Front end knock under moderate braking

[MarkJ]

1999 Aprilia RSV, 30,000 miles. I changed the head bearings a few months ago as the last ones were shot. Replaced ball bearings with taper roller bearings. It has made the bike handle a hell of a lot better, however I now (possibly had it before, but couldn't tell due to the poor handling with shot head bearings) have a knocking feeling come through the bars when I brake a moderate amount or more.

I checked the tightness of the head bearings at the weekend and they seem fine, although I did it with the drift & hammer method as I don't have a small C spanner. The yokes turn smoothly with no notchyness.

With the front wheel off and the front end up I checked for play in the new head bearings and couldn't see or feel any. I also checked for play in the fork bushings on both legs and couldn't see or feel any.

Last night I checked the discs - all bobbins spin freely (I cleaned them all at the weekend to make sure) however the discs themselves can move a little bit forwards and backwards the same direction the wheel turns. I have another RSV track bike with another set of wet wheels with discs and all these have the same movement, however not as much.

If you get off the bike, push it forwards and jam the front brakes on you get the knock, but if you don't bounce the bike backwards and push it forwards again and jab at the brakes it doesn't do it - it's like whatever the problem is gets locked in place until you ride it. You can also make it knock by pulling the bike backwards and jabbing the brakes on.

So my question is, is it likely to just be the discs that are doing this, and it's nothing to worry about? The head bearings seem fine to me, but is this a specific problem to taper roller bearings? The forks are currently set up quite hard, but I've never had fork bushes go on me. What do fork bushes feel like when they've gone? Reason I ask about the forks is the bike has a handlebar conversion on so the forks seem to be set up quite hard as there's not as much weight over them any more.

Cheers

[whitedevil]

Is the caliper loose? And im pretty sure the disc shouldnt move.

[MarkJ]

Caliper and pads are fine. This is pretty much exactly what I'm experiencing.

[MarJay]

The discs shouldn't move backward or forward at all, they should only have a little side to side movement...
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Kickstart]

Hi

Full floaters might have enough play for that (the Bimota does have a bit of play like that, and they had that even when new) but didn't think the RSV had full floating disks.

Pads can move in the calipers to give a click, but not sure you would notice it that much.

Fork bushes shouldn't click when worn normally, and the seals will probably provide some side ways location and stop much noticeable knock.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[MarkJ]

Sorry I forgot to mention, the discs on the bike with the knocking problem has non Aprilia discs. Bloke I bought it off said it had racing iron discs or something. Bike had been kept outside for a month or so and the discs were a bit rusty too which probably didn't help. The discs themselves are quite dull in appearance instead of the normal shiny surface of standard discs. I'll try and take a picture when I get home, but there doesn't seem to be any manufacturer markings on the discs.

Think I might swap the front wheel off the track bike over to this one and see what it feels like on the ride to work tomorrow.

[Kickstart]

Hi

Might explain the movement then. Sound like the disks the Bimota has as standard. If they are cast iron disks then be careful with your choice of brake pads.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[binge]

My NC29 used to exactly this, It was an early bike, but had been fully restored.

I always put it down to the full floating discs.





Ben