Topic: Front end shake- Not your typical thread for this!

[ef9tuning]

Hello guys,

 it's been awhile since Ive posted on here but you all have always been super helpful! I promise this isn't the average why does my front end shake thread.
I have been battling this for some time now, years actually. The front end shakes beginning at around 50mph, doesn't matter if its maintaining speed,deceleration or accelerating. Anything below 50mph doesn't seem to cause any issues. Now here's the real kicker, below you'll find everything I have done/replaced to resolve this.

1978 CB750K

New front and rear tires 28lbs psi front and rear (solo riding) 100/90/19 Bridgestone Commander II  130/90/17 Bridgestone Battlax BT45R
New spokes front and rear, trued
New all balls wheel bearings front and rear
New brakes front and rear
Fork oil replaced...twice
New all balls steering head bearings
New bronze swing arm bushing, greased filled using zerk
New rear cush drives
New suspension bushings
New rear suspension shocks/springs
New front and rear sprockets (OEM sizes)
New chain, properly cleaned and lubed

Only thing else I can think of getting is steering damper.

Here's a short youtube video of me riding so you can see the shaking:
https://www.youtube.com/watch?v=3kH_eGzH64g

[Kevnz]

Ever dismantled the forks to check for bent tubes\damage? Never been in an accident that may have bent the frame? Not liklely, but is the master cyl standard? Causing an oscillation because of imbalance (long shot, I know, just a suggestion). Certainly a weird one.

[Don R]

 I'm assuming the wheels were properly balanced but don't see it on the list. I had a shop screw mine up once so I started doing it myself. 

[ef9tuning]

Ever dismantled the forks to check for bent tubes\damage? Never been in an accident that may have bent the frame? Not liklely, but is the master cyl standard? Causing an oscillation because of imbalance (long shot, I know, just a suggestion). Certainly a weird one.

You may be onto something here... I am the third owner of this bike. I did have a low side spill at about 15-20mph that gave me a level 3 clavicle separation. My shoulder and center stand ( the part you use with your foot) took all the brunt. I am unsure how to check if the frame is bent in anyway. When I did the steering bearing the forks did not seem bent but, that isn't really checking them. Ive also read that someone found one of their fork spring split in half that also caused this.

I'm assuming the wheels were properly balanced but don't see it on the list. I had a shop screw mine up once so I started doing it myself. 

I have to assume the shop properly balanced them.

[bryanj]

Try 30/32 psi cold for the tyres first

[MauiK3]

What cal said…
Also, check front to back alignment by stretching a string along each side of one tire and up to the other tire, make sure you can have the front pointing straight and the string is parallel with the back tire.

[jonda500]

& re-check the adjustment of your new steering head bearings...
I will be following this thread with much interest as my new(to me) KTM380 has the same problem - I have ordered new rims & steering head bearings but feel like I'm just grasping at straws and it seems likely that this is not gonna fix it. Maybe I'm too light (130lbs) or maybe the frame's bent, IDK.
Does it do it when you have a pillion?
best of luck with it, John

[PeWe]

Fork springs old stock or newer progressive springs?
I got fork wobble when I installed  progressive springs  with too high spacers on top on my CB750K6.

No spacer or 5mm work fine.
I fill my tires with Honda recommended pressure according to label on fender.. 2.1 BAR front, 2.4 BAR  rear.
I guess this bike can have other numbers.

[pjandrew99]

Ever dismantled the forks to check for bent tubes\damage? Never been in an accident that may have bent the frame? Not liklely, but is the master cyl standard? Causing an oscillation because of imbalance (long shot, I know, just a suggestion). Certainly a weird one.

You may be onto something here... I am the third owner of this bike. I did have a low side spill at about 15-20mph that gave me a level 3 clavicle separation. My shoulder and center stand ( the part you use with your foot) took all the brunt. I am unsure how to check if the frame is bent in anyway. When I did the steering bearing the forks did not seem bent but, that isn't really checking them. Ive also read that someone found one of their fork spring split in half that also caused this.

I'm assuming the wheels were properly balanced but don't see it on the list. I had a shop screw mine up once so I started doing it myself. 

I have to assume the shop properly balanced them.

I wouldn't assume the shop balanced them correctly. Before I did my own tires I got tires back from a shop that didn't balanced them at all. Some think you don't need to. Also, +1 on alignment. Both easy to check and get off the list of possible causes.

[ef9tuning]

Thank you for the feedback everyone, to answer some of your questions:

Fork springs are the old stock ones

I will try to take the bike out on my lunch break today & put 35f/36r psi in the tires. Don't have an air compressor in my new house just yet, it will be 90 degrees Fahrenheit today & about 1-1.5 miles to the nearest air pump. Warm/hot tires will read about 39 psi with the added air?

Before making the video I tighten the steering nut about 1-2mm but since I did not loosen the top pinch bolts that most likely did nothing

I have seen the string method but in my opinion there's too much room/variables for human error. How about using the motion pro chain alignment tool?

[ef9tuning]

Also, how is the fork height on my triple?  Here's a photo https://imgur.com/gallery/xOauPpi

[BenelliSEI]

Do you have any accessories on your bike? I chased this same issue on my 2008 KLR650. My wife has the identical bike, purchased at the same time. Mine “shook” at 120 kph. Took me a while, but the only difference was small GIVI hard bags on mine..... unclip them, shake is gone.

[Bodi]

The "new tires" is maybe a clue.
Since tube type tires are barely available now and what there are aren't great tires, you probably used tubeless tires. Not a problem, derate them one speed rating and all is well.
But the tubeless bead profile doesn't fit tube type rims quite right, tubeless ties are a considerably tighter fit on tube rims. Getting the bead to seat evenly is tough. Check the bead lines, I think all tires have this raised rubber line around near the bead. This must be the same distance from the rim edge all the way around the rim. If it isn't, the tire isn't seated properly. I have had this and mystery wobbles at certain speeds a few times. Let the air mostly out, break the beads off the rim, add a LOT of tire mounting lube (soapy water is fine) around the bead and rim, reinflate to high pressure (be careful going above the max pressure rating on the sidewall, exploding tires can kill) and get the bead lines even. Might need some spirited whacking with a mallet or board to convince the bead to stretch and drop into place.
Tire balance will be affected afterwards.

[BenelliSEI]

The "new tires" is maybe a clue.
Since tube type tires are barely available now and what there are aren't great tires, you probably used tubeless tires. Not a problem, derate them one speed rating and all is well.
But the tubeless bead profile doesn't fit tube type rims quite right, tubeless ties are a considerably tighter fit on tube rims. Getting the bead to seat evenly is tough. Check the bead lines, I think all tires have this raised rubber line around near the bead. This must be the same distance from the rim edge all the way around the rim. If it isn't, the tire isn't seated properly. I have had this and mystery wobbles at certain speeds a few times. Let the air mostly out, break the beads off the rim, add a LOT of tire mounting lube (soapy water is fine) around the bead and rim, reinflate to high pressure (be careful going above the max pressure rating on the sidewall, exploding tires can kill) and get the bead lines even. Might need some spirited whacking with a mallet or board to convince the bead to stretch and drop into place.
Tire balance will be affected afterwards.

This is excellent advice! The last few tires I mounted drove me nuts. But, look closely and follow these instructions. It matters!

[PeWe]

The "new tires" is maybe a clue.
Since tube type tires are barely available now and what there are aren't great tires, you probably used tubeless tires. Not a problem, derate them one speed rating and all is well.
But the tubeless bead profile doesn't fit tube type rims quite right, tubeless ties are a considerably tighter fit on tube rims. Getting the bead to seat evenly is tough. Check the bead lines, I think all tires have this raised rubber line around near the bead. This must be the same distance from the rim edge all the way around the rim. If it isn't, the tire isn't seated properly. I have had this and mystery wobbles at certain speeds a few times. Let the air mostly out, break the beads off the rim, add a LOT of tire mounting lube (soapy water is fine) around the bead and rim, reinflate to high pressure (be careful going above the max pressure rating on the sidewall, exploding tires can kill) and get the bead lines even. Might need some spirited whacking with a mallet or board to convince the bead to stretch and drop into place.
Tire balance will be affected afterwards.

This is excellent advice! The last few tires I mounted drove me nuts. But, look closely and follow these instructions. It matters!

Possibe with bad tire too. My K2's front tire was bumpy making rides irritating shaky.

But no real wobble in any speed. Tested up to  around 170kmh.
I had tire lifted 2 times, one due to a flat tire ending up in new tube. Inflated tire after it had got tire assembly lube to more than double pressure, release all air to 0, inflate  again, lowered to less than final pressure so the final pressure was  done by inflating it.

Fixed this winter replacing the entire front wheel. It got my K6 wheel with same type of tire but a little bit more wear. That bike got another wheel with new rim and tire

Now very comfortable rides.
The bad front tire look like it is seated correct with those mold rings parallel to rim which is the first thing I check when tire is inflated.

It is the outer part of tire that bumps. Visible when riding.
That wheel will get a new tire.

[Maltboy]

I'm assuming the wheels were properly balanced but don't see it on the list. I had a shop screw mine up once so I started doing it myself.

How did you do it?  I completely rebuilt the wheels on my 750K3. Spokes, rims, tires, rim strips, bearings are new.  My bike has zero wobble at 70 mph. Do the wheels still need to be balanced?

[Alan F.]

I'm assuming the wheels were properly balanced but don't see it on the list. I had a shop screw mine up once so I started doing it myself.

How did you do it?  I completely rebuilt the wheels on my 750K3. Spokes, rims, tires, rim strips, bearings are new.  My bike has zero wobble at 70 mph. Do the wheels still need to be balanced?

Your results imply that your wheels and tires are in good balance already. If you raise the front wheel and spin it, it will stop rotating with a different spot at bottom every time. Probably the same for the rear.

[Maltboy]

The "new tires" is maybe a clue.
Since tube type tires are barely available now and what there are aren't great tires, you probably used tubeless tires. Not a problem, derate them one speed rating and all is well.
But the tubeless bead profile doesn't fit tube type rims quite right, tubeless ties are a considerably tighter fit on tube rims. Getting the bead to seat evenly is tough. Check the bead lines, I think all tires have this raised rubber line around near the bead. This must be the same distance from the rim edge all the way around the rim. If it isn't, the tire isn't seated properly. I have had this and mystery wobbles at certain speeds a few times. Let the air mostly out, break the beads off the rim, add a LOT of tire mounting lube (soapy water is fine) around the bead and rim, reinflate to high pressure (be careful going above the max pressure rating on the sidewall, exploding tires can kill) and get the bead lines even. Might need some spirited whacking with a mallet or board to convince the bead to stretch and drop into place.
Tire balance will be affected afterwards.

Tell me about it.  I had to walk away from a rear tire (Avon) for a day because it was kicking my ass.  It finally seated, but it took a lot of soapy water and massaging and coaxing like you said.  A buddy who worked in a shop said don't be afraid to inflate it over spec to get it to seat.  I went to 70, but my you-know-what was puckering the whole time.

[tlbranth]

I have seen the string method but in my opinion there's too much room/variables for human error. How about using the motion pro chain alignment tool?

I agree. You should check your alignment though. I use a strip of plywood on blocks with cutouts for whatever gets in the way.