Crankcase Ventilator Tube dripping oil '37 Flathead 6

[Kels]

'37 flathead 6 all new 10 years ago.. Show car so maybe has 30 miles on it..

 

Got it out to start driving it.. Whilst idling the crankcase ventilator tube is dripping a fair amount of unburnt oil.

 

I do not remember having this happen before (maybe small drips here and there BUT this is a larger amount.)

 

Is this a concern?, if so, what might be the cause?  I could not find anything in the service manual

 

Thanks in advance!

 

[Sniper]

They drip oil that's for sure. How much is normal? I can't say

[Jerry Roberts]

You might give it some time and miles to seat the rings . 30 miles isn't much . 

[bhoward]

I recently rebuilt my 217 c.i. Plymouth and had the same problem. I took some Aluminum screen patches used for window screens and cut them to fit in the opening of the pipe where it bolts to the block. 

Mine was circular approx. 2" round. I drilled a hole in the center for the bolt to go through and put a little gasket RTV around the outer rim to keep the screen from moving. It stopped leaking oil out of the pipe, and I still have good air flow through the pipe.

[keithb7]

My understanding is engine oil becomes a fine airborne mist inside the crankcase. The block vent down-tube is cut on a 45-ish degree angle. This creates a scavenging effect while the car is moving. Crankcase fumes are released and sucked into the atmosphere. The oil mist surely exits too.  I would expect oil to be collecting on the draft tube walls. How much? I’m unsure.
 

Is your engine oil level a bit high maybe? As mentioned, blow-by from new, un-seated piston rings could contribute to excessive crankcase pressure. Then increased exit of misty oil.  What about adjacent piston ring end-gaps lined up together? That could do it too. 

Edited July 10 by keithb7

[Kels]

19 hours ago, bhoward said:

I recently rebuilt my 217 c.i. Plymouth and had the same problem. I took some Aluminum screen patches used for window screens and cut them to fit in the opening of the pipe where it bolts to the block. 

Mine was circular approx. 2" round. I drilled a hole in the center for the bolt to go through and put a little gasket RTV around the outer rim to keep the screen from moving. It stopped leaking oil out of the pipe, and I still have good air flow through the pipe.

That is interesting.. So, you determined that the oil drip was due to the excess being able to "roll" down the tube and the screen kept this from happening?  Did it completely eliminate the drop of just lessen it?

[bhoward]

I am having trouble with the rings seating since the rebuild. The oil was leaking out of the the tube on the driveway. I remembered seeing screens in breather caps on various engines without a PCV system, so I figured I would give it a try. The vent tube still "free flows" as it did before. I sandwiched about 4 of the screens together. I was able to blow through the tube without any effort. The oil should hit the screen and leak back down. I have put about 500 miles on it since then and haven't notice any oil or issues since I did it. I think it kind of acts like a baffle would on a more modern engine that uses a PCV valve to evacuate pressure and gases. Modern engines that have a PCV valve in the valve cover usually have a baffle built into the valve cover.

 

My engine is still smoking due to the rings not seating yet but, at least it's not coming out of the tube now. I am not sure, but I am assuming I have more pressure build up from the rings not seating yet. I am new to building this type of engine, maybe someone with more knowledge than me could weigh in. 

 

 

[bhoward]

Update:   I have driven an additional 650 miles and it is starting to leak a little into the down draft tube. I had a half dollar size spot on the driveway. I still haven't got the rings to seat yet  either.

Mr. Asche  told me it could take up to 4000 miles for them to seat. 

 

 I picked up my overdrive transmission from him about 2 weeks ago. He is pretty quick on the turn around time. One week and it was done. Great man, and a wealth of information.  His sons are great to talk to as well. If you are looking for old parts and can't find them give him a call. He is sure to have it.

 

 I went for a ride in his 1950 Plymouth. If you get a chance, take a ride in it with him. It's pretty fast. He said the roadster is faster. We were going to take that out as well, but the weather wouldn't cooperate.  

[Sniper]

Old school cast iron rings can take awhile to seat, that is for sure.  We get spoiled these days with the more precise and finer machining and better materials availability.

 

While you can probably benefit from the better machining these days, assuming you find a shop with the latest tooling and the willingness to deal with old iron, we are still stuck with cast iron rings or chrome rings as the choice.  It is what it is.  Of course there are custom options.  The Freewheeling Tony Smith sells a custom rod and piston package, with modern style rings, but it isn't cheap.  About $4500 last I looked

[RobertKB]

When I rebuilt my engine, I drove it hard right from the start. Drive it like you stole it to seat the rings.  Babying a new engine is not good. I don’t mean drive it like a NASCAR but don’t be afraid to rev a bit, back off, and then hit the gas again. I have no leaks anywhere and great compression within 600 miles. 

Edited August 13 by RobertKB