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jimbauman's Avatar
 
Join Date: Mar 2005
Location: CA
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3.2 Carrera flywheel bolt torque ERROR

In the Dempsey book (2003 edition), page 139, the tork spec for the flywheel bolts is given as 120Nm, OR 88 foot pounds. The spec page on page 200 specifies 90Nm, or 66.3 foot pounds. This matches the Bentley book, so I assume the latter is correct.

BUT, I torked the flywheel bolts to 88 foot pounds. The threads on the last bolt I tightened started to collapse. So, after a little investigation, I noticed this error in the book (in a real BAD place!). So, I replaced the bad bolt with a good used bolt (I know...I know....). But, what about the bolts tightened to 88 pounds? Leave em alone, or loosen and retork to 66?

Help!!

Thx,

JB

Last edited by jimbauman; 09-03-2005 at 09:43 AM..
Old 09-03-2005, 09:38 AM
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They should be fine.
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Old 09-03-2005, 12:09 PM
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The factory is pretty good about calling out what bolts should be replaced. I haven't seen "replace flywheel bolts" in the factory manuals (until the 964 dual mass flywheel came along).
-Chris
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Old 09-03-2005, 06:51 PM
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I'm a little surprised that all of your bolts didn't hold up with the 88 lbs/ft (versus 66). I say that because on my 2.7 motors I routinely torque the larger (12mm) bolts to 150 lbs/ft despite a factory torque of 110. If you spin your engine above the factory redline with any frequency on these 70.4mm 6 bolt cranks you need the extra bolt torque or the bolts will back out. But I've never had that sinking feeling you get when something starts to give when torquing a bolt. I looked up the supposed max torque for these bolts (Maryland Metric had a chart) and it was around 137 lbs/ft.

My conclusion was that torque is set rather conservatively in most applications. MM's chart shows that for grade 12.9 10mm bolts, coarse thread max recommended torque is 98 Nm/72 lbs-ft, and for fine it is 104/76. So you are over, but not by a whole lot.

With your 9 bolt crank that issue seems to have been resolved, and one does not hear of the need for tricks to keep the bolts in place.

I am pretty sure the factory manual says to replace these bolts. If it didn't I suspect I'd be reusing mine (at least I would have before I started overtorquing them on purpose). A shop owner once told me he routinely reused these bolts on street motors, though, and had had no problems at stock torques. But because of the overtorquing I have a bag of them I try to use for other purposes less critical than the flywheel.

But perhaps Porsche decided that with the lower torque and the 9 bolts it was no longer necessary to replace these for the 9 bolt cranks?

Myself, having had one start to fail I'd be inclined to replace them all. Sure, having different torque on only one of 9 may not mean anything. And perhaps that one bolt was a hair off its nominal strength. But why take the risk? As I recall, buying 9 of these smaller bolts was less expensive than six of the 12mm ones for earlier cranks.

Walt Fricke
Old 09-06-2005, 09:16 AM
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