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  #1  
Old 05-16-2002, 11:48 AM
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Unhappy Uh Oh! Stripped a rocker arm thread in the head!!

Apparently others have too. The MB 103 manual says that you should replace all the M8 X 70 rocker bolts with M8 X 73 10.9 bolts. Too bad I read the manual AFTER I stripped it. No big deal. I'll put in a threaded insert and get some bolts, but what does the "10.9" refer to?
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Old 05-16-2002, 01:02 PM
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10.9 refers to the hardness of the bolt (it meets ISO 10.9 strength specs.) A 10.9 bolt can take more torque than an 8.8 bolt, for example.

Bruce
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  #3  
Old 05-16-2002, 01:59 PM
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Thanks. I would imagine that's like our (US) grade system, like Grade 8 etc.
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Old 05-16-2002, 02:56 PM
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Exactly. I believe an ISO 10.9 is very close in hardness to a SAE grade 8. ISO 8.8 equates to SAE grade 5.
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  #5  
Old 05-16-2002, 11:21 PM
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Dang it!! This is worse than I thought!! The stripped out hole is next to an oil gallery!! There won't be enough room to drill it out and install a threaded insert!! If anybody has experience with this problem, please feel free to offer your solutions!!
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  #6  
Old 05-20-2002, 09:43 AM
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After consulting a buddy in the tool and die shop, doing some measuring and looking at a conversion chart, here's what we came up with. The next larger size to 8mm that would cut threads and not enlarge the bolthole would be a 3/8 SAE. In fact all I had to do was cut the threads without even drilling the head. What follows are the highlight pics of the whole affair. First the rocker assembly with the bolt passage enlarged for the 3/8 bolt. The bolt on the right is the original showing the pulled out threads. The other bolt is a 3/8 hexhead capscrew with the shank milled down to 7mm to allow oil to pass to the rocker shaft.
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Old 05-20-2002, 09:45 AM
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Next the two taps used, an alignment tap, pointed and a bottm tap, flat, to keep from tapping too far down.
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Old 05-20-2002, 09:46 AM
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The rocker assembly in place for the alignment tapping
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Old 05-20-2002, 09:48 AM
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Then the rocker removed and the bottom tapping. Notice how most of the debris clings to the oily tap. I used a shop vac to clean up the finished job.
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  #10  
Old 05-20-2002, 09:50 AM
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Everything cleaned up and ready for the new bolt.
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Uh Oh! Stripped a rocker arm thread in the head!!-dcp01053.jpg  
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  #11  
Old 05-20-2002, 10:49 AM
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It will be in the archives from now on unless I or a moderator removes it. If you just want the pics then right click on your mouse and save them. Mail your check for the royalties to: just kidding, we post this kind of stuff for all our forum brothers to share.
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Old 05-20-2002, 10:51 AM
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How did my reply get posted before cdunne's question?
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  #13  
Old 05-20-2002, 11:06 AM
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Nice work Cap'n

To avoid stripping a thread in the future, turn the cam as you put on and tighten down each rocker arm.

You should be able to put each rocker arm on so that no pressure is on the cam lobe and arm, which causes the uneven tightening down of the 4 bolts and very likely strip as you encountered.

I almost stripped one of mine as well until a machine shop guy told me that trick. I think at TDC though, only 2 and 3 are under some pressure.

~Paul

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Old 05-20-2002, 11:34 AM
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My mistake was getting in a hurry and doing exactly what you described.. while using an air rachet!! I knew better than that but had a lapse of reason. The MB balancer is marked at 0 TDC, 120 derees and 240, which are you TDC's for the other cylinders. Also the fact that there is an upgrade bolt to M8 x 73 suggested should have been a red flag. Again, experience is what happens when you screw up.

Last edited by Cap'n Carageous; 05-20-2002 at 02:04 PM.
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  #15  
Old 05-20-2002, 11:48 AM
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God I love this forum!

Is there a way I can save a thread with pics? This one is great! For a new guy like me to get a blow by blow description of a fairly tricky repair with pics!!
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