Oil Filler Cap Question

[rpowers]

What is the purpose of the ventilation holes in the oil filler cap?

What would happen if the cap were completely sealed?

The reason I ask is that I notice most of my excess engine smoke seems to come out of the filler cap gap and holes, and not much is going out the PCV tube.

Any thoughts?

-Rick

[Al Schober]

Rick,
Best you'll do is to force the smoke to exit around the flywheel end of the crankshaft, which has no seal.
Short of a ring job, give the Indigo PCV kit a try. If your smoke isn't too bad, the PCV kit will give you some more time until you need rings.

[hanleyclifford]

I have the Indigo pcv kit and it works perfectly. I plugged up the oil filler tube by threading it for npt and then using an npt plug.

[rpowers]

Pcv

Thanks Hanley,

It would seem that a new PCV set-up is in my future...I like the plug idea, too. What size tap was that?

No blow-by smoke would be a real treat!

-Rick

[thatch]

Rick,
Before switching to a PVC system, you might try "tuning up" your existing setup. Since the filler cap and the flame arrestor are subjected to oily blowby, they tend to become plugged, over time, and loose their airflow efficiency. Using spray carb cleaner or soaking in carb cleaner, is probably the easiest way to clean them. Finally, and this is the most important thing, make sure that the curved rubber hose is cut at the correct angle and is actually touching the flame arrestor element (see the Moyer photo). My "high mileage" A4 displays almost no blowby after performing this "tuneup"
Tom

[Dave Neptune]

Cap

Rick the vents are so the engine can breath on the inside. Actuall it is mostly to expell the nasty gasses that get by the rings. My A-4 is going on it's 41st year and is a bit tired to say the least. I replaced my cap with an automotive type when I bought the boat. The type I bought has a hose bib connection instead of the vents underneath. I attached a long hose and ran it up through my exhaust fan pick up hose. That vents most of the gasses out of the cabin and out of the cowl on the transom, I use my exhaust fan WHENEVER THE ENGINE IS RUNNING. Since then I have installed the PCV kit as soon as I saw one available and it made a huge differance in the amount of blowby venting out the fill tube. I did leave my hose and automotive cap in place and I have no fumes or smell in the cabin. Note~ my engine is in the middle of the boat on top of the keel.
Everyone should have a PCV setup as they keep the inside of the engine much cleaner!

Dave Neptune

[thatch]

Dave,
You forgot to add, be prepared to do a carb adjustment because of lost manifold vaccum, after the addition of the PVC kit.
Tom

[hanleyclifford]

One of the reasons why I blocked off the breather was for exactly the reason of preserving vacuum. The pcv system when allowed to pull freely thru a breather cap does two things. It robs the manifold of vacuum by drawing air in from the outside. The breather cap also reduces the effectiveness of the pcv by reducing th amount of crankcase air being drawn. I believe there are sufficient air leaks in the engine to preclude a dangerous pressure environment.

[thatch]

Hanley,
I certainly agree that if adding a PVC kit, plugging the breather cap hole or using a "non breather" type of cap will add to the effectiveness of the system. The amount of air drawn through the PVC system should be governed by the PVC valve and hopefully will flow all of the blowby gasses. As a side note, it is not uncommon in race engines to use vaccum pumps to pull as much air out of the crankcase as possible which has proven to add measurable horsepower.
Tom

[rpowers]

Pcv

I found this nice cap (see photo) at the hardware store. When tightened the rubber gasket (I trimmed it) expands out and seals.

I tried it out today, and it seemed to work great, with just a bit of blow-by from the black tube missing the flame arrestor (has been cleaned).

I'm still going to install a PCV kit to capture all gases. What carb adjustment is necessary?

-Rick

[Dave Neptune]

Adjustments

Rick the carb adjustment directions come with the kit. What it amounts to is because of the additional air through the PCV valve need a bit more fuel~~about a 1/4~1/2 turn in on the adjustment.

Dave Neptune

[Dave Neptune]

Breathing

I think that with the pcv kit you need the breathers to work. They are calculated for the engine with the breather. Without it gasses will still collect in the crankcase because there is no incoming air to displace the gasses other than what blows by the rings. You need the flow of clean air through the breather for the pcv to function as designed.

Dave Neptune

[rpowers]

Breather

Dave,

Ah, yes, good thought. I can try it both ways. Hanley has a persuasive argument and so do you.

Thanks for the carb adjust tip. I'm presuming that is with the idle mixture screw on the back side of the carb facing up.

I'll report back on Wednesday after I get it installed.

-Rick

[Dave Neptune]

Adjustment

Rick, yes it is just a bit of a tweak on the idle mixture screw.
Dave

[thatch]

"Automotive style"

Although I don't seem to need a PCV system yet, I have been following those threads closely. Input from Hanley and Dave sparked an idea that might just be the ideal PCV system, so here goes. If the original rubber hose system was left in place and the pcv valve was plumbed from the intake manifold or a carburator adaptor plate, to a non vented filler cap with a hose bib, this would very closely "mimic" most automotive systems. In essence, any excess fumes that were not removed by the pcv valve would be pulled into the carb air stream.
Tom