Do valves clearances get smaller or larger when engine is hot?

[somerandomguy1]

Good afternoon,

I would like to know if valve clearances on a 1990 corolla toyota 1c diesel engine with aluminum head and iron block get smaller or hotter when engone is hot?

Thanks

 

[xgmad]

Because it is metal, it starts to expand in the heat. This is called thermal expansion.

 

[zrxkawboy]

Valve clearances typically get smaller as the engine heats up.

 

[PWMDMD]

Because it is metal, it starts to expand in the heat. This is called thermal expansion.

But all the metal expands with heat and so the question is as the valve metal expands and it gets slightly longer does the metal in the combustion chamber also expand an equal amount making the net different zero-ish? No idea and even though thermal expansion is a thing my guess is not enough to make a practical difference.

 

[somerandomguy1]

I am adjusting valves with mechanic and he says valve clearances get larger when engine is hot.
Toyota 1c engine factory repair manual says intake valve clearance when cold 0.20-.30mm and exhaust valve 0.25-0.35 mm.

Exhaust valves seem to be in spec
All 4 Intake valves are tight at 0.05 mm.

I dont know if this is because engine is a bit hot and valve clearances decrease when engine is hot or it is just out of spec.

Mechanic says i will see better fuel economy with adjusted to spec valves.

 

[xgmad]

But all the metal expands with heat and so the question is as the valve metal expands and it gets slightly longer does the metal in the combustion chamber also expand an equal amount making the net different zero-ish? No idea and even though thermal expansion is a thing my guess is not enough to make a practical difference.

Oh yes, valve clearances do get smaller when the engine starts to heat up, due to the expansion of the metals but not to the degree of where the valves cannot move due to a complete seal, when you use an aluminum cylinder head, typically aluminum valves and valvetrain components are used, so everything becomes relatively equal or reliable enough for operation. I hope this helped

 

[vw7674]

But all the metal expands with heat and so the question is as the valve metal expands and it gets slightly longer does the metal in the combustion chamber also expand an equal amount making the net different zero-ish? No idea and even though thermal expansion is a thing my guess is not enough to make a practical difference.

the exhaust valve face is absorbing more heat/sq.in. than the head casting. The valve face is absorbing combustion heat & carrying that heat to the valve seat when seated. Some radiates up the stem, to the bronze guide & the head casting.
Valve clearance is there to ensure the valve does continue 'seating' on the seat insert even when at full engine temperature.
If the valve didn't get a chance to transfer heat to the insert, it would burn before the first oil change.

 

[xgmad]

Spec tightening valves should suffice, as they are tested for this same reasson.

 

[somerandomguy1]

Valve clearances
1a is cylinder 1 intake 0.05 mm
1e is cylinder 1 exhaust 0.25 mm
Apparently two intake valves had 0 clearance from cylinder 3 and 4.
Values are in hundreths of mm

there are shims for valve adjustment.The mechanic is tipping or shaving off material to get clearnces within spec.

 

[Trav]

Valves get tighter in iron heads and looser in aluminum heads.

Edit: This explains it better than I can.

Setting Valve Lash - How to Check and Set Your Lash the Right Way - Circle Track Magazine

In this tech article CIRCLE TRACK shows you how to check and set your valve lash to ensure your race engine will be trouble-free for the entire season - Circle Track Magazine

www.hotrod.com

 

[somerandomguy1]

Cylinder 1 intake clearamce improved to .20 mm
Cylinder 2 intake clearance improved to .25 mm
Cylinder 3 intake clearance didnt improve enough for the 0.05 feeler gauge to enter
Cylinder 4 intake valve clearance improved to somewhere between 0.10 -0.12 mm
Cylinder 3 and 4 intakr valve clearances are still not in spec.

Update cylinder 4 intake clearance is between 0.20-0.22mm

Cylinder 3 intake valve clerance is still not in spec.

 

[mk378]

Maybe I'm missing something but why not measure when cold, warm up the engine, then measure again when hot?

Zero clearance-- in either case-- is a problem. That will cause misfiring at idle and also likely a burned valve.

This looks like the type of engine where you will have to take the cam out and change shims to adjust. Compared to others that are simply adjusted with a screw at the end of the rocker arm -- if it had rocker arms.

 

[Jimmy_Russells]

Rule of thumb is to set cold lash 4 thousandths smaller than hot lash. Valve clearance increases when hot, 100%.

If the valve cover is easy to remove check it and reset if necessary after it is warm.

 

[Jimmy_Russells]

Oh yes, valve clearances do get smaller when the engine starts to heat up, due to the expansion of the metals but not to the degree of where the valves cannot move due to a complete seal, when you use an aluminum cylinder head, typically aluminum valves and valvetrain components are used, so everything becomes relatively equal or reliable enough for operation. I hope this helped

Aluminum valves? What?

 

[somerandomguy1]

The mechanic shaved all shims down and intake and exhaust valves are all in spec. I will report back with fuel economy for current tank of diesel to see if this changes.

 

[zrxkawboy]

Rule of thumb is to set cold lash 4 thousandths smaller than hot lash. Valve clearance increases when hot, 100%.

My experience has been the opposite. Look at a service manual that specs a cold valve setting. Exhaust valves are always spec’d with more clearance, because the clearance decreases more on the hotter exhaust side. If clearance increased with heat, the exhaust valve would spec a cold setting smaller than the intake.

 

[Jimmy_Russells]

My experience has been the opposite. Look at a service manual that specs a cold valve setting. Exhaust valves are always spec’d with more clearance, because the clearance decreases more on the hotter exhaust side. If clearance increased with heat, the exhaust valve would spec a cold setting smaller than the intake.

Yes, I'm sure. Here is just one example:

@ 2:45

 

[barryh]

There is no answer to this question that will be applicable to all engines. Simple solution is measure them hot then leave overnight and measure again stone cold. Then you will know the answer better than anyone here.

I've did just this so that I would know it's safe to do an oil change and then measure the clearances on a still warm engine.

 

[zrxkawboy]

Yes, I'm sure. Here is just one example:

@ 2:45

We all have our own preferences for sources of info... I prefer Factory Service Manuals to Youtube videos. Here's a snip from a FSM for one of my Plymouths. Notice how the exhaust valve (subject to most heat) gets set to 0.013" cold, which is equivalent to 0.010" hot?

 

[Jetronic]

I am adjusting valves with mechanic and he says valve clearances get larger when engine is hot.
Toyota 1c engine factory repair manual says intake valve clearance when cold 0.20-.30mm and exhaust valve 0.25-0.35 mm.

Exhaust valves seem to be in spec
All 4 Intake valves are tight at 0.05 mm.

I dont know if this is because engine is a bit hot and valve clearances decrease when engine is hot or it is just out of spec.

Mechanic says i will see better fuel economy with adjusted to spec valves.

See that the hotter exhaust valve needs more clearance when cold? That's because the clearance shrinks when the engine gets hot. But clearances can drop permanently as the valves and valve seats wear, so they need to get adjusted, on a cold engine.