Technical 20v turbo valve stem seal replacement

[robinsearle]

Hi guys, can someone help me on this problem please. I have a 20v turbo with only 54k in near showroom condition which i have had off the road for ages. Anyway i have just completed a full engine flush replaced spark plugs and preplaced the oil. She is now running lovely. Except she is smoking badly with white smoke. Its bad. it doent clear at all. Its not the turbo as does it on idle. I have been told its the stem seals. I agree. Can these be replaced without taking the head off? is it a big job? what woud you expect to pay for this or can a amateur do it them selves. By the way the smoke may be white every so often you get a real stink burning oil in the smoke. But trust me the engine is runniing lovely apart from this.

 

[NigelO]

The head has to come off to do the valve stem oil seals, as the valve spring needs to be compressed

However, I'd be willing to bet that it IS the turbo that's causing the smoke

The standard turbos use what's called a pressure differential seal - it relies on pressure in the exhaust side of the turbo to keep the seal, er, sealed.

If the exhaust has been de-catted, the pressure in the system drops and the seal will weep, causing LOTS of smoke. It will smoke more when the exhaust pressure is at its lowest (which is at idle)

Even if the cat is re-fitted, the damage is done and the seal will continue to leak. The only time that the smoke will stop is at high revs, when the pressure in the exhaust is so high that the seal is forced shut (and also when there's so much gas flowing that the small amount of oil is burned cleanly, rather than producing smoke)

For what its worth, I've been around Coupes for well over a decade now and I can't remember ever hearing of valve stem oil seals requiring replacement