How Cold is Cold (for valve adjust)

[Nessism]

Will a fan blowing on an engine for an hour make it "cold" enough to perform a valve adjustment? Offered to help another member but need to figure out logistics.

[Ranger]

I would imagine its along the lines as a dyno set up, probably for 15min at a time at most to keep a respectable operating temperature consistent until the airflow won't be enough to keep the temperature low anymore.

I saw a calculation somewhere online regarding fins, air temp, fan volume and airflow yielding an average engine temp.

[salty_monk]

Ed,

I think the manual recommends leaving it overnight.... I guess you might get it cold enough in a few hours with a fan.

Ranger - he means engine heat affects the valve measurements although I'm not sure how you can run the engine for 15min whilst doing a valve adjust.... maybe you're thinking of carb syncing?

Dan

[Ghostgs1]

Ed, I would think you would want the temps under 100 F and probably more like ambient temp. Steel grows a lot with little heat input. Just my thoughts. Ray

[BassCliff]

Hi,

In this case I always thought "cold" meant the engine temperature should be the same as as the ambient air temperature. After running the engine (if he's coming to your house) it could take hours (4-8?) to get there.


Thank you for your indulgence,

BassCliff

[JEEPRUSTY]

Old Suzuki factory guy told me overnight cold.

Engines are weird things and there is a lot of stress and dimensional distortion once they get to op temp

[Ranger]

Ed,

I think the manual recommends leaving it overnight.... I guess you might get it cold enough in a few hours with a fan.

Ranger - he means engine heat affects the valve measurements although I'm not sure how you can run the engine for 15min whilst doing a valve adjust.... maybe you're thinking of carb syncing?

Dan

Yeah, I was visualizing something else.

My mistake, I couldn't see adjusting the valves with the bike running.. I had a long night.

[dr_fosg8]

I would say at least 8-12 hours. The engine has to cool all the way through. That is a lot of aluminum to cool that is not exposed to the outside of the engine. The service manual I have says to not adjust the valves unless the engine has not been run for at least 12 hours.

[Steve]

Ed, I would think you would want the temps under 100 F and probably more like ambient temp. Steel grows a lot with little heat input. Just my thoughts. Ray

And aluminum grows even MORE with the same heat input.

Yes, ROOM TEMPERATURE is the proper temperature at which to adjust the valves. Even firing up a "cold" engine to move it onto the lift is too much warmth to do the job properly.

The big issue at hand is the fact that alumimum and steel expand at different rates. At some time during the development, the engineers felt that the clearances that are now specified are what they should be, and the only way to guarantee those numbers is to do it "cold". There is no telling what the clearances change to when the engine is up to operating temperature, so just do it at "room" temperature and be consistent.

.

[Smokinapankake]

Besides, if its still hot, you'd burn yourself, right?

[tkent02]

Cold is correct but checking them hot would be somewhat useful if that's all you can do, at least to see if any are way too tight and are damaging themselves. Certainly better than not checking at all. For any true measurements and proper adjustment, overnight cold is the only way to go. I would be interested in knowing how much they change from cold to warm to hot. Some cars have a cold spec and a hot spec, but on an air cooled engine hot can mean most anything.

[SqDancerLynn1]

I go with tkent02. If you don't have a choice just get it as cold as possible and do the adjustment

[Dogma]

I agree with Tom also. Cold enough to not burn you hands is probably cold enough for valve clearances. You might favor the loose side a tiny bit to compensate for the aluminum head expanding more than the steel valve stems, but I really doubt it's necessary.

You might maybe have some cam cover screws come loose later if installed on a warm engine.

[JEEPRUSTY]

Why is this open to debate? Why take any risk? Unless someone wants to measure the change in clearance per unit time or width then its a bit of academic nonsense.

Overnight cold in mojave is a tad different than in other locales. But any mech that I ever met has said overnight cold.

The engines are wee and this is not like doing a 350 smallblock with the engine running.

[bwringer]

I would be interested in knowing how much they change from cold to warm to hot. Some cars have a cold spec and a hot spec, but on an air cooled engine hot can mean most anything.

I'd be very interested in learning the difference between hot and cold clearances too.

Do it for SCIENCE!