Wastegate air leaking into exhaust

[ian4455]

With my engine in bits i just tried testing my wastegate using compressed air. There's a really bad problem with air passing into the exhaust from around the area where the shaft enters the cast housing!

Is there an acceptable leak between the shaft and bush in the casting or should there be none?

Are there parts available to recon the standard audi S2 wastegate?

[driftin jo]

Sounds like your waste gate diaphragm could be fu*ked

[prj]

Diaphragm is between top and bottom chamber is it not?

Try plugging the top chamber with something. If then the leak "stops", it's the diaphragm, otherwise it's the wastegate play.
All of these wastegates leak somewhat, but some leak so much that they significantly hamper spool / boost.

[ian4455]

Diaphram is fine the boost pressure is offered into the unit from underneath - bottom chamber, I have no leak out of top chamber. The leak is as you mentioned its waste gate play around the shaft and bush into the lower chamber.

Are new parts available for these ?

[A80Avant]

i will be having mine checked as well next week for play and possible losses that way. I was always under the impression that they cannot seal completely, and as far as i know, there are no parts in etka for wastegates. They are sold as complete units from audi (i think)

[prj]

I have not seen a single car yet which does not leak air through the wastegate.
The question is how much they leak.

I spent today the whole day trying to get a RS2 to boost, but it would have none of it. Considering there are no leaks, the bypass is fine and the wastegate has LOTS of play, I am pretty sure I found the issue...

Then again, my car audibly leaks, but has no issues spooling up early and boosting 1.6 bar on stock spring and stock turbo...

[driftin jo]

Sorry I miss read this, I thought you had control pressure leaking, as in from the N75 that opens the gate. You are talking about leaking that would be exhaust gas past the valve.

[A80Avant]

the idea is that with the spring+ WGFV it should be able to keep the wastegate as shut as possible. But the only real test is to be done with either an aftermarket wastegate or one that does seal completely. Then you can tell if it would make a significant difference in spool. I dont think it would unless there is quite a lot of wear and damage on the sealing surface.

I expect to find some blowby carbon debris in mine now, but we will see...

[ian4455]

Its control pressure leaking around the shaft, given the N75 valve controls boost not sure what effect a bad leak has vs small leak or new wastegate. Any thoughts anyone?

I'll try agian tomorrow to confirm exact pressure, but putting @ 20 Psi into the wastegate (removed from the car) the valve wouldn't open just a bad leak coming out the outlet. i turned the pressure / flow up on my regulator and the wastegate opened whilst leaking badly.

I've got it in bits now, looking at the area of leak there's a bush pressed into the casting where the shaft enters. Doesn't seam to be any worn areas on the shaft so may be worth me getting a replacement bush made to improve tolerance thus improving leak.

[driftin jo]

This doesn't matter then as in operation you have exhaust gas pressure acting against it, so it wont leak control pressure.

The only real problem I can see if it is really bad is that the exhaust gas could leak past and assist
the opening of the gate and you would get sluggish boost response. Did your car spool up OK ?

[newsh]

Thats correct, there is exhaust pressure the other side which tends to balance the leak. Its a moot point whether the exhaust gas leaks up into the WG and opens the valve thereby reducing boost or if the control pressure leaks down and hinders the opening of the WG thereby increasing boost, I think it depends on the running conditions, ie. what rpm, how much boost how much throttle etc..
If the play is really bad the valve can hook up on the edge of the seat and the WG sticks open.
Renewing that bush is worth doing I'd say.

[cooperquattro]

i had the same with mine..when asking for 2 bar boost the wastegate would stick on the burr in the shaft..
i couldnt find replacement parts so opted for a new leak free one...a good engineering company will sort it,new bronze guide and reemed to suit..
let us know how you get on
the leak needs to be very minimal no matter what!!

[ian4455]

thanks, I'll get this looked into. I'm sure a new diaphragm is avaialable for safe measure?

Being my first S2 not familar but spool did seem very laggy considering it was standard S2turbo with cats removed although Boost really didn't kick alive till after 3000rpm.

Upgrading now to Hoffers RS2 Hybrid unit so need to make sure everything is good.

[A80Avant]

hmm, interesting info. I will tell my garage to make one for me as well, as it will be getting looked at this week...

[ian4455]

This shows what i mean with leaking into the exhaust - http://www.youtube.com/watch?v=WjNbMTLzZck