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  #1  
Old 11-05-2000, 04:58 AM
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Join Date: May 1999
Location: Calgary, Alberta, Canada
Posts: 190
Need help with 300E headgasket replacement, FSM says measure head bolt stretch

I have a 1988 I have just replaced the headgasket. I read in the manual to measure head bolts before reusing them. They measured within spec. I was on my last sequence where you torque them one last 90 degrees and I got interupted. I don't remember which one I was on in the order it says in the book. I may have missed one or two. I relize the head bolts are torque to yield therefore I do not want to repeat the torqueing sequence. What should I do? Will it be OK if I maybe missed the last step on 1 or 2 bolts? I am probably getting myself worried for nothing. The bolts are already very tight.
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  #2  
Old 11-05-2000, 06:08 AM
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Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
If it were me, I would start all over again. Take 'em all out, new head gasket, etc. I wouldn't want to do a job this big and this critical, unless I was 100% sure it was done right. But, having said that, this is a rule for me. You can try and check all the other bolts that have been angle torqued and get an average reading on the torque it takes to move them like 1 degree. If any are below that reading, then that's where you left off. Don't let anyone interrupt you this time. You've already done enough work as it is. You don't need to keep redoing the same job. Good Luck..

------------------
Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE

[This message has been edited by jeffsr (edited 11-05-2000).]
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  #3  
Old 11-05-2000, 11:07 AM
LarryBible
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I recommend that you jeff's words of wisdom. It will be very easy to start over with a new headgasket at this point, before you hook everything else up. Don't forget to remeasure the bolts for stretch.

I just went through all this with my 300E and it came out beautifully, I hope you have the same experience.

Good luck,

------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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  #4  
Old 11-05-2000, 03:58 PM
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Join Date: May 1999
Location: Calgary, Alberta, Canada
Posts: 190
Is it necessary to replace an already new head gasket? It has not been damaged but it may have been torqued down. Just wondering and I do appreciate your help.
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  #5  
Old 11-05-2000, 04:25 PM
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Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
When you torque a head down, you crush the gasket between the head and the block. The seal areas around the cylinders and head passages are crushed. This crushing starts with stage 1 of the torqueing procedure. These crush areas DO NOT rebound when the head is removed. You are asking for early failure if you try to use the head gasket again. Think about it. You get it all back together and it blows again in 5000 miles. Now you've got to pull it all down again because you tried to save $15 or $20. Are you a gamblin' man. Not me bro'. Get a new one and do it up right. Remember the famous advice of Bob Vila from this Old House. "Measure twice, cut once". Good luck and I hope you have a happy outcome. Be good to that M103 and she will make you happy!!

------------------
Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
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  #6  
Old 11-05-2000, 06:10 PM
LarryBible
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jeff,

I enjoy and get the advantage of all your wisdom. But, I heard my Granddad use the term measure twice and cut once probably twenty years before Bob Vila was on TV.

I think it's an old carpenter's rule, and Bob Vila is no carpenter, he probably stole it from Norm Abram, now THERE's a carpenter.

You always have great and appreciated posts, so I hope you don't mind my calling you on this. I guess I never really liked Bob Vila. He ended up causing problems on This Old House and they have done much better without him. Just my opinion.

Thanks and have a great day,

------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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  #7  
Old 11-05-2000, 06:23 PM
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Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
Hey Larry. Don't worry. I wasn't even sure if he said it. It probably was Norm. I met Norm at the New England Trade Show about 6 years ago. This guy is gifted. I wonder how he got hooked up with Mr. V?? (pompous name dropper).. Any way, he's on is own now. Has a great show called New Yankee Workshop. Where does he get all those tools?? . Anyway, we all know what's involved in a head gasket R&R.. Maybe I should have said "Think twice, torque 3 times" .

------------------
Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
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  #8  
Old 11-05-2000, 09:07 PM
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Join Date: Apr 2000
Posts: 166
Aw shucks. Now I AM disillusioned!

I thought H. Ross Perot originated it.

------------------
Ted
1979 240D
160,000 miles
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  #9  
Old 11-05-2000, 10:45 PM
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Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The reason for angle of rotation torquing is that the force necessary for continued rotation reduces once the metal goes into non-elastic deformation. In other words during normal torquing the bolt is stretched elastically (if released it would return to its exact length and diameter). In this case aditional tightening will require extra force linearly.

During angle of rotation torquing the bolt goes beyong elastic deformation and stretches (it gets longer and smaller in diameter). Once this point is reached the torque necessary for deformation goes down; thus the actual stretch can't be measured by torque.

Anyway, I would back the torque off to less than the second step and start over. Years ago we retorqued all head gaskets after getting them hot. We no longer have to do this because of better gasket materials (they say). I would have no problem with retorqing though. I believe it will be better than if you had done it right in the first place.

BTW, I say to back it off to below the second level because torquing should be done with a continuous rotation. You should not stop close to the final level as the torque necessary to continue torquing (dynamic friction) is much less than the torque it will take to get it moving again (static friction). You can check this by torquing a bolt to say 50 ftlbs and then use your torque wrench to loosen the bolt. The torque will be much higher to get it moving. You can also see it by going to 50 and stopping and then watching what torque it takes to start retightening.
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