Head Bolts

[Langers]

I've been doing a bit of reading, and it seems that the head bolts on these cars are rather fragile. The link I have posted, however, is not clear on how to tell whether the bolts have been replaced or not. One person says that if the bolts look as though they will take a hex head they are fine, whilst another says that if it looks like it will take a hex head, replace them ASAP.

Anyone know for sure?

Pictures? (Wayne? Should be somewhere in your book)

Thanks in advance

[Jared at Pelican Parts]

BMW reccommends that you upgrade the head bolts to the Torx style head if they have not already been changed. I performed this on my car about three months ago. With the head still on the mtoor, just replace them one at a time and you'll be ok.

[Jared at Pelican Parts]

Pelican can supply you with these bolts. Keep in mind that the ealier hex head bolts become brittle over time. One day i was driving home when all of a sudden I head a loud "PLINK" from under the hood, then there was this wierd vavle noise, I immediatley pulled off the valve cover to find that one of the hex heads had broken off the bolt and was flying around indside the valve cover. Thank god it didnt get under the camshaft, or It would have cracked it. I changed all the head bolts the next day.

[Langers]

Aah thankyou very much for your help, you must have ESP, I was going to ask whether they could be replaced one at a time to save the head gasket but you got there before I even asked. Great service!

[Jared at Pelican Parts]

Just keep in mind that BMW has a odd way of torquing them. You need to first torque the bolt to 22 ft/lbs, then turn the bolt exactly 180 degrees. I would reccommend also staggering the sequence in wwhich you do the bolts. for instance start with the frontmost intake side, then the rearmost exhaust side, then the rearmost intake side, etc.. This will help relieve pressure on the head gasket.

[pianodan]

I'm starting to see more and more of the "torque to yield" kind of installations.

BMTroubleU uses the...

Give them all a 22 Foot pounds of torque, then...
Go back over them with a "Stage 2" torque of 90 degrees, then...
Go back over them with a "Stage 3" torque of another 90 degrees.

My helicopter has several items that require a 30, 60, 90 inch pounds setting, but not a combination of inch pounds AND degrees.

Dan

[Jared at Pelican Parts]

Im not even really sure why they have these types of settings. seems to me that the composition of the bolt would not vary enough to actually require this. And besides if the bolts were of a metal that flexed that much, wouldn't you not want to use them in the first place?

[pianodan]

I'm not so sure it's a matter of bolt metallurgy (it WAS in the beginning, prompting the need for a batter grade bolt, hence the TORX type head, to distinguish from the old stock), but, rather the expansion coefficient of the aluminum head when heated. The amount of repeditive expanding and contracting (when cool), tended to cause fatigue in the old bolts.

If I was a betting man, I'd bet that the engineers said .. "lets get a Grade 8 bolt, set a tare, or running torque as a baseline, and find a good happy medium of "goodentight" and see how the head holds up after many cycles of this expansion thing.

The old adage of "let's use some German torque, which is defined as tighted down till the bolt smokes, then back it off one flat," may have some basis of truth, after all.

"Torque wrench?... Don need no steenkin' torque wrench....."

Dan

[Jared at Pelican Parts]

Piano,

Thanks for the info. I was not aware of that. Im glad to hear that they at least dont use these bolts on helicopters. Can you imagine what cars would be like if they built them to aircraft standards?

[pianodan]

Yep. Helos use VERY expensive, critical dimension, one time use hardware. The rotating bolts (on the rotor head),have serial numbers and lot numbers and get changed every 600 flight hours, no matter how good they look.
Dan