Rambler 195.6 OHV crankcase ventilation (PCV)

feb 2019

you can contact me at it is as if at protonmail dot com

positive crankcase ventilation, aka PCV

i've been developing a suitable PCV for this engine. none of the factory systems worked well. crankcase ventilation is absolutely necessary. even the best rings in the best engines don't seal perfectly; water is a major combustion byproduct and it definitely collects below the rings and needs to be removed.

AMC tried out various crankcase-ventilating schemes between 1956 when this engine variant was new through it's final year in 1965. this was originally a road draft tube system; a 1" or so tube dangled down to the ground where it was hoped a mild vacuum would be generated by the car moving along the road, and draw out "fumes". mainly it served to spray dirty oil and mist over the chassis beneath, and of course the roadways and the air. (older drivers well recall the black stripe down the middle of every roadway; those are mostly long gone,)

the factory schemes were all variations of the same idea: draw fumes from the front-most side-valve access cover (recall this engine is the flathead with an OHV head slapped on in 1956), with clean (damp) air drawn in via screened vents in the valve cover and/or a mesh-stuffed oil filler cap.

road draft

this lovely but poorly photographed 1961 color diagram shows fairly well the useless road draft tube but also the oil-mist/crankcase vapor volume that needs scavenging. the filler neck is not shown, but is on the right side lower crankcase and extends up to nearly valve cover height.

early PCV

this excerpt below from the 1962 TSM shows the side cover with 1/2" hose nipple, the most commonly seen system on most 195.6's. the TSM page shows the PCV screwed into the edge of the L-head but on the OHV it's on a brass street elbow.

looking at an actual engine, you too would assume that the baffled side-cover location would be fairly free of mist and flying oil, but you would be wrong. every system i used had much oil mist out that cover.

i won't go into details of the factory systems here; it's all in the TSMs if you care. none of them work well, but the California PCV is least-worst, a fairly typical PCV valve attached to the head (OHV and L-head) that drew gases via that misty side cover. however some years have desireable components so i'll describe them somewhat for identification.

late PCV

final model year 1965 had more or less all of the PCV variants available at once. 1V carb OHV, 2V OHV, and L-head each had their own arrangements. the drawing below are detailed and acccurate, but very hard to read even in print; suffice to say in real life it looks like most 1960's..1970's PCV system. no big deal here.


the above two components are desireable for an improved PCV system.

PCV improvements

before the canister velocity-based demister (below) i had a modified valve cover scheme; it sucked oil mist too. i use a too small baffle however, a small square of sheet steel tacked over the grommet hole. it wasn't very good, hence the demist can.

but i believe the top of the valve cover, towards the front of the engine, is in fact the correct location to draw from, and that the best clean air inlet is the very long oil filler neck. this draws gases more or less diagonally through the crankcase, and gravity is of some help, and though the rockers are tossing oil, oil volume is overall not that high up there.

demist-can PCV

after the valve cover PCV, i went back to a side-cover draw but with a special can between side cover and PCV valve. this is not a collection can; the hose from the side cover feeds the bottom of the can, the valve in a grommet on top. inside are two perforated separators and coarse bronze wool.

the operation of the can isn't immediately obvious -- it is a widening of the hose to drop velocity, not a catch can. whatever the air flow (fractional CFM) is inside that half-inch hose, it is obviously sufficiently fast to keep oil mist in suspension. the same volume of gas in a three-inch hose is far, far slower; this allows mist to fall out, and condense/collect, onto the bronze wool. this system works great. oil that condenses in the can drains/dribbles back into the side cover, and out the top is nearly dry.

this system has worked well for half a year, but it's ugly and inconvenient under thwe hood, but the velocity chamber solved the basic problem.

valve cover PCV with velocity chamber

the new (feb 2019) scheme combines the valve cover draw with velocity chamber. time will tell if it works.

the current scheme has a much larger baffle system inside covering a 3/4" hole in the cover.

this is a '61 or '63 valve cover, which had open ports fore and aft, which i tapped flat and welded up.

the draw hole was placed in the frontmost full ribbed section. the ribs provide the gap for the baffle. the draw hole and two drain-back weep holes live under the fitted velocity chamber which was welded onto the cover.

there's a bit of 80%-open steel screen over the draft hole. coarse bronze wool is very loosely packed in, then a rectangle of screen slips over it.

JB Weld was smeared over the welds to seal any pinholes and the cover got painted, wool stuffed and screen and grommet inserted.

PCV valve

there seems to be utterly zero information on valve flow rates, restrictions, or anything at all. one time i actually stood in the back of an Autozone, gently lifting the business end of each valve from it's container and sucking on it. i'd made a list of candidate part numbers via images on web search and via my rigorous characterization process determined that the valve for a 1980 Honda Civic had the highest restriction and the right physical form factor. looking like a crazy person For Science.

the valve i'm using has the pleasant part number of PCV1234. common as dirt and very cheap.

oil filler cap and dipstick

it may not matter too much, but i believe at the moment that the closed 1965 filler cap is best. it doesn't have the large area vents and steel wool that was necessary for low restriction with the old road draft system (the cap was retained in most PCV systems until 1965).

with positive ventilation, the flow through the unvented cap will be fine. it also means when shut off, oil mists won't waft out the cap all over the engine compartment. with adequate ventilation, that won't matter.