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Join Date: Mar 2011
Posts: 598
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Query regarding bent exhaust valves?
If a SC motor previously had bent exhaust valves, and the engine builder ONLY replaced the exhaust valves, is that a bad thing?
Wouldn't they also replace the pistons too? Would the pistons be damaged at all as a result of touching the valves? What about damage to the heads? Could compression be affected in any way! Just curious 
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11-17-2011, 09:47 PM
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Unless the piston was severely damaged it would not be necessary to replace it, simply being nicked by a valve would not cause concern to me.
Probably no damage to the head valve seats either, if there was it could of easily been repaired simply when lapping in the new valves. Unless a significant chunk of metal had been removed from the damaged piston it would not effect compression. The truth is told by way of a compression test or a leak-down test by a trusted, competent, recommended mechanic, they can also look at the inside of the cylinder and check your piston for damage. What causes you to be curious, does your engine feel under-powered or is it hard to tune?
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78’ SC 911 Targa - 3.2SS, PMO 46, M&K 2/2 1 5/8” HEADERS, 123 DIST, PORTERFIELD R4-S PADS, KR75 CAMS, REBEL RACING BUSHINGS, KONI CLASSICS |
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11-17-2011, 10:08 PM
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Thanks Shane. No, this is not my car.
This is a car my friend is looking at buying. He asked for the top end rebuild invoice to see what was done by the PO, and it showed bent valves were identified and all were replaced. It's a really nice looking car, so we are hoping it's still worth buying despite this previous damage. He will get a comprehensive PPI done with leak down and compression test too. Fingers crossed. Apparently the car runs fine, no smoke etc... Having said that, He is planning to do a top end rebuild anyway, so I guess whatever he finds, he will fix up. He's also going to fit ARP fasteners throughout too. Last edited by 911TT33; 11-17-2011 at 10:28 PM.. |
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11-17-2011, 10:24 PM
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abit off center
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I hope they replaced the guides too.
Sent from my iPhone
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______________________ Craig G2Performance Twinplug, head work, case savers, rockers arms, etc. |
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11-18-2011, 10:04 AM
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Join Date: Oct 2003
Location: Central Fla
Posts: 1,864
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Valves
Inquire as to when it was done, and what caused the problem, Its not a common thing on an SC with all things being normal. But think about a track event or auto cross where you get the 4th to 1st mishift and it bends valves breaks rockers etc.. and just fixed the obvious damage but dinged a rod bearing or stretched a rod bolt during the over rev and all of a sudden a few miles later spins a bearing.
Mike Bruns JBRacing.com
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The two most useless things to a driver are the braking distance behind you and nine-tenths of a second ago. |
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11-18-2011, 02:04 PM
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Quote:
 Looks like they just replaced all 6 exhaust valves and ground in all the valves. They also replaced the CAM sprockets. I suppose the valve guides were OK?! Mike, apparently it was caused by a mis-shift into 3rd gear, instead of 5th which cause the over-rev! OUCH! BTW, the top end was rebuilt approx 44K miles ago, back in 2000. There's ~95K miles on the Odometer. Last edited by 911TT33; 11-18-2011 at 06:11 PM.. |
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11-18-2011, 06:07 PM
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Stella
1969 and 1986 Porsche Targa and Coupe 1720cc and 3
