Knocking Forks

[Mick Taylor]

My Classic is back from the esteemed Richard Negus with a freshly Moly'd engine, the side seals have been unstuck, and now she starts and runs beautifully thank you Richard, another happy customer.Before the engine work I had never so much as sat on the bike, but as it has less than 4,000m on the clock from new I didn't anticipate too much grief.Given that the front forks are Italian I was expecting them to be stiff, rigid and unforgiving, but I was totally wrong, they are soft, supple, almost floaty in a BMW ish way. So far so good, but touch the front brakes on anything less than a billiard table smooth surface and those forks knock and clatter. The fork oil has not been touched yet, but before I look at the fork oil etc, has anyone else had the same problem and hopefully fixed it?Mick.P.S. My seat is a 'wrong un' hand made for the first owners specific requirements and the Norton original has gone AWOL, so if anyone has or knows of a Classic seat for sale, please speak.

[Richard Negus]

Mick,I too thought the forks were unusually supple - quite a change from the norm. Maybe the oil is thinner than recommended? Should be Medium/SAE10.That rattle is one of life's little mysteries - Doug Hele tried to cure it, to the point of having a batch of anti-rattle shims made to go inside the damper.Didn't work, though. I'm not even sure the rattle comes from the damper valves. The speedo cable slapping on the guard?When you've solved it, a mention on here would be good .

[Richard Negus]

Mick,Just done a search for 'fork knock' and found an old thread. Dave Perry found one of the damper valves wrongly assembled on his IP2 forks ..........

[Mick Taylor]

Thanks for that Richard, I will experiment with different fork oils and if it makes any difference I will let you know.Strangely enough, I was glad the Classic didn't have the Yamaha front end because I had a few of those back in the day (XS1100s) with knocking forks.....I even invested in a brand new (NOS) pair for one bike....and they still knocked.So I was really happy the Classic had the Italian forks.....right up to the moment I first touched the brakes....oh well I suppose it goes down as 'character'She does run beautifully though, which more than makes up for minor annoyances.Best.......Mick.

[bodgerbloke52]

I have found "fork knock" on several occasions is in fact slightly slack head race bearings. The latest case was my IP2, I had fitted new bearings but lower one was not fully home in its housing. First time brake was applied it went the last few thou (can I say that these days over there?) which led to a little play that was most noticeable as the brake was applied.Roger in the Pacific NW

[Mick Taylor]

Thanks Roger, I will check that....I'm pretty confident that it's not steering head bearings....but it wouldn't be the first time I've been wrong, so I will check. Mick.

[johnbirchjar]

Hi Mike,I expect I will have to let Richard work his magic on my bike before too long,so while he has it you can use my seat as a pattern and have one made up.Re:knocking forks,my Classic has done this from day one,"They all do that sir"didn't affect the road holding one jot,(as umpteen track days at Cadwell Park have shown)ride safe,J.B.

[bodgerbloke52]

Yes Mike, loose stearing head bearings is more of a "clunk" that is felt as much as heard. I agree, your description of a "knock' with no feel to it is more likely to be fork internals related. Head race adjustment checking is just one diagnostic action.Roger

[Hunter]

Hello Mick,My Classic does it too, But it happens if I am riding over a rough bumpy road. It clunks quite badly. I have changed oil with heavier grade and no difference. I am feeling that is as they rebound. That is, as forks go to the longest length they clunk. I have not taken forks apart, but in the parts manual there is a reference to anti knock shims. 3 thicknesses are listed.As soon as I need to replace seals I intend to check or add to these shims.Also I intend to talk to old Ducati dealer nearby to see if he knows of this happening in any of the fork types they used.This id just another idea to look at.

[Mick Taylor]

It seems "They all do that sir" really fits the bill in this case...and it's very good to know mine is not the only afflicted example, so thank you for that.I certainly intend to have a good look at them to see if I can understand what causes the knock, but as Richard says, the matter was addressed in house unsuccessfully by Norton, so I doubt anything I can do will bear fruit.My forks only seems to knock (rattle might be a better description) under braking on uneven surfaces...apart from that it's pretty serene.No harm in looking though.Mick.