How to keep your V6 oil cap from leaking

[GTRS Fiero]

Because it's a hole.  When metal expands, it follows the path of least resistance.  The metal wouldn't contract into itself to allow the hole to get larger.  Remember the railroad track expansion?  Initially, the rails buckled and pulled the spikes.  The rails expand into the open air, but the thing of note is that, if you have a hole for a spike, the hole must be slightly larger than the spike, so that the rail does not squeeze the spike out when the rail gets hot.  Or so I was taught in physics class.

[Slyp]

When I worked at a gas station the owner had to put a stud into head.  Since he also did car airconditioners the took some freon cans and froze hole and the stud.  when he had frozen them both the stud went into the hole easily.  and after the freon thawed you couldnt get the stud out if you wanted.  He said the freon on the stud shrunk the stud and it also made the hole bigger because the greon caused the metal to contract.......

[GTRS Fiero]

Yes.  If the valve cover was frozen, the hole would get larger.

[GTRS Fiero]

As I think of it, it's the same theory of applying heat to a stuck bolt.

[scottb]

Yall have me confused now..... 1st it has been said that if you apply freon to a threaded hole (which lowers the temperature) it expands the hole to allow the stud to turn easier, then you say can apply heat to remove a stuck bolt....... doesnt sound right to me that if you lower or raise the temperature the hole gets bigger

[GTRS Fiero]

The oil cap leaks while the car is running due to the pressure being built up and the thermal expansion of aluminum; i.e. the hole in the valve cover gets bigger. You want the cap cold so that it is at its smallest dimension so the oring fits tighter.

Um...

[scottb]

See the contradiction?

[GTRS Fiero]

Yes.  You stated that the hole would enlarge when the metal was heated, on the theory of expanding metal (molecules further apart).  DeShoe's post stated that the hole would enlarge when frozen, because the metal shrunk (molecules closer together).

You then posted that it didn't sound right that temperature changes would affect the size of the hole.  There is the contradiction.

My theory is that, when heat is applied to a bolt, the bolt expands (molecules further apart).  As the bolt cools, it contracts, creating a small gap, just like heat forcing the spikes out of the rails.

Also my theory, when freon is applied to the head, the hole expands (molecules contract).

[scottb]

I dont think I said temperature changes wont affect it. If I did, it was not intentional.

Temperature does affect the size. As metals heat up and expand a hope will become larger. Case in point: one Saturday at Northlake I spent some removing a broken stud out an exhaust manifold on the AeroDon car. Applying heat to the flange caused it expand  (along with the threaded hole) and the stud was removed.
At work there are parts that I make that consist of an Aluminum tube and a lead puck that fits inside the tube. The engineers have called out on interference fit. The only way that i can get them assembled is to heat soak the aluminum to around 160F and cool the lead to around 30F. Even then I only have a few seconds to get it assembled before temperatures equalize and they are stuck

[TopNotch]

This is my O-ring set. I bought it at Pep Boys back when they used to sell parts and tools. It was a sad day when they quit doing that, because they had one of the best selections of car tools. Now all they do is fix cars (or at least, claim to. I wouldn't take my car there).

There are no sizes given in this kit, so I just had to pick one that fit for my oil cap fix

[GTRS Fiero]

Yes, you heat a tube, it will expand (least resistance, thin metal tube expands in diameter and length).  Take a piece of plate aluminum, drill a hole of that same size perpendicularly through the plate.  If the plate is then heated, the hole will contract.  My yheory.

[GTRS Fiero]

I am wondering how to properly measure the size of a flexible seal.

[Fierofool]

If you place the o-ring on a flat surface, you can carefully use a set of dial calipers to measure its diameter.  You can also measure the thickness of the ring. 

As far as a hole getting larger or smaller.  I can tell you from experience that I installed many a large bearing set onto an electric motor shaft or pump shaft.  I'm talking about bearings with an outside diameter of 8 to 10 inches.  In order to get the inner race to go onto the shaft it was put on a bearing heater which heated the inner race.  The inner diameter of the race would expand and the bearing would drop onto the shaft and as it cooled, it would shrink and be considered an interference fit. 

We also heated parts of machinery in order to extract a shaft or broken bolt or stud.  By heating the surrounding metal, the threaded hole would enlarge, loosening its grip on the bolt.  Sometimes when it wasn't feasible to use heat, we would use dry ice or freon to super cool a shaft, rod, or bolt.  An interference dowel pin laid on a block of dry ice for an hour will usually drop right into it's hole. 

[GTRS Fiero]

I was always yold that using heat made ghe hole expand, but as I've thought on it, today, I believe heat makes the bolt enlarge and the hole shrink, resulting in a gap when they cool, thus allowing the bolt to be removed.

Heated metal expands in 3D.

[Fierofool]

Question asked:  "Does a hole in metal expand when heated?"

Answer:  Metals expand when you heat them, so the circle should expand. There's no real difference between the circle and a hole (of the same size) cut out of it. The circle is, in effect, the circumference of the hole you put into it. So the hole will get larger.


If the hole didn't enlarge when heated, there could be no explanation as to why the bearing would only go on the motor shaft after being heated.