Aluminum bolts...why?

My old man rant of the day.

What is the advantage of using aluminum bolts?

PRO : less weight

CON: more expensive

Can only be used once

Break easily

Often break when the 2 parts being held togther expand due to heat.

I don't understand. I see these used in varoius applications from bellhousings to valve covers.

For aluminum on aluminum action, better to mess up the bolt than the aluminum piece it's threaded into.

I just hate that they're not magnetic because I drop carburetor screws all the time.

Another advantage is thermal expansion doesn't change preload.

Its probably bolting onto a magnesium alloy.

Slippery said:

Its probably bolting onto a magnesium alloy.

This is why BMW does it as I understand it.  If you buy some parts that work on N52 and N54, it will come with both aluminum and steel bolts.  Magnesium block gets the aluminum bolts, aluminum block gets steel.

Tyler H said:

Slippery said:

Its probably bolting onto a magnesium alloy.

This is why BMW does it as I understand it.  If you buy some parts that work on N52 and N54, it will come with both aluminum and steel bolts.  Magnesium block gets the aluminum bolts, aluminum block gets steel.

Meanwhile, VW used steel bolts into magnesium blocks and magnesium valve covers and didn't have issues.

Aluminum bolts create more issues than they solve, IMO.  And I am the resident defender of wheel bolts and Torx fasteners.

My 924 had aluminum lug nuts.  First thing I had to replace for track days.

There are places I use them and places I don't. Same with nylon bolts.

My two-part test on what fastener material to use:

1. How likely is <material> to fail in this application?

2. How berkeleyed am I if it does?

Well... similar to "torque to yield" bolts.  Germans seem to love those.  Every time I did a timing belt change on my TDI, the kit included all new bolts for most fasteners.  The pack-rat in me always felt weird throwing away a dozen bolts, but they were such specific bolts, even I could see no reason to keep them. 

Ian F (Forum Supporter) said:

Well... similar to "torque to yield" bolts.  Germans seem to love those.  Every time I did a timing belt change on my TDI, the kit included all new bolts for most fasteners.  The pack-rat in me always felt weird throwing away a dozen bolts, but they were such specific bolts, even I could see no reason to keep them. 

I'm told that in some cases, German parts come with replacement bolts not because they're TTY, but because the bolts have the requisite amount of thread locking compound pre-applied.  I guess they don't trust the mechanics to use a bottle of loctite properly?

In reply to codrus (Forum Supporter) :

Possibly, but VW didn't use those on the ALH.  These bolts are those types where you torque to a value and then add additional degrees of rotation.  Also called torque-angle.  If I still had the TDI, I would have bought one of the newer torque wrenches that can also do additive angles, since it most of these applications you can't get a full swing of the degrees specified.