HS4 : Follow up question

I'm considering swapping out my HS4 carb bodies for bodies that have the brass crankcase ventilation tubes. No, i'm not going to [url=http://www.mgexperience.net/phorum/read.php?1,1971051]drill[/url]. ;)

The tube system, as i understand it, is pretty simple:

1) a hose from crankcase vent to the "Y" connector
2) hoses from the "Y" to the brass vent tube at the back of each carb

My assumption is that the "Y" and/or the brass vent tubes are sized to provide the proper level of vacuum in the crankcase.

Is my assumption correct, or is there a restrictor or something similar in the system that i've missed?

Frank

the restrictor is where the air comes into the system. either a vented oil filler cap OR a certain sized hole on the tube coming from the valve cover.

D'oh! 8-) I knew that... :D

thanks, Drake(tu)

Hi,

I would suggest fitting a standard PCV valve, which is really only a one way vale, so that there is no chance of a backfire getting into the block. This PCV valve is shown in the attached photo, top left hand corner.

Herb

Herb,
the top of the pic looks cut off.

Frank

Hi Frank,

Yes the picture is a bit low, but wasn't originally taken to show the PCV valve. I have just gone and taken one of the valve and annotated it.

Herb

Herb,
Ah, I see.
PCV valve sized for 4-cyl engine?

Thanks
Frank

Hi Frank,

The valve is generic. As far as I know there is no differences for different engine sizes, it's just a simple one way valve, with a ball in a cage, that allows air to pass one way and seals off the other.

The only purpose of it that I can deduce is to stop a flame front into the block, if there is a backfire.

Herb

Perfect.

Thanks, Herb.

Frank

Check out this article about PCVs. http://autos.yahoo.com/maintain/repairqa/engine/ques079_1.html

If I was going to add a regular PCV I would probably get one from a 70s car like a Toyota Corolla 1600 and plumb it directly into the intake manifold. Then make sure you have a vented cap on the valve cover to let fresh air in to purge the engine.

If you change the carb bodies and hook up the vent system like the 70and 71 then an orifice should be used. I made one out of a piece of 1/2" rod about 1/2" long with a 1/8" hole in it. Seems to work fine.

Dan,
That orifice you made is about the size of the orifice in the vented valve covers. Matches what Drake mention earlier at the beginning of this post.

I'm good to go now.

Thanks everyone(tu)
Frank