Breathing

[miked]

Can anyone advise me on the following. I have run 3 twin cams all with the breather to atmosphere. I suffer the drips and odd smell when stationary. Also the oiling of under the car in the area of the breather down pipe.

On my S4 (stomberg) which i spent a lot of time getting right i am annoyed by the mess. Is the breathing to atmosphere a vaild thing to do?

When I stripped this engine (bought as restortation, not run since 1989, standard breathing into air box) I was appalled by the carbon deposits in the area of the inlet valves. The cross section was reduced by about 35%. There was a broken top ring on one of the cylinders so it was breathing heavily. Because of this I vented to atmosphere on the rebuilt engine. The engine runs very well and is up to 2600miles.

Shall I put my pipe back to the air box?.
Will the pull fron the induction assist in taking away the positive crankcase pressure and tend to help with leaks.
Or as I have been told, the blow by gases upset the carbuartion.

I await some advice!

Thks Mike

[elancoupe]

I had similar concerns. I didn't like the coating of oil from the downtube under the car, and I didn't like the adding more oil to the intake mixture (aren't the valve guides adding enough? ).

I did two things. I added a valve cover breather to reduce internal pressure, and I added a catch bottle, to which I routed tubing from both the cam cover breather and the existing breather. With some careful use of routing, and nice looking tubing, this setup looks reasonably good. And it works! Less pressure, fewer leaks and no oil coated chassis.

I am sure that such a thing horrifies the purists, but function was and is my concern, and it looks decent, too.

[rgh0]

I also run a breather off the front of the cam cover as do most people racing twin cams. This location breathes much better than the standard point of the head and the blowby has less oil carryover. I run a hose to a catch tank in front of the radiator. With the better breathing and thus lower crankcase pressure you get less oil leaks out the front seal at race speeds which is the one location I have never managed to get to seal completely like a modern engine.

However for a road car the standard breather should be fine if the engine is in Ok condition. Modern synthetic oils dont burn as easily and burn more cleanly when they do and thus dont coke up the ports. I see in my race engines a clean path from the exhaust valve guide down the exhaust header where the oil washes away the carbon deposits. My road plus 2 inlet ports stay clean despite using the normal breather arrangment to the air box after 70,000 miles since the last engine rebuild.

Rohan

[richboyd]

Rohan,
Mike,

I would like some more details about catch bottles (from each of you, please). Are these "dead -end" bottles, or do they feed oil back into the sump? What capacity are they? How do catch bottles and oil separators relate to each other? What brand and model catch bottle are you using? Where did you mount it?

Thanks for the information,
Rich Boyd

[elancoupe]

While my TC is not a racing version, I found that when I upgraded it to a 1700cc modified version, the stock breather was simply overwhelmed. Especially when cold, way to much oil for my liking was pumped out.

As far as the catch bottle goes, I have a plastic, one quart size, similar to a small windshield washer tank. I have my two breather hoses joined by a "tee" just above the bottle lid, so that only one tube passes into it. The tube itself is extended inside the bottle, to about an inch from the bottom. The opening in the lid is slightly larger than the tubing, thus allowing pressure/vapor to escape, yet any liquid remains in the bottle. I have found that with this setup, I get just a very small amount of liquid in the bottle, not even enough to be concerned with.

I have a digicam, and could take a few pics if anyone needed them.

[patrics]

Mike,
Tony Thompson does a shaped catch tank which fits in triangle bit in front of the passenger foot well. It looks very neat - but more expensive than an old washer bottle.

Steve

[elancoupe]

Thanks Steve, good info. I would assume that would be for a RHD car?

[rgh0]

Mike

I have posted some photos of my installation in a photo album in the Yahoo LotusElan group photos sections under "twincam breather". I cant figure out how to attached photos to LotusElan.net

The conection to the cam cover uses standard oil hose fittings and the catch tan I made up myself out of heavy duty galvanised sheetmetal. The blow by gases and condensed water are corrossive so you need to make sure the catch tank does not rust.

The tank I made is about 3 litres but about 1 litre would do. The local race regulations set the minimum size I could use.

Rohan

[patrics]

Mike,
The one I looked at was right hand drive but I think Tony has them for both. I have a picture some where and could mail it to you if want.
Steve

[miked]

Thanks for the replies about this subject.

Mike