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-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Yikes, I just got off the phone with the machine shop- my #4 cylinder exhaust valve was bent(!) from the detonation going on in that cylinder. Otherwise, it looks like the head came out fairly unscathed from my previous meltdown. The combustion space in that cylinder is hammered up pretty good, but I need to take a couple cc's out of it anyway for the flat-top VW pistons. So I'll be able to clean it up and smooth it back down.

Just wanted to share the good (and interesting) news!

nick

Lizard · Posted: Fri Apr 29, 2005 10:49 am Post subject:

wow, that is kinda crazy, were these new valves, or reused?
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Smoothie · Posted: Fri Apr 29, 2005 11:00 am Post subject:

How's that get explained? Did a chunk of piston came off and got stuck between the valve and piston, causing it to bend?
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

This could easily happen with valves, and the cause is detonation, not the chunk of the piston. Heard several times about this, but never had it in my car

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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

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Smoothie · Posted: Fri Apr 29, 2005 10:19 pm Post subject:

Really? I'm thinking that detonation has to happen anywhere from the later part of the compression stroke to early and possibly mid power stroke - all while the valves are closed. Is it possible for detonation to be happening as late as when the exhaust valve is trying to open?
-Or would the bending be caused only by extreme heat, melting the valve stem, then the valve bending by its' own weight + exhaust flow?

_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

The entire crown and top compression ring were *missing* in that cylinder, I'm not sure that I understand how detonation could bend a valve either since they are shut when all the nastiness occurs. Apparently the valve seats were just fine though. ??

nick

Paul · Posted: Sat Apr 30, 2005 7:46 am Post subject:

The crown breaking up most likely caused your bent valve.

Joes924Racer · Posted: Sun May 01, 2005 3:53 am Post subject:

ya think paul I agree.
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-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Here's one for the archive-

Apparently it was just the heat from the detonation. Machinist said he's seen it before. The heat warps the stem slightly. You can't even tell the valve is bent. When he tried to lap it in he could see it. Looking at the valve you can see where it was trying to cut itself in differently around the seat. Very slight. Interesting stuff...

nick