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Registered
Join Date: Jul 2005
Location: Cleveland, OH
Posts: 1,371
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964 head machining... Chain box compensation?
At what point do you need to compensate for head sealing surface machining by shortening chain box or installing using sealant vs gasket?
Also, what is the thickness of this first fin area on factory 964 heads? ...pic is 930 head, didn't have shot of 964 one. 
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12-09-2009, 08:34 AM
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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
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One solution is the oversized idler arm gears Jerry Woods sells to take up the slack.
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 |
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12-09-2009, 08:51 AM
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Registered
Join Date: Jul 2005
Location: Cleveland, OH
Posts: 1,371
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Concern box being too "long" for cam loc'n.
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12-09-2009, 10:59 AM
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GAFB
Join Date: Dec 1999
Location: Raleigh, NC, USA
Posts: 7,842
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A bit of a judgment call, but yes, eventually the cam will be out of center in the chain housing aperture, and you will have difficulty sealing the cam. I have done a couple engines with 1mm off the heads, with some extra shim on the cylinders to take up some slack. I think I ended up getting something like .25 to .50 taken off the chain housings. The cams were still offset ever so slightly in the housings, but both engines sealed fine and both have thousands of miles on them.
The Weiners and Schmidts of the board will have much better experience than me, but I'd say .5mm offset would be too much.
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Several BMWs |
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12-09-2009, 11:12 AM
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Join Date: Nov 2004
Posts: 219
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Is there anyway to measure if the machine boxes have been machined?
Bill |
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12-09-2009, 12:37 PM
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Certified User
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Quote:
Can't get at it to measure for you at present, but pictures of an un-molested head might help ... .    
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Bill 1988 Carrera - 3.6 engine with ITBs, COPs, MS3X 2024 Macan S Day job ... www.jesfab.com.au Memories: '68 912, '72 911T, '80 911SC, '84 911, '85 930, '86 930, '87 911, '21 Macan S |
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12-09-2009, 03:09 PM
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Registered
Join Date: Jul 2000
Location: So. Calif.
Posts: 19,910
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Seems like the chain box is in the same vertical stack alignment as the cylinders and cylinder heads. Therefore, I'd trim the chain boxes an equivalent amount as taken off of the cylinders/cylinder heads to re-establish the cam position within the chain box center line.
Using a larger camshaft idler sprocket only compensates for the increased slack of the timing chain when the stack height is reduced. There's still the camshaft to remain centered in the chain box opening. Sherwood |
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12-10-2009, 10:58 PM
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XBJ-930
1988 Porsche 911 Carrera
3.6 conversion
