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Top Breather Pipe Repair

Mod Description
If your top breather has failed and you are having problems changing it, repair it instead.
Mod Details
PremiumNo Difficulty Mod ID1034 Creditevilution For450 Fortwo452 Roadster Link Copy to Clipboard

Repaired Top Breather Pipe

Here is the top breather pipe found on the 450 Fortwo and Roadster. The black puck is a one-way (check) valve. It allows vapor from the crank case to be sucked into the engine but stops any boost air from passing into the crank case which can push oil out of the lower breather pipe and into the turbo.

If you have air conditioning, replacing this pipe is hard so instead of replacing it, just replace the broken part. In this case, we will be replacing the one way valve with a better one.

Fixing Options

Here are a few of the better repair options for this pipe that doesn’t involve removing the whole thing from the car.

Valve Options

Here are some of the options of replacement valve. Many people go with a metal style vent. I don’t like metal valves.

As we all know, metal expands and contracts with temperature. The problem occurs when these types of valves get very cold (freezing outside temperatures). They shrink and can cause the valve disc inside to become deformed or stuck. Generally they stick open, let boost through until the heat of the air unfreezes it. That cycle occurs over and over and you may not notice it happening.

If you are going to use a valve such as this, I would recommend lagging it (insulating it) with something. Either pipe insulation or something similar just to stop the freezing temperatures reaching the valve body.

I personally prefer and recommend any of the plastic valves.

The white valve is a nylon variant. Click
The black valve is a Febi 102362 and is an exact replacement to standard. Click

You’ll also need some hose.

It’s 10mm ID, reinforced and suitable for oil and gas. Click

It would also be a good idea to get suitable size hose clamps. I used zip ties which worked OK for me.

Valve Replacement Option

Remove the rubber hose that sits between the throttle body and the check valve.

Cut or snap the old valve off leaving the rest of the tube intact.

Push the 10mm ID hose over the end of the pipe.

Cut it short, add the valve (facing the correct direction so you can suck but not blow) and add more hose to the other end.

Cat the length of hose to a suitable length and reattach it to the throttle body.

Add hose clamps between the valve and throttle body as this is where pressure will build up. There’s no pressure on the other side between the valve and the top of the crank case breather pipe.

Doubling Up

Since the existing valve doesn’t work, it’s essentially just a straight through pipe. There’s just enough room to place a replacement valve between the broken valve and the throttle body.

Pull the pipe off…

…and you’ll see you have about 60mm gap between the hose connectors.

The FEBI valve is 60mm long…

…and the white nylon valve is 50mm long.

I’ll use the white valve since I used the black valve earlier. Cut 2 lengths of tube, 40mm long.

Push the hose onto each end of the valve…

…and connect it up.

Ensure you can suck but cannot blow down the pipe to check that the valve is facing the correct direction.

Fit hose clamps to stop the pipes popping off with the pressure.

Niall B’s Fix

Niall had a different idea for a fix. He took a replacement breather pipe but used the other end for the fix.

He took the rubber elbow that normally goes down the back of the engine and disonnected it from the rest of the pipe. He then pulled out the failed valve and cut the plastic pipe just after the 1st bend behind the valve.

The elbow is then pushed between the existing plastic pipe and the replaced valve. He fitted pipe clips however this isn’t necessary as there is no pressure in the pipe behind the valve.
Handmade Top Breather PipeMister Bridger from the forum came up with a radical idea. Because he has air conditioning,
replacing this breather is a much harder task. Originally Stuart thought about just changing
the valve but found that it was hard to get off and thought that the pipe may split.

He decided to make his own breather pipe that would make it easier next time around.

Mister Bridger’s Story

A trip to a plumbers merchant and for £1.41 i bought 1m of 10mm soft copper pipe.
On the way home I bought 1.5 m of Net curtain wire for £2.48 at Homebase. After taking
a look at the original, I bent the copper pipe as close to the original in shape as possible.

I cut the end going onto the valve a little shorter for 2 reasons. I wanted to have some flexing to be allowed at the join to the valve as it is very hard to get every angle spot on when bending the pipe by hand. It makes it easier to pull the valve off when the time comes to change it.

Now for the easy bit. Make sure you change the valve before an oil change is due. Pull off the old valve. Squirt some brake cleaner fluid/carb cleaner/ or WD 40 down the pipe. Then insert the net curtain wire and push it back and forth to move any crud. Give it a final squirt and all the fluid and crud goes into the sump and is sucked out with the old oil.

WARNING- make sure you do not loose the straw of whichever cleaner you use down the pipe. A good tip is to apply a large bit of BLU TAK to the straw and this will stop it going down the pipe.

Extra Info For Bending Copper Pipe

You have 4 ways to bend the copper pipe to the required shape. Carefully bend it by hand – be careful as you can kink the pipe. Pack the pipe with sand and hand bend it – be sure to clean the pipe out after. Use a proper mandrel pipe bender – expensive if you can find the right size. Use a pipe bending spring – if you can find one the right size.


If you have air conditioning, plan to keep your smart for a long time and don’t fancy lowering the engine more than once, this is a good alternative. Once the DIY top breather pipe has been installed in position, the valve can be swapped in minutes which tends to be the part that fails. Saving you from mucking about behind the A/C pipes again.