Small breather hole 30u engine

[Tinkeys]

Hi all !
I have just finished repairing engine breather dump tube only to discover just above and to the rear of valve cover there is a tiny hole that looks to be purpose drilled ,it's approx 4mm,while engine is running there is a hint of engine blow-by coming from this tiny hole.
Would anyone know why it would be there?

[chetbrz]

You got me, if you have the breather tube why the need for the small hole.  If it's threaded maybe it is there to hold some modification or a clamp to keep the breather tube in place.  Just some wild guesses.

Chet...

[Tinkeys]

I hade a similar thought , there is no thead in thAt hole .
Sounds like a no brainer somebody thought of , I think I will just plug it.

[1930]

I am pretty sure I know what it is and what its purpose is and it does have a purpose and I would not just plug it  but just to be sure we are on the same page it would be best if you could post a picture

[Tinkeys]

Will post a picture in next day or 2, if it has a purpose what would it be ?

[1930]

I dont know unless you post a picture if we are thinkng the same thing but it sounds like your air cleaner shutter, it is part of your crankcase ventilation and it sounds like you may be missing a piece.
It is important as it helps ventilate the crankcase

[Tinkeys]

Here is picture of breather hole at rear of engine just above side valve cover.
Just above 2 black hoses its approx. 4 mm

[1930]

That is a small hole and so close to the edge of the pan, it does not look like what I had been reffering to but I would ask other Plymouth owners to verify they do not have the hole before you cover it up

[Tinkeys]

Thank you for that info , will ask if any other owners of 30u have this same hole as in picture above.

[Tinkeys]

Thank you for that info !
Does anyone with a 30u engine have the same hole as in picture above ?

[Doug]

Mine has the same hole. I stuck a rifle bore brush through it, Just came out oily. That's the great thing about these old cars.

[1930]

It almost has to be your crankcase vent then and I would not plug it

[Tinkeys]

Looks like I jumped to a silly conclusion !
Do you think the hole should be plumed to air cleaner or left as is ?

[1930]

I may have a 29 or 30 Plymouth instruction book if you do not. Let me know. My 29/30 Dodge instruction book reads as follows ( and again I am only assuming this is the same deal, I know very little about Plymouth other than I would like to own one )   Crankcase ventilation.............
Due to natural operating condition of a gasoline engine, gasoline and water vapors form in the crankcase which under certain conditions may cause an etching of the brightly finished steel bearing surfaces in the engine and dilution of the crankcase oil. These gases are expelled (before condensing ) from the crankcase thru the ventilator pipe connected to the intake of the air cleaner from the rear valve spring cover.............
There is an actual air cleaner shutter on Dodge and most often the very small bolt that acts as the handle for the sliding shutter is missing from these engines, I had assumed when you said 4 mm hole you were referencing the spot where the small bolt might be, it is this small bolt that again acts as a handle and when moved slides open or closed this shutter.
You Plymouth may not be designed quite as intricately as this and that would not surprise me as it was a bit of a cheaper car so this is why I would still suggest that this hole of yours is still this breather and by plugging it you will eventually cause serious damage to your engine.
Just a thought

[Tinkeys]

Thank you again (1930) sorry don't know your first name ,what you have pointed out sounds 100% ,it goes to show "don't assume anything until proven otherwise" I do tend to jump to conclusions to early sometimes . Would you have a picture of this sliding valve of were it is?
Just wondering what the purpose is for valve.
Thanks again Tony.