Cam Tower Bolt - PeachParts Mercedes-Benz Forum

GaryF · #1 10-20-2010, 09:39 AM

Hi All,

Took the timing cover off to find the source of a weird metallic noise and turns out the lower bolt in the front tower has snapped and was rattling in the hole. The rest of the bolt is a long way down, has anyone had a similar issue and is there a cunning plan that avoids taking the head off?
If not what is the risk of driving the car? The rest of the bolts felt ok.

Thanks,
Gary

Stretch · #2 10-20-2010, 10:34 AM

Is that an OM616 / OM617 - it looks familiar.

I guess a "proper job" would involve a head removal and a bloody long easy out... if you can find a really long easy out that would reach.

May be you can get hold of a long left hand drill bit to drill the rest of the bolt out? Tricky tricky tricky...

I personally would not start the engine until this is fixed.

Nightmare.

Tomguy · #3 10-20-2010, 10:41 AM

The blue injectors would give it away as a D-Jet 4.5.

That is NOT a good sign. That's a head bolt. It could be just random bad luck that snapped it, but it's usually worse. To do it right you need to take the head off and potentially drill the old bolt out & helicoil the hole. You may get lucky and have enough sticking out of the block to grab on to.

Remove the head, replace it (the bolt), I'd replace the others while in there out of paranoia, and since you have the head off do the valve stem seals if they have not been done recently.

GaryF · #4 10-20-2010, 11:00 AM

Thanks for the feedback and should have mentioned a 117. I got lucky....so far. The bolt had sheared with a rough joint so putting the bolt back in the hole and turning slowly I got enough traction to unscrew the remaining bit and pulled it out with a mag pickup.

Quote:

Originally Posted by Tomguy

It could be just random bad luck that snapped it, but it's usually worse.

Tomguy, Do you mean the head could have warped putting the extra load on the bolts at the end?
The valve guide job definitely needs doing at some point...
I'll get a full set and replace them all, if its down to metal fatigue alone then the others could be close to failure.

230/8 · #5 10-20-2010, 11:08 AM

Gary:

Good grief do you have good luck!...being able to back out the fugitive fragment is simply an unbelievable stroke of good fortune; thank your lucky stars, and if possible, please share some of that good luck pixie dust with the rest of us...

GaryF · #6 10-20-2010, 12:17 PM

Quote:

Originally Posted by 230/8

Gary:

Good grief do you have good luck!...being able to back out the fugitive fragment is simply an unbelievable stroke of good fortune; thank your lucky stars, and if possible, please share some of that good luck pixie dust with the rest of us...

I'm overdue some good luck this year and that was probably my ration used up until January

I guess once the bolt has snapped the remaining bit is not under any load and soaked in oil so getting any kind of grip on it will get it out. I've got no war stories for the grandkids so that will have to do !

Tomguy · #7 10-20-2010, 12:53 PM

Lucky indeed!

Replace all the bolts, you may not need to pull the head. Replace that one and torque to the 60 ft-lbs specified, then do the others torquing each to 60 ft-lbs in their proper torquing order. That should help re-seat the head without removing and replaning and hopefully prevent any issue that may have caused the failure to begin with.

If you PM me your email address I can send the one pdf I have of m116/m117 head bolt torque instructions

Mike D · #8 10-20-2010, 01:52 PM

Gary, pop on over and pick me up a couple of Irish sweepstakes tickets. YOU pick the numbers. You seem to be on a good luck streak!

Good to see this was an easy fix for you. Every now and then ya gotta get lucky!

Stretch · #9 10-21-2010, 03:18 AM

Quote:

Originally Posted by Mike D

Gary, pop on over and pick me up a couple of Irish sweepstakes tickets. YOU pick the numbers. You seem to be on a good luck streak!

Good to see this was an easy fix for you. Every now and then ya gotta get lucky!

Oh yes indeed you've gotta push that luck!

bwostosh · #10 10-21-2010, 11:02 AM

Those head bolts are on the edge of torque holding because of their diameter. The 6 cyl cars have large diam's and I re-use them, the V8 always replace even though I had a new complete set and just one started stretching upon final torque-up, Fortunately the torque wrench and experience told me to stop and pull the bolt out before breaking, there was measurable shank diameter decrease.
Take a peek at rod and flywheel bolts for sophistication of holding.

GaryF · #11 10-22-2010, 03:59 AM

Quote:

Originally Posted by bwostosh

Those head bolts are on the edge of torque holding because of their diameter. The 6 cyl cars have large diam's and I re-use them, the V8 always replace even though I had a new complete set and just one started stretching upon final torque-up, Fortunately the torque wrench and experience told me to stop and pull the bolt out before breaking, there was measurable shank diameter decrease.

And if that's the official part, using an OEM version of the bolt with any defect or wrong grade will be a disaster. The other thing that concerned me was that the stub I retrieved was less than 1/2" in length, which doesn't seem like enough thread holding a lot of torque.

bwostosh · #12 10-22-2010, 06:47 AM

I've been operating on the 1.0 to 1.5 depth of threads to bolt diameter ratio for holding full torque. Usually works well.

Mike D · #13 10-22-2010, 07:00 AM

60 ft-lbs isn't a "lot" of torque. A coarse thread bolt achieves its maximum of holding power at 5/8's of its diameter (shaft diameter minus the cut for the threads). The extra length is simply insurance against the receiving threads' strength.

GGR · #14 10-22-2010, 09:24 AM

Man, you're lucky!

All the head bolts are not the same length and it may well be that a shorter one was fitted there during a previous job.

If you plan to take your head off to work on it then replace the bolts at the same time. If you don't plan to take it of soon I would refrain from messing with the other bolts. You got lucky once, but these bolts can snap with no other way than a grinder to remove them. I saw some heads being sacrificed because of that. Put another bolt in of the correct lenght, torque it and drive up to when you're ready for the head removal.

GaryF · #15 10-22-2010, 10:55 AM

There are three different bolt lengths and this is the longest one by a big margin so must have been the correct bolt to even get a bite with the thread. I have a full set on order and won't drive it until I've at least put this one in.
I know for sure that I wouldn't get this lucky again so I am tempted to keep the other bolts in reserve and as you say leave it until I have to do the valves.