Topic: Front end "hop" at 35 mph.

[MCRider]

Certainly absolutely front end hop can originate in the rear. Someone said maybe not, but its certaily a possibility.

And fork oil could be the culprit as you say. With no rear suspension the front must be totally compliant. A lighter oil may be in order, or lower oil level.  A reprint of the proper fork alignment tightening sequence is in order for this thread.

Have to return to this: But he did say it didn't do it at first. And with no actual changes by him, it is still supsicious that the tire has bubbled internally.

[Alan F.]

He?

OK so after some more investigation, I found my actual receipts and not generic fleabay invoice.
My front tire is a KENDA 100/90/19 k673 and my rear is a Cheng shin 130/90/17 c907.

OK, so the rear is a Cheng Shin, this supports the theory that there is a tire at fault.  A ply separation or something, possibly a bead not seated correctly, and possibly a bunch of inner tube caught under the bead somewhere. Also you could simply have a high spot on the tire, if you have a center stand please raise the rear wheel off the ground and run the same checks as were recommended for the front for wheel true and runout. Maybe you'll find something that stands out.

KingCustonCycle.com had a post where he had a front end hop on two (or was it 3) different bikes, all hard tailed, all modified frames, all rebuilt everything, running Cheng Shin front tires, for the King it was the tires themselves, for each bike a different brand of tire cured the hop he was experiencing.


http://forums.sohc4.net/index.php?topic=8909.0;all   In reply #8 Hondaman says:

Here's how roadracers align the front forks after new seals:
1. Tighten the fender brace first.
2. Tighten to spec, then slightly loosen, the axle caps. Just a 1/4 turn loose from tight will do.
3. Loosen the lower triple tree clamp bolts about 1/4 turn.
4. Get a friend to help next.
5. Bike on centerstand (preferably), lock the front brake and force the tubes down-up-down about 4-6 times, like a pogo stick, rapidly. Don't leave the ground with the front tire, or start the count again. This sets minor twist imperfections and alignments out of the lower end of the sliders.
6. Finish the pogo business with your weight ON THE BARS and have your friend tighten, in order, the axle clamps, then the lower fork tree clamps.

The result of this little trick will be smoother sliding, less stiction and ultimately less seal leakage. Especially at 100+ MPH. 

Cheers.
-A

[mlinder]

She still hasn't told us what her tire pressure is.

[HavocTurbo]

Kenda makes a pretty decent tire, but with all "cheaper" tires they can have defects. They are more known for their dirt tires.

I agree with 754. A lot of wheel people forget that a wire wheel can be out of round also. Not just out of shape.

One thing to try right away, get the front end in the air and rotate the tire running your hands over it slowly. Looking for any and all imperfections in the "feel" of the tire. Be sure to check the sidewalls also. Most high end tires I have noticed are prone to sidewall defects than anything else.

If that checks out then I'd move on to the wheel - then forks - then steering bearings - then trash it. 

[754]

I said it, Back end problems, can easily transfer to the front, but more like a wobble or shaking its head.

I suppose it is not impossible that the rear could cause front hop..BUT, the defect should  be easily seen by eye, or by spinning the wheels..

[mlinder]

WHAT IS YOUR TIRE PRESSURE?

[Pinhead]

Here's how roadracers align the front forks after new seals:
1. Tighten the fender brace first.
2. Tighten to spec, then slightly loosen, the axle caps. Just a 1/4 turn loose from tight will do.
3. Loosen the lower triple tree clamp bolts about 1/4 turn.
4. Get a friend to help next.
5. Bike on centerstand (preferably), lock the front brake and force the tubes down-up-down about 4-6 times, like a pogo stick, rapidly. Don't leave the ground with the front tire, or start the count again. This sets minor twist imperfections and alignments out of the lower end of the sliders.
6. Finish the pogo business with your weight ON THE BARS and have your friend tighten, in order, the axle clamps, then the lower fork tree clamps.

The result of this little trick will be smoother sliding, less stiction and ultimately less seal leakage. Especially at 100+ MPH. 

Hmm... Looks like I've got another thing to do on my day off.

[stephan]

i had this problem too at 2 bikes K7 and F1
the problem comes from the fork the slider tolerance was too high
you can test it when you take off the fork tubes and pull it in a face block and rebuild the oil gasket now you can handle the standpipe up and down it should not more than 5mm.
i tested all forks i had and the most older k forks was defective the getting oval over the time and many miles.



sorry my english is so bad

[MCRider]

Here's how roadracers align the front forks after new seals:
1. Tighten the fender brace first.
2. Tighten to spec, then slightly loosen, the axle caps. Just a 1/4 turn loose from tight will do.
3. Loosen the lower triple tree clamp bolts about 1/4 turn.
4. Get a friend to help next.
5. Bike on centerstand (preferably), lock the front brake and force the tubes down-up-down about 4-6 times, like a pogo stick, rapidly. Don't leave the ground with the front tire, or start the count again. This sets minor twist imperfections and alignments out of the lower end of the sliders.
6. Finish the pogo business with your weight ON THE BARS and have your friend tighten, in order, the axle clamps, then the lower fork tree clamps.

The result of this little trick will be smoother sliding, less stiction and ultimately less seal leakage. Especially at 100+ MPH. 

Hmm... Looks like I've got another thing to do on my day off.

Yes, and after reading this, I see the object. It might be that one should remove the top nuts, let the forks collapse entirely, then tighten up the clamps. That would ensure the most parallelism.

[Inkscars]

Sorry. super busy weekend. One of my forks is a little low on oil from me not tightening the bleeder screw up immediately when I changed my seals and I had less than effin 20 lbs in the front tire. After airing my tires to 29 or 30
my hop is gone. I'm still going to add some fork oil. I can't believe I forgot about that. ugh.


Thanks for the tip on the forks. I will be using that.

[mlinder]

Sorry. super busy weekend. One of my forks is a little low on oil from me not tightening the bleeder screw up immediately when I changed my seals and I had less than effin 20 lbs in the front tire. After airing my tires to 29 or 30
my hop is gone. I'm still going to add some fork oil. I can't believe I forgot about that. ugh.


Thanks for the tip on the forks. I will be using that.

Heh. Always check your your tire pressure

[Alan F.]

Ah the simplest cause, good thinking Mlinder! 

Well at least we all put together a good thread with all of the bases covered, should fill in some blanks for those searching the topic.

[Inkscars]

Absolutley, this thread will help someone that it may not be so simple.
Great job guys. Now, hopefully they'll hold air.
How often do you guys think you have to add air to tubed tires?

[mlinder]

Absolutley, this thread will help someone that it may not be so simple.
Great job guys. Now, hopefully they'll hold air.
How often do you guys think you have to add air to tubed tires?

That all depends on how fast it loses it's air

I check my tire pressures about twice a weekm but fact is, the more you ride, the quicker you'll notice that something has changed adn needs to be checked.

[Inkscars]

I figure I'll check twice a week for a couple weeks, but then If I notice it's ok, ill just do it when I get gas.
I'm so glad it was me beinga  twit and not something more serious. 

[Alan F.]

Sounds like a good plan Ink, I check pressure every couple fill-ups, along with checking/lubing the chain, and checking the oil.  Or at least I try to...

[Inkscars]

DAMNIT!
Thanks for reminding me, I meant to lube my chain before I took off this morning. Lunch time I guess.

[HavocTurbo]

I check oil, chain, tires, and anything else that can lose anything every other fill up.

I ride almost everyday so the constant use warrants the checking.


Too bad these old bikes aren't like new cars. 

[754]

I am not buying the whole old roadracer trick.. but if your frontend is of unknown straightness, its the way to go.

 I think a few forks have slightly bent tubes, when these are run, especially  not with the bends going same way (after being re & re'd) you are going to get  binding and a lot of wear, when it is near bottoming.

 If your components are straight, you can check the fork alignment by eye or straightedges. Has to be checked again if you lay it down or hit something.

 The fork lower caps being tightened under compression, makes sense, should be able to do easier maybe if you hold down with tiedowns  (trick is to tighten both at once..)

[stresssolutions]

How often do you guys think you have to add air to tubed tires?

Great thread.
I have not added air since the spring start, at the end of March.  Nearly 4,000 miles later...

[Inkscars]

so yesterday i tightened my clamps, and trees after measuring the fork height difference. One of my tubes was sitting close to a half inch further out of the upper tree than the other one. I jacked up the front of the bike and loosened bolts, adjusted and the tightened all of the upper and lower bolts. Then, went on a 70 miles round tripper. Since the hop happened the first time, I've been very weary of experiencing the same sensation.
The bike was fine, the first 30 miles or so (highway riding as well) and i had no complaints until i got off the highway. the hopping started again.... Pulled off into a gas station, checked the air pressure in the tire, checked all my bolts to make sure they were tight and then, decided that I only had a mile to go, rode it out the rest of the way to my desination. I checked my spokes for a loose one, i checked the tires for bubbles and separation... NOthing.....I asked my partner to make a note of the road condition on the way back when we left.  hop hop hop all the way to the highway, get on the highway, hop stops. WTF. we get home and I ask, "how was the road over there?" he replies that it was bumpy, but it didn't make his bike wobble. I explain that it's not a wobble. it's up and down and he says "yea, that road sucked."
Uh. ok. So, my bike is picking up on road imperfections moreso than other bikes..... Now I find myself wondering if it is because it's so low and hardtail or because of bearings, tires, etc....
Blah. This winter when I do the transplant, I'm doing every bearing on this bike.

[HavocTurbo]

Bearings sometimes make that sensation.

It's one of the stops on our way to figuring it out.

[Pinhead]

What road were you bouncing on?

[Jerry Rxman Griffin aka MuthaF'er]

I'm voting for the hard tail and less than optimal brand front tire. Your front end is having to do the work of the back end too. Where are you at as far as front tire pressure?

[andy750]

Im with Jerry on this...hardtail will affect the front end differently compared to stock. Why not find a good-surface road and run up and down it a couple of times at varying speed. This will tell you if its the road or the bike. I dont think its the wheel bearings....

good luck
Andy