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Head studs/nuts or bolts


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So you learned lot , what’s the benefit to using head studs over the factory bolts if any ? Do you have to replace them every time you remove the head as with factory bolts ? Reason I’m asking is I’m fitting an m57 to my 110 and head bolts need to be replaced when you remove the head , as I do to get the glow plugs drilled out , I will be upping the power on it from stock as well  . 
Cheers Ian 

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When you screw in a bolt the tension is applied as the bolt screws in. There may be friction on the bolt from what it passed through. In an Ali block, you may chew the top of the thread, which to grip Ali has to be reasonably coarse. With a stud, the stud can be screwed right in with no tension, and helps locate the head. The top end that applies the tension can have a finer thread, and the nut can be longer than normal if need be, and made of strong stuff. Why not always do this then? Slower production, and can make removing parts difficult as sufficient clearance has to exist to get the part off the studs.

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Older vehicles with cast iron heads & blocks nearly always had studs & nuts, but alloy head engines seem to favour bolts instead, maybe the clamping force is higher with bolts & alloy head. 

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I think too, the tools that fit the head in factories improved and with torque to yield bolts they could get get a well defined clamping pressure - and of course faster and not needing to be re-torqued. But, if I was building a V8 I would want to use head studs. In a pinch a stud can also get you out of a problem by using a section of tapped hole further down beyond what a bolt might have previously chewed up, ie a previously unused bit of thread. 

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All that cackshifter said - it would cost more in production as it's two/three fasteners (stud, bolt, and a washer) not one bolt, but it is kinder to the aluminium block and AFAIK the studs don't stretch so are re-usable (ARP's info would confirm/deny this)

I've got the same setup on my exhaust manifolds too, they're aftermarket Mini parts, 3/8"UNC into the block and UNF with a brass nut the other end, much loveliness and cheap enough.

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If you do change to studs (my recommendation also) just make sure you will still be able to remove the heads from the engine with the engine in the vehicle - in some circumstances the heads may not fit over the studs and clear the body.

Garry

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The problem garry col mentioned above I alluded too as well. There is a dirty fix especially if it is just one or two studs that are causing the problem, and that is to get them out before attempting to remove the parts, like you would a bolt. 

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Similar with the exhaust manifold studs - if they're too long you can find you can't get the manifolds in over the studs near the bulkhead, also if the un-threaded section is too long you can't tighten them down properly, but it's easy enough to spot once you know and not hard to work around.

The ARP head studs have hex key holes in the top to wind them in/out and once the nut's undone there's no tension on them so they should wind out fairly easily.

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Before you swap to studs, they aren't always better. I know this isn't one, but take the Cummins crowd, mostly stateside they love to swap the original bolts out for studs, but ARP studs are utterly pointless in that application (steel block) until you're pushing the limits of block integrity. I can't remember the exact details but a chap in the Cummins LR group was part of the team developing the 6BT and it was something like ~900-1000bhp before the cylinder pressures started lifting the heads.

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Cheers all for the replies, mines one of the earlier  m57’s with a cast block , aluminium head . Do you think studs or bolts would be better ? Tuning could go up to 250bhp , after Ross’s comment I’m not sure whether it’s worth spending £360 on studs , I have read that the cast blocks are more solid than the later Ali ones .

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Yes that’s what I was thinking, they reckon the older engines won’t go above 250bhp because the turbo holds them back so possibly not at the end of there power . I’ll have a nose around the BMW forums but thought I’d ask here first as we have a lot of very knowledgeable people on here .

 They were never fitted to the Range Rover version of the engine cackshifter, which I have so that’s one less job to do.

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£360 is a lot of cash, ISTR a set of ARP's for the Rover is about £80 so a no-brainer. As others say, I'd look at the BMW tweakers see if they're recommending it, some engines can have weak spots and others will take big power with minimal trouble.

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