Front end knocking sound on bumps

[Guest]

Hi all,
On my GS650L I noticed that there is a bad knocking sound when I go over rougher bumps. It doesn't always happen but if I hit something just right there is quite a THUNK coming from the front end. I recently replaced the fork springs with Progressive springs in the front, but I don't necessarily think that's related... I do think I recall having this problem before the spring swap. Although it's been a long time since I really rode this bike so I'm a little bit unsure.

Anyhoo, I got the front wheel off the ground and tried my best to move it around, up down, front to back, trying to see if maybe my head stock bearings (correct terminology??) are shot. That doesn't seem to be the case. Everything seems tight, no notching when I turn the handlebars back and forth, no wiggle to be found.

Any ideas? Could it possible be the size of my preload spacers? The sag seemed fine when I measured. I love riding this bike now with the new suspension but I'm nervous about that sound. Just want to make sure it's not something serious. But I can't seem to pin it down.

[Steve]

Two good sources of knocking noises from the front end. You already suspect one of them.

The head stock bearings (also known as steering bearings) are a good possibility. They don't only make noise if there is a notch in the steering. The notch is usually noticed when there is weight on the front, but in really severe cases, can be noticed any time.

Another way to check for play in the head stock bearings is to roll the bike forward, then apply the front brake. Bike does not have to move very far or very fast, you can do this by straddling the bike and nudging it forward. Your feet don't even have to move, just hit the brake, watch the center pivot to see if it moves in the bearings. If it does, it would be a simple matter of tightening the bearings to spec.

The other possible noise source would be worn bushings inside the fork tubes. A little bit harder to check for play there, without disassembling the fork tubes. And if you are going to go through the trouble of taking the forks apart, it's not much more effort to simply replace the bushings. I believe you are looking for parts 5 and 22 on THIS FICHE, it will cost about $50 for the parts and $5 for the shipping, if you remember to enter the code on checkout.

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[exzachtly1]

Thanks for the input Steve. I did try the rolling/braking and I could not detect any play in the steering head. Everything seems tight.

I think I am going to try slightly longer spacers (increase from 1.25" to 1.75") to go with my new progressive springs. Regarding the PVC, I used a 3/4" from the local hardware store because it was the closest fit I could find... but the outer diameter is smaller than the inner diameter of the fork tubes by a fair bit. Maybe I can find some thicker PVC that has a closer OD to the forks? Also, since my bike did not originally have spacers, I had the same situation with the washer that I added between the spring and the spacer. Slightly smaller diameter. I am really wondering if either the spacers are just too short or if the smaller diameter is causing them to knock around inside the fork tubes over bumps.

I will probably try tightening up the steering head bearing a bit also, just for good measure.

Hoping to get some time to mess with it today.

[Gorminrider]

I had a similar thing on a Honda. The fender hit the horns , so check that. It's suprising how far forks do move on occasion, so check everything in their way... a pulltie around each stanchion will show just how far they are moving.

[exzachtly1]

Will do - I did increase the spacers by 0.5" and took it for a test ride. Still knocking. I think it's coming from down low... but yeah, I will double check to see if anything might be bumping on the fender.

[salty_monk]

You can use a Penny washer (Fender washer) on top/bottom of spacers that are a bit small in diameter.

Other things to check.. Brake pads moving in caliper, caliper moving on sliding pins. Wheel bearing?

[jsandidge]

You can use a Penny washer (Fender washer) on top/bottom of spacers that are a bit small in diameter.

Other things to check.. Brake pads moving in caliper, caliper moving on sliding pins. Wheel bearing?

My 850 makes a knocking noise down low too. It is the calipers moving on the sliding pins. My 750 has the exact same calipers, but they're not loose like the 850.

[Redman]

If it is always right when the front suspension is fully compressed, well, then I would look for something related to that.

If it is somewhat random, then maybe, might it be the tank? Does it do it more or different if tank is full or if tank is low...?
THe front of the tank is suppose to have those rubber cushoins. Maybe one is missing or deformed or something.

[Gorminrider]

I recently replaced the fork springs with Progressive springs in the front, but I don't necessarily think that's related... I do think I recall having this problem before the spring swap. Although it's been a long time since I really rode this bike so I'm a little bit unsure.

As my rule of thumb, I ALWAYS suspect the last thing I did when something new shows up. it needn't be the springs done but it might be too. Sometimes, other things get changed in the process....

...maybe put a jack under the engine to free the front, take the springs out and try to reproduce the rattle/clunk.

[Tom R]

Shake the fender to see if the rivets are loose.

[mrbill5491]

My 750 started doing that when I had just got it. Think it had 600 miles on it, took it in and they couldn't find what it was. When I got it home, I took my turn and searched for the problem, found it, one of the front wheel bearings was going bad. Took it back to them and they were a bit embarrassed they didn't find it. One bearing had a bunch of slop in it and the other one was getting there. Warranty work.

[80GS1000]

Worn out floating brake discs can cause this too. I had this issue on my GSXR: https://www.youtube.com/watch?v=bCW6qaztQuU

[Steve]

Worn out floating brake discs can cause this too.

Good thing to keep in mind, but GSes don't have floating disks.

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[exzachtly1]

I sprung a leak in the left fork so I took the forks completely apart to put new seals in, everything looks ok as far as I can tell. No broken or deformed parts, and the bushings look fine to me.

Things were very, very dirty in there though as you can see in the pics... I should have just done this the first time I had them apart

What should I look for to know whether the bushings are bad ?

Pics:

20191029_131926.jpg

[exzachtly1]

Another pic:

20191029_133434.jpg