Breather hose functionality
 

I’m (hopefully) finishing up a battle with the triangle of death on my recently rebuilt motor, and I installed a piece of generic rubber hose to replace the old, hard cloth covered crankcase breather hose. At the 90deg bend to meet the filler neck, the new hose closes up. I tried installing another hose clamp over the corner to keep it circular, but that just seems to move the restricted area. How can I get the hose to hold its shape?
Also, I’m hoping somebody can explain exactly what the functionality of the breather hose is to me. Will it be a problem if I start the engine and air may not be able to pass easily through the hose? Thanks.

What year? Breather hose keeps vaporized oil and gasses contained In the oil tank and engine. Not sure what a blocked breather would cause, perhaps a leak from a weak valve cover gasket or somewhere else? There are pressure pulses when the pistons move in the cylinders.

It’s a 1980 911sc

Preformed or generic hose?

longer hose - more gentle bend. no?

911pcars, as I said in the original post, it is generic rubber hose.

creaturecat, maybe that would help, but it already seems a little long, and no matter how much I tried to coax it into a gentle bend, it would just fold over sharply somewhere.

I ended up putting three more hose clamps spaced half an inch or so apart around the bend to force it to be more gradual and to try to hold the circular shape. It seems to have worked! The hose is no longer completely closed at the bend.

Gently use a heatgun to help the hose take shape. Rob

Sorry. Overlooked your generic hose description. Your hose clamp fix does offset the tendency for the hose to collapse due to the bend. Other than sourcing the correct factory hose, here are some solutions that may work in various situations.

Splice in a pre-formed angled/curved transition tube that fits the ID of the hose, then secure with clamps. However, not easy to source off-the-shelf shaped tubes. Another idea is to source an off-the-shelf hose containing the desired formed bend to match your requirements. Cut out the needed section and splice with transition tubes on each end. Again, other than coolant hoses, lube-rated large diameter hose (coolant hose not readily available in the automotive world. Coolant hose will also deteriorate in contact with lube oil.

A third option is to source a preformed silicone hose adapter (pics below). These can be had in many shapes (straight, angled, U-bend, etc.) and diameters, with a different ID on each end if needed. Here, to connect the air duct from the engine surround tin to 993 heat exchanger air inlets. I scoured eBay and came up with the following:

45º silicone hose adapter: 2.5>3":
http://forums.pelicanparts.com/uploa...1589357019.png

Target: 3" OD heat exchanger inlet (modified to allow valve cover R&R):
http://forums.pelicanparts.com/uploa...1589357019.jpg

Completed: 2.5" SCAT/SKEET hose ducting > 2.5" Al connector tube > silicone hose adapter and hose clamps:
http://forums.pelicanparts.com/uploa...1589357019.jpg

All connections relaxed, no tension.

Another area needing an angle change:
http://forums.pelicanparts.com/uploa...1589359873.jpg

Sherwood

The factory hose is just a straight hose. Not sure how you can kink this hose, its pretty much a straight shot from the breather to the tank. How have you routed it?

Agree with Magnus. The problem with the Porsche hose is that eventually it leaks, not that it needs some specific shape.

However, one way to prevent a kinked hose is to insert a spring inside it. That is common on large diameter hoses which are subject to a vacuum, but should work here also. I'm unsure how much effect the reduced effective diameter would have, but my guess is not enough to matter.

Doesn't the filler neck have two tubes for hoses? One for the crank breather, and one, pointing a different way, which connects eventually to the center of the rubber boot between the two halves of the intake system? Maybe you have these reversed?

Although it looks like two hoses are on the oil filler tube.However, the large breather hose from the crankcase routes to the oil tank where a lot of high velocity oil + blowby dissipates before venting to the filler pipe. The other hose vents the oil from the oil filler tube back to the intake, catch can and/or atmosphere. Any significant hose restrictions will increase crankcase pressure and exacerbate any potential oil leaks.

Pics from a related thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/958569-3-2-vacuum-leak.html

I mirrored Walt's suggestion to insert a large spring in the large hose from oil tank to oil cooler.

Sherwood

My top breather which is connected to my airbox on my 75 2.7 is spewing oil into the airbox.
Could it be the cold start valve causing this?

The 80/83 was a 2 piece hose with a connector about 6 inches from the tank
Order the later hose from 84 to 89 and it’s one piece from the case breatheR to the side of oil tank
930 207 386 01. It’s way better than fooling with steel wrapped rubber hose
Bruce

there is also a restrictor on the tank end (looks like brass) if you still have the CIS.

I'm pretty sure the restrictor is in the hose that connects to the rubber CIS intake boot, isn't it? I didn't think the crankcase breather had a restrictor.

Mark

http://forums.pelicanparts.com/uploa...1595614719.jpg
http://forums.pelicanparts.com/uploa...1595614719.jpg
http://forums.pelicanparts.com/uploa...1595614719.jpg

pretty sure its in the oil tank end of the breather hose, but anywhere along the hose is fine.

Do you have to use a restrictor on the crank case breather hose going to tank not filler neck on a 2.8 with carburetors?

A 2.7, 2.8 doesn’t have a sealed oil tank. It breathers on the hose on the side under the air filter
The restrictor is used on 78 and later through Carrera to keep the engine from dying when checking the oil level. The restrictor permits the engine to stumble and is located between the filler neck and the throttle body cover.
Bruce

I run a Carrera oil tank that has a breather connector on the filler neck also. I run race filters , so I dont use a hose from filer neck to filter. What do I put on that connector?

Here's a picture http://forums.pelicanparts.com/uploa...1595642059.jpg