Topic: Front End Bounce

[DaveBarbier]

I mentioned this in another post but thought I'd have something dedicated.

At around 35-45 mph my front end bounces. It's a pretty substantial bounce up and down. No lateral movement. I notice it more while at a sustained speed or when slowing down from like 60 or 50 mph, it's much less severe while accelerating. It doesn't increase in frequency as I go faster.

I balanced both wheels on a static balancer I made. Only the front required weights. When I had them on the balancer I didn't find the wheels to be out of round much. Then spun pretty smoothly.

I'm not ruling out the rear as the culprit but I compressed and relaxed the springs with channel locks and that didn't seem to do anything.

Any ideas? Front forks need to be rebuilt? New wheel bearings? Thanks in advance.


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1978 Honda CB550K

[Grabcon]

Make sure that the wheels have been properly trued, side to side and ovality (make sure it is round). Check the tires for flaws, ply separation, bubbles, etc. If the tires are more than 3 or 4 years old I would replace. That is about the life of a tire regardless of the mileage.

If the is no seal leakage on the fork seals I would drain the fork oil and flush, then replace with the recommended amount and weight of fork oil.

Make sure your head bearing is greased and torqued properly.

If these things don't resolve the issue check the rear shocks, they may be shot. Spring tension is not the issue it is the dampening of the rear shock or fork that will allow for the bounce.

[InTheStreet]

I had a similar issue once right after I had new tires mounted and balanced by a shop.  Even took the bike to them to complain.  I had a spark plug boot that was going bad and had the wrong resistance.  I guess 35-40 was just the right speed/RPM, etc for it to bounce the front end.  I've also had shakes like that from out of sync carbs, using the wrong screw for a vacuum port plug, fouled plug and probably some other tuning issue.

[DaveBarbier]

I had a similar issue once right after I had new tires mounted and balanced by a shop.  Even took the bike to them to complain.  I had a spark plug boot that was going bad and had the wrong resistance.  I guess 35-40 was just the right speed/RPM, etc for it to bounce the front end.  I've also had shakes like that from out of sync carbs, using the wrong screw for a vacuum port plug, fouled plug and probably some other tuning issue.

It seems like it's based on speed and not RPM. It revs up nice and smoothly with power across the whole rpm range. No stuttering or anything. I'm thinking the ignition and carbs aren't the issue, but I'll definitely look into that just to be sure. Thanks.


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1978 Honda CB550K

[strynboen]

mine 550 did the same..the tire (avon) vas flat in mitten of tire ,,but not veared down..it gave a unstabile steering..got a new tire..and all vas gone..

[DaveBarbier]

Make sure that the wheels have been properly trued, side to side and ovality (make sure it is round). Check the tires for flaws, ply separation, bubbles, etc. If the tires are more than 3 or 4 years old I would replace. That is about the life of a tire regardless of the mileage.

If the is no seal leakage on the fork seals I would drain the fork oil and flush, then replace with the recommended amount and weight of fork oil.

Make sure your head bearing is greased and torqued properly.

If these things don't resolve the issue check the rear shocks, they may be shot. Spring tension is not the issue it is the dampening of the rear shock or fork that will allow for the bounce.

I put on new tires and tubes back in October. I just did a balancing but not a truing. Is there a lot of risk of the spokes breaking due to age if I try and true them? I got a quote from 2 places for balancing and truing and it would be over $300 total. Not to mention replacing spokes if one breaks. Does that seem high? Oh, also, I forgot to mention that when I put the new tires on I DIDN'T line up the yellow dot with the valve stem. On both tires they're about 180° off.

Do I have to remove the forks for draining and flushing? The fork seals are good, I don't see any seepage.


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1978 Honda CB550K

[strynboen]

air pressure as book says...

[Grabcon]

I have my wheels trued every time I put tires on. My wheel guy here in Denver has never mentioned anything about being risky to damaging spokes or rim. On spoked wheels especially with old Alloy rims like mine he says that is required because the loosen overtime while riding.

[flybox1]

You don't have to remove the forks to service them. There should be a drain screw on the outside of the lower, just above the axle.

+1
New fluid cured the bounce on my 350f.  Rinsed them several times with mineral spirits before new was added.  They hadn't had new fluid in 35 years.

[DaveBarbier]

I have my wheels trued every time I put tires on. My wheel guy here in Denver has never mentioned anything about being risky to damaging spokes or rim. On spoked wheels especially with old Alloy rims like mine he says that is required because the loosen overtime while riding.

Ok, thanks. That makes me feel better. I'll do the fork oil change (manual says use premium ATF fluid) and then if that doesn't do it I'll dismount the tires and make a truing stand and get them nicey nice myself.

You don't have to remove the forks to service them. There should be a drain screw on the outside of the lower, just above the axle.

+1
New fluid cured the bounce on my 350f.  Rinsed them several times with mineral spirits before new was added.  They hadn't had new fluid in 35 years.

Mineral spirits eh? I was planning on just flushing with oil a few times. I'll look into this. I'd love to get them as clean as possible.

Thanks


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1978 Honda CB550K

[tlbranth]

Is your tire seated properly? Tube caught under tire lip?

[DaveBarbier]

Is your tire seated properly? Tube caught under tire lip?

Don't think so. I was very careful mounting the tires and tubes. I've done it a few times before. The tire seems to be seated evenly and securely and there's no sign of the tube being pinched.


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1978 Honda CB550K

[tlbranth]

Does your balancer have its own bearings or does it count on the wheel bearings to turn?

[DaveBarbier]

Does your balancer have its own bearings or does it count on the wheel bearings to turn?

It has it's own bearings. It's a suuuuper simple setup that took a couple minutes to make.



There's the picture. Just bearings bolted on pieces of wood clamped to saw horses that the axle sits on. I had to move it indoors after this shot because a slight breeze would spin the wheel.


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1978 Honda CB550K

[tlbranth]

Yup, that's good. Skate bearings are the inventor's salvation.
Looks like maybe you're down to forks not damping sufficiently.

[DaveBarbier]

Ok, so I'm changing the fluid right now and my clymer manual says there's a locknut between the spring and fork bolt. But on my '78 CB550 there was no lock nut. It's just the fork bolt, oring on the bolt and spring.  Missing something or just the manual showing a different fork?





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1978 Honda CB550K

[strynboen]

my 1978 have also no bolt at top..it are for older modells

klik on photo to make it bigger..i took the bottom aut vhen shift sealings...but the oil have to fill in at top..

[DaveBarbier]

my 1978 have also no bolt at top..it are for older modells

Thanks! Also I checked my tire pressure earlier and it's the amount the tire calls for.


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1978 Honda CB550K

[BobbyR]

This could be air pressure also. If you use the Honda recommended pressures, they were too low for the construction of modern tires.  When you say you put in the amount of air they call for, it does no say where the number came from? Most of us go up a few lbs and test.

 
It will cause a deceleration wobble. One of the other usual suspects is the steering head bearing.

Changing the fork oil is always a good thing to do on a regualr basis.   

[DaveBarbier]

This could be air pressure also. If you use the Honda recommended pressures, they were too low for the construction of modern tires.  When you say you put in the amount of air they call for, it does no say where the number came from? Most of us go up a few lbs and test.

 
It will cause a deceleration wobble. One of the other usual suspects is the steering head bearing.

Changing the fork oil is always a good thing to do on a regualr basis.

On the side of my rear tire it says max load and pressure cold is 617 lbs at 36 psi. Right now it's about 32 lbs. the front is also a couple lbs under the max psi. Should I go right to the brink?

To me because it's such a sustained rhythmic bounce it seems like it would be suspension. If it were tires I'd think it would increase as I go faster. Same with bearings. Bad assumption?


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1978 Honda CB550K

[DaveBarbier]

Did you remove #10 to drain the oil first? Then it's just a matter of "cycling" the forks to insure all fluid is out. As another ousted, flush with mineral spirits.

Then add an exact amount of fluid to each fork and return the fill cap.

Yup, I removed the little bolt and copper washer and pumped the forks up and down and the fluid shot out. Then I raised the bike and removed the filler bolt caps. I didn't flush with mineral spirits. Is that necessary? I flushed it with ATF 3 times then put about 5.1 oz of ATF like the OM says. I'm going for a test ride now. It's not easy to measure the exact 5.1 oz because I don't have a graduated cylinder that's that accurate.


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1978 Honda CB550K

[DaveBarbier]

You're probably fine. Remember to inspect he drain hole after riding; those copper washers some times will not re-seal after first service in 25+ years.

Went for a ride and it still bounces. Then added a little more air in the tires. That maaay have helped a bit but hard to tell. The fork drain plugs are bone dry.

I'm thinking the two next things to try are steering head bearings and dismount the tires and make sure the wheels are true. Then remount, balance and install. Just to be sure, the yellow dot is supposed to be lined up with the valve stem, right?


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1978 Honda CB550K

[BobbyR]

You're probably fine. Remember to inspect he drain hole after riding; those copper washers some times will not re-seal after first service in 25+ years.

Went for a ride and it still bounces. Then added a little more air in the tires. That maaay have helped a bit but hard to tell. The fork drain plugs are bone dry.

I'm thinking the two next things to try are steering head bearings and dismount the tires and make sure the wheels are true. Then remount, balance and install. Just to be sure, the yellow dot is supposed to be lined up with the valve stem, right?


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1978 Honda CB550K

I think you are doing all the right things. If you do a search on air pressures, you will find people are running 36lbs and higher. These are expereinced long distance riders. I have done head bearings last year, it will lay your bike up for a while unless you have time or are very good. For most guys it is a prject for after the season. Who want to be wrenching when you can be riding!

I would run them up to 40lbs try it and if it works, back it down and see if it comes back.

[DaveBarbier]

You're probably fine. Remember to inspect he drain hole after riding; those copper washers some times will not re-seal after first service in 25+ years.

Went for a ride and it still bounces. Then added a little more air in the tires. That maaay have helped a bit but hard to tell. The fork drain plugs are bone dry.

I'm thinking the two next things to try are steering head bearings and dismount the tires and make sure the wheels are true. Then remount, balance and install. Just to be sure, the yellow dot is supposed to be lined up with the valve stem, right?


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1978 Honda CB550K

I think you are doing all the right things. If you do a search on air pressures, you will find people are running 36lbs and higher. These are expereinced long distance riders. I have done head bearings last year, it will lay your bike up for a while unless you have time or are very good. For most guys it is a prject for after the season. Who want to be wrenching when you can be riding!

I would run them up to 40lbs try it and if it works, back it down and see if it comes back.

Ok, thanks for the heads up. I'll definitely try more air pressure first. Then true and balance the wheels. I'll save the head bearings for a last resort, ha.


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1978 Honda CB550K

[DaveBarbier]

If you do steering bearings, get tapered All Balls. Makes the swap a snap, and improved handling. Not saying this is your issue, but with a little planning, you should be able to do them in a long night.

Ok yeah that sounds good. Might as well do an upgrade while I'm at it. Thanks for the info.


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1978 Honda CB550K