Quite interesting not more people use 7A valves.
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Modified head - what valves do you run? Poll!
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Originally posted by igor136 View Post1. Was valve springs OEM or stronger? Maybe too strong.
2. Was OEM exhaust cam? Maybe 7a?
3. This was exhaust valve. That can be overheating, bad fuel/air ratio.
2. Schrick 260/10.9 cams.
3. Yes, exhaust valve. Usually you get a burnt valve(have experienced it twice), but this has snapped off totally and bounched between the head and piston. Did make a hole in the piston.
This was on my friends car from last summer. No idea of the total km driven with the head, but it was serviced before this.
Audi UrS4 Avant 2.5 20vt - twincharged - Project
Audi 80q B4 Sedan 2.2 20vt - Daily user
BMW 320d Touring e91 M-Sport - Daily user
BMW 740iA e38 - Project
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My new setup will be ferrea stock sized valves x20,
Supertech dual valve springs & titanium retainers,
Supertech valve stem seals, INA oem lifters, 7a cams,
new timing chain, adjustable cam sprockets, tommi
adjustable cam gear, Febi valve guides if needed.
Does anyone know if ferrea and supertech valves
require different valve locks or are the stock locks
fine?
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Originally posted by Thuppu View Post1. Stiffer springs, not sure about the brand. Not OEM.
2. Schrick 260/10.9 cams.
3. Yes, exhaust valve. Usually you get a burnt valve(have experienced it twice), but this has snapped off totally and bounched between the head and piston. Did make a hole in the piston.
This was on my friends car from last summer. No idea of the total km driven with the head, but it was serviced before this.
If a valve guide is worn, it has a wider diameter at the top and/or the bottom end - like a trumpet (so to speak). When the valve is returning to the valve seat, the valve disc and the valve seat are not 100% concetric. So the valve disc hits the valve seat first at one edge and bounces from one edge to the other until it fits concetric in the seat. Maybe the valve is also forced to bend a little bit in this moment (without bending it actually) (you know what I mean). Over the time the stress to the valve is to big and the result is a fatigue fracture.
I hope I found the right words to describe this in english
here a similar result:[__]=oooo=[__]
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Yes, that makes perfectly sense. Even that the guide work is done the valves can already be tired and just snap at some point.
Audi UrS4 Avant 2.5 20vt - twincharged - Project
Audi 80q B4 Sedan 2.2 20vt - Daily user
BMW 320d Touring e91 M-Sport - Daily user
BMW 740iA e38 - Project
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Also when the valve guide is worn and the valve head is not touching the seat the correct way, the cooling of the valve is not working. Sodium filled valves are cooled about 40% through the valve stem and valve guide and 60% through the valve seat. So with the worn valve guide you get the combination of fatigue stress and over heating. Also with enough heat it is possible to get the sodium inside the valve stem to overheat and actually boiling and then it's game over. I don't know which one usually kills these valves, fatigue stress or lack of cooling, or both of them combined, but I wouldn't simply just blame the valve. The sodium cooled exhaust valves where high tech 20 years ago and they are still up there. Nowadays the hottest **** could be the sodium filled inconel valves which are available from some manufacturers.
Compared to the sodium filled valves the regular solid stem valve is cooled about 20% through the valve guide and 80% through the valve seat. So it should be clear why Audi used or still uses the sodium filled valves, it's all about heat control.
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Mahle exhaust valve 029 VA 30889 100 http://catalog.mahle-aftermarket.com...&embedded=true
So this isn't sodium filled? Anyhow it says AAN/3B...
Audi UrS4 Avant 2.5 20vt - twincharged - Project
Audi 80q B4 Sedan 2.2 20vt - Daily user
BMW 320d Touring e91 M-Sport - Daily user
BMW 740iA e38 - Project
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Thread lift...
If I go with inconel ex-valves do I need to change the guides or is stock ones good to go(if not worn).
Audi UrS4 Avant 2.5 20vt - twincharged - Project
Audi 80q B4 Sedan 2.2 20vt - Daily user
BMW 320d Touring e91 M-Sport - Daily user
BMW 740iA e38 - Project
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Originally posted by Thuppu View PostI would just do backcuts on them, nothing more.
96 URS6 plus speck saloon
96 URS6 plus speck estate
94 2.6 80 Avant
99 2.8 final edition Cabriolet
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