Headbolts - Is there a difference?

[FinalD]

Right so tonight I've removed the head to replace the gasket (precautionary for the most part but also to cover myself due to idiocy earlier) and until I'd taken it all apart I didn't bother to open the box of new head bolts.



Is there a difference between the two types of bolts? The old ones are the usual hex bolt head type (on the right) and the new ones are the star head type (on the left). Both are the same length and I obviously reuse the washers but I'm just wondering if I can/should use these bolts or if I should send them back and find the right ones?

The car is a 1988 325i Cab with the facelift engine.

[Brianmoooore]

Those hex bolts should have been removed and replaced by the torx version years ago!
Some of the hex. headed bolts used by BMW are defective and it's common for a bolt head to break off, potentially reeking havoc under the rocker cover. There's no way of identifying the faulty bolts, so the only solution is to replace them with the (single use) torx. headed bolts, which are of the stretch variety.

[daimlerman]

Throw those old hex headed bolts as far as you can.
You are lucky that one,or more,has not snapped and ruined your cylinder head.

Follow the torque procedure that came with the new torx bolts to the letter.I do not use a dial gauge to measure angles,rely on my judgement to gauge 90 degrees.

[Topblag]

The best ones to use are the Torx headed bolts, I believe they are less likely to shear when they are being removed.

[FinalD]

So by doing the 'replace gasket, also replace headbolts' thing I have unintentionally done the right thing by getting some sensible bolts? Good to know, guess I better crack on putting it all back together again.

[daimlerman]

So by doing the 'replace gasket, also replace headbolts' thing I have unintentionally done the right thing by getting some sensible bolts? Good to know, guess I better crack on putting it all back together again.

We all hope that you have had the head surface skimmed as well!

[Brianmoooore]

Follow the torque procedure that came with the new torx bolts to the letter.I do not use a dial gauge to measure angles,rely on my judgement to gauge 90 degrees.

After the initial torquing, mark a line on the head of each bolt with a permanent marker. This will give a good indication as to whether you have turned each bolt through the subsequent 90 + 90 degrees, and, more importantly, make it obvious if you've missed one.

[FinalD]

Now you're asking too much (re head skimming).

The engine runs/ran fine, I'm just changing the gasket because when I was putting the timing belt on I knocked the cam out of alignment with the crank and couldn't find the TDC marks on the head. I removed the head, found the TDC marks and made sure both were at TDC separately so as not to mash a valve on piston. Stupidly I didn't replace the gasket or head bolts at the time.
Since then the engine hasn't really been run for long enough to even get hot or even warm but when testing it at the weekend (damn cold out at the time) I noticed a fair bit of steam (quite likely just due to outside time) so decided to redo the gasket and bolts to ensure there is no leak. The old gasket looks fine as do the cylinders, pistons, valves etc. literally doing it as a precaution to avoid cooking the engine or drinking coolant and producing mayo.

I will of course clean the head and the block surfaces from any contaminants, I'm not THAT stupid.

[daimlerman]

Now you're asking too much (re head skimming)

I will of course clean the head and the block surfaces from any contaminants, I'm not THAT stupid.

Not suggesting that you are,but a skim costs me just £20,consumables to swap the gasket about £100,so you are saving money by spending on a skim...


I think!


But see my avtar...

[Brianmoooore]

I removed the head, found the TDC marks and made sure both were at TDC separately so as not to mash a valve on piston. Stupidly I didn't replace the gasket or head bolts at the time.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
If you haven't assembled anything yet, get it lightly skimmed.

[Morat]

You should really skim it to make sure it is flat our you could be forking out for another gasket and set of bolts...

[Brianmoooore]

You should really skim it to make sure it is flat our you could be forking out for another gasket and set of bolts...

Plus a new head, if it blows out the coolant and cracks itself.
On the subject; when you do get it back together, make sure you know how to refill it with coolant properly, or this could become a long and expensive thread!

[aimlessrock]

hmmm...when i rebuilt my head about 6 months ago i purchased a new set of head bolts (from the dealers) and they were the hex type!!!

Brian, given your remarks is it wise i order a new set of bolts and replace?

my cabby has only does a few hundred miles since the rebuilt (head was pressure tested and skimmed etc)..

[jimmyspeed]

so all hex ones are scrap, i have a set of 12.9 tensile hex ones in mine which i had presumed to be safe to re-use - being the non stretch type ?

[Brianmoooore]

hmmm...when i rebuilt my head about 6 months ago i purchased a new set of head bolts (from the dealers) and they were the hex type!!!

Brian, given your remarks is it wise i order a new set of bolts and replace?

my cabby has only does a few hundred miles since the rebuilt (head was pressure tested and skimmed etc)..

Don't really know how to answer this one, except go back to the dealer and make further enquiries.
The TIS regarding these bolts, and the replacement torx headed stretch bolts were issued many years ago, and I haven't seen a new hex headed BMW head bolt for years.
There's nothing wrong with hex headed bolts per se, other than a stretch bolt gives more accurate tightening down of the head, and, IIRC, the story was that BMW sourced their head bolts from three different suppliers, only one of which was producing the faulty ones, but they were mixed at the factory and there is no way of telling them apart.

[Brianmoooore]

so all hex ones are scrap, i have a set of 12.9 tensile hex ones in mine which i had presumed to be safe to re-use - being the non stretch type ?

See my post above. Statistically 2/3 of them will be fine, but you may have no faulty bolts, all faulty bolts, or somewhere in between. If a head breaks off, it may fall harmlessly into a corner of the head, or it might get involved with the camshaft, and get punched clean through. Are you a gambling man?
The head doesn't have to be removed to renew the bolts. It's quite in order to remove the old bolts one at a time, and replace with the new, fully tightening each one before removing the next.

[jimmyspeed]

Are you a gambling man? No

they are definetly getting changed , thanks J

[aimlessrock]

Brian, thanks for your remarks..ive had a chance to properly read your comments earlier today. Im equally not a gambling man and have ordered a new set of bolts from my local main dealer.

I was going to ask if i could do them one by one, but you have already nicely addressed this point.

Thanks for your ever helpful comments, you should be called "the Zone Sage"

[Andyboy]

I've seen this problem on a 1987 520i and two 1989 325i 's.