Some of you may have picked up recently on my turbo failure, sadly I'm an eager beaver. So I went about wanting to know why the turbo seals, in particular, fail.

essentially there are two seals, for the purposes of discussion we will call them front and rear. To define what I mean by this the front is the one pointing towards the front of the engine (cambelt end) the rear is obviously the opposite end which is the exhaust compressor end. The seals themselves sit in a recess on the turbo shaft and look very much like a piston ring.

 

The rear one is the commonest one to fail, it seems for our turbos. The reason for this is over pressure from the oil side, causing it to go some where it was never intended. With decatted cars the area of low pressure behind the turbo at idle is an easy route out past the worn seal straight into the exhaust causing white/pale grey smoke, not blue. so this may be because your pcvs are not functioning correctly and are over pressurising the sump pan, this makes it difficult for the oil fed into the turbo to drain out via gravity as easy as it should, hence it finds its way out the shaft seal. Mine was odd in that it wouldn't smoke at idle but at 2k rpm smoke would pour out, this was because the passing oil was puddling up in the compressor housing (the snail shell) then when the flow built up out it came. Within the turbo you will find some small oil galleries that the oil drains out via gravity, in teh scenario where the car isnt run down properly or oil changed regularly enough the oil cokes up and blocks these galleries, causing the same issue as the pcvs ie an back up in oil within the housing.

 

So next time some one says the reason your turbos failed and started smoking is because you decatted its not the whole picture, and this is why refitting them can mask worn seals, that backpressure at the cats will up the limit of pressure able to build up in the housing, before they leak. In situations where the seal isnt damaged simply refitting would sort the smoke, but you will still have a system that isnt running as intended. However replacing your pcs may go a long way further to solving the issue.

 

One of the tubs I had as a spare the front one was leaking, all i can assume is that this one came from a car with cats and the easiest place to pass was the front one, or the seal itself had worn just like a piston ring.

 

I chose to take the extra precaution, and fit both 360 degree bearings and stepped rear oil seals. the stepped rear oil seal is well pretty self explainatory it is stepped both sides to make a better seal. the 360 bearing we all discuss i found out are neither 360 degrees or a bearing. its actually a flat piece of metal 270 degrees to look at that the thrust bearing sits on. below is an exploded veiw so you can see what all the componets are and were they are. There isnt really much in there.

 

 

the rear seal is number 5, and the thrust bearing is number 8 the front seal is located into this. and clips into the cover plate(number 11) to make the seal.

and number 6 is that "bearing" in the stock shape, the 360 degree one looks like a D shape.

 

The other common issue is oil starvation causing excessive wear on the bearings and subsequent failure or damage due to well not enough oil passing through the turbo. The bearings themselves are hydro statically filled, this is why you will get a small amount of play side to side but not forwards and backwards on the shaft when there is no oil pressure. Once the oil pressure increases it locks the shaft into suspension hydro statically. The bearings are labled 1 and held into the housing with the funny circlips labeled 2. there is also a retaining spring after the rear one on our turbos not the tab in this picture this was added later to make it easier, labled 4.

 

If your thinking of doing a home rebuild the worst part is removing the massive circlip labled 15, the easiest way to do this is pry it out with some old flat blade screwdrivers. I also found removing the coverplate a little tricky with it being made of some kind of graphite it chips easily if you lever it, much better to grab the notch of it with some needle nose pliers and pull. once apart clean the housing thoroughly and check the mating surfaces of the seals very closley. Lastly and most importantly they MUST be balanced afterwards otherwise your wasting your time. They are spinning incredibly fast and a slight imbalance will rip them apart sooner than later.

 

I hope this all helps explain some of the mysteries of what those snails contain and why they break, sorry for the poor English and if you have any questions if I can help I will do my best. I used CRturbos based in Hampshire for the rebuild kit and the balancing, Craig and the team there was very helpful and informative.

nice write up, cheers steve

What about the gases coming from the intake rockers to the intake of the turbos adding dirty oily air into the system. Ever wondered why when you take off these pipes there is dirt and grime in them? Full PCV delete and breather tank will stop this.

Edited December 28, 201212 yr by Gonzo12c

Well yeah I see your point but is part of a breatherr system thats not working 100% is it not. The pcv on the vg isnt the best as we know but thats a genera engine issue not a reason for tub failure I dont think, especially with the exhaust housing its so hot.