View Single Post
  #1  
Old 05-28-2002, 11:37 PM
scanny scanny is offline
Registered User
 
Join Date: Sep 2001
Location: Menlo Park, CA
Posts: 23
M103 Cylinder Head Bolt did not torque up like others. Stripped?

I recently completed a valve job on my '90 300TE, roughly 120,000 miles. Everything went smoothly, except one thing. As I was torqueing down the head bolts, the very last one, the passenger side one nearest the firewall, was not as hard to turn as the others.

The spec for this head is to tighten the bolts in order and phases until you reach a certain torque. Then tighten each bolt a remaining 90 degrees (or maybe 180, whatever. I did it according to the instructions that I don't have in front of me at the moment.)

All of the bolts were quite tight in the final crank, as I remember I did it in two 90 degrees instead of a single 180, as was an option. But the very last one did not give the same resistance on the final crank.

I was kind of in a pickle at this point, as you can imagine, since the head was on, the head gasket crushed to a seal, and taking it off to see what I might see would have required I buy another gasket set. For better or worse, I decided to go with the flow and hope for the best.

Well, I didn't luck out. Now it is about 10,000 miles later and coolant is leaking from the cylinder head to the outside right in the neighborhood of the bolt in question. It's hard to tell exactly, as the residue is somewhat collected along the whole passenger side of the head (can only be seen when looking up from below, as the head overlaps the block by an inch or so on that side. But the consumption has started to become noticeable and I'm going to have to put a new gasket in sometime within the next couple of weeks.

My question is, have any of you ever come across a situation like this before and perhaps explain what might have happened? My possible theories are these:

- The cylinder block hole for this bolt somehow became stripped for no apparent reason. The old bolt was original, and came out perfectly normally, with no galling or other abnormality.

- The new cylinder head bolt (I replaced all of them) for some reason yeilded, perhaps due to a hidden defect. (The bolts were from MB).

- The gasket was faulty, as I have heard some of them can be (although I heard this was limited to the Elring make, this was a Victor Reinz), and the problem is not related to torque at all.

- I was careful to blow out the threaded holes for the bolts in the block before installing the bolts, but perhaps somehow I can't imagine, some fluid went into the bolt hole and produced a temporary hydraulic lock which gave a false torque reading initially. (I'm really stretching on this last one. Would have felt the difference if this were the case, I'm pretty sure.)

Any benefit of your experience you can give me here I will greatly appreciate. The only thing worse than doing the job twice will be doing it a third time if I don't get it right this time around.

Cheers,
Steve Canny
Reply With Quote