Don't trust valve clearance measured on a hot engine

[Burque73]

Or even warm for that matter!

Right after a ride the other day I got busy on some much needed maintenance. After draining the oil and having lunch, I pulled the tank and valve cover to check clearances. They all measured the same as 8k miles ago. The engine was cold and hadn't been run at all for days at the last check. This time it was still hot. I know the measurements should be done on a cold engine, but I wanted to compare the results just for giggles and things. Four of the measurements tightened up in the 36 hours or so that it sat.

Intake cyl 2 Hot measured .064mm and the feeler was way loose, the next size up almost fit. Cold the .064 feeler was barely sliding in there.
Exhaust cyl 2 Hot was .102. Cold was .076
Intake cyl 3 Hot was .076. Cold was .064
Exhaust cyl 4 Hot was .102. Cold was .076

Just thought this an interesting experiment and wanted to share results.

 

[Nessism]

I put a fan in front of the engine after riding and after 45 mins or so the metal in the head is barely warm to the touch, so it's green light time to adjust the valves. I've never checked "hot," though. My point is that it's not necessary to wait hours and hours before doing the work.

 

[Burque73]

In my case, the engine had some time to cool, but had been run a couple hours prior. Hot, warm, cold can be a judgement call. Bottom line, temperature can make a difference.

 

[zed1015]

Bottom line, temperature can make a difference.

That's the whole point of setting the clearances cold.
This ensures the correct running clearances whether that be wider or tighter than the specified cold clearance.
The two main reasons they would never be done hot is -
1 - The difficulty maintaining running temperature to perform the adjustments whilst the engine is shut off .
2 - Eliminating the chance of burn injuries.
Not much of a judgment call really as don't know any experienced mechanic who would try to adjust the valves while the engine is hot or pretty much any other similar task except maybe draining the oil as it flows quicker when warm..

 

[Grimly]

As always, the factory manual rules.
I can think of a couple of engines that called for hot setting of the valve clearances and you can guess how popular those were with the mechanics.

 

[Burque73]

Thanks for the replies. I really just wanted to experiment and document the importance of how temperature can affect the measurements. The "judgement call" I mentioned, since the manuall doesn't say the engine has to be below X? to measure clearances, was that one has to judge for themselves if it's too warm still to measure. I would not have thought 45 minutes after shutting it off, even with a fan running, would have been enough time to cool. I personally wanted to wait till the following morning before being comfortable that I had accurate measurements, but I didn't have time the following morning. That's why 36 hours passed. It wasn't like I waited for icycles to form before getting back to it.

 

[Nessism]

I would not have thought 45 minutes after shutting it off, even with a fan running, would have been enough time to cool.

Well, in truth, I use a pretty powerful fan.

Reason I learned this method is because I help a friend maintain his 850. He rides the bike 25 miles or so to my house, and when he arrives we crank up the fan and crack a cold beer (or two) and talk before getting down to work.

 

[sacruickshank]

Overnight cooling for me. when we're talking about .03-.08 mm i don't want any thermal expansion.

 

[bwringer]

Thanks for doing the science, Roger. I have one of those inexpensive infrared point and shoot thermometers -- it would have been interesting to get a reading on the cylinder head temps while the engine was warm.

 

[Gorminrider]

"Cold"? whatis "cold"?... Winter? or Summer? . but I assume Suzuki engineers work in a heated building Human Mean is 65-72F
.