what do I do OM603 head bolt broke on 87 300d - PeachParts Mercedes-Benz Forum

madcat21 · #1 05-22-2011, 02:38 PM

My brand new head bolt broke off while installing the cylinder head. All the parts came from MB do I call them? will it be covered under gasket warranty from them because It will need a new gasket if I take it off correct it broke under less than 35 nm stage 2 of tighting.

Matt L · #2 05-22-2011, 02:41 PM

My guess would be that something else is wrong. Perhaps the threads in the block are trashed, or blocked with debris or oil, keeping the bolt threads from going deep enough into the hole. That puts all the torque on the shaft, instead on the head where it belongs.

Diesel911 · #3 05-22-2011, 03:04 PM

In line with what Matt L said.
Did the Bolt actually snap in two, did the Head of the Bolt Strip or did the Threaded area in the Block Strip?

If the threads in the Block Stripped look to see if the proper length of Bolt was used in that hole or if the Bolt was the proper diameter and thread pitch.

madcat21 · #4 05-22-2011, 03:06 PM

The bolt snaped in 2

DieselPaul · #5 05-22-2011, 04:30 PM

Unless you're a certified repair shop I'd doubt Mercedes is going to warranty work done in your garage.

Did it break off high enough that you could attempt an ez out?

leathermang · #6 05-22-2011, 04:39 PM

Did you use two taps in each hole in the block ...one regular and then on bottoming to make sure the threads were clean all the way to the bottom of the hole first ?

dieseldiehard · #7 05-22-2011, 04:47 PM

Very important is after chasing the threads, insert a long thin air nozzle all the way down and blow the crud out.
DDH

Jeremy5848 · #8 05-22-2011, 07:13 PM

Interesting problem. Which bolt # (use the diagram that shows the order in which you torque the bolts).

A bolt that size breaking so easily must have had a flaw. A metallurgist should be able to see signs of crystallization at the point of the break. (The other half of the bolt will be damaged when you drill it for an EZ-out.) I would at least take the broken half back to your dealer and talk to them about it. Maybe they'd take pity and give you a new head gasket.

Depending on the depth of the hole to the break, you might be able to extract the broken piece without pulling the head. I suppose you could even try doing without that bolt but it would depend on which one and might be risky.

When I changed the head on my '87 (last month), I used one of the old head bolts as a thread chaser and got each hole clean enough so the the bolt could be screwed in all the way with just finger and thumb. I was surprised at the amount of water, oil, and general crud that had collected. It gave me a feeling of confidence to place the head on the block and know that the new bolts were going into clean threads.

Jeremy

madcat21 · #9 05-22-2011, 07:46 PM

It was bolt hole number 20

Jeremy5848 · #10 05-22-2011, 10:01 PM

Here's a picture of my head with all of the bolts numbered per the torquing diagram. I did this last month when I installed my new-to-me (ex-Sixto) #20 head. To help myself keep track of which bolt to torque next, I numbered all of them by applying strips of masking tape to the head and writing the numbers for each bolt with a felt-tip marker. Then I didn't have to look at the diagram while torquing.

I put an arrow in the picture to show the position of bolt #20. Now we need the experts on the forum to tell Madcat whether he can get along with a broken bolt in that position or whether the broken stub must come out and be replaced with a new bolt.

Jeremy

leathermang · #11 05-22-2011, 10:12 PM

Isn't a 603 head famous for something bad ? Like head gasket blowing or overheating or something ?
If the answer is yes... then it pretty much has to come out .... It really needs to come out either way actually...
But it is not my car.... and I have no manuals for it either...

babyjames · #12 05-22-2011, 11:54 PM

Can you get to the stuck portion of the bolt without taking the head back off? Left-hand drill bits are amazing! They'll often catch on the offending fastener and spin it out for you. I, personally, would try EVERYTHING I could think of before taking it all apart, again. Was the bolt going in smoothly? Were you having to use more force on that one in particular before it gave? Did it snap violently?

Jay.

barry123400 · #13 05-23-2011, 07:38 PM

That bolt stub should remove fairly easily with a little luck. The torque requirement up to the point of breakage is now gone. So the boken bolt still in the block should be pretty loose. There is absolutly no loading on the threads now.

Yes it has to come out and be replaced. I really feel you will be able to do that with the head on unless something is really wrong. Do run some form of bottoming tap down when you extract the remainder of the bolt. Blow out the hole as well. The bolt did thread in as easily as the others until the cap portion touched the head?