Valve shim clearances

[liljegren]

Just re-shimming my valves (81 GS 550 postie). According to the manual, I'm setting them at 1-3thou, cold! Question for all you knowers out there- where does the expansion in the v/v stem go, surely the v/vs wont seat when they're hot?? Maybe I'm getting this wrong? Cheers, Matt.

[Supertwin Don]

Just remember, the valve stem isn't the only thing that gets hot!
By the time everything else - barrels, head, camshaft, etc have expanded the clearance will probably actually increase.

[Max Preload]

Just re-shimming my valves (81 GS 550 postie). According to the manual, I'm setting them at 1-3thou, cold! Question for all you knowers out there- where does the expansion in the v/v stem go, surely the v/vs wont seat when they're hot?? Maybe I'm getting this wrong? Cheers, Matt.

What's v/v?

Check your specs - 0.001" to 0.003" seems very tight.

The head expands at a higher rate than the valve stem due to it's material, mass and proximity to the heat with little cooling (the inlet valve at least gets cool air), thus the valve seat moves away from the cam lobe. The cam lobes expand at a similar rate to the valve stem although slightly less, again due to proximity to the heat. Overall the clearance probably increases hot.

This is one of those rare cases where it's better to be loose than tight too... nothing burns a valve faster than a tight clearance.

[Max Preload]

Hmmm this says 0.03mm to 0.08mm which is 0.001" to 0.003" so that's probably right.

[liljegren]

Yeah thanks for your input Mr Preload, I guess I read the manual correctly. I dont think its even possible to but a .001" feeler guage! Cheers, Matt.

[Max Preload]

The units aren't on that page I referenced so I assumed mm since 0.030" is 0.762mm - I doubt very much they'd be that big. And the other units are mostly metric too.

I've just measured some tin foil with my micrometer and that's 0.01mm or 0.0004" (4/10 000" or 0.4 'thou'). I can't find my feeler gauge but I'm sure it will go as low as 0.001" because I tore the tip off the thinnest one once. Depends on the brand though, I'm sure.

[marsheng]

I've seen many a manual getting the decimal point in the wrong place with regard to tolerances. You will ok setting them to between 0.05 -0.08 mm. Too small and you burn a valve and too large, the noise increses. Your choice.

[Ixion]

My feeler gauges go down to 1 thou (and 1.5 thou) . Not sure what the metric set go to. I tend to rely on my carefully calibrated ear. Correct to the nearest tickety.