Technical Adequate Crankcase Ventilation.

[Bleeding Knuckles]

Greetings All, I've been giving my car some hard driving of late and due to the use of a Solex twin choke I don't have a crankcase vent recirculation system feeding into the air intake. I was somewhat perplexed when I noticed that my oil catch can was showing a higher level of oil after my last run as the car has not given such an indication before (hard driving?) So I burned the midnight oil and researched for any possible causes. After consulting with my engine man I have arrived at the following conclusion - It seems that my crankcase is becoming pressurised at high rpm (6000+) As the engine has run-in there may be some blow by occurring too, now I'm not concerned with this as All engines suffer blow-by to some extent and as mine is running 10.5:1 compression ratio it's a given that it will happen. and both of the pistons plunging down together will increase the effect. I have tested the plugs and found them with good colour and no contamination, the exhaust gas has no oil smoke, so I'm happy that the oil is only being fed to the catch can at high rpm. I've consulted some literature from 'Burton Power' that covers this area and have decided that if I'm going to continue running the car as I have I will need a better oil recovery system, and as I'm not one to vent any oil vapour through a tube onto the road
it will have to be of sufficient size to stop frequent can emptying procedures My original can was only 400ml and noting that this seems to be insufficient I went straight to 1Ltr
The literature recommended venting the crankcase too so I've fashioned a simple take off that fits onto the fuel pump mount and fed silicone piping from it and the rocker box vent to the can on the bulkhead, now all I need is the time and weather for an extended road test - more later
Pics show before and after.
Ian.

 

[Bounding Bambino]

Your modification brings up a interesting concept that I thought about for a bit and seems to make sense. Normally crankcase ventilation is fed from the top valve cover port, where in theory the natural airflow would be traveling up and down the push rod tubes as the cylinders move up and down. Because the head is also fed pressurized oil to the rockers, oil will naturally trickle down the push rod tubes back into the case. At higher RPM's i would assume/guesstimate that the higher airflow velocity thru the tubes would cause the oil to atomize into the stream, and a significant amount of oil mist would find its way into the catch can (there isnt alot of surface area / & time in the valve cover for the oil mist to collect on the side surfaces and re-combine).

Having the crankcase vent feed from the fuel pump block off port would/should significantly reduce this phenomenon as there isnt any oil trying to trickle back into the case thru that high velocity air stream. Only the natural oil spray going around inside the case from splash. But it isnt directly in the vicinity of that vent. The hole, iirc, is not directly inline with any rotating crankshaft surfaces, isnt it hidden/shadowed behind the front main bearing cap/cover?.

Engine is lookin good fyi

 

[Bleeding Knuckles]

Your modification brings up a interesting concept that I thought about for a bit and seems to make sense. Normally crankcase ventilation is fed from the top valve cover port, where in theory the natural airflow would be traveling up and down the push rod tubes as the cylinders move up and down. Because the head is also fed pressurized oil to the rockers, oil will naturally trickle down the push rod tubes back into the case. At higher RPM's i would assume/guesstimate that the higher airflow velocity thru the tubes would cause the oil to atomize into the stream, and a significant amount of oil mist would find its way into the catch can (there isnt alot of surface area / & time in the valve cover for the oil mist to collect on the side surfaces and re-combine).

Having the crankcase vent feed from the fuel pump block off port would/should significantly reduce this phenomenon as there isnt any oil trying to trickle back into the case thru that high velocity air stream. Only the natural oil spray going around inside the case from splash. But it isnt directly in the vicinity of that vent. The hole, iirc, is not directly inline with any rotating crankshaft surfaces, isnt it hidden/shadowed behind the front main bearing cap/cover?.

Engine is lookin good fyi

Hi BB, If you have a 500 'Haynes' manual (check downloads section) look at page 73 and fig 3.14 it shows an engine cross section and actuating rod from fuel pump to the camshaft, that should help you get your head around the pathway.
Ian.

 

[500nuova]

If you were to go that route, couldn't you put some kind of valve in-line to get true, positive crankcase ventilation and maybe a simple oil separator to drain some of the "ventilated" oil back into the crankcase instead of the combustion chamber? That way you wouldn't have to worry about the can overflowing.

 

[Bleeding Knuckles]

If you were to go that route, couldn't you put some kind of valve in-line to get true, positive crankcase ventilation and maybe a simple oil separator to drain some of the "ventilated" oil back into the crankcase instead of the combustion chamber? That way you wouldn't have to worry about the can overflowing.

Hi, True you could, and I would have probably done that with a larger engine. But given that I wanted to avoid any extra complexity and that fact that with a 4Ltr alloy sump and an anti-surge plate fitted there is not a lot of room to fit an oil return. Draining the oil is no biggie anyway
Ian.