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

I feel for you buddy, man, this sounds like MY luck!!. I would suggest that you remove the suspect bolt and inspect it. You should be able to determine if the bolt or bolthole stripped by the looks of the bolt. Then you can determine a course of action.

Remove that bolt and visually inspect it .... I seriously doubt you stripped it as you are tightening down into a steel block with a steel bolt. In the meantime, order another bolt and torque it down. You most likely won't have to change the gasket again if this corner hasn't been compacted yet even though it's saturated with coolant. Maybe let it sit for a day or two to dry out, and then replace the bolt.

Did you possibly forget to add a washer to this bolt?

Good luck...

~Paul

____________________
'91 300E, 212K miles

I also suggest pulling that bolt and having a look at it. Is it possible that you dropped some gasket material in the hole as you were scraping things clean? It may not have come out when you blew the holes out. I would dig around the bottom of that hole with a long screwdriver and see if there's anything in there. You can also use some kind of a rod to measure the depth of the hole. Compare that to your new bolt and make sure you have some clearance without bottoming.

Hopefully the bolt threads gave way rather than the block.

I'm less optimistic than Paul about the gasket still sealing up properly after 10,000 miles of use, but I'd sure try it before re-doing the whole job!

__________________
D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.

This head uses stretch bolts. Although the bolts should be good for two uses, it may have been out of spec. Before removing the whole head, try removing the bolt in question. Measure it to stretch specifications. If it is out of spec, buy a new one and retorque.

I know it will not be the correct sequence for tightening head bolts, but it may be OK for only one. If the bolt still will not torque, then it is the threads in the block. You will be no worse than now.

If you take them all out, then you will probably have to drain fluids, take the head off, clean the surfaces again, use a new head gasket and all new bolts. You may only find out that it was the single bolt.

Just trying to save you a whole lot of work. I had the head off my M103 so I know what a PITA it is.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Thanks to all of you for your responses.

I like the idea of pulling and replacing the single bolt to check.

The old bolts, which I still have, turned out to be well within stretch specs. I bought replacements because I knew I wouldn't be able to inspect the originals until it was too late to get new ones. Since I had the new ones, I used them.

My only concern would be removing a single bolt and its possible consequences for the straightness of the head. I suppose it wouldn't be much worse than it already is if that bolt has not been holding proper torque. And if the cinch-down doesn't work I can always check the head when it's off and have it shaved again if need be.

Thanks again to all of you.

I know this is hindsight but always get a bottom tap of the proper size and chase/clean out those cylinder head bolt holes, make sure all liquid is out from the bottom of those holes and lightly oil the threads of the head bolt and the top of the head bolt washer. The hardest part is getting that liquid out from the bottom of those holes.

__________________
Jim

I haven't tried it, but I always thought a micro vacuum attachment kit would be the easy way to do it. I saw one of those kits at Harbor Freight tools. They are just miniture nozzles that work with your standard shop vac.

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D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.

A lot of you might already have those micro-vacuum attachments in the form of computer vacuum hoses and brushes. Great for detailing nooks and crannies also.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

I'm still awaiting my repair manual and do not have the head bolt torque specs and sequence. Does anyone know what it is for a 1990 benz wagon with the 103 engine?TIA

To temporarily lessen the amount of coolant leaking from your head gasket, you may want to try loosening the cap on the radiator. Doing that stopped the leak on my M103 so well that I have put off replacing the head gasket for two years now.

In your case I would still try to replace that one head bolt though. Being a corner bolt, I don't think that stage torquing would be as critical.

It is likely, that the threads are stripped in the block. Remove the stripped bolt and examine, the stripped threads wiil be attached to the blots as it is drawn out.

You will need to get either a helicoil fitted or a time sert fitted, I prefer the latter. It might be an idea to have all bolt threads to be time serted, I experienced before after one stripped thread, refitting the head another thread would strip at the final torqueing stage.