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Location: Windsor, CT
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Taper in new exhaust valve
How much taper is acceptable in a new exhaust valve?
Top of stem: 0.3527" Bottom of stem: 0.3518" Note, my micrometer doesn't have a vernier scale, but I snapped pictures of the measurements and estimated the 4th significant digit with some accuracy. This exceeds the factory specs. |
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01-19-2016, 02:20 AM
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Brand new, out of the box.
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01-19-2016, 02:39 AM
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  Somewhat self-explanatory. OK 0.3526" Factory spec is .3519-.3523.
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Mike '82 911SC, SSI, 22/29 tbars, 22F/22R Adj swaybars, Bilstein Sport, Elephant polybronze & monoballs, Cambermeister bar, turbo tierods, Carrera oil cooler, front brake cooling ducts, Sparco Sprint 5 & Recaro SRD PAX seat, Teamtech harness, DAS Sport rollbar. Last edited by VFR750; 01-19-2016 at 04:04 AM.. |
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01-19-2016, 03:14 AM
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abit off center
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What brand of valve? Intervalve by chance?
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______________________ Craig G2Performance Twinplug, head work, case savers, rockers arms, etc. |
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01-19-2016, 11:56 AM
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No, TRW. Nice smooth ground surface.
But it felt looser in the guide than the intervalve. That is when I checked. Multiple times. Intervalve had virtually no taper. TRW valve did. Pelican has authorized the return. And I'm going with an intervalve replacement. |
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01-19-2016, 02:44 PM
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Good news. Sent the TRW valve back to pelican for a full refund.
Glenn said he had better luck with intervalve. So I ordered one of them. Wow. 0.3526" top to bottom. Perfect. Not a hint of taper! And the stem was nice and smoothly ground. A very nice exhaust valve. Which is a little ironic, because lately intervalve has gotten a bad rep. That's why I chose TRW. Well maybe the Swiss made intervalve is the better valve after all. At least the one I just bought. |
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01-29-2016, 03:22 AM
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I used the Intervalve 5 years ago on my 3.2 rebuild with no issues.
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01-29-2016, 06:02 AM
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Valve
This is all wrong.
The exhaust valve need to have taper, because the head end of the valve get more hot and expand more. If you have a valve with no taper it's not porsche or OEM like TRW. From porsche data book: Exhaust valve (conical) 8,94 - 8,96 x 109 mm Intake valve (sodium) 8,97 x 110,1 mm The inlet valve is both thicker and longer. Daugaard
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01-29-2016, 01:56 PM
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Except the running clearance new is 2-3x the thermal expansion. And a worn in guide ( within limits) is 5-6x more clearance than the thermal expansion of the valve stem. So it is not possible to seize the stem in the guide.
The data I have doesn't say anything about a desired taper. Just cylindrical dimension. |
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01-29-2016, 02:38 PM
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valve
Hi.
The data is from this 964 / 993 engine repair manual: http://www.pcarworkshop.com/images/a/ae/AfterSales_Training_-_Air_Cooled_Engine_Repair_-_geolab.pdf Page 16. But the taper for the exhaust valve is the same 3,0 and up. Daugaard
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01-30-2016, 02:22 PM
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Daugaard
Thanks for the link, great info. |
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02-01-2016, 06:45 AM
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1969 and 1986 Porsche Targa and Coupe 1720cc and 3
The Other Woman
RS
SC
914
