Crankcase Venting

[type26owner]

Now dealing with a myriad of oil leaks from under the heads all sorts of 1/4" bolts on the front of the engine along with trying to seal up the dipstick. Last one found was the pan bolt just above the oil filter, the one which gets threaded into the timing chain cover. Hey, it's tapdrill hole goes all the way through the cover into the oily region and oil comes streaming out of that one right through the split lockwasher. Also had to seal up the outside penetration through the timing chain cover of the flathead screws which fasten on the rubber rubbing strip for the timing chain witt a glob of RTV too. Finding it leaks from everywhere now that the pulley seal is leak-free I can find all the other leaks and so far I've been very busy. Guessing I've had to fix at least a dozen different places that leaked. Mostly by making up a custom steel washer fitted with an o-ring which seals to the bolt's smooth shank just under the head and face seals to the cover. They must have started leaking when the engine first fired up and never stopped. Well mine is going to stop doing it over my dead body!

This would be easier if there were a better crankcase pressure management system installed. A pollution control valve (PCV) immediately comes to mind. Has anyone gone for it and retrofitted one onto the twincam. What pitfalls are there to avoid? How did you exhaust the pcv valve into the induction system? Behind the Weber butterflys?

Besides if I heat up the oil with an intercooler to revaporize any volatile stuff in the crankcase then having a way to efficiently remove it would be prudent too.

[type26owner]

My son points out there is potentially a challenge to overcome which is the pulsating pressure behavior of the induction system if it's tapped into a single throat will cause the pcv valve spring to try and open and close with each pulse. Not a problem for a common plenum induction system but on the DCOE it would likely wearout the valve quickly. It was simple until now, thanks son. <_< Can get around this by incorporating a bypass manifold and aperturing down the passages I suspect. Noticed someone was selling the o-ring compliant soft mounts for the DCOEs which were slightly thicker and had the threaded hole needed for nitrous nozzles on E-bay. Those would do nicely to port the bypass manifold into possibly. Hey, it's a good thing I fixed the airleaks around idle mixture screws because I'm about to purposely introduce some new good ones to replace the old bad ones. :huh:

[type26owner]

Okay, upon further pondering it's apparent incorporating a PCV valve that relies on a steady vacuum signal onto the pulsating induction system of the DCOE is silly. Got it figured out though. What's needed is a simple mechanical valve based on the way a peristaltic pump works. It''ll close off the flow completely at idle so there is not any extra vacuum leak degrading the idle system mixture. What little blowby there is I'll allow to backflow through the filtered air supply hose which gets it air from upstream of the butterflys. Both hoses will have flame extinguishers of course. Only question is where to feed in the fresh air into the engine so the crankcase fumes are swept up clean when the system scavenges when off idle.

Finally occured to me to pull the oil breather tube out of the head's breatherbox and look for white emulsion goo. There's none. The end which sticks into the catch bottle is full of it. Suspect the reason I've had the Webers acting up the and the engine running poorly recently is I've been buying premium grade fuel loaded with water. Who do you report these a**holes too in the Wonderland of Arnold?

[GrUmPyBoDgEr]

My understanding of the abbreviation PCV is Positive Crankcase Ventilation.
Apart from preventing combustion gases escaping to the atmosphere these systems produce to a greater or lesser extent a vacuum in the crankcase and adjoining areas in the cylinder head. A simple & commonly used method is to run a pipe from the cam cover into the cold air collector box which is fitted to the carbs. There is a small amount of vacuum here under certain driving conditions due to the resitance in the air stream caused by the air filter.
Tapping into the area between the carbs and the cylinder head opens up a whole bag of worms, it will provide a much higher degree of vacuum which needs to be carefully controlled and that can be very complicated. Failure to control this vacuum can result in the the engine swallowing up a large quantity of the engine oil via the combustion process.
In any case I don't think that a vacuum in the engine wil help much with oil leaks. If there's a way out hot oil will find it.
I have seen quite a few racing twin cam engines with quite heavy oil leaks and those engines had dry sump lubrication systems. Dry sump pumps nearly always provide a degree of vacuum in the crankcase.
Regards
John

[type26owner]

Ah but if you can arrange the vapors to be sucked into the induction system behind the butterflys then the problem of the crud condensing out around the progressive holes goes away and that would be very beneficial. The flow rate required is typically like 6 cubic feet per minute and it's done with an orifice. What's so hard about that? Some scavanging system must exist for the DCOE. I'm going to call Mike at Pierce Manifolds and get some advice. The only real impact I anticipate is this will SLIGHTLY reduce the vacuum signal on #1 which supplys the headlights.

BTW, I have a dry sump BRM race engine. I've never placed a vacuum gauge on the crankcase and tried blocking off the breather tube to the catch bottle but I'm willing to bet you that story is a wise tale and not true. The vent line from the oil resevoir is so small in diameter and snakes it's way through the entire length of the chassis that there is no way that much airlfow can be going through it to evacuate anything. Plausible theory but just not true I'd guess.

Got a soft spot in the brain for getting the meaning of PCV wrong . My son has corrected me on numerous occasions too now that I think about it. After a short period I'll be back to having it wrong again. I'm doomed.

[GrUmPyBoDgEr]

The dry sump theory is based on the fact that the scavenge pump is always larger than the pressure pump (usually approx. 33%) because this pump returns a larger volume of aerated oil to the tank. If this were not the case then the engine would flood with oil. The aeration is a product of the blow-by gases in the crankcase mixing with the oil. So to a certain extent the possibility of excess pressure building up in the crankcase is greatly reduced.
Tapping into the manifold after the carbs will also have an effect on the mixture.
Most modern engine makers do use the higher vacuum source that you are proposing, most incorporate a valve that has one side open to atmosphere in order to regulate the crankcase depression & in order to remove the fluids being carried by the blow-by a cyclone separator is also part of this system.
John.

[type26owner]

Hi John,
IIRC, the gears on the dry-sump pump we have are the same size. The flowrate of oil that cycles through the engine is not all that much. It's not going to carry off that much air as a result. The primary purpose of the oil reservior rather than providing the engine with de-aerated oil is to lessen the chance of cavitation happening between the reservoir and the supply-side pump. Cavitation is a common killer of engines. Just another one those instances where having too high a viscosity oil can hurt.

I've dealt with many PCV systems and have not been overwhelmed with their complexity yet. Not understanding how they work can definitely screw you though.

BTW, dry-sump oil systems are a real pain in the rearend. They only did it on the formula and sport racer cars to get the engine/gearbox lower by an inch or two. IMHO, it's rather silly to put one on an Elan.

[type26owner]

My son tells me there are kits to retrofit a crankcase evacuation system right into the exhaust system instead. Moroso and Mr.Gasket sell them. Interesting. Wonder how big a plume of smoke it would produce?

[elj221c]

Thought dry sumping was primarily to eliminate surge. Lower engines were not so much an issue in tall tyre days.
Roy
'65S2

[type26owner]

Hi Roy,
Mr.Chapman designed his racecars to take advantage of the fact lowering the center of gravity was the faster way. We used to have a 1960 Lotus18 and it had a gated oilpan If I remember correctly. Don't remember which car he actually applied the dry-sump system to first. The technology of the tyres and car design were rapidly changing in the sixties and it was lots of fun to have been there at the racetrack and see it happen first-hand. What put us off to the whole scene was by the early seventies the gentlemen driver phase was ending and the rough driving started. It was dangerous enough but that stuff pushed it over the edge.

[twincamman]

good point about rough driving--- I watched it develop from the 50s and 60s sportsmanship and respect for competitors to the gang fight mentality of today ---everone is going to f 1 --here at least-- it has become prevalent as witnessed by the fatality of one competitor and the end of my racing through injuries in a needless accident for a corner at practice -after ever session the track looks like a yard sale with cars at every other corner and after the race its worse we started 19 cars and finish with 10 or 11 regularly --I think that the ME ME ME generation is very active now in the amateur area of the sport----coming from carting they don't realize what happens when things go wrong in a 1000 pound car as opposed to a 100 pound cart --or starting from novice dont care --and worse the officials dont see it -- ed

[Hamish Coutts]

Twincamman,
You have touched on a subject the would run to many pages of posts. I cannot agree more with your comments and am completely fed up with the attitude of today's drivers and teams. Unfortunately the Me Me bit is now endemic in out culture (I see it more & more at work - thank god I retire in 4 years.) so I can only see drivers' bully boy tactics getting worse.
I too fondly remember racing from the 60s - the cars, competitive but fair driving and the power slides and 4 wheel drifts.

Hamish.

[GrUmPyBoDgEr]

There's still good competetive historic motor racing to be seen most Summer weekends in the UK. A whole days racing for the princly sum of 10 pounds. Superb cars & good drivers who drive to the limit.
Great for all those enthusiasts that live there.
Homesick!!

[elj221c]

DJ,

I think you may have started a new line/thread type thing there!

Did a lot of UK HSCC stuff. [ low mechanic level ]

Not sure even that still has the same feel.

Need to embrace change.

Been trying since I was born!

Roy
'65S2

[type26owner]

The bung for those crankcase evacuation exhaust check valves are huge judging by it requires a 7/8" diameter hole to accept it. These things on a large V8 evacuate the crankcase down 3" to 6" of mercury. Anyone pull that kinda vacuum on the twincam before? Hate to distort the block or collapse the oilpan and 'blowed' it up as a result. I need a smaller displacement unit which only pulls about 1/2" I'm thinking.