Bridgestone Motorcycle Parts Discussion Board
General Category => General Discussion => Topic started by: Hap on September 13, 2019, 09:09:38 AM
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I had the tire tubes replaced in my Sport 90 and when I picked up the tires I noticed the nut was placed just under the valve stem cap and not tightened on the rim. I asked the mechanic why the nut was only halfway on the stem behind the cap and he stated it is not supposes to be tightened on the rim- he said the stem is supposed to move a little along with the tire. Is this correct? I always thought the nut should be tightened all the way down onto the rim do that the stem doesn't move????
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a google search on the subject reveals a lot of controversy but I see the mechanic has a point after reading this:
The Michelin tube came with a conical washer and two lock nuts on the stem. A search of many motorcycle forums shows that there is a lot of misunderstanding of where the nuts are fitted, some people advocate one is fitted inside the rim against the washer and the second on the outside. Many people also think they should tighten the outer nut tight against the rim. Such advice is incorrect.
I have checked with Michelin to make sure their advice has not changed and have received the following email from them:
The conical washer sits over the inner tube valve stem and should follow the contour of the valve so that the convex side sits against the wheel rim when fitting.
Once fitted to the wheel the two lock nuts sit on the valve cap side of the wheel rim. After fitment and inflation to the correct pressure, the two nuts should be backed up towards the valve cap, and locked against each other.
This is not usually an issue on correctly inflated road going tyres, but should there be any slippage of tyre on the rim, during heavy braking or acceleration for example, the inner tube could be pulled around slightly with the tyre and if the inner tube is bolted to the rim the valve can be ripped out. If the lock nuts are raised towards the valve cap then inner tube has some leeway to move before this happens. Any movement is thus obvious as the valve stem will no longer be straight and pointing at the centre of the hub, but will be pulled round at an angle.
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Thanks Hap.
Randy
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Well, that is a surprise, I've been doing it wrong for 60 years !!. Always thought washer and lower lock nut provided a secondary seal and/or security on valve attachment to tube. They always come with the lower lock nut firmly tightened against the washer !
It is possible early tubes did rely on this for a seal but looked at a BS tube and the valve appears secure without washer and LN. We live and learn, nice research Hap. Brian.