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flaps10 · 01-20-2015, 02:37 PM

78,
The continuing myth of CNC machinery is that it's more accurate than conventional machinery. All the "computer" side of the equation gets you is the ability of F up a whole pile of parts as effortlessly as a conventional machine scraps out just one.

Precision and accuracy (two different things) are still a product of machine rigidity, set up and the condition of the machine tools (cutters, drills, boring bars,etc).

I'm not a fan of the choice Porsche made to run cams right in the aluminum head without any form of bearing, and much less enthusiastic about their choice to use the cam cover as the outer bearing half. It is light, simple and cheap (to produce) however.

When they bore a head and cam cover as an assembly it doesn't really matter much if the centerline of the bore is off, say 0.005" from another head in the pile. But if you grab a mismatch set of head/valve cover and they have a 0.005" difference in the location of that bore it is a 0.005" step, and the running clearance on the cam shaft is WAY less than that (I think I saw Jake post that 0.0015" is his limit)

Props for offering up the piece though.

I'm with JFP. Suck it up and take it to a machine shop. It won't be that expensive to do a proper repair and save the valve cover.

Oh, and the M96 may have a "few" short comings but you can build up a pretty nice M96 with way less problems than the original engine and it will be cheaper than doing a full conversion using a Subaru or LS by the time you do it correctly and get the bugs worked out.

01-20-2015, 02:37 PM	#8
flaps10 Registered User Join Date: Jul 2014 Location: Tacoma Posts: 430	78, The continuing myth of CNC machinery is that it's more accurate than conventional machinery. All the "computer" side of the equation gets you is the ability of F up a whole pile of parts as effortlessly as a conventional machine scraps out just one. Precision and accuracy (two different things) are still a product of machine rigidity, set up and the condition of the machine tools (cutters, drills, boring bars,etc). I'm not a fan of the choice Porsche made to run cams right in the aluminum head without any form of bearing, and much less enthusiastic about their choice to use the cam cover as the outer bearing half. It is light, simple and cheap (to produce) however. When they bore a head and cam cover as an assembly it doesn't really matter much if the centerline of the bore is off, say 0.005" from another head in the pile. But if you grab a mismatch set of head/valve cover and they have a 0.005" difference in the location of that bore it is a 0.005" step, and the running clearance on the cam shaft is WAY less than that (I think I saw Jake post that 0.0015" is his limit) Props for offering up the piece though. I'm with JFP. Suck it up and take it to a machine shop. It won't be that expensive to do a proper repair and save the valve cover. Oh, and the M96 may have a "few" short comings but you can build up a pretty nice M96 with way less problems than the original engine and it will be cheaper than doing a full conversion using a Subaru or LS by the time you do it correctly and get the bugs worked out. Last edited by flaps10; 01-20-2015 at 02:41 PM.