Shouldn’t head bolts all be the same?

[thejimlab]

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?

[15Michaeljoseph]

About all I can say is it's definitely not factory... Sent from my moto g(6) using Tapatalk

[roguetoaster]

I think all of the hex head bolts were superseded by torx fasteners, but as to why they are that way, probably laziness by whoever swapped the head. Is it running well, no HG leak or stop leak residue in the coolant system?

[whodwho]

As mentioned above those were superseded by the Torx version back ~1990.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..

[AndrewBird]

As mentioned above those were superseded by the Torx version back ~1990.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..

This right here. That is a ticking time bomb (literally if you haven't adjusted your valve clearance lol).

[ZeeVaughn]

I have a set of OEM headbolts brand new in packaging that I ended up not using for my build because I went with arp studs. If you’re in the U.S. I’ll flat rate them to you free of charge.

[TobyB]

Oh, just- ouch...

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[e30strokr]

correct ,me if im wrong... you should be able to change the individual bolts without doing a full HG change.. ...

[ForcedFirebird]

correct ,me if im wrong... you should be able to change the individual bolts without doing a full HG change.. ...

Correct. That's how they were done when the bolts were recalled. I have swapped out many engines to ARP studs this way, never had an issue.

[Andre3127]

You can replace the bolts as long as you only replace one at a time. I would upgrade to metric blues while you're at it, even for a stock motor.

[ForcedFirebird]

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.

[digger]

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 there

[ForcedFirebird]

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 there

I stand corrected. 12.9 is the OE and blue bolts. Either way, I agree - BMW stopped using rigid fasteners for a reason (nearly every auto maker did, actually).

[digger]

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 nightmare

[ForcedFirebird]

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.