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How Cold is Cold (for valve adjust)

Nessism

Nessism

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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.
 
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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.
 
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? :D

Dan :)
 
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
 
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
 
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
 
salty_monk said:
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? :D

Dan :)
Click to expand...

Yeah, I was visualizing something else.

My mistake, I couldn't see adjusting the valves with the bike running.. I had a long night.
 
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.
 
Ghostgs1 said:
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
Click to expand...
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.

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

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

Do it for SCIENCE!
 
bwringer said:
I'd be very interested in learning the difference between hot and cold clearances too.

Do it for SCIENCE!
Click to expand...


I agree as well, as someone on here has said before :rolleyes:, "to measure is to know..." right Ed?? :D
 
My little pea brain is working OT here.

I think that the requirement for a cold engine is to assure things are as loose ans they can get. There is more involved than just the clearance of the lobes to tappets. There is the cumulative space in the cam bearings and any of the other mated surface between them.

So its better to go a bit loose and know its loose than to guess that it may or may not be too tight at operating temps?
 
bwringer said:
I'd be very interested in learning the difference between hot and cold clearances too.

Do it for SCIENCE!
Click to expand...

You are tempting me to give it a go. Brings up many questions, such as is this engine specific or model specific or will it vary with 2V vs 4V engines. Likewise, how hot is hot? How quickly will clearance change with engine cooling off?
 
waterman said:
You are tempting me to give it a go. Brings up many questions, such as is this engine specific or model specific or will it vary with 2V vs 4V engines. Likewise, how hot is hot? How quickly will clearance change with engine cooling off?
Click to expand...


With a cast engine it mat difffer form bikes of the same engine.
I read a nice article by the motorcyclist dud form the 80s.
In it he delved into the intricacies of the stresses on engine components going form fully contracted to fully expanded.

Said it takes engines a long time to reach the temp at which all stresses are relieved.
I think it was more than an hour but that seems crazy.
 
Ed, if the guy is riding it to your house to do the valves, dump the oil & put a fan in front of the engine. It will take no longer than 2 hours to cool it off this way. If you leave the oil in it, it WILL take longer to cool off. The oil holds the heat is the issue & if you drain it you will be good to go in a couple of hours. Make the guy bring enough beer for the wait time!!! :D Ray.
 
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