It’s an 88 325 produced 12/87. I’m replacing the timing belt and upgrading to motronic 1.3. There’s 2 different types of head bolts. It also has double valve springs. What gives?
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Shouldn’t head bolts all be the same?
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As mentioned above those were superseded by the Torx version back ~1990. The Hex head version were known for the head of the bolt breaking off and bouncing around like a pinball game until it got under a cam lobe and destroying the head.
Those have obviously been reused and even more prone to breaking. Get a new set of headbolts and change them out one at a time(blow out the hole when you get a bolt out), it is much cheaper and easier to do then replacing the head. I would also change them all out as I would question whoever would do a such of a repair would have torqued them correctly..
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Originally posted by whodwho View PostAs mentioned above those were superseded by the Torx version back ~1990. The Hex head version were known for the head of the bolt breaking off and bouncing around like a pinball game until it got under a cam lobe and destroying the head.
Those have obviously been reused and even more prone to breaking. Get a new set of headbolts and change them out one at a time(blow out the hole when you get a bolt out), it is much cheaper and easier to do then replacing the head. I would also change them all out as I would question whoever would do a such of a repair would have torqued them correctly..
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Originally posted by e30strokr View Postcorrect ,me if im wrong... you should be able to change the individual bolts without doing a full HG change.. ...
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Metric blue aren't really an upgrade as they are just grade 10.8 fasteners - just like the original OEM hex bolts were, and like ARP need to be re-torqued after heat cycling (non-stretch bolts). The external Torx fasteners are stretch bolts and continue clamping after the head gasket has compressed to final thickness.
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Arent metric blue 12.9 grade? nevertheless the higher grade are not needed on a NA m20. Personally i'd not use cheap coated 12.9 grade bolts though for something like this as there's a bunch of things that can go wrong if the QA/QC isn't there89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...
new build thread http://www.r3vlimited.com/board/showthread.php?t=317505
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Originally posted by digger View PostArent metric blue 12.9 grade? nevertheless the higher grade are not needed on a NA m20. Personally i'd not use cheap coated 12.9 grade bolts though for something like this as there's a bunch of things that can go wrong if the QA/QC isn't there
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the OE are 10.9, so 12.9 the blue bolts are stronger. Most OE use whatever methods that are easiest and most consistent to control in a mass production environment. None of the fasteners are rigid, all rely on stretch to provide resistance against loosening its just a question of how much and the process to arrive at it.
With a Metric blue or ARP style that is tightening to around ~70% +/- yield you are going to have to periodically re torque if you use a OE/OEM composite gasket, with an MLS there is not really a need as the relaxation is far less. On some newer engines having to retorque head bolts after heat cycling is a nightmareLast edited by digger; 01-20-2020, 05:27 PM.89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...
new build thread http://www.r3vlimited.com/board/showthread.php?t=317505
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I actually went and looked at an OEM hex head bolt before posting. I have a box of them that have accumulated over the years. Clearly have ”12.9" stamped on them.
Correct. With ARP it any other rigid fastener, graphite/composite gaskets require retorque. This applies to the m30, s14, and many early m20's. It wasn't until about 1990 iirc that the bolts changed to torque to yield.
Yes, penny pinching and assembly time are a big factor when you are making 2 million cars. TTY bolts make the assembly process automated. A machine can spin all the head bolts at the same time 180° (90°+90°) vs having to heat cycle and retorque.
Also, yes, MLS gaskets won't compress like a fire ring made of sheet metal rolled around graphite.
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