N52 Valve Cover Gasket Alum Bolt Installation Sequence & Method

[basuni90]

Hello all,

I decided to save some money and am planning on replacing my valve cover gasket (got a broken bolt) this weekend on my '06 z4 3.0i. I've done a good amount of research on this already but still have a couple questions regarding the installation of the aluminum bolts:

1. I was told however by my local private german auto shop that there is a sequence to be followed on installing the bolts on the gaskets. Does anyone know of this sequence?

2. I also have read that the bolts are torqued to 7 Nm. But then there's this method of doing a 90 degree tightening? Can someone provide some further explanation on what this is exactly?

Thanks in advance!

[dc_wright]

Here's a decent DIY on this task. The bolts are torque to yield and are one time use only. The torque values are the initial torque value, then after you've set them to that torque, let them rest for 30 minutes or so, then verify the torque, and finally turn them an additional 90 degrees.

[basuni90]

Originally Posted by dc_wright

Here's a decent DIY on this task. The bolts are torque to yield and are one time use only. The torque values are the initial torque value, then after you've set them to that torque, let them rest for 30 minutes or so, then verify the torque, and finally turn them an additional 90 degrees.

Ok thanks! And was it only one additional 90 degrees or two?

[dc_wright]

Originally Posted by basuni90

Ok thanks! And was it only one additional 90 degrees or two?

One additional 90 degrees.

The initial torque puts the bolts in tension and stresses the molecular lattice of the aluminum. It will settle a bit after a rest period, which is why you verify the torque after the rest. The 90 degree final turn takes the bolts into the yield strength stress on the aluminum which gives a consistent tension on each of the bolts. Going further takes the aluminum into ultimate tensile strength forces which is where you have snapped them in two.
Because you take the bolts into the yield strength region you can only use them one time. If you try to reuse them, you'll find the ultimate tensile strength has come down and you risk either snapping them when you do the final 90 degrees or having them fail on their own the first couple of heating/cooling cycles of the engine.

[basuni90]

Originally Posted by dc_wright

One additional 90 degrees.

The initial torque puts the bolts in tension and stresses the molecular lattice of the aluminum. It will settle a bit after a rest period, which is why you verify the torque after the rest. The 90 degree final turn takes the bolts into the yield strength stress on the aluminum which gives a consistent tension on each of the bolts. Going further takes the aluminum into ultimate tensile strength forces which is where you have snapped them in two.
Because you take the bolts into the yield strength region you can only use them one time. If you try to reuse them, you'll find the ultimate tensile strength has come down and you risk either snapping them when you do the final 90 degrees or having them fail on their own the first couple of heating/cooling cycles of the engine.

Great, appreciate the advice dc_wright.

Now, anyone have any info on the installation sequence?

[pokeybritches]

I haven't seen what's in the DIY, but on my Jeep you start in the middle (cyl 3/4) and work your way out. Something like 3/4/2/5/1/6.

[Forbes]

Damn! I did a VCG replacement 9 months ago and before I read this. Then I only did the initial torque down. Next time I'll do it right.
I had a leak free car for 8 months or about 10,000 miles. The new leak is at the center point of the exhaust side. I'm currently losing about a quart every 5-6 fill-ups, so this probably isn't super urgent.

My z4 3.0i is a dd with about 110,000 miles on it.
I did the spark plugs and all valve cover gaskets at 100,000 and everything else looked good then. And except for the obvious leak everything still does look good on the outside.

All else being equal, I didn't follow the proper torquing procedure as outlined in this thread.

Does anyone think I need to consider anything else when redoing the VCG, such as replacing the valve cover itself?

Otherwise:
center bolts first,
star pattern around the edge starting at the middle of each side
torque to 7nm;
wait 30 minutes,
verify torque is 7nm,
turn an extra 90 degrees (1/4 turn).

(also adding 90 degrees to vanos motor bolts torqued to 4nm)

[Forbes]

So I resealed my valve cover a couple days ago. I had replaced the gasket about 9 months ago because it was leaking then. My earlier replacement lasted about 7 1/2 months before it started leaking again. I followed this Youtube video to the letter. The guy's camera angles and dialogue are very good. But he didn't mention the extra 90 degrees.
Anyway, so when I resealed it a couple days ago, I found 4 bolts were loose. I redid everything rather than just re-torquing the bolts. It went much, much easier the second time.
And I now have a greater appreciation for the Z4. Watching videos of a 3, 5 or X series,..those cars are much bigger, but you can't see the engine unless you take off a shtload of stuff. Mine, I just take off the strut brace and I'm ready to go.
Now, however, I'll be up at night thinking that maybe I tightened the bolts too far and they might snap. My torque wrench isn't the greatest... I'm guessing Ill be into the VC again in the next few months.

[inTgr8r]

7nm isn't much force.

FWIW, when dealing with such low torque values its very easy to blow right past the torque wrench 'click'
I practice a few times to get the feel of it by using the torque wrench on a bolt that is already tightened to a value larger that your setting.

Once I have a feel for it, I make an initial 'snug' pass on the bolts at less than torque required following the proper sequence.
Then a second pass to the torque value.
And then the rest of the normal proceedure called for ; rest, re-torque, angle torque as required.