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  #1  
Old 10-26-2005, 03:48 PM
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damaged head bolt threads..

After cleaning up the head bolts and using a die to make sure I didn't miss anything, I ran across two bolts that had faulty threads. One had a flat spot on a small section of a thread, the other had some dings across two threads. I'm a little ticked that they were used in the first place and hope the block threads will be o.k.(I have no clue which hole they came from). After using the die on them they cleaned up o.k., but would it be a good idea to replace them anyway?
Matt

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  #2  
Old 10-26-2005, 04:04 PM
BusyBenz
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Quote:
Originally Posted by 96E300D
After cleaning up the head bolts and using a die to make sure I didn't miss anything, I ran across two bolts that had faulty threads. One had a flat spot on a small section of a thread, the other had some dings across two threads. I'm a little ticked that they were used in the first place and hope the block threads will be o.k.(I have no clue which hole they came from). After using the die on them they cleaned up o.k., but would it be a good idea to replace them anyway?
Matt
Head bolts on these engines are stretch type head bolts. I have read here quite some time ago that you should not use the old bolts but instead buy new bolts. When I did a head gasket a year ago, I used new bolts. None had defective threads, nor did I notice such with the old bolts.
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  #3  
Old 10-26-2005, 04:15 PM
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Yeah, I recently had a discussion here about the stretch bolts and mine are well within the tolerances given by the tech manual. I'm just a bit peeved about the condition of two of these bolts.
Matt
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  #4  
Old 10-26-2005, 05:08 PM
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Re-threading the bolts

As a machinist by trade, anytime a die is used to clean up the threads the minimal 10% thread tolerance is lost...I would get new ones...The slightest misuse of a die can alter the thread depth and create slop in the threads not only in depth but also the tolerances between threads....but do what you feel will work best....just an opinion here...
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  #5  
Old 10-26-2005, 05:31 PM
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Quote:
Originally Posted by iceman3876
As a machinist by trade, anytime a die is used to clean up the threads the minimal 10% thread tolerance is lost...I would get new ones...The slightest misuse of a die can alter the thread depth and create slop in the threads not only in depth but also the tolerances between threads....but do what you feel will work best....just an opinion here...
My sentiments exactly, that is why I advised against using a tap to clean the holes in the block a while back. Unless they are damaged they can be cleaned with a small bottle brush without endangering either a broken tap or removing metal and winding up with a bolt that is too loose (remember a block isn't easy to change! .

Headbolts are cheap enough that I always buy a new set when working on one of my cars. Speaking of that, the last set I bought for the 603 engine was short one bolt, I dunno how that happened!
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  #6  
Old 10-26-2005, 06:58 PM
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I went ahead and ordered the bolts which is where I was leaning anyway(thanks for the input). In regards to the tap, because two of these bolts that had bad threads, I think I'd feel better chasing the threads with the tap.
Matt
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  #7  
Old 10-27-2005, 12:17 PM
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boogering up threads

yeah then you will be up the creek with a heli-coil insert and trying to dig the insert tang from an ungodly place
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  #8  
Old 10-27-2005, 04:19 PM
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Hey Iceman, out of curiosity and probably necessity, when I used the die, it wasnt' a real tight fit, however when it went over the damaged threads it caught enough so I knew there was an issue. On the other hand, while using the tap, it does feel snug, but there are no metal shavings that are coming out with the tap. It's a little nerve racking using the tap making sure I'm not counter-threading any of the holes, making sure it's straight and there's even pressure so as not to break the tap. I started out using a penetrant for lubrication, but found that a 10-30 worked better. Any other tips or things to be aware of?
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Old 10-27-2005, 05:57 PM
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I'm not sure what the standards are for the metric taps and dies you are getting.

In the old US of A system, there were 2B and 3B taps -one giving a loose clearance and one being a tighter fit.
I've got no problems with ppl cleaning with a tap. I use one with my fingers to clean the block threads ... I wouldn't recommend chucking it on your cordless 1/2 drill.
Bolts are cheap- inspect them : threads, heads, shank, radius under head all for damage. Clean with a brass brush if they measure short enough for reuse.

Michael
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  #10  
Old 10-27-2005, 07:13 PM
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Curiosity

Quote:
Originally Posted by 96E300D
Hey Iceman, out of curiosity and probably necessity, when I used the die, it wasnt' a real tight fit, however when it went over the damaged threads it caught enough so I knew there was an issue. On the other hand, while using the tap, it does feel snug, but there are no metal shavings that are coming out with the tap. It's a little nerve racking using the tap making sure I'm not counter-threading any of the holes, making sure it's straight and there's even pressure so as not to break the tap. I started out using a penetrant for lubrication, but found that a 10-30 worked better. Any other tips or things to be aware of?
It is possible that there was a problem with the threads before since you didnt drop them or damage them..so its likely that someone else may have damaged the bolts before...when using the tap..you are correct that true alignment is an absolute...I have seen guys just start running a tap into a hole with no regard to the trueness of the threads...Remember that in the event a thread is warped or misaligned the result will be a sloppy fit at best...the power in a thread is allowing 100% of the threads to contact the mating threads or else eventual heli-coil will be required..as always take your time and add even pressure with no tilting of the tap whatsoever...and make sure you have the right type of bottom on the tap. Some taps are bottoming taps...some tapered...if the hole is blind into a hole...make sure a bottoming tap is used at least....in maintaining a threads trueness...remember that there are areas of concern

1. Am I maintaining the distance between each thread

2. Is the thread depth maintained

3. Is the diameter of the bolt, or OD of the bolt where the threads are located consistent with the tolerances..

4. Use ample supple of tapping fluid

5. Dont allow thread shavings to fall into places that will cause harm
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  #11  
Old 10-27-2005, 08:58 PM
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I always wondered why the bolts come loose in a paper bag, at least the ones I ordered twice looked that way. I get them from WorldPac.
If you ever see how aviation hardware comes packed you'll wonder too. Bolts for critical aviation use are covered with plastic tubing or a woven soft plastic finger puzzle looking cover that prevents the threads from getting damaged during shipping and handling.

I suppose at a buck and half for Mercedes stretch bolts someone figured they aren't that critical and don't justify using protector sleeves.

(Vent mode) There has been so much time spent on this subject that a few new bolts could have been ordered and installed and this job would have been completed. Whew!
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  #12  
Old 10-28-2005, 12:03 AM
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I wish it were that easy, this is my first diesel head so I suppose I am being overly cautious. But in a post yesterday, I stated I had ordered the bolts. Still waiting for them along with the head from the machine shop($750 later).
Matt

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