Rono 

If it is leaking down the outside, then you could have a misaligned cannister or the top of the cannister where the single hold down bolt goes may have been crushed a smidge so that when fully cinched down, the bolt cannot keep the bottom of the can from wobbling. If this is the case, then you would need to remove your cannister, turn it upside down on flat surface, get a sizeable socket and strike it with a hammer to get the sheet metal to go back towards original spec. Check that pesky flat-o-ring at the bottome of that cannister too.. that could be a problem...misalignments are easy to do.

If it is leaking down the inside of the tube (I have had this happen to me too), you have too much blow by from new rings. In the past, I have removed the downdraft tube completely, installed a flat plate to cover the hole (FoMoCo made those to spec also), and then installed a valley pan up top that had the vent opening for Crankcase Ventilation. You could either run a down draft tube from there like most of the late 50s model cars had or you could use this a PCV port to send over to your carb/intake. There are plenty of posts about how to plumb that kind of job to your Y.

How much are you leaking? Does it get worse with higher RPM or remain the same?

Keep us up to date, we are here to help.

I had a very similar situation with my 57 Fairlane (292).  After a complete engine rebuild, I was advised by the engine shop to run the engine at 1800 RPM for 20 minutes to "run in" the cam (something that is common after an engine rebuild with new camshaft).  After shutting down the engine there was a large puddle under the draft tube.  I had installed a new filter when re-installing the engine and the gasket to the block was new and tight.  I had quite a bit of oil spray when driving the car and the source appeared to be the draft tube as well.

I decided to try a modification to the draft tube cannister (pictures attached) that worked very well right from the start (the engine was rebuilt in early 2009 and now has around 5,000 miles on it).  I replaced the filter with a section of 2" PVC pipe (the filter is 2.25" outside diameter and the 2" PVC is 2.375" so it seemed to fit within the cover okay).  I made the pipe length 1.875" (same as the filter) and cut a notch out of the front upper portion of the pipe to allow for air flow.  The PVC pipe was glued in place using JB Weld and it acts as a "dam" to block oil from flowing into the draft tube before it can flow back into the block through the return tube.  My reasoning for eliminating the filter is that the air flow is always from the engine out to the draft tube, so it is doubtful that that any dirt could enter the engine from the draft tube.  I also never drive on dusty roads, so that may be a consideration if you do.  You could "patch in" a portion of filter in the notch of the pipe if concerned.

In any case, the modification has worked very well.  There was no longer any expulsion of oil from the tube while driving or accumulation after parking the car.  I'm sure there are other fixes, including adding a PCV valve and directing the flow through the carburetor, but I found this to work well for me.

Regards,

Dave

Welcome to the site.  You might double check the face of the draft tube where it bolts to the block and insure it’s flat.  These are easily deformed and the gasket simply doesn’t do its job in sealing against a surface that’s not quite flat.

For what it’s worth, the exhaust driven system on my roadster is working well at 2500 rpms and just gets better as the rpms go up.  Many high end race cars (and especially those that use mufflers) incorporate either electric or belt driven vacuum pumps to maintain a negative pressure within the crankcase in lieu of using an exhaust driven evacuation system.  I’ve seen as much as 30HP on engines that use a belt driven vacuum pump versus no pump at all so there’s definitely some power to be found in running a negative pressure on the crankcase regardless of the method employed.

A PCV valve is simply a controlled vacuum leak which requires an adjustment to the air fuel ratio in which to compensate.  PCV systems utilize the engine manifold vacuum to pull air from the crankcase whereas auxillary pumps (electric or belt driven) or exhaust driven systems do not require engine vacuum in which to operate.  But the purposes for each do vary.

PCV valve systems are specifically for removing moisture or excess pressure from the crankcase which would be an environmental concern if not reburned through the engine.  PCV systems are typically a flow through design that do not pull a vacuum on a crankcase but can remove enough excess pressure that any existing oil leakage can be significantly reduced.  If a PCV valve is used on a sealed system, then a reduction in crankcase pressure will be realized but its ability to actually remove any moisture or condensate from a warming up engine will be compromised.  It’s that flow through design that actually allows contaminates to be moved to the PCV valve where it can be reburned through the engine.

Auxillary driven pumps are for removing air itself from the crankcase and are realized more for their performance gains than for environmental purposes.  This is because these air pumps are designed to remove air on a sealed system rather than simply allowing air to flow through the engine.  Removing air from the crankcase frees up horsepower simply due to the pistons not having to work as hard in moving it around.  Air has mass and as a result it takes a given amount of power to move it around.  These same auxillary systems can also improve compression ring seal but there are some detriments to having too much negative pressure in the crankcase.  First is a reduction in oil pressure and secondary is some starving of oil in top end parts such as around the wrist pins.  For this reason, many auxillary engine vacuum systems will have an adjustable vacuum break to limit the amount of negative pressure that can be generated within a crankcase.

Let me know what you fi9nd.

Cheers, Louie , NZ