Crank case ventilation / oil smells
 

I'm not sure my crankcase breather is working properly, and I'm not even sure it is correct for the engine.

It's a '64 car but I've rebuilt the engine from a rusty bare block that was found in the car and using spares from a donor. It has an unvented oil filler cap, and an open breather that sticks out of the side of the block with a flame trap on it, which then goes down and out under the car. That's it.

I get a bit of an oil vapour smell when driving. I have also noticed that the bottom of the gearbox is covered in oil film. The film has a slight petrol smell so I'm thinking it's coming from engine rather than box. The engine oil level doesn't really drop at all, just completed a 900 mile journey and the level on the dipstick barely moved.

Where could the oil smell and the film be coming from? Would the wrong cap and breather cause pressurisation and therefore oil vapour to be pushed out from somewhere? Or is this all just a characteristic of an open breather?

You have the correct breather for the age engine

65 on breathers have a hose linking it to the air filter so that the fumes are burnt off and oil smells reduced. You could convert to the later setup

You could clean out both the filler cap mesh and the side exit pipe and teardrop but with this set-up there should be very little blow by if the engine is in reasonable nick. I would check to see if the hole around the steering shaft has the sponge seal in place. It is held by a wire clip fastened on by a single screw. Buy or make one easily. If not in place a good source of noise and smells. There are other various holes in the bulkhead that lose their sealant too.

What you have is probably normal. The attached diagram shows the different crankcase ventilation systems applied to the 140 and I expect that yours is probably like part #3 on the diagram. Some early cars just had an inverted U tube attached to the side of the engine. So, your crankcase is ventilated; however, it lacks the positive ventilation associated with the later PCV systems.

The smell of oil vapour from the engine is probably normal for a car without PCV system. It will be made worse if you have ring blow by.

With some parts switching, fiddling and modification you can convert to a PCV system which has two benefits
- forced air flow through the engine will help to reduce the build up of moisture and other contaminants in the engine oil
- directing the crankcase air flow into the intake manifold where it is ultimately burnt in the cylinders reduces the unpleasant oil vapour smells.

The later PCV equipped cars had two different PCV systems distinguished by the air flow direction. Some (earlier cars) had air flow into the filler cap and out the oil separator / flame trap and into the intake manifold. Later B20s (Djet for sure) had air flow into the oil separator / flame trap and out the oil filler cap and into the intake manifold. Depending on the application they use a PCV valve or a restricting nipple so don't go mixing and matching the designs. If you want to add PCV to reduce the smell pick a design and use the parts numbers from the parts manual to get the correct matching parts.

Ron K's web site has a hall of shame showing creative incorrect PCV systems along with the correct PCV systems

https://www.sw-em.com/pcv_diagrams_and_notes.htm