I guess at this point I need a review of what we are discussing in this thread. PCV (positive crankcase ventilation) is a method of removing "blowby" and "condensation" that forms INSIDE an engine. (am I on track so far?) Flatheads NEED help, (the "crud" that forms inside flatheads is mostly due to condensation that forms and doesn't get "boiled off.") The way I understand PCV is; as long as there is a "strong" vacumme "signal" (for lack of a better word) the valve is held OPEN and draws "fumes" (blowby) and "condensation" and is "reintroduced" back into the incoming air/fuel mixture that winds up being burned in the cylinder(s). To allow air to flow through the crankcase and draw off the "crap", (blowby and condensation) there has to be a point of entry. That entry point should be well filtered otherwise the incoming air flow will just introduce dust and dirt into the engine. Reason would seem to indicate that the "point of entry" (fresh clean air) should be at the OTHER (well as far away as possible) end of the engine so the incoming air will sweep the "crud" away when the PCV valve is open. (am I still on "track" up to this point??) Now for the "sticky" part. Any engine under hard acceleration will show a "drop" (reduction?) in vaccumme "signal." Without the "signal" the PCV would close. It's a known fact that at "cruise" with only partial throttle, the vaccumme is the strongest. Which means the PCV valve would (should) be open. If we (or I) only tap into ONE vacumme source on the intake manifold, would the PVC function correctly without upsetting multi carb balance???
just my uneducated opinion but I think if it's plumbed from the base of one carb or the central plenum, the additional air would homogenize into the mixture. On the Eddie Meyer the controled vacuum leak is concentrated on one intake port right above the valve. You could tie the left front barrel to the right rear barrel with a tee in the middle going to the PCV valve. That should distribute any lean condition. When they ask... just tell them it's an early NOS prototype from the 50's.
Digger Dave, I have my PCV valve set up similar to Fourdy's and it works well. I do get some 'breathing' oil out back but not a heap compaired to other flatheads I see. I took mine off the rear carb underside runner on a 2x2. I'm real happy with it. and plan on doind the same set up on the new motor when I build it soon. Dont know if it needs to be plumbed into both carb bases or not.
Here's the Ford of Canada write up on flathead PCV from 1941: "All vehicles (military) incorporate a directed flow sealed crankcase ventilating system. Its purpose is to prevent contamination of the engine oil. Oil dilution is minimized. The condensation of water vapors which help to form sludge, and freeze in cold weather, blocking the oil circulation, is also minimized. When water vapor is kept out of the engine oil, the formation of rust inside of the engine is materially reduced and one of the most frequent causes of engine wear is lessened. Crankcase ventilation also tends to eliminate the collection of corrosive acids. It maintains a higher lubricating value for the oil and helps to reduce the frequency of oil changes." A lengthy description follows. There is a schematized picture. It seems to show the PCV hooked into an adaptor plate under the carb, which makes sense as the big fitting on the back was probably hooked to a brake booster on most of these military trucks. The PCV (which seems to be the same design as any common modern one) mounts right near there, and the hose then goes to the forward part of the manifold right over the vent tube from the crankcase. Presumably the old vent outlet at the front of the pan is sealed. By the way, that vent down on the pan on most early flatheads is not a pan vent--it is isolated from the pan, and actually communicates with and draws from the tube that goes up into the valley. The vent is down there, just like the later draft tube, just to put it into moving air which supplies the pull on the non-PCV system. It is the outlet on the standard system, the filter on the oil filler tube being the inlet.
I don't have any suitable tech to post the picture, but will try to paint a picture in prose. Some is indefinite, because the picture is a schematized cutaway, not a picture of real components in their actual locations. Here goes: Fitting is tapped into front of carb riser on manifold (I see now this is NOT drawn as a separate plate. It isn't shown, but I would bet money this is tapped into both risers). PCV is mounted vertically right below the tap. It is diagrammed looking just like a modern one, except made to come apart for cleaning. From here, a hose goes forward to the area beneath the generator and right above the vertical vent pipe. Actual attachment is not shown, but Canadian wartime engines have an oil filler right here and presumably this is used. Air enters the crankcase via the rear oil filler and travels down to the pan via the pipe mounted below that. The inlet carries an oil bath filter, just like a carb filter but smaller, in place of the civilian wire mesh filter. The air from the crankcase is then sucked up past the valley baffles into the pipe to the PCV at the front of the manifold. It is not mentioned, but presumably the civilian vent at the front of the pan area is blocked to seal the system. This is, in other words, what you would find on a typical 1962-1967 American car. I have also read that PCV systems of some sort were commonly used back into the thirties on delivery trucks and taxis and such. Now, surely some of you Canadians or Australians know of a derelict WWII Ford truck somewhere that might have the system intact??
I know this is an old thread, but I was hoping that people may answer my question. I'm new to flatheads, and I'm currently cleaning mine up and adding new heads. I was recently told about pcv valves and they sound like a good idea, so I bought a kit from ebay. I haven't got it yet, but I was wondering about getting a good vacuum source for it... I'm not running the mechanical gas pump, and I've just got it blocked atm. It I was to drill and tap the cover, would this provide a good vacuum source for the pcv valve? Also, I was hoping to get vacuum from there for my brakes, is it OK to pull vacuum and send it to the pcv and the brakes? Thanks
I now have more Canadian military parts...actual PCV was cast iron* and made so it could be taken apart and cleaned...replacing it with something modern would make sense. The Ford PCV has large passages, and is apparently throttled at the plate below carburetor...this plate is a thin casting (actually same as the ones used for Southwind heaters) with a fitting at front center connected to both bores by a thin drilling. This is clearly the restriction handled at the PCV itself on modern installations that prevents the thing from being too big a vac leak. The valve is hooked to the plate and also to the engine innards by a 1/4 steel tube, connecting to the right side of the generator hump on manifold so it pulls right over the internal vent tube at RF of manifold...the normal exit hole at bottom of the tube on the pan was simply left closed. Intake was as normal, via the oil filler cap at back of engine, but it got a fairly large oil bath air cleaner to handle the increased air flow through engine. WWII Ford and Willys jeeps used a similar, perhaps identical, fat iron PCV which is now reproduced for WWII restorers...no reason to actually use the big lump, but interesting.
The breather on the pan is an old trick. The real draw back on a street vehicle is that it does just what the name implies, breath. mounted down low it would draw in a lot of crap, but if you were to put a filter in it that would slow down the big pieces. if you were to use a PCV up top and a breather on the pan it would actually ventilate the crankcase which is the ideal situation.
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