TheSamba.com :: View topic - Replace 12mm femalhead bolts on 1.6 l diesel, n 83 Vanagon?

Sun Sep 20, 2009 4:41 pm

I am re-torquing the head bolts of my 1.6 liter n/a diesel. I am NOT taking the head off, just re-torquing it to specs.
I currently have female 12mm polygon head bolts. My Bentley manual states that I should ALWAYS replace these head bolts with hex head 11mm bolts.

Why is this? Was there a flaw in the female 12mm polygon head bolts? Am I taking a risk in re-torquing the existing bolts?
TIA

Sun Sep 20, 2009 4:57 pm

the 12 point bolts are stretch bolts. You torque to a value, then 1/4 turn more.
the 6 point are reusable.

Sun Sep 20, 2009 4:58 pm

I have to assume you are misreading the Bentley. There are two types of stock head bolts and which version is used is determined by the threaded holes in the block. The measurement of 11mm or 12mm refers to the diameter of the threads of the bolts themselves and the matching threads in the block. Obviously you cannot replace 12mm bolts with 11mm bolts. The threads of the bolts need to match the threads in the block. When the Bentley is saying to "always replace" the 12mm bolts, they are stating that each time they are loosened they should be replaced with new 12mm 12-point head bolts. The reason for that is that they are TTY (torque-to-yield) bolts that are actually torqued to the point that the metal deforms to create the proper torque on the head gasket. Once they have been used, according to VW they are done for. The 11mm bolts, on the other hand, are conventional bolts that are not torqued to the point that they deform and so can be reused. So, if you are ever doing a head gasket job with 11mm bolts (heaven forbid - the blocks are extremely prone to cracking) then the bolts can be reused. If doing a head gasket on with 12mm bolts, then you should always replace them with new 12mm bolts.

On to your particular project. Why are you re-torqueing the head bolts? Did you just replace the head gasket and are doing the final 1,000 mile torquing procedure? If so, then do the quarter turns and be done. If you are re-torquing an engine that has been running for a while, then I have to ask why? If the head gasket is already leaking, then it is very unlikely that re-torquing is going to fix it. If it is not already leaking then I would certainly just leave it alone. Considering the proper torque procedure which includes a base torque in stages followed by a series of quarter turns, how are you going to determine the correct torque at this point? You can't really loosen them and start over... Give them all a quarter turn while your fingers are crossed hoping you don't snap a bolt head off?

Andrew

Sun Sep 20, 2009 5:16 pm

Thank you Andrew.
I recently bought this diesel Vanagon. the previous owner had very good documentation on a complete engine rebuild 20k miles ago. I believe her.

I was planning on re-torquing them because I saw a bit dreaded engine oil in my coolant reservoir. This has happened in the last 150 miles. I see no evidence of antifreeze in the oil (no coffee-with-cream color, or frothing). The engine runs fine with no loss in power and no visible leakage. I see no evidence of compression leakage into the coolant.

I was hoping (perhaps against hope) that I had loosened head bolts. I thought a re-torquing of the head would not hurt, and this could possibly stop the oil from getting into the coolant.

Where else would you look for oil getting into coolant?

thank you

Sun Sep 20, 2009 5:20 pm

the oil cooler

Andrew,
you write so eloquently.

Sun Sep 20, 2009 5:32 pm

kd4yor wrote: the oil cooler

Andrew,
you write so eloquently.
Shazam,
Andy killer job on the expo 8)
Bill W :wink:

Sun Sep 20, 2009 6:25 pm

Thanks guys.

Yes, the oil cooler is another potential source of coolant and oil mixing and certainly worth investigating before pulling the head. One way to test it is to plug one hose connection on the cooler, add a piece of hose and shrader valve to the other one, pressurize the cooler and stick it in a bucket of water and see if there is a steady stream of bubbles.

Oil getting into the coolant could also certainly be the head gasket. There are lots of ways in which a head gasket can blow and the various ways and symptoms that result are usually unrelated. Here's a good summary:

http://www.vwdiesel.net/forum/index.php?topic=16699.0

Even if a blown head gasket is the cause of the oil in the coolant, it doesn't surprise me that there is no coolant in the oil or compression gases in the coolant. Those are different channels in the gasket.

Andrew