2F/3F hot/cold valve set

[Godwin]

I've read the arguments about setting valves hot or cold and I know that in the FSM hot is recommended. Today I decided to give it a little test. I adjusted valves on a '77 2F, '81 2F, and '88 3FE. Initially my plan was to warm up the engines, adjust the valves, let engines cool and recheck. I made it 1/2 way through this process before I lost patience, these engines hold heat for a long time.

Engines were warmed to ca. 180-185 F and the valves were adjusted to the stock setting of 0.008 IN and 0.014 EX. I allowed the '77 2F to cool before rechecking the valves; radiator was only very slightly warm. Ambient temp was in low to mid 70s F. I think there was ca. a 100F degree difference between the hot and cool settings.

When I rechecked the valves there was at most a 0.001 inch difference with any of the settings. For example with some EX a 0.013 feeler fit better than the 0.014 or a 0.007 instead of a 0.008 for some IN. There was a similar trend with the 3FE valves that I checked.

From this meager test I would say that hot is better but in a pinch you can get away with setting valves cold.

 

[Dynosoar]

I hate burning myself! I set them slightly (.001) tight when cold. I have never noticed a difference.


Dynosoar

 

[mp_cude]

The other day when i set mine, I decided from now on i'll do them cold. That little bit of a difference does not bother me at all

 

[2mbb]

When I rechecked the valves there was at most a 0.001 inch difference with any of the settings. For example with some EX a 0.013 feeler fit better than the 0.014 or a 0.007 instead of a 0.008 for some IN. There was a similar trend with the 3FE valves that I checked.

I always thought that the clearance would be larger when the parts were cold vs. the warm setting. I wonder how much the measurement is influenced by the viscosity (and therefore temperature) of the oil and how much on the temperature of the metal.

The gap on the exhaust valve is larger because it gets hotter than the intake valve, and therefore needs "more room to grow". The temperatures that the valves reach by running the engine to operating temperature at idle (per the water temperature) are still probably low compared to those when you are screaming 3000 rpm on the highway.

 

[D'Animal]

I used to do them hot, I did the same as Godwin did and went back and checked them cold. Not enough difference for me to burn myself ever again.

 

[mp_cude]

the tolerances are tighter when done cold, because metal expands once heated

 

[2mbb]

the tolerances are tighter when done cold, because metal expands once heated

Right. Metal expands when heated. Therefore the valves get longer and the gap (valve lash) gets smaller. If the engine and head are made from different materials (aluminum head and/or block vs. steel valves) then the situation is more complicated because the aluminum expands at a different rate. Here's some information from the weblink below. According to this the cold valve adjustment for our engines should 0.010 intake and 0.016 exhaust.

Century Performance Center, Inc. :: Adjusting Valve Lash

 

[Cruiserdrew]

Setting them hot is not that big a deal.

Nice correction factor though!

 

[Godwin]

Agree that setting them hot is not that much trouble. For me the worst part is getting the valve cover back on without knocking the gasket loose, at least on the 60 series.

This could be done more scientifically and under more controlled conditions, i.e. measure the temp of each valve, take more care with the adjustments, whip up a nice regression of valve expansion vs. temp. But I don't think all the effort would be worth it since these are, after all, nothing but old F series motors.

 

[Yoda60]

the 2F clearances should actually be set Hot and with engine running!!!

 

[lehiguy]

the 2F clearances should actually be set Hot and with engine running!!!

Only if you like pain, hot oil splashing around and mangled feeler guages. I too used to do this but I found better ways of setting the valve lash. I also ran my clearances at .005 and .007 and I noticed that she ran a tad stronger, not to mention quieter.