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Join Date: Apr 2010
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Head Bolts - Approx Breaking Torque?

The head bolts on my Boxster 2.5L are being *****es to take off. I know that installation requires a modest torque and then a total of 120deg of rotation. Does anyone have an idea of what the average breaking torque is required?

I've been using a 20" 1/2" drive breaker. I got two bolts to move 30 degrees (the amount I plan to move each bolt per pass in a reverse of installation order). After that I've broken two T-50 bits in a row.

I am considering the impact wrench route. Anyone have any luck with a particular rating on their head bolts? I'd like to go electric rather than pneumatic, but the highest electric torque is about 350ft-lbs and am wondering if that is enough. The bits could be the limiter, I'm not sure how strong impact bits are. Hopefully much stronger than the "standard" bits.

I guess in the end drilling out the bolt heads (since they must be replaced anyway) might be the answer to the really stuck ones.
Old 05-27-2010, 04:57 PM
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Wayne at Pelican Parts's Avatar
Nope, something is wrong somewhere. When we tore down the Boxster motor we had, the head bolts came off quite easily. I'm just guessing that maybe the Torx bits you're using are not strong enough?

-Wayne
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Old 05-27-2010, 05:04 PM
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I've talked to folks that have had to drill out their Boxster head bolts due to over-torque before. Going 120deg after a bolt is already tight is a helluva lot of torque (I estimate close to 300ft-lbs). My two bits were a Chinese harbor freight special (which twisted the bit so looks like a worm gear) and a Crafstman where the bit shaft shattered.

I guess I'll stop by HD and pick up a 300ft-lb electric impact (and impact bits) to see if that does the trick. If not - return - and pick up a 500+ ft-lb pneumatic. Failing that, drill baby drill!
Old 05-28-2010, 04:23 AM
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Snap-On Torx Bit "Accept no Substitute" & 17" breakerbar removed mine easily.
Old 05-28-2010, 06:23 AM
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Right. There is a time and place for Harbor Freight tools. Avoid using HF tools that require a lot of force, or lift things that you then are going to be standing under. Other stuff from them can be pretty good for basic tasks.

As for the torque spec, Porsche sets a lower torque setting and then says turn the nuts 120 degrees. This is a more accurate method of tightening bolts than a simple torque specification, which may be influenced by other factors (temperature, lubrication on the bolt, etc.) It doesn't necessarily mean that the bolts are in there tighter.

Here's a link to me removing the head bolts: Pelican Technical Article: Porsche Boxster / 996 Engine Teardown & Disassembly As mentioned previously, I don't remember them being difficult to remove.

Thx,

Wayne
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Wayne R. Dempsey, CEO, Pelican Parts Inc., and Author of:
101 Projects for Your BMW 3-Series 101 Projects for Your Porsche 911 How to Rebuild & Modify Porsche 911 Engines 101 Projects for Your Porsche Boxster & Cayman 101 Projects for Your Porsche 996 / 997
Coming in 2014:
101 Projects for Your MINI Cooper
Old 05-28-2010, 12:17 PM
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Old 05-28-2010, 12:17 PM
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