Front fork jerking on acceleration and deceleration

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Haven’t posted here in a very long time. But I hope someone will point me in the right direction or to a few pertinent threads at least.

As the title of my post states, I get a nasty jerk in the steering (straight up or leaned over) whenever my Mk3 accelerates and/or decelerates. Not a wobble, but a noticeable pitch that is not fun to work with. Intuition tells me my Dave Taylor head-steady needs adjustment. Am I close?


Thanks in advance for any advice!


Peter
 
First thing I'd check is the front bearings tightness: by holding the front brake on and pushing the bike forwards and back while holding the neck to feel for motion. It should not rock at all between the steering parts.
Jaydee
 
I'm no expert (few miles on my Commando) but when I first bought it the swing arm bushes were very worn. It felt very odd. Agree with Jaydee - more likely to be front end but worth a look if nothing obvious there.
 
jaydee75 said:
First thing I'd check is the front bearings tightness: by holding the front brake on and pushing the bike forwards and back while holding the neck to feel for motion. It should not rock at all between the steering parts.
Jaydee
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That was actually my first thought. The steering has always felt kind of loose to me. But this is the first time with the front end jerking.
 
Not sure my description was totally clear ... the jerking corresponds to the change in RPMs from the engine. It’s not resistance in the forks, if that’s what is meant by “stiction”?
 
Loose steering head bearings, loose swingarm, loose headsteady so something else is loose like an axle.
 
Next time I am home I will try to rock the front end as jaydee75 suggests. Though I believe the mechanic who installed new iso mounts for me already checked that.

I checked the swingarm last year when I was riding it - seemed fine. The head-steady I installed a couple of years back made a huge difference in vibration control. Is there reason to suspect it is not set correctly now and might have something to do with the problem? Does it also buffer the changes in torque from the engine?
 
I have had the head steady hold down bolts in to the head come slightly loose and the bike felt different, only took a 1/4 turn to re-tighten them but if they had loosened off more it would have felt much worse.
 
Iso's or gearbox not secure in the cradle or both. The forks are just transmitting the clunk to you so you notice it, there is most probably nothing wrong with them .
 
Once you've eliminated the steering head bearings first check that all the engine to cradle & tranny to cradle bolts are secure. Then check that there's no excessive clearance in the ISOs. The DT head steady is a fairly simple device but it can go out of adjustment if the ISOs are not kept in check. The simple test for the DT steady is to support the bike by the lower frame so the engine ISOs are not loaded, with the bike upright and wheels inline the balls of the two heim joints should have an equal range of motion on their respective bolts (you'll see what I mean when you look at it). The unit's joints should move freely with the engine in this upright & unloaded state.

Though based on your description I think something else (loose engine fixing or tranny) is causing the problem
 
Since we know that the headsteady isn’t required to go down the road that’s probably not it. But it should be checked for loose bolts.
 
Sounds like the rear wheel is deflecting under changing load. First thing I would check is the rear axle bolt for tightness.
Then, I’d do a complete chassis assessment stating from the front to the rear.
As mentioned, the rear need to be checked with the iso’s Unloaded.
Check all fasteners, mounts etc. including transmission.
 
MichaelB said:
Sounds like the rear wheel is deflecting under changing load. First thing I would check is the rear axle bolt for tightness.
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Shortly after the iso mounts were done I noticed the rear wheel kicking out a bit under the same conditions I’ve described for the front end issue. I immediately suspected the cush drive rubbers, but when I went to remove the rear wheel I saw that one of my new shocks had slipped totally off the lower mount bolt. Apparently the washers were not large enough to hold them back. It was after I addressed that problem that I began to feel the front end pitching. So the axle bolt is a good place to start, I guess.
 
Put your front wheel against a solid brick wall. Rev the engine up to 2500 rpm while stradling the bike and slowly let out the clutch until it begins to grab, then engage the clutch fully while you observed the forks/ steering head/frame attitude. (or have someone stand to the side of you and watch carefully) When you begin to release the clutch and then engage the clutch, it should load force on the rear tire and into the frame of the bike, then release that force. If your steering head bearings are toast, you may see the forks cock slightly at the yoke when you perform this exercise.

Bear in mind that you may see movement in other places IF they are the actual problem, such as swing arm, cradle, wheel bearings, etc. If you see the isolastics load a bit and relax that would be expected. As far as the dave taylor headsteady goes, the design of that kind of headsteady is to only resist lateral forces so inline forces like accelleration and decelleration probably wouldn't be a cause that makes the "forks jerk".
 
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The rear axle is secure? Tight, with chain/wheel/axle adjusters in place snugged up and equal distance front to back on both sides?
The rear axle isn’t scooting front to rear depending on acceleration or deceleration?

I throw this idea in the pot as it sounds almost duplicate to what I found on my BSA Lightning.
 
Very much a newbie to the forum, but have you had the front wheel out lately and pulled the forks together with the pinch bolt tight causing deforming and binding. Just a thought as they will stick.
 
comnoz said:
Last time I rode a Norton with a broken headsteady I thought it was downright dangerous. Jim
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You’re right of course. I’m recalling the discussion here years ago when people claimed the headsteady wasn’t required.
 
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