How to strengthen aluminum block threads.

[N7Quarian]

I have a 1999 BMW 328i and I was curious to know what could be done to strengthen the threads on the aluminum block. What would happen on these engines is that with F/I and an iffy tune the cylinder head would rise and rip the threads out of the block. (If using Arp hardware.) Now this can be avoided by lowering compression or getting a better tune.

People said to timesert the block. Can Cryotreating the block work?

 

[Kool1]

I've used ARP head studs on everything from my small block Chevys to my 22RE Toyota pickup. I've been told that the studs can actually pull so hard on the block when stressed that the line bore where the crankshaft rides can distort. I've always had the line bore checked when I rebuild my short blocks and haven't found the line bore off yet. I've never used a turbo or supercharger on these applications so I don't know if boost would create enough stress to cause problems. The blocks I'm using are cast iron so the threads have never been a problem but if you solve the potential aluminum block thread problem, think about the potential line bore issue that may also arise.

 

[default]

Helicoil or timesert.

 

[Cujet]

A long helicoil, or a series of them. Also, high temp loctited studs with very long reach and full thread engagement May help a bit.

 

[JDenyer232]

Originally Posted By: Cujet
A long helicoil, or a series of them. Also, high temp loctited studs with very long reach and full thread engagement May help a bit.


I agree, we sometime use helicoils in aluminum for this very reason. They make a helicoil that already has the thread locker on it. Just redrill, and retap, drive them in and you're done.

 

[A_Harman]

It's a lot cheaper to retard the spark than to lower the compression. Get rid of the iffy tune so you can drive your car with confidence. If you must add spark, keep it to 2 or 3 degrees. There is no good way to strengthen aluminum threads. The best aluminum threads are produced by roll-form tapping when the block is first manufactured. This work-hardens the material, instead of cutting it away. I've seen too many Helicoils pull out to ever be comfortable with them. Timeserts or Slimserts are better, but I would be surprised if you can find them long enough to replace the long thread engagement of the original block threads.

 

[N7Quarian]

http://store.vacmotorsports.com/vac---time-sert-kit-for-m52tu--m54-p2920.aspx

They do have the kit. And there is a guy on e46 fanatics running on boost 26psi I believe with stock cast iron internals. Mine are forged however.

http://forum.e46fanatics.com/showthread.php?t=993935

 

[1 FMF]

Originally Posted By: N7Quarian
I have a 1999 BMW 328i and I was curious to know what could be done to strengthen the threads on the aluminum block.


- use studs instead of head bolts
- use more fasteners holding the head to the block
- increase the diameter of the holes in the block if possible, it's the diameter of the thread that gives you the holding power. putting an insert of harder material into the holes in the block doesn't necessarily give you more holding power, if you're ripping the old fastener out of the block then you might also rip an insert out of the block also unless the diameter of the insert is significantly larger.

- you might be incorrectly over-torquing the fastener holding the head to the block causing damage to the threads in the block and that's causing them to let go. especially if the fastener is a different and harder material than the aluminum block. i find it a little hard to believe that so much cylinder pressure is being made to actually push the head off the block. the only time i know of that happening sort of is on diesels like the duramax where guys modify the computer to gain more power, and they end up blowing the head gasket first because of the increased cylinder pressure (and gm caught on to this which is why any gm truck running any kind of bullydog or other programmer automatically voids warranty). On your bmw you also might simply be exceeding the design of the motor if the block has fewer holes for cylinder head bolts, i don't know bmw so i'm speculating. and you mentioned forced induction and iffy tune, if that were the case then i would expect broken pistons and rings and blown head gasket first.

 

[A_Harman]

Studs are a good solution because more of the torque that you apply to the nuts goes into actual clamping force on the head. Since studs do not turn in the block threads, there is no loss of load due to friction down there. Any steel used in a head bolt is going to be harder than the aluminum in a block thread. There is a limited number of times that the head bolts can be torqued onto an aluminum block before the threads start to fail. Probably about 10 times before you start pulling threads out of the upper part of the bolt holes, then it's all downhill from there.

Adding fasteners is good, but selection of the location for these fasteners is very difficult in an engine that has intake ports, exhaust ports, water passages, and oil passages. If you do find a place on the cylinder head deck to put more bolts, chances are that you will create water leaks.

Drilling and tapping for bigger bolts is a good way to get more clamping force, but this may be unsuccessful if there is not enough boss material in the head and block to accommodate the larger bolts.

 

[N7Quarian]

My engine has been up to 250 degrees once before I shut it off. Is the block ruined? I consume NO oil and NO coolant.

 

[The_Eric]

Very doubtful.

 

[Merkava_4]

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