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951, head pulled off finally to find a chipped piston
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#1
08-04-2010, 11:38 AM
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951, head pulled off finally to find a chipped piston
I finally got around to pulling the 951 head off and getting ready to put the spare head on. When I pulled the old head off I saw that the first cylinder piston has a small fingernail sized chip / dent in it from where the valve came in to contact with it. Does this need to be replaced or can I get away with using it? Im expecting the worst. I can shoot some pics when I get home this evening.
Greg
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Greg "Procrastination is like masturbation, your only screwing yourself" -CURRENT- 00 Jeep Cherokee Forest Green/Grey, Lifted 4.5", 31x10.5x16s 86 951 Guards Red/Black - Running, but leaking boost -PAST- 91 Jeep Cherokee Flat Black/Grey, Lifted, ticking, and leaking - Traded 78 Yamaha XS750 Special - SOLD 78 924 blue/black - gone 83 944 Guards Red/Brown - gone 84 944 Guards Red/Black - SOLD 
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#3
08-04-2010, 01:37 PM
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Check the valve. If bent, even ever so slightly, it won't seal on the seat. Can use bright light, liquid, air pressure, etc to check (often in combination.) Can even try to relap the valve to the seat and look at the pattern.
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Stephen www.salazar-racing.com 1970 914/6 - 3.0L GT 1983 911SC - 3.32L IROC 1984 930 - 3.6L dirt bikes (some gas, some electric), Sherco trials bike Sold: 2001 Boxster (hers), 2003 996tt x50  , SpecE30, 1996 E36M3 GTS2 racecar, 2015 Mustang GT, 2008 S2R1000
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#4
08-05-2010, 07:47 AM
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Yes, the reason i am taking the head off is because I bent a valve. I have a replacement head with good valvles in it, so I just wanted to be sure nothing catastrophic would happen due to the chip in the piston. ill shoot a pic tonight, didnt get home til 10 last evening and went right to bed.
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Greg "Procrastination is like masturbation, your only screwing yourself" -CURRENT- 00 Jeep Cherokee Forest Green/Grey, Lifted 4.5", 31x10.5x16s 86 951 Guards Red/Black - Running, but leaking boost -PAST- 91 Jeep Cherokee Flat Black/Grey, Lifted, ticking, and leaking - Traded 78 Yamaha XS750 Special - SOLD 78 924 blue/black - gone 83 944 Guards Red/Brown - gone 84 944 Guards Red/Black - SOLD
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#5
08-05-2010, 08:23 AM
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Is it a dent from the valve edge (i.e. smooth indentation) or an actual chip (meaning piston material has come off)? If just a dent, it should be OK to re-use, but I wouldn't use a chipped piston.
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Jerome Welte '97 Spec Boxster '20 Nissan Titan XD '02 BMW 330i convertible
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#6
08-06-2010, 11:46 AM
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yes it is a dent from the valve edge, it seems to only be on cylinder 1 and not 4. it looks like it has just been marred, not like a piece cracked out of it or anything like that.
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Greg "Procrastination is like masturbation, your only screwing yourself" -CURRENT- 00 Jeep Cherokee Forest Green/Grey, Lifted 4.5", 31x10.5x16s 86 951 Guards Red/Black - Running, but leaking boost -PAST- 91 Jeep Cherokee Flat Black/Grey, Lifted, ticking, and leaking - Traded 78 Yamaha XS750 Special - SOLD 78 924 blue/black - gone 83 944 Guards Red/Brown - gone 84 944 Guards Red/Black - SOLD
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#7
08-06-2010, 04:51 PM
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Depending on the hit I would check for a bent rod.
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http://vimeo.com/29896988 “Those that can make you believe in absurdities can make you commit atrocities.” Voltaire. "There is grandeur in this view of life...." Darwin. The mountains are calling and I must go. “The earth has music for those who listen” Shakespeare. You Matter. (Until you multiply yourself times the speed of light squared. Then you Energy) “We’ve got lots of theories, we just don’t have the evidence’.
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#8
08-07-2010, 10:47 PM
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FWIW, I had two valve hitting piston occasions when my 951 was turbo powered, one of which left a large smiley on the piston. On both pistons I used emery paper to smooth the edge of the indent while the shop vac was sucking next to the "smiley" There were no ill effects caused by the dent or repair.
While I agree with Kurt 99.99% of the time, the valves head will bend into submission before a rod is damaged as will the piston head. I do agree with Jerome about the chip vs indent. Marc
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'05 Mustang GT '08 E350 '06 LR3 '86 951 LS1 (C-2) Gone '77 911 3.2 (C-1) Gone  3.2 Conversion and 915 Rebuild Home Page The 958 Conversion
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#9
08-08-2010, 10:56 AM
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Having a small dent or dents on the top of the piston won't hurt a thing. Bent other stuff might. The texture of the piston top could effect intake/exhaust if it was heavy texture. Lots of pistons have recesses in them and I think some have experimented w/ more general textures on the piston top.
I once ran a 400 KTM single cyl. (4 stroke) motorcycle whose piston's top was covered in a bunch of small dents from a broken piston ring bouncing around. We fixed/replaced/rebuilt what was required but reused the otherwise undamaged piston - new ones were $$.The bike ran great - we used to joke that it was faster w/ our "trick" piston! SRG
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