to year and when they did make changes you could usually retro fit them to earlier models. This practice has probably ceased now and the changes all started with the invention of the k bike, which kind of followed the same pattern for a fair while. So what I am saying is your forks were most likely designed in the early seventies, when they were a breakthrough. If you have never actually checked your fork stantions how do you know that they are straight to start with or that where the clamps were loose some thing has'nt worn, ever so slightly.
One day you will solve this and then let us all know.

Motorhobo · « **Reply #41 on:** November 29, 2014, 06:04:02 AM »

If you rode loose pinch bolts then just tightened the bolts then the wheel wasn't given the chance to self-center. Did you follow the procedure for centering Johnny shared below?

It does sound like the forks are out of alignment based on the axle not coming out easily. Did that symptom first appear after you rode with the loose pinch bolts? If it did and I were I were in your shoes, I'd loosen everything all the way up to the fork tubes, make sure the fork tubes turn in their bores at the triple tree, reassemble everything and hope it centers out again on reassembly. Take you a couple hours hard work. If you still have a problem, then at least you know you have a problem.

I learned that there's a sequence to follow in tightening the front wheel mounting assembly:

1) Put on the wheel and calipers leaving all bolts loose.
2) make sure the calipers are retracted all the way back in the bore (use screwdriver to push them back or just rock the calipers back and forth with bolts off)
3) Tighten the hex nut on the axle to spec.
4) Tighten the clamp bolts adjacent to the hex nut to spec.
5) Bounce the wheel up and down a couple times so that everything self-centers.
6) Tighten the clamp bolts on the other side.
7) Tighten the caliper mounting bolts to spec.

This is a little different than what Johnny suggested. I'd try that, and if it doesn't work, disassemble to the triple tree and reassemble and recenter. Btw I don't mean taking the sliders off the tubes, I just mean making sure the tubes aren't seized up in the bores.

i-man · « **Reply #42 on:** November 29, 2014, 05:51:50 PM »

thanks y'all.
i've loosened and re tightened and bounced and spun in every way I've found here and on the net in general.

I now don't think It's the forks. Here's why-

the visibly evident wobble is in one spot. doesn't it seem the whole rim/wheel would be out of sorts in stead of everything looking good and straight except for this one spot?

I spun the front wheel with the wheel off the ground, seems the forks would have to be really out of whack to show an obvious localized wobble with no load on them.

I've tried to see if I can tell if the wobble is the tire or the rim, and it's hard to say, but if I had to say I'd say it's the tire. the break rotors spin true, near as I can tell.

I'm certainly not trying to argue with anyone. If anyone thinks my reasoning is way off, please say so. I just want to get this figured out.

Dennis de Vries · « **Reply #43 on:** November 30, 2014, 03:26:24 AM »

Not to sound like a know it all, but if you can see a wobble while spinning the wheel, there's your problem....
So your forks are fine if i read it correctly.

Try to find out if the wobble is in the tire or in the wheel, maybe the tire is not properly seated, maybe there's a fault in the tire or your wheel itself has seen beter days.
What i mean to say, stiction in the forks doesn't show when spinning the wheel freely of the ground....

Just tried to do some logical thinking here from reading your topic, hope it's of some help....

Greats Dennis

hector planter · « **Reply #44 on:** November 30, 2014, 04:02:44 AM »

it is relatively easy to check for a buckled wheel, just spin it at you'll see, it helps if you can construct a device for measuring any deviation a fixed pointer mounted some how near the wheel rim will easily show how true the wheel is as you turn the wheel the gap between your pointer and the rim should remain the same, however a small deviation is allowable, there will be a limit set by BMW. You should also be able to check that the tyre is fitted properly. i had this problem on my R80, there are a set of concentric marks on the lip of the tyre which should be visible where the rim and the tyre meet. The gap between any of these marks and the wheel rim should be the same all the way around the wheel.
This was a problem on my R80 and it took me years to sort it out. Eventually having tried professional tyre fitters and changing tyres I mananged to sort it out myself by blowing the tyre up to 120 psi and finally getting it to seat correctly. The symptons of this badly fitted tyre were only noticable at high speeds 80 mph plus.

i-man · « **Reply #45 on:** November 30, 2014, 08:38:27 AM »

i think I'll try putting a LOT of air in it and see what happens. it acts just like a tire that hasn't been set properly. The only reason I haven't considered it to this point is the problem (bounce) came on all the sudden. Seems if the bead wasn't set, it would have been there all along.

Motorhobo · « **Reply #46 on:** November 30, 2014, 11:00:26 AM »

That still doesn't answer the question of why the axle won't come out easily. Were you able it get the axle out at all and was there any corrosion or grease on it? There should be a little grease on the axle to help it slide in and out. It's always slid in and out easily for me. Gotta wonder what that's all about if it doesn't.

i-man · « **Reply #47 on:** November 30, 2014, 01:08:23 PM »

Yes, I have the same concern. The axle doesn't, nor has it ever, come out easily. I greased it the first time I had it out, and through this whole ordeal i've probably had it out 3 or 4 times, and it's only marginally easier now, with the grease, then it was the first time I pulled the axle.

johnny · « **Reply #48 on:** November 30, 2014, 03:09:11 PM »

i recall the first time i pulled my axle... i had help... seka...

j o

Motorhobo · « **Reply #49 on:** November 30, 2014, 03:46:07 PM »

Quote from: johnny on November 30, 2014, 03:09:11 PM

i recall the first time i pulled my axle... i had help... seka...

j o

You can still get help from that source...apparently the person in question is still active...but somehow it just ain't the same and my guess is your axle won't budge.

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Author Topic: strange bounce (Read 50407 times)