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Mercedes Benz 320cdi

Rebuilding the turbo

So the Mercedes failed it's MOT or rather the annual emmisions test here in France. In fact it's every two years out here but then again, without an MOT I can't get a French license on it. I already cleaned the intake manifold out and the EGR valve. Still blue smoke was coming from the exhaust and it failed on emissions bigtime. I did notice some oil buildup in the intake pipes and the intake side of the turbo was oily as well. First suspect was the turbo, new ones are expensive and even rebuilt ones go for a fair amount of money.

I decided to rebuild it myself and ordered a kit which contained every single part needed. Well, allmost.
There were still some gaskets to be ordered to install the turbo back in the car. I had to take the exhaust manifold off so a new exhaust gasket is the first one.

Anyway, let's get started. This is what was in the kit, very good value for money at like €40,- (or $50 US-dollars / 32 GBP).


First, I had to get the turbo out of the car. After removing the airfilter box and a heatshield it was in plain view.

I removed the oil supply line, it was where the red cap is now.

Had to take the particle filter out as well.

This side of the turbo, the exhaust side, is not oily at all. That particle filter is in pretty good shape.

And when the turbo was finally out you could see the oil that was at the pressure (to the intake manifold) side of it.

Even at the intake side of the turbo was oil to be found.

I didn't take the wrong decision to rebuild it, if this much oil is entering the intake I'm not asking myself another question on why it blows out blue smoke. It's obviously burning oil.

Getting the exhaust manifold off developed another surprise, it has been leaking badly and was not sealed against the engine at all anymore.

The hole you see at the bottom is where the oil return line from the turbo goes.

A look at the exhaust manifold and the gasket told the whole story, this has not been sealed up.

Right, so there it is. The turbo is on the bench. The left side of it should have been bright shiny metal but instead it's covered in exhaust soot.

At this very point in this chapter I wll make a copy to put in the How-To section as well. The rest goes for any modern turbo so it's only logical to do so. I could redirect you to the How-To section but I decided not to.

Modern turbo's don't have a waste-gate anymore, instead the ring you see on the outside is operating those "fingers" which in their turn rotate the vanes which are attached to it to control the pressure the turbo deliveres. Those vanes can just been seen at the top of the big hole in the middle.
To say it in other words, the exhaust gasses don't spin up the turbo that much when they are in the closed stage. This whole system is controlled by vacuüm.

The intake side seems like it received some soot as well, that's not true! It's only dried up oil that's making it look like this.

So, got both of the detachable housings on both sides off, inlet and exhaust side. On the housing you can see the oil which colored it brown.

Here in greater detail.

And a look at the impeller and the back plate. It's obvious oil has been leaking at this side.

Took the thing apart and this is how the central shaft looked.

The backplate at the intake side has a bolt pattern ensuring it can only put back together in one way. In the centre you see the bearing.

Quite greased up on the other side.

Here is the shaft, pay special attention to the ring that's just below it, that's the oilseal at the exhaust side and it will be replaced with a new one.

The two oil seals for the intake side are still on the pieces that hold them, they are badly worn. Just to give you an idea of the size of them I put a medium size screwdriver in the picture.

There it is, all parts that make up the turbo. I did put the old and new parts next to each other so I knew which items had to go.

Having cleaned all the parts and sorted the ones that have to be replaced I continue with the actual rebuild.

Here you see everything layed out with only the new parts, this way it has go go back together.

First of all the oil seal which goes on the exhaust side. The old one is in the top-right of the picture.

The shaft with the new oilseal in place. The lower bearing is already in place.

Here the top bearing and the gouvernor are installed. That being the oil control valve to the top of the intake side of the turbo.

The top oil seal pressed into the front of the housing.

In this picture it's been screwed in place.

The impeller in place.

This is the core of the turbo completed, all new parts inside which are exposed to wear. At this time the red cap has to be there avoiding any and every even so minor particle to enter. Just one grain of sand can destroy the turbo at the first spin-up.

We've seen this part before, now the vanes are more visible.

The control ring back in place, that took a while but it's in.

To place it in the right position is a fiddley job, in the pic above you see an indent in the ring at the top left. That's where the control lever goes which in it's turn is controlled bij vacuüm.

When you're absolutely sure the lever is in the right place to catch the ring it's time to bolt the exhaust side of the turbo together using new bolts.

It's got to be torqued up to spec in a cross pattern, more or less how you have to torque the wheelsbolts up.

Now the exhaust side is done we have to get the intake side on. See how clean it is compaired to the photo I took when it came off.

There is a snack here, there is absolutely no marking or whatever to line this piece up to the housing. You'll have to go by the indents which were made by the rings on the original bolts. Thus, lining it up is a bit of a gamble. If it's not exactly in the right place it won't damage the trubo but the outlet won't line up to the hose it's supposed to meet.

So, this is as good as I could get it, should have marked it up before I took it apart but hey, this is the real world and things like this happen. Just don't be a fool and give it some thought before you bolt it up, it will safe you a lot of headaches.

Put the vacuüm control valve back in place.

This looks really nice! I didn't go for the brand new look because the most important is the inside. Had to clean up the sucker just as well. And yes, it looks nice enough.

Just some more pics.

Very clean outlet to the intake system.

And here it is, one rebuilt turbo to be mounted in the car and hopefully the emisson test will be fine.

Went to get "Der Benz" tested again and after the rebuild of the turbo the emissions were spot on! The blue smoke is gone but there is still black smoke coming from the exhaust under load.

I'll keep you all updated on the matter. up to this date I didn't find the real problem but I will eventually!

Stay tuned!

Last update : August 29th, 2017