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PCV System- What adjustments to make after fitting

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DavidThorn

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Hi All.

My car is a late BJ 8. It is running fine, drives well and returns good fuel consumption. However it would be true to say the engine is a little tired, it does not have particularly good oil pressure and clearly their is some (not excessive) blow past on the pistons which shows itself as an oily haze if the oil filler cap is removed with the engine running. Their is also some leakage from the rear crank seal which leaves drips on the ground and some times seems to get on the clutch as it can judder if the car has been standing for some weeks. A few years ago I replaced the rocker shaft so their is no excessive oil flying around the rocker box.

Also few years ago I purchased a PCV Valve mainly to try to stop the leakage from the rear crank seal. Howver on fitting the engine went from running fine to running very poorly especially on tick over. I took the Valve off it the engine once again ran fine immediatlely.

Its cold here in Southern England so I thought it may be time to have another try,and of course same result immediate poor running.

I have connected the valve via a rubber pipe and connector provided with the kit to the T piece of the rocker box and to the small drilling (normally plugged) on the manifold which I suspect may have been for a vacum gauge.

If I disconnect at the T piece and put my finger over the end of the pipe (to the PCV) the engine immediatly runns fine again ,but the suction on my finger is considerable. Is this correct or could it be that the valve is not working correctly? The car does run reasonably at some revs and under load but not at tick over. Clearly there is now far more air getting into the cyclinders than before so I richened up both carbs by one whole turn but no noticable difference -so have now returned them to normal.

I can undertand that the carbs may need considerable adjustment to cope with the weaker mixture but dont really know 1,where to start 2,if perhaps the valve is faulty and 3,if its really worth the trouble.

Suggestions please. Sorry to be so wordy but thought it would be best to put the full facts in the first place

David Thorn - Near Bath England
 
When I put a PCV valve in I adjusted the rear carb slightly richer. Car runs fine and my oil consumption went down by almost half. The kit sold in the colonies by British Car Specialists includes a rubber gasket to seal up the dipstick hole and instructions to seal the hole in the oil filler cap (I put a small sheet metal screw in the hole).

Try this: with the PCV valve installed and the engine at tickover, remove the oil filler cap and seal the hole with your palm. You should feel a fairly significant vacuum pull. If not, you're getting a lot of air drawn into the crankcase from somewhere, or your PCV valve is not functioning properly.
 
What you and many others have is not a true PCV system as the original intent was to circulate fresh air through the crankcase to reduce oil acidification among other things. Any system will seek an average over time so if acidic combustion gases dominate the atmosphere in the crankcase then the oil will eventually stabilise at the acidity of the blowby gas. Having mostly fresh air in there proportionally lowers the oils acidity and therefore extends its life and that of the mechanical parts.

The 4 cylinder Healeys had a properly functioning PCV system as did most vehicles of the era. They used the depression from the air rushing under the car at speed to draw fumes out of the "road draft" tube while pulled filtered air into the rocker cover via the air cleaner. I'm guessing DMH took exception to the horrid smell and had his engineers remove the draft tube and connect the side cover (originally the draft tube vent) to the rocker cover as a last minute fix. Anyone else think the crankcase vent arrangement on a Healey looks a bit last-minute and somewhat illogical?

There was never any OEM PCV design that pulled a high vacuum on the crankcase (at least that I am aware of). Under full power when there is no vacuum to speak of, the blowby gasses still have to exit somewhere and will pressurise the crankcase if they can't find a way out. Depending on a lot of things, the PCV valve line may not be sufficient to prevent this.

Anyway, back to your issue at hand. Does your valve rattle when shaken? It should. When installed with engine idling, does it make a clunk-hisssss sound when you release your thumb from covering its inlet? It should. If it just hisses like there is nothing going on inside it then it might be duff. There should be a spring and plunger in there that clunks shut to limit the amount of air going in there at idle and it might not be working properly. Try the same test on a modern cars PCV valve to get an idea of what I'm talking about, they are usually just pressed into a rubber grommet somewhere on the cam cover.

You'll achieve better results by creating a manifold tapping point equal distance to all cylinders so the fumes aren't concentrated into one or two cylinders. Adjusting the mixture nuts to compensate for the extra idle air/fumes increases the richness throughout the range and therefore increases your high speed fuel consumption. In a perfect world you'd use leaner needles.

Another issue is that the PCV valve will make your carbs far more sensitive to leaky throttle spindles as the air sucked in through there changes the mixture. Open the throttles about 10% and wiggle the shafts, they should not have any visible movement.


Andy.
 
I think Andy hit the nail on the head. As previously said on the Oil-Catch-Can thread, PCVs have been installed on a hope that a unit, previously specified for a reasonably similar engine, would have sufficient operating properties to fit the Healey engine. How did you choose your PCV?

You indicated your engine works properly without a PCV and, again, when the PCV is blocked (i.e. no PCV). I would suggest that vacuum is being applied to an open PCV but is not being held in the engine. This condition applies additional air into the rear combustion cycle through the intake manifold and leans your mix. This additional air can also reduce carburetor fuel draw and further diminishes your mix.

Andy had some good tests for the PCV and Bob Spidell suggested, you can test for the presence of vacuum within the engine by placing your hand over an open valve cover oil filler with the engine running at idle. Since the engine pulls high vacuum at idle, you should be able to feel it. If no vacuum is present, your engine is not sealed sufficiently for your PCV.

As Andy presented, air ventilation of the crankcase in Healey-era engines was considered a good condition and the only reason I can see to install a PCV is to reduce, or eliminate, oily floor staining….something a piece of cardboard can do nicely. Since there is no easy way to match vacuum-draw requirements to a specific PCV or a Healey’s blow-by production, I have chosen to put up with the oil drips from my car.


Good Luck,
Ray (64BJ8P1)
 
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Good info, Andy. We have a 100 and a BJ8; on the 100 it doesn't seem to me the 'road draft' tube extends low enough to get any airflow--i.e. venturi effect--vacuum. On the BJ8 there is probably some as the vent on the carburettor is open near the carb intake. Either way, on a worn engine at least, I suspect the blowby pressure mostly pushes the gasses into the carb (or to the road). Also, common wisdom--for what that's worth--is that Big Healey engine bays don't allow enough airflow, hence overheating issues, installations of bonnet louvers, side vents, etc. so I wouldn't be surprised if there isn't a slight positive pressure in the engine bay at cruise.

I put a PCV valve in when I installed aftermarket K&N air filters, and couldn't think of a decent way to route the crankcase vent. I track oil consumption fairly closely on my annual long (3-4K miles) road trip, and consumption went from a quart every 1,000-1,200 miles to over 2,000 miles per quart. I attribute this to the slight vacuum/lower pressure in the crankcase pushing less oil past my stock 'seal.' I wasn't expecting that, but I'm not complaining.

I did consider a different needle--richer, actually--for the rear carb near the 'PCV' intake. However, when checking the specs I saw that all the needles were the same diameter at the base and a couple station below (IIRC). Since I was looking for a little richer at idle--where the PCV is pulling most vacuum--I decided a different needle wouldn't help. Plus, I don't have access to a dyno to really test that modification.
 
Bob,

I also believe that blow-by pressurizes the crankcase and pushes the oily gases to the carburetor as well as past the slinger. I am, however, very surprised that your PCV installation has reduced oil consumption/loss to such an extent. I wonder if the lion’s share of oil savings is in oil previously lost past the slinger as I can’t imagine that blow-by has been reduced or a lower volume of oily gas is reaching your combustion cycle. But, then, I don’t know.

All the best,
Ray (64BJ8P1)
 
RAC68 said:
Bob,

... I wonder if the lion’s share of oil savings is in oil previously lost past the slinger as I can’t imagine that blow-by has been reduced or a lower volume of oily gas is reaching your combustion cycle. But, then, I don’t know.

All the best,
Ray (64BJ8P1)
Click to expand...

Ray,

I'm assuming the drop in oild consumption IS due to less oil making it past the slinger. I think at least as much oily blowby is probably reaching the intake manifold--I'll know when I tear down the engine in a couple years.

Bob
 
An update - sorry for the delay but there has been a lot of salt on the roads here recently. Anyway I have now completed the checks you all mentioned above. My car is running without the standard air filters but with an ITG airfilter. In relation to wear on the throttle shafts I checked mine seem to have no noticable wear,the PCV valve does rattle when shaken,when removing the pipe from the T peice on the rocker box there is a hissing sound and finally with the valve connected there is considerable suction at the rocker box filler cap when I put my hand over it. (also I read some where about sealing the dip stick hole and I have done this as well as possible with a ruber gromet on the neck of the dip stick)

So these checks seem to confi,r that the PCV vallve is working as it should. Thanks for your ideas.


With the valve fitted though the car has gone from running sweetly throught the range to being lumpy on tickover and when running under light load - it even spits back through the carb on sharp throttle opening. It does however run fine under load.


Some time ago I set up the carbs using the methods descibed in the various manuals including removing the suction chambers and leveling the jets, the setting always seemed to end up quite close to the book settings ie unscrew 2 1/4 turns etc. This is how the car is set now so I could always return to it.

My question is how do I go about adjusting the carbs (perhaps just the rear one) to compensate for the PCV valve and return to sweet running ? Before I had the standard settings to work to but what now? Is it just trial and error or is thei a logical way to work through. I did try richening the rear carb but that did not seem to make any noticable difference.
 
Something else going on here. When I installed a PCV valve just like you did there wasn't a big change in running behavior at all. I just enrichened a little (a little more for the rear carb). Sounds like you have an air/vacuum leak somewhere (tickover and light load are, of course, where you have most vacuum).

Have you driven for a while and checked the plugs?
 
Sounds like the PCV valve is too big- try one off a small 4 cylinder engine. Keep in mind though that under full power there is nowhere for the excess fumes to go and you'll pressurise the engine.
 
Hi Dave,

Again, I believe Andy is very likely correct and you may have installed a PCV that is much too big for your engine. I previously asked how you picked you PCV and received no reply. Based upon your lack of response, I concluded that you must not have thought your PCV selection was important to your problem and assumed you chose one that worked well for others. If these assumptions were not the case and, like some others, you chose something available that fit the connecting hoses, then Andy's conclusion is most likely valid.

I would also extend that your symptoms seem to indicate a very lean mixture in the rear carburetor. Although there will always be some air invading a properly sealed Healey engine, you may have a substantial amount of air being pulled in. Without maintaining a vacuum within the engine, you will be introducing additional air into your mix after carburation and providing a very lean charge to your rear cylinders.

If the hypothesis above proves valid, it would also explain why you have no problems running without your PCV. Since the engine was designed to run vent, a lack of proper sealing is unimportant to performance. Without the introduction of additional air as a result of a vacuum leak into the intake manifold, your carbureted mix is maintained and you run normally.

2 things are required for a properly operating PCV installation, 1. An appropriately sized PCV and 2. A sealed engine. Without both, you have a problem.

Good luck,
Ray (64BJ8P1)
 
Hasn't been my experience. Under full power, the throttle is wide open hence very little vacuum and the PCV valve is also wide open, allowing full porting to the intake manifold (it closes under high vacuum like at idle when a large 'air leak' would cause unstable running). I accidentally pressurized my crankcase one time by installing aftermarket air filters which had a much smaller and less effective intake for the breather tube. The pressure got so high it blew oil out from under the valve cover--I ruined the valve cover trying to stop the oil spray from the engine compartment. I've been running a PCV valve only for several tens of thousands of miles and--except for oil consumption cut by almost half--have had no other issues.
 
Bob,

As I understand it, when the car is at idle and High vacuum closes the PCV, no additional air is introduced past the carburetors and, as Dave indicated, the car runs fine. I believe Dave’s engine is not properly sealed and when under acceleration and the throttle plates and PCV are open, even though vacuum is low, it draws additional air into the manifold, after carburetion, and leans out the combustion mix. This lean mix is what, I believe, is causing Dave’s problem and could be further exacerbated by having a PCV that is too large for the engine, allow a greater amount of air into the combustion stream and cause an even greater mix differential.

I would appreciate hearing where I may be mistaken as I am always open and eager to learn.

All the best,
Ray (64BJ8P1)
 
I also have the ITG air filter on my BN4 w/ 3000 engine and HD8 carbs. I used a Fram FV183 PCV valve to route oil fumes to the inlet manifold. My experience has been similar to Bob's - it runs fine.
 
Hi Gents Thanks for the quick replies The PCV valve is from Norman Nock at British Car Specialists so I am sure its the correct one for the car.

Perhaps my car is running a little lean as is suggested but the plugs and exhaust pipes always look the correct colour.

I could try just richening it up, say perhaps a quarter of a turn at a time and try. Is that a reasonable way to go? Should I adjust the slow run air valve at the same time or is it just the mixture screw?

I am a liitle confused by the operation of the valve as you all mention previously, with it fitted at tick over their is considerable suction with my palm over the oil filler cap hole. I assume this means the engine is `sealed` reasonably. I also undertand that the suction is greatest at tick over or at least not under load with big throttle openeings,but isnt that what a correct working PCV should stop - High suction at low throttle openings. If it isnt stopping that what is it doing?
 
Hi Dave,

Your assumption is correct and the valve should be closed when at idle (or tick over). Based upon your comments, it seems that you are using a PCV that others are using successfully and your test for a reasonably sealed engine eliminates that as an issue also. However, based upon your initial result in blocking the T side of the valve with your finger and having felt high vacuum at idle, I must ask (with no negative personal implication);

Are you sure the PCV is installed correctly and not backward?

If installed backward, the valve would stay open through all speeds and create a lean mix by injecting additional air after carburetion.

Good luck,
Ray (64BJ8P1)
 
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There's things I've never understood about this mod, although I've read everything I could find on PCV systems. First, the Nock--or similar--mod isn't a true PCV 'system.' On cars fitted from the factory with PCV there is usually a source for fresh air to be drawn into the block (hence the 'V' for ventilation in PCV). On some V8s, for instance, there is a small air filter, usually on one of the valve covers. Others vent filtered air from inside the air cleaner. Filtered air is pulled into a head and through the block by manifold vacuum--'negative crankcase ventilation' might be a more correct term--from the PCV valve, and burned with crankcase gasses to reduce emissions. Presumably, mixture is adjusted to compensate for the unmixed fresh air. With the Nock setup, there is no source for fresh filtered air. I believe the idea is that there's usually enough blowby and leakage from the rear seal, etc. to provide an air flow (I think this is why my oil consumption went down after installing the kit). I installed the entire kit, which included a gasket for the dipstick tube and instructions to seal the hole in the oil filler cap (IIRC they suggested soldering it shut; I put a small sheetmetal screw in the hole). It has never seemed to me that sealing up these very small potential leaks would make much difference, but I did it.

Also, I've checked a few and no PCV valve seems to seal completely when closed--there's just a small metal (or possibly plastic) piston inside the valve, with nothing to prevent quite a bit of leakage even when closed. At WOT, with maybe only an inch or so of vacuum--all induction systems have some pressure drop even at WOT--the PCV valve is held open by a weak spring and for all intents and purposes it's a sizable air leak; however, the volume of air is inconsequential compared to the large amount coming in through 'legitimate' sources (the carbs). It's actually a fairly clever device, and works well enough that even modern engines with considerable other emission controls devices still have them. However, there is at least one pretty well-known problem with them: since you're venting oily crankcase gasses into the intake manifold the inside of the manifold can get gunked-up. My Ford Ranger used to get a sticky accelerator pedal due to residue around the throttle body due to the PCV venting. Every 20K miles or so I had to take the air inlet system off and clean around the throttle with carb cleaner to get rid of the sticky pedal. Hasn't been an issue on my BJ8 so far.

Since a couple of us have installed the Nock kit with no significant issues I have to say I'm stumped by David's(?) problem. It certainly sounds like a sizable air leak at idle. However, with a huge air leak there should be little or no vacuum at the oil filler hole at idle since, well, the leak would prevent that.
 
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I bought my PCV by appearance - it's small and metal and looks more appropriate than a plastic one. The spring is weak enough to allow me to blow through it by mouth and for the valve to rattle when I shake it back and forth. The other direction it seals all except a minute amount of air.

I didn't install the Nock kit, but guess my dipstick seals OK because I can feel a vacuum at the filler opening per Bob Spidell's suggestion.

Am running a K&N Air-fuel meter attached to an O2 sensor on each exhaust downpipe. This shows the rear carb to be slightly leaner. The difference in richness with the PCV seems to have manifested itself by the front carb running rich with black near-fouled plugs. Adjusted the front jet up .005" and that took care of the difference.
 
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