Odd noise - suggestions for things to check?

[Allrover]

Hi oh wise forum readers,

I recently took both wheels of my Super Four as part of my project to replace them with new gold powder coated ones. (See cosmetic thread for some pictures of that, to go up soon).

Anyway, I took both wheels off and put them both back on again to check that I actually could, as a test run for when I come to take them off to swap the tyres, sprockets and discs over to the gold wheels.

Glad I did, because after taking them off and putting the back I am now hearing a strange whirring noise. Its pitch starts low at low speed, and rises as the speed increases. Its is definitely speed related, not rev related. When riding, it sounds like its coming from the front wheel, but I cannot be sure at all. If I turn my head, it could be the back. It's loud enough that I can hear it over the engine noise. Other than that the bike seems fine. Noise is loud and worrying though, especially at high speed.

When I took the front wheel off all I did was check I could remove both discs then put them back on again. On the back wheel I took off the sprocket to clean it, the disc, and removed and refitted the hub with those rubber blocks in.

Here is the kicker...at the weekend, I then changed both wheels over to the gold ones. The new wheels has new bearings and seals on them, and I swapped over the old discs & sprocket. The noise is still there!!

Any suggestions, however crazy as to things I might have a look at to try to find its cause?

[mattUKNC]

Did you make sure the front discs went on the same sides is originally?

[Allrover]

No I didn't. I didn't realise they had a particular side actually, I just put them on at random. Hey look its an easy thing for me to try tonight anyway, not take long to swap them over.

[Allrover]

Actually my last answer isn't true, they went on the side indicated by the arrow to show direction of rotation, so they only have one possible side each can go on.

[dobbslc]

How is the speedo driven on a super four? Could be the cable or its drive not meshing correctly.

[Allrover]

Problem solved!

Deeply frustrating as I spent many hours taking the front wheel apart, and re-fitting it in various ways. It was actually caused by the chain being too tight, though it wasn't the chain itself that was noisy, it was whatever it was putting pressure on inside the gear box casing.

Obviously when I took both wheels off and refit them, I didn't put the rear on in exactly the same place as it was before. I did actually check the tension of the chain when when I was refitting it, I know I did. But am thinking as I did the nuts up maybe that cause it to move a little. Anyway, there was no slack in the chain at all, causing it to put pressure on the gearbox.

In hindsight, although the pitch of the noise changed in line with the speed of the bike, it did vary slightly when going on and off the throttle, which now makes sense as it meant there was weight pulling on the chain, or not. Similarly, it also explains why when I span the back wheel with it on its centre stand I didn't hear anything, because in that situation their is no stress being put on the chain.

So I learn another lesson. Very frustrating as I checked loads of things before dismantling the front wheel, and wasted loads of time, when it was actually very simple. All part of gaining experience, next time I take the wheels off, I know what to watch out for.

Thanks to you if you commented. Regards, Chris

[mattUKNC]

Glad you got it sorted.

[SevenThreeSeven]

The final drive of a motorcycle is such a finicky thing to set up perfectly. There are various machining tolerances that come into play (any deviation from perfection in the overall roundness of the sprocket and counter-sprocket and of the cut of their individual teeth and in the placement of the locating holes in the sprockets and in the location of the studs on the sprocket carrier, etc.) which, in the worst case scenario, can sometimes result in "tolerance stack up", which is the perfect storm of those tiny tolerance issues.

And to make it all the worse the situation is dynamic rather than static, with the two sprockets turning in a ratio that results in constantly changing chain contact relative to those two sprockets.

Anyway, there was no slack in the chain at all, causing it to put pressure on the gearbox.

Viewed from a long-term perspective this is the only truly worrying thing about your (now sorted) problem. I don't know how robust the Honda gearboxes are but on the Bandit400 (and probably the GSX-R400s too) it doesn't take long for an over-tight chain to ruin the gearbox's output shaft bearing.

[Allrover]

Hi SevenThreeSeven,

yeah, good job I didn't just ignore it so at least it was only like that for about a week. I took the bike to the Classic Bike Trackday at Cadwell Park last weekend and ragged it around there against much bigger and sportier bikes, so it is fair to say the problem is solved. The little beauty put up with being revved to the limit all day without so much as a hiccup.

This is exactly why I am cutting my teeth on a bike like this though...when I make mistakes the bike is very forgiving and the problem usually rectified inexpensively.