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Wastegate Rebuild

 
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TonyMechanic  
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PostPosted: Fri Apr 19, 2002 11:32 am    Post subject: Reply with quote

Has anyone attempted a wastegate rebuild on these? A friend of mine is looking for a place to supply all the parts for it? Thanks
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Smoothie  
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PostPosted: Fri Apr 19, 2002 12:15 pm    Post subject: Reply with quote

I don't know if it's considered a rebuild, but I replaced the diaphram in mine a few years ago. It cost about $60-$70. I think I got it from PAR in NY. Other places to try are Zimms, Pelican?, Tweeks, Performance...
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TroyDest  
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PostPosted: Fri Apr 19, 2002 8:18 pm    Post subject: Reply with quote

If you're really serious about a total rebuild, you need to replace the diaphragm, spring, gaskets, valve guide, and grind or lap the valve seat. You probably only need to replace the diaphragm and gaskets. Andial.com has the diaphragm for $57 and gasket for $10. They also have banjo bolts and fittings if you want to add a pressure line to the top of the wastegate to adjust boost. They have new springs but they start at over 1 bar boost. If you really need to grind the valve or replace the guide your best bet is a machine shop. You can lap the valve seat yourself. -Troy
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Rick MacLaren  
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PostPosted: Fri Apr 19, 2002 11:34 pm    Post subject: Reply with quote

I did a total rebuild on the wastegate a year back. On reinspection, it was still perfect.

There's a thread here I contributed to that outlines how you can take it apart, grind out some roughness where the spring has worn into the aluminum, fill with a liquid aluminum, bake it in an oven, resand, refill, and so on. You need to heat treat it mildly to make sure it hardens properly.

If you don't find the thread I'll go into more detail.
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924RACR  



Joined: 29 Jul 2001
Posts: 8114
Location: Royal Oak, MI, USA

PostPosted: Sat Apr 20, 2002 12:47 am    Post subject: Reply with quote

I seem to recall that Andial sells the stock spring as well - if not, you should be able to buy one from the usual aftermarket or dealer sources.

I added a hose to the top of my wastegate for later addition of a bleeder valve (once I finish mechanically restoring the car). All I had to do (thanks to John Heaney for the instruction) was to remove the little pressed steel noise baffle on the top of the wastegate (obviously after it was removed from the car) and there's a little nipple for a hose on top. I then attached a hose with a hose clamp to it, and fed the hose up the back of the engine to the intake, where I plan on later tapping into the upper pressure duct. I'll have a bleeder valve to control how much boost I bleed off to the wastegate. This adds pressure to the top of the diaphragm, reducing the pressure differential, delaying the opening of the wastegate.

The benefit of this arrangement is that if any damage occurs to this hose, the added pressure will be lost and I will be back to stock boost. No interference with the stock boost sensing line. This is much more safe for the engine, assuming you don't dial in too much boost to start with. Naturally I'll add a boost gauge to keep an eye on it.

While the wastegate was out I did also test the opening pressure, applying 10psi to the sensing line port. As desired, the valve opened, confirming that the diaphragm was good.

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Tom_in_LA  
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PostPosted: Fri Apr 26, 2002 2:13 am    Post subject: Reply with quote

I think this is a good place for me to jump in with a stupid question. If the wastegate is supposed to open at 10 psi, and my boost gauge tells me I'm getting well past 15 psi at times, does that mean my wastegate is stuck ? Or is the gauge not accurate ? It doesn't take much for it to go to 15+ psi, I just have to punch it to around 4000 rpm. Also, what is the function of the over boost switch at the intake duct, does it cut off the ignition when it senses too much pressure or what ?
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Rick MacLaren  
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PostPosted: Fri Apr 26, 2002 2:32 am    Post subject: Reply with quote

Yep. Wastegate sticks. Cylinder head pressure builds. Boost rises. RPM's don't move much, and a silent, almost inaudible event occurs beneath the cowl that is your engine bonnet, as the engine detonation builds and your engine whispers...


Boom...

[ This Message was edited by: Rick MacLaren on 2002-04-26 01:36 ]
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numbers  
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PostPosted: Sat Apr 27, 2002 7:00 am    Post subject: Reply with quote

Tom, could be either one. The overpressure switch supplies ground to your fuel pump. When pressure exceeds 21 PSI, it opens and fuel cuts off. However, both of the switches that I have tend to open at around 17 PSI, so the manufacturing tolerance must be pretty broad.
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Rick MacLaren  
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PostPosted: Mon Apr 29, 2002 1:31 pm    Post subject: Reply with quote

...but even the cutting off of the fuel pump won't help you when you're bouncing air pressure, fuel and heat off the cylinder head and combustion chamber. Tom, the point of my message above was that this is a serious matter that can destroy your car. Screw the hypothesis of a bad gauge. That'll get you nowhere. Every occurance of 'ping' or 'knock' simply equals engine damage. There is no 'harmless' ping or 'harmless' knock. When the wastegate sticks like this your turbocharger is POUNDING air at the combustion chamber, and the combustion chamber is EXTREMELY HOT, but the wastegate won't let the gasses out, so everything in the engine becomes chaos. So combine gas, extreme heat and air being pounded in at somewhere between 11 and 21 PSI and you've got all the necessary ingredients for small explosions inside the engine 'knocking' around your internal components.

The limit set by the cutoff switch is trivial. It is entirely possible to blow your engine at 13 PSI. And how old are these cutoff switches? Numbers is right, the tolerances are VERY BROAD. Mine was 19 years old when I bought the car. Within 2 months of my wastegate behaving like yours my engine blew and I ended up paying about $10,000 in engine rebuilding.

If the car is worth more than $4K USD take it to a really competent Porsche mechanic, pay the money, bite the bullet. Or fix the wastegate yourself. But don't drive it.


[ This Message was edited by: Rick MacLaren on 2002-04-29 13:03 ]
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Cbass  
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PostPosted: Thu May 02, 2002 8:51 pm    Post subject: Reply with quote

Quote:

On 2002-04-26 01:32, Rick MacLaren wrote:
Yep. Wastegate sticks. Cylinder head pressure builds. Boost rises. RPM's don't move much, and a silent, almost inaudible event occurs beneath the cowl that is your engine bonnet, as the engine detonation builds and your engine whispers...


Boom...


Thats twice that you've made my day, I just couldn't stop laughing.

Rick is very right. Rebuild the thing before you take it any higher than 3000 rpm, or face the unpleasant consequences. Or it could be a horribly inaccurate guage, but they do random tests at the factory to prevent that sort of thing.

There is another option of course, install an intercooler. It helps in two ways.

1)cools the charge, preventing most detonation even at high boost levels

2)you can integrate a blow-off valve, set for whatever boost level you want, or rather, don't want.

There is also a third option, get a intercooler that isn't very well put together. Run more than a bar of boost through it and IT blows, not your engine
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