Rebuilding a K03 or K04 Turbo - Picture Heavy

Back in 2009, I bought a unique K04 turbo off a chap from the MKIV forum. It had a proper K plate/plaque say k04-0402 for which there is no information. I won't go into the K03, K03s, K04-001 and K04-02x discussion here but the simple information is that the early 1.8T 150bhp cars had the K03 whilst the 225bhp cars had the K04-02x. They use a different manifold and various other parts so swapping from the smaller K03 to a K04-02x was not simple.
The K03s was introduced during 2001 and was an improvement over the K03 with a larger compressor wheel but still in the K03 housing with the same turbine wheel. The K04-001 was also an upgrade on the K03 in the same housing, it is rumoured to be an improvement over the K03s too, it has a compressor wheel size in between the K03 and K03s but the turbine wheel is bigger.

So what is the K04-0402 that I have? The only information we have is from borgwarner:

Dear Sir,

I think that this K04 0402 is an upgrade turbo from the company SRS Motorentechnik GmbH (Ober-Ramstadt).

There is also, written in pen the encouraging information that the turbo is rated to 230ps
What we can tell is that it is in the correct housing to fit as an upgrade from a K03x turbo and from the outside we can tell that the compressor wheel is the same as the K03s so this is not a K04-001. The only way we can tell more is to take the thing apart and at the same time I can rebuild the seals and bushings. I followed this excellent vagdrivers.net guide and taking the time to take pictures and clean things up took about 3hrs with faffing and looking for a blow torch.
No special tools were required.

10 & 11mm spanners
13mm socket
Chisel
Punch
Hammer
small, jewel flat blade screwdriver
Large flat blade screwdriver
Circlip pliers
Blow torch

Lets start with pictures of the victim:






It is worth starting with removing the actuator completely, plus any pipes.





Now find a place to mark where the exhaust turbine body meets the centre part, I found a place with a good indentation and marked it with blood (actually it was the gf's nail polish as I couldn't find the tipex).



Also note the tabs holding this together, these are held by 10mm bolts which you won't be able to remove with a spanner as you will round the edges off. What you are going to do is use the punch and a hammer to tap the tabs and loosen the bolts.



Once they are all loosened, you will find some can only be loosened so far before they hit the exhaust turbine body. Use this to press off the body. Eventually you will have two bits.



Now mark how the compressor side and body line up and then undo the remaining bracket on the compressor side but put the bolts all back in to use them as leaver points.



This was the bit where you light up the blow torch and heat the outer housing and then get the chisel over the bolts but under a point on the centre. The centre will spin which was fun with a hot metal to hold but once the casing was hot enough it was easy to get out. I tried this with gentle heat but it did not do anything and then I remembered that these turbos work in immense heat so felt less worried about really going to town with the blow torch.

And you should now have the guts of the turbo.



Be very careful with the blades on the compressor and turbine, they are sharp and we don't want to damage them either.

Important step: See the red on the top of the bolt, this is there to help me mark how the compressor blades and shaft meet up for reassembly. The unit is meant to be balanced, I have put some paint on the blades and the top which line up.
When the paint is dry, undo the bolt at the top of the compressor shaft and remove the compressor. Now measure it and work out what you have. This is the same dimensions as a K03s which is not a bad start.



The centre plate now slides off.



That centre part pops out and should be part of your rebuild kit. A metal bush and a clip.



Back to the main body.



Remove the centre parts and lay them out, there is a circlip holding the remaining parts as can be seen.



All the bits lined up.



Now you should have the turbine wheel out and can measure that as well. There is a clip on the shaft near the turbine end that needs replacing too.

My turbine is bigger than a K03s but smaller than a K04-001 more on that later.

Once you replace that clip on the shaft and checked it for scores and other damage, time to reassemble with new parts.
The long brass cylinder is best to be put into the centre housing first with the groove section assembled as shown below.



Then place the next section and put on your new circlip.



Put on the remaining bushes and plates.



Now I found it was easiest to put the exhaust turbine housing bolts and tabs back on loosely and slide the body back in. The tabs are what holds the centre in. Use your paint marks as a reference of where the body and housing line up.



Now pop the compressor housing back over the body and align them up. Refit and if you have one lying around, fit your uprated forge actuator and other pipes.



So what sort of turbo do I have. My compressor is the same size as a K03s which is bigger than a K03 and K04-001, my turbine is bigger than a K03 and K03s but slightly smaller than a K04-001. This means it should perform better than a K03s so is worth fitting. More on that when it actually happens.

nice bit of tech there cali it makes me wanna turbo ,

will be interesting to see the results of your mutant

Thanks! This is a huge help. I just took my K03s off of my MK4 Jetta becuase I've been finding quite a bit of oil in my intercooler.

It will need to be balanced once you rebuild it but there are a lot of cheap balancing services around though Pittsburgh is a little far for the guys I will use.

From what I understand, as long as I make defining marks on the impellers and shaft while it's all assembled, it should be balanced just the same as it already is... right?

Someone more in the know than me, pointed out the speed these can spin at and said how much vibration even a fraction out would cause.
I won't be taking the risk with this turbo as I would want to get 23+psi out of it.

Ok thanks. I'll see if I can find any reasonable shops around here. I'm only looking to push the stock 11 psi. out of it. Maybe 14-15 a little down the road. This is going to be my daily driver and hopefully I'll get another motorcycle as my "go-fast" toy. (I had to sell mine to afford this rebuild since my timing belt died)

ok... so I got all my stuff back together. Car runs, started right up.

Sorry I didn't get a whole lot of pictures but this DIY saved my life!! I have about 20 mi. on my newly built head and turbo, taking it easy for the first 100 mi. hopefully. It's really tempting to start using boost again since I've been driving around a little S10 for a while now.

Good job. Did you get it balanced?
My car is taking a back seat at the moment due to work so mine has still not been fitted.

did you have to get it balanced or not?