How cool is cool enough

[guzzisteve]

The next time an 8V Norge comes in for service, I'll check the valves after the fans kick on at 125*C . Usually gets there while setting throttle bodies on a warm day.
Interesting to see what they are while you are sitting in traffic boiling your oil and scraping your flat tappets.

[canuguzzi]

  Short answer, Yes. Thats why engineers that design this stuff have to know what the properties of the materials they plan on using are and consult with metallurgists and suppliers to find the best for their application. Thats why many years ago they filled valves with sodium and utilized stainless because of it's stability under temperature fluctuations.

    Paul

And then any concerns about temps are kind of irrelevant if there is a reasonable cooling off period to get the engine close to ambient temp since temps change throughout the year?

The temp differences between summer and winter could easily be more than 20 degrees and thus so could the valves, even after sitting overnight. It would seem the manufacturer knows this and builds in enough tolerance so that we really don't need to worry about it.

I'd be more concerned that the set of feeler gauges being used were accurate and the piston was at correct TDC than if the engine was at 60 degrees vs 80 degrees because that was the temp of the engine after it cooled to ambient air temp.

[racasey]

BMW specified 35C in the 70/80s R bikes factory workshop manuals.  That converts to 95F.

Ciao,
Dick Casey

[skippy]

nail head hit!

From the factory perspective, all concerns are addressed by stating that adjustment be done on a cool 70* engine. I still adjust after the bike has set overnight.  I'm curious nonetheless at what temperatures the expansion/contraction really mean something.   

Well, off the top of my head, I can remember that the thermal coefficient for most steel alloys is right around .000006" per degree Fahrenheit per linear inch, and that the thermal coefficient for most aluminum alloys is approximately twice that at .000012" per degree Fahrenheit per linear inch.
To answer the question at what temperature does the whole expansion/contraction thing makes meaningful difference? I suppose that depends how accurate your instruments are. but if you run the math plus or minus 20 degrees (F.) the change in relationship in the parts is about .00048".
I am not going to sweat checking the valves on a cool 50 degree morning or a hot 90 degree afternoon so long as the bike has been off for at least 8 hours prior.

Skippy