Rocker Cover Air Filter?

ThoR_ · 25-02-2007, 05:07 PM

Hey guys.

Some things i dont know about cars and this is one of them. I know you can get small air filters for your rocker covers. What exactly do these things do. Improve performance im guessing. Do they do much?

Thanks

Rollin · 25-02-2007, 05:17 PM

They are to vent crank case vapours, and are illegal on anything post 1976 I believe, but it could be even further back than that.

Since 1976 all crank case vapours have had to be routed back into the motor and be burned.

The 'air filter' on the rocker cover does not increase performance...

ThoR_ · 25-02-2007, 05:18 PM

so why do people put them on then?

**GasoLane** · 25-02-2007, 05:31 PM

Quote:

Originally Posted by ThoR_

Hey guys.

Some things i dont know about cars and this is one of them. I know you can get small air filters for your rocker covers. What exactly do these things do. Improve performance im guessing. Do they do much?

Thanks

Now I'm curious. Got any pics?

Wally · 25-02-2007, 06:22 PM

Quote:

Originally Posted by ThoR_

so why do people put them on then?

1. Because they can look cool
2. Because others do it and get 50% increase in power
3. Because engines with excess blowby will make smoke and foul the carby/throttle and combustion chambers
4. Because excess oil vapour will affect the oxidisation rate of the fuel

GXL078 · 25-02-2007, 07:03 PM

What is the difference between drawing filtered air from inside the air cleaner and drawing it through the little fliter in the oil cap? WHY are they illegal they only filter the air going in. nothing is let out, it is still a closed system assuming you have a PCV valve in the other rocker cover thats connected with a hose to the base of the carb? Am I missing something? The hose that connects form the oil cap to the air fitler just supplies clean air to the Crank case, right?

**GasoLane** · 25-02-2007, 07:30 PM

Quote:

Originally Posted by xcgxl

What is the difference between drawing filtered air from inside the air cleaner and drawing it through the little fliter in the oil cap? WHY are they illegal they only filter the air going in. nothing is let out, it is still a closed system assuming you have a PCV valve in the other rocker cover thats connected with a hose to the base of the carb? Am I missing something? The hose that connects form the oil cap to the air fitler just supplies clean air to the Crank case, right?

Um, I think thats back to front. The hose that connects to the oil filter from the engine is to direct the fumes/smoke/pure oil (depending on the state of the engine) back into the engine and not let it vent into the atmosphere.

Engine blocks dont, as far as I know, suck air. They tend to build up pressure not create a vacuum.

nugget378 · 25-02-2007, 08:11 PM

Quote:

Originally Posted by Wally

1. Because they can look cool
2. Because others do it and get -50% increase in power
3. Because engines with excess blowby will make smoke and foul the carby/throttle and combustion chambers
4. Because excess oil vapour will affect the oxidisation rate of the fuel
5.It looks good when they fill up with oil and leak it over the engine bay

Added one to your list,and modified another..

GXL078 · 25-02-2007, 08:22 PM

Quote:

Originally Posted by GasOLane

Um, I think thats back to front. The hose that connects to the oil filter from the engine is to direct the fumes/smoke/pure oil (depending on the state of the engine) back into the engine and not let it vent into the atmosphere.

Engine blocks dont, as far as I know, suck air. They tend to build up pressure not create a vacuum.

Oh, OK. Maybe I should put one on then seeing as my air cleaner has provision for it. I would need to change my cap though.

Wally · 25-02-2007, 09:05 PM

Quote:

Originally Posted by nugget378

Added one to your list,and modified another..

Well done

Wally · 25-02-2007, 09:27 PM

Quote:

Originally Posted by xcgxl

What is the difference between drawing filtered air from inside the air cleaner and drawing it through the little fliter in the oil cap? WHY are they illegal they only filter the air going in. nothing is let out, it is still a closed system assuming you have a PCV valve in the other rocker cover thats connected with a hose to the base of the carb? Am I missing something? The hose that connects form the oil cap to the air fitler just supplies clean air to the Crank case, right?

You need to understand that the PCV valve is closed when the manifold is under reasonable vacuum. It only opens when there is a slight vacuum approaching atmospheric pressure. Under heavy load the breather hose will flow oil vapour to the carby/throttle body. If you replace the hose with a filter, the heavy droplets may gravity feed back into the rocker cover, but you will end up with a nice dirty patch on the covers and probably on the underside of the bonnet.

GXL078 · 08-03-2007, 01:49 PM

Quote:

Originally Posted by GasOLane

Um, I think thats back to front. The hose that connects to the oil filter from the engine is to direct the fumes/smoke/pure oil (depending on the state of the engine) back into the engine and not let it vent into the atmosphere.

Engine blocks dont, as far as I know, suck air. They tend to build up pressure not create a vacuum.

I checked in the XC factory workshop manual and the PCV system works like I thought it did. The hose going to the air filter housing supplies FRESH air to the system and the vapours get drawn into the motor through the carb base plate via the PCV valve on the RH rocker cover.

nos_james · 08-03-2007, 08:04 PM

that seams to be how the clevo in the xd works

jaydee · 08-03-2007, 10:21 PM

Ok, now I'm thoroughly confused and just to add to it. I have a Clevo with crinkle finish rocker covers with a flot top with a chrome flat oil filler cap that doesn't breath.
So am I screwing up my engine, are there bad vapours not escaping that should be or what?
My air cleaner is an open type sports so i cant connect a hose,and my engine runs on dual fuel.
Any advice?? Should I have a breathable filter type oil filler cap.?

GXL078 · 09-03-2007, 08:57 AM

Quote:

Originally Posted by jaydee

Ok, now I'm thoroughly confused and just to add to it. I have a Clevo with crinkle finish rocker covers with a flot top with a chrome flat oil filler cap that doesn't breath.
So am I screwing up my engine, are there bad vapours not escaping that should be or what?
My air cleaner is an open type sports so i cant connect a hose,and my engine runs on dual fuel.
Any advice?? Should I have a breathable filter type oil filler cap.?

yes!! But are you sure your cap doesn't breathe? The normal, chrome push in ones all do. Suck it and see, lol.

jaydee · 09-03-2007, 07:42 PM

No, the cap is like a radiator cap with a rubber O ring and closes off completely with no way to breath.
I tried your idea too but the taste of oil was real bad.

jaydee · 10-03-2007, 12:45 PM

OK, I've dug out my own workshop manual to get the low down for myself.
It has a picture of the engine titled "Positive Crankcase vent System" showing the oil filler cap with the hose going to the air cleaner and a note saying "Hose from valve rocker cover to air cleaner for fresh air to crankcase".
Air goes both ways through this pipe to get fresh air to the crankcase and when theres a build up of contaminated fumes that can't get through the PCV valve (located between the valve rocker cover and carb spacer) in the crankcase it is redirected intothe carby back into the combustion chamber for burning.
Clear as mud???

Ghiadude · 10-03-2007, 07:48 PM

on decelleration its sucking air into the crank case - under power the crank case is being pressurised by blow by from the cylinders. in positive pressure situations it can creat real issues if not vented correctly especially if rings are worn or if tollerences arent fine enough