Valve shims!

RCGBOB44

RCGBOB44

Hero member
Location
Coulsdon,Surrey, sometimes Germany
Having had my Jota since 1984 I have done valve shims many times without any real problems, untill now!

As usual measured the valve clearences and realised I needed a couple of shims.  Shims arived and a couple were ground a couple of thou to achieve the desired size.

Fitted then to the bike and the clearences were way of....WTF?

To cut a long storey short, the new shims are slightly longer than the originals so the bottom of the skirt was touching the valve collets so when you measured the actual thicknes of the shim all looked ok but when fitted gave a totally false reading..................beware.
 
I have also seen the underside of the shim can be ridged, meaning that the micrometer does not read a true value as only the outside face is flat.
I have also seen badly 'hand ground' shims with the top surface faceted like a bloody diamond. Pick your favourite thickness from a range of values!
It's also possible for the cam bucket top surface to be warped/distorted, so there are many ways to rox up valve clearance measurements.
 
Ta for the 'Heads Up', Bob.  Where did you get the shims?  One of 'our' normal sources, or someplace else?  Have you let them know?

Ciao

Craig
 
If you search this forum for "Ralph and shims" you will also find the term "horrific" . I've not had personal experience of the shims he's selling but i'm inclined to avoid.
                                  Tim
 
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