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Smart quod bastardus
 
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clearance between valve guide and stem for OEM 930 wastegate

What is considered a normal clearance between the valve stem and the valve guide bore for an OEM 930 turbo wastegate?
I can here air blowing past the valve guide and into the exhaust port when I pressure test the wastegate housing. I realize a small amount of air will inevitably pass thru the clearance gap between the 2 parts, but when is it time to replace the valve guide from wear? I have not been able to find a spec on this yet. Would like this info in order to be able to machine a new guide and have it pressed into the housing if need be.

Air leaking past the guide is air lost to opening the wastegate valve so ideally this should be a minimum.

Appreciate any info,
Fred

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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 03-14-2013, 01:00 PM
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Can't help you there, but I do know that someone several years ago posted some info on the topic of having a machine shop insert and ream a new guide. Might have to spend some time searching to find it.

My OEM WG was doing the same thing, and leaking enough 'blow-by' to where I was having occasional issues with slight overboosting. If too much of the boosted air signal leaks out, then the valve won't open enough or quickly enough to waste the exhaust and slow the turbo. So I just said fock it and bought a Tial.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 03-14-2013, 05:00 PM
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Smart quod bastardus
 
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Mark,
I know what your saying. Alot of issues with overboosting come up on the forum attributed to the elephant nose design of the typical GSF or B&B headers.

Of course this is part of the problem but I wonder if the wastegate leakage is another big factor. Its funny you found this in your case and I had a few instances last summer when I might have overboosted and nailed the overboost cutoff switch myself.

I have been wondering if the Tial has a different design that avoids this issue or do you think it was just the fact it was a new unit and everything is tight?
Did you ever take a look at the way Tial handles the valve stem and guide interface? I wonder if they run a seal on top to prevent leakage.

I will dig deeper and see what I can find on the forums.

Thanks,
Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 03-15-2013, 04:43 AM
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Quote:
Originally Posted by fredmeister View Post
Mark,
I know what your saying. Alot of issues with overboosting come up on the forum attributed to the elephant nose design of the typical GSF or B&B headers.

Of course this is part of the problem but I wonder if the wastegate leakage is another big factor. Its funny you found this in your case and I had a few instances last summer when I might have overboosted and nailed the overboost cutoff switch myself.

I have been wondering if the Tial has a different design that avoids this issue or do you think it was just the fact it was a new unit and everything is tight?
Did you ever take a look at the way Tial handles the valve stem and guide interface? I wonder if they run a seal on top to prevent leakage.

I will dig deeper and see what I can find on the forums.

Thanks,
Fred
It's been some time since I had the Tial apart so can't really remember how the design differs from stock. There's also an asbestos gasket between the body and bell of the stock WG that deteriorates over time (mine did) and can leak there as well.
You may have to search over on Rennlist as well...that might have been where I saw reference to the dude who had a machine shop make a guide for him.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 03-15-2013, 04:52 AM
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My O.E. wastegate was leaking a ton at the valve guide when I replaced it. The thing was so rusty that I had no desire to overhaul it.
Switching to a Tial cuts the weight by a lot.
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Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 03-15-2013, 09:43 AM
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I have suspected i have a big air leak somewhere in my intake system. i had previously pulled the WG and PRESSURIZED it thinking that was the only test it needed. today i tried to pull a vacuum on the entire WG plumbing. (i have a dial a death in the car. thinking a hose might be leaking). well, it would not even pull a vacuum. in the end, i determined the WG must be the vacuum leak.
i just pulled it apart and i noticed the valve has a TON of play in it and that it must be pulling air in past the valve stem.
am i correct with this analysis?

BTW, the spring is gold. i did not think the spring was that big.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 05-31-2013, 10:04 AM
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i just put it back together and put 20psi into it. it is leaking so much air its not even funny.
i put my hand over the outlet pipe and it pressurized the exhaust pipe!.
__________________
86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 05-31-2013, 10:16 AM
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i actually feel very relieved. i go to sleep at night trying to think of where the air leak could be.

if it is worn out this much, does that mean the car was driven quite hard? it only has 42k on it.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 05-31-2013, 10:18 AM
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You are not alone apparently with this issue. In your case its extreme it sounds.

Perhaps the diapragm is not sealing on the housing lip or its split somewhere that exascerbates your leak. Check this out.

I think the guide to valve clearance is one number I would like to get consensus on....one member responded to me with the info but I cannot find it right now.

Anyway, the guide can be replaced with a new machined guide and pressed into the housing.
I think its worth looking into to keep the stock wastegate from Porsche because it is such a good unit. Or buy a Tial like lots of other members keep pounding on. Depends upon your personal taste and if its cheaper to fix the OEM or buy new I guess.....
I like the stock OEM wastegate and I have modified them for myself and another forum member to make it adjustable, Of course it has to be in good working order and the bushing not leaking appreciably for my mods to work correctly, but it is possible to get the valve guide machined by a good machine shop. I just wish I had a drawing of the proper guide dimensions to get this done.....hard to get any info on this anywhere.

Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 05-31-2013, 10:36 AM
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Smart quod bastardus
 
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Overboost problem solved

I did not like leaving you hanging in my last response.

I found the post on this forum with the guide clearance info....have a look,

hope this helps..

Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 05-31-2013, 10:42 AM
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thanks. it takes about 20psi for it to start opening. about 22 to fully open. anything less than that and i can cover the exhaust pipe and it builds some pressure under my hand.

i have never overboosted. i suspect partly due to the air leak between the turbo and IC, which could be related.

mine is setup for variable boost. i have 2 line on the side, one to the IC and the other to the knob, then back to the top of the WG. i have a gold spring with a shim under it and on top of it. dont know if this is to increase the boost or not.

i am thinking i may just get a new one. a lot faster.
i tried to call rarely8 to see about getting a WG from him. i would like to support him since he helps out here a lot, but i dont understand the 46mm bit and i would like his input.

even if this is not my air leak, i guess it still needs to be replaced.

perhaps opening pressure might be a better concern than play. if you have a .8 bar spring and it takes 1bar to open it, what good is the spring? in my case 1.5bar.

i would still like to know about it going bad so soon. my brother has a 130k on his car and he does not seem to have any WG problems.

you know, i have been playing with the DaD(dial a death) and i have not been able to go above .8bar. only once did i ever see .9. i guess if enough boost can get past the valve, it wont go very hi. also, i asked my brother what is sounds like when it opens, he said you will know. i dont htink i have heard it open.

thanks again fred.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 05-31-2013, 11:07 AM
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HOLY SMACK!
i put the WG back on and plugged the output of the IC to the WG. i was just driving it easy but holy cow, the boost is MUCH more responsive. i did not go over .5bar except once for less than a second. it popped up to .9bar faster than i have EVER seen it move before.
the bad news is my AFR's did not change. 12.3 at idle and 14.4 at cruise.
the idle is better than it has been this week.

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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 05-31-2013, 11:47 AM
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