Fingers Crossed

[Bryan Boyle]

Well…had a chance to take 3291R out for an extended ride today.  This after tearing the oil pan off, replacing gaskets and seals at front and rear, new header and exhaust…and filled with 4.5 US Quarts of VR-1 20/50. 

Had taken it out a couple weeks ago, and there was still oil coming from somewhere on the left side (the right side drain tube needs to be replaced…it’s still leaking, so I know about that, and a small weep at the back of the head/block joint). Harkening back to my experience with 693R (even though that's a Renault mill), I was thinking that there is some being blown up the dipstick tube..so, just to prove out the assumption, I shrank a piece of adhesive-lined shrink tubing up by the bulge on the dipstick handle (covering about 2” from before the bulge down the stick), and inserted back in the dipstick tube.  It all fit nicely..pulled out and checked oil level: right on Full.

Backed out of the garage and headed off...20 miles later with mixed limited access and stop and go city driving, with some trepidation, pulled back into garage over my cardboard mats on the floor, and popped the boot.

Nothing on the shift tubes that wasn't there before, on the battery heat shield, or dripping down from that side…or showing up as fresh spots on the cardboard (discounting the other side, ok?  I know about that…one thing at a time).

Thinking that adding a second breather fitting to the front of the cam cover, plumbing that together with the one on the carb side of the head and feeding, through an air-oil separator, to the carb air box may lessen the pressure in the crankcase even more by using whatever minor vacuum exists in the airbox to pull the vapors out rather than pumping them up and down by the motions of the rotating mass and pistons and lessen the oil mist escaping to rustproof the chassis even more.


Incremental improvements are a good thing, right?

[BDA]

I’m amazed that your motor requires that much ventilation! If seen lots of pictures of racing twin cams with fairly sizable vent coming out of the front of the cam cover (the usually seem to be -8 or nominally 1/2”) and I believe the vent at the carb side of the head is usually plugged up. Being race motors, they are vented into a catch can of some description.

On my motor is really the same as yours but with a different head. I have one vent probably almost 1/2” ID   - similar to -8. I vent that to a catch can. I’m not aware of any racing BDAs that use more ventilation than that I have. Since I don’t have a dipstick, your symptoms wouldn’t happen to me.

So my questions are: Does your motor require more ventilation than “normal”? Why? If my motor requires more ventilation, how would I know? What symptoms should I look for?

[Bryan Boyle]

I’m amazed that your motor requires that much ventilation! If seen lots of pictures of racing twin cams with fairly sizable vent coming out of the front of the cam cover (the usually seem to be -8 or nominally 1/2”) and I believe the vent at the carb side of the head is usually plugged up. Being race motors, they are vented into a catch can of some description.

On my motor is really the same as yours but with a different head. I have one vent probably almost 1/2” ID   - similar to -8. I vent that to a catch can. I’m not aware of any racing BDAs that use more ventilation than that I have. Since I don’t have a dipstick, your symptoms wouldn’t happen to me.

So my questions are: Does your motor require more ventilation than “normal”? Why? If my motor requires more ventilation, how would I know? What symptoms should I look for?

Not that it needs, necessarily, that much ventilation...but it does seem like it's pressurizing the crankcase a bit, since there is no active scavenging of the air much like what a PCV valve connected to the intake on more common engines does.  My compressions are ok, so, just thinking of two ways forward: as I describe above or just reconnect the missing head-to-stromberg airbox pipe and see from there if I need additional scavenging of the crankcase.  Right now, I've just plumbed it into a catch bottle in the right rear with a filter stuck on the cap...

FWIW, when I started down the path of getting my previous Europa on the road in 07, it wasn't until I got the original Renault PCV/vapor recovery system plumbed in that I was able to control the blow-out through the dipstick by actively extracting into the proper fitting on the carburetor. 

[jbcollier]

Engine ventilation varies depending on the design of the engine and condition.  Some engines have more blow-by than others, blow-by increases as the engine wears, and increases with higher revs.  Early engine ventilation was pretty primitive.  They had some labyrinth or mesh to control oil droplets and exited out of the block and onto the road.  This created enormous amounts of pollution and real mess under cars.  Regs were passed where engines had to consume their own fumes.  Various systems were designed.  Some passive with gases flowing out of the engine as pressure develops, and, some positive with manifold vacuum assisting in engine venting.

The TC engine's crankcase ventilation system is fairly crude with only minimal provision for separating oil droplets and some crankcase pressure allowed to develop.  It works best with the stock air box (and performs better that way as well).  TC engines are short stroke and like to rev.  Drivers also like to rev them so they tend to wear more rapidly than other engines.

I'm not familiar with the BDA's venting system but it would not surprise me greatly to find it was better than a stock TC's.

[BDA]

Thanks for the explanation, JB.

On my engine, the cam cover has a tube built into it to vent the engine. I’ve attached a vinyl tube to it and ran it a fitting on the top of my oil tank. From another fitting on the top of my oil tank, I ran another vinyl tube to a plastic catch can vented to the atmosphere.

[Richard48Y]

Maybe take a look at the Alfa Romeo Spider late 70's system?
Similar DOHC engine.
They vent to a separation canister which returns accumulated oil to the sump.

[Bryan Boyle]

Maybe take a look at the Alfa Romeo Spider late 70's system?
Similar DOHC engine.
They vent to a separation canister which returns accumulated oil to the sump.

Sounds like the system I have on my Cessna; admittedly a different type of engine (air-cooled horizontally opposed versus in-line water cooled), but the same idea: I have the crankcase vent going to an air/oil separator; the 'cleaned' air gets vented to the slipstream, and the recovered oil is returned via a cylinder head oil return fitting.  Works well...and the belly of the aircraft is less full of spooge that before.  But, the clearances and fit of an aircraft engine would horrify an auto engine guru (we seal the cases with form-a-gasket into which a silk thread has been laid)...which means that we expect to consume oil (average 4-8 hrs per quart) where on road engines...we start tracking down leaks when we see a spot on the floor.

I think I'm closing in on the whack-a-mole process of tracking down the weeps.  All a part of 'catching up' on what (D)POs failed to address, either through neglect or apathy.