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  #1  
Old 10-29-2009, 09:55 PM
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Dumb question of the night: measuring head bolt stretch?

I'm checking my OM602 head bolts for stretch to see if I can reuse them. I assume I should be measuring only the shaft itself (MINUS the head), no? Otherwise, mine are all WAY out of spec! I have the specs from the manual, but nothing assuring me that I'm measuring in the right places.

Thanks, all!
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  #2  
Old 10-29-2009, 10:05 PM
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bolt stretch

Checked my computer version of the FSM: hold a straight edge against the threads, they all should touch, if some don't, they have been stretched, replace the bolts. I'd have to re-read it, but I think you are supposed to replace in sets.
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Old 10-29-2009, 10:17 PM
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Thank you, sir! I just found a section in the FSM that covers proper measuring technique, and mine are all in spec.. good to go!
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Old 10-30-2009, 06:16 AM
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I believe my favorite machinist measures in the necked area. The diameter there. It is a go no go situation. Each time they are stretched it gets narrower until it is too thin to use.
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Old 10-30-2009, 07:47 AM
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IMHO this isn't worth messing around with. Every time I've re-used stretch bolts it's not gone well. My time is valuable so to me it costs less just to replace them every time then not worry...

-J
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Old 10-30-2009, 08:41 AM
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Quote:
Originally Posted by compu_85 View Post
IMHO this isn't worth messing around with. Every time I've re-used stretch bolts it's not gone well. My time is valuable so to me it costs less just to replace them every time then not worry...

-J
What's been the problem with reusing head bolts? Why would the FSM advise checking them for stretch if they shouldn't ever be reused? If they're in spec, and clean, and you chase the threads in the block with a tap first, what would the problem be? I'm not asking to be argumentative, but rather to learn about the matter.
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Old 10-30-2009, 08:58 AM
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Quote:
Originally Posted by t walgamuth View Post
I believe my favorite machinist measures in the necked area. The diameter there. It is a go no go situation. Each time they are stretched it gets narrower until it is too thin to use.
Tell me more, Tom. The FSM illustrates the measurement as the shank -- the length from the bottom of the head (or the seating surface) to the tip of the threaded ends. Mine are all very close to spec in that regard. Thanks!
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  #8  
Old 10-30-2009, 07:31 PM
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Apparently there is more than one way to measure a stretch bolt. He measures the diameter of the necked down area in the center, but that is what the fsm showed for that bolt.

To the fellow who's time is too valuable to measure mercedes diesel head bolts I would ask have you ever bought a complete set? They don't cost what a chebby bolt costs and they are made out of some serious steel.

IIRC they are nearly $20 a peace. I am not missing any meals but I surely would not buy a new set just because I had a bad experience with some other brand of bolts.
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..I also have a 427 Cobra replica with an aluminum chassis.
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Old 10-30-2009, 07:38 PM
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Thanks, Tom. I think the head bolt are down to 2 or 3 bucks apiece now, so I can see why someone would just replace them all, but if you have the means to measure them accurately, and they are all in spec according to the FSM, I don't see the issue with reusing. Why toss perfectly good bolts? If someone's got a compelling reason not to reuse them, I'm all ears, though.
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  #10  
Old 10-30-2009, 07:46 PM
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bolts get superceded

When I did my 603 (14 head), I checked around and discovered that MB had gone through three revisions of bolts. The aftermarket ones (local shop I use frequently) were not the new super-dupers. I used the MB supers. Check EPC to see what's "new" for your engine, then check to see who's selling what.

To my mind I can't imagine spending a day of labor and $100 on gaskets and save $70 on bolts (for my six; YMMV on labor, bolt qty and $).
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  #11  
Old 10-30-2009, 11:06 PM
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If they meet mb specs they are good enough for me. I'll spend my $70 on something else.

But you are free to replace them if you want.

I just looked at fastlane. I thought they were a lot more expensive than that. Have they gone down?
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..I also have a 427 Cobra replica with an aluminum chassis.

Last edited by t walgamuth; 10-30-2009 at 11:11 PM.
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