To Tap or Not to Tap.. to clean block threads for head bolts or any other..

[97oldscutlas]

SO, i didn't realize there was debate about bottom tapping the block treads for head bolts, but I guess there is:

 

http://www.v8buick.com/showthread.php?243651-Torque-To-Yield-Head-bolts-Can-they-be-reused-or-not-on-a-3-1-3-4-L-GM

 

Always been standard practice for me and most anyone I’ve worked with. i guess some are concerned about removing metal and affecting torque..

What do you guys think???

 

Also, I’m having trouble finding the tap for the olds’ 3.1 which I’m pretty sure is

15mm x 1.5.. does that sound right or am I missing something???

[White93z34]

I've never done it, maybe spray it out with brakeclean if there is concern of junk that got down into the threads, but never been a problem here.

 

I don't even get why they were questioning to replace the bolts or not, its $15 I'm not going to break a bolt in a head or have a gasket leak for a $15 set of bolts. That said, i've done it. Would not do it now though.

[19Cutlass94]

your not building a race motor. Just make sure everything is clean and put it together. Dont over think this or make more work for yourself than whats really needed

[RobertISaar]

torque to yield.

 

keyword = yield = they're purposely slightly stretched during install.

 

would not reuse.

 

as for tapping/chasing..... probably in no way necessary. if you were really adamant about it, it wouldn't hurt anything to make sure the threads are where they should be, but being an iron block, i don't think that will be a problem.

[Galaxie500XL]

X2...used torque to yield bolts are just asking for trouble. The very concept of using two dissimilar metals, iron for the block, and aluiminum for the heads, each of which have differing coefficients of expansion is scary enough...reusing torque to yield bolts that may not actually be giving you the clamping force you think they are..something you'll have hours to think about while pulling the engine back apart to replace yet another blown head gasket...please don't ask me how I acuired that knowledge..it was a painful, expensive lesson, because I didn't want to spend 30 bucks on new head bolts.

torque to yield.

 

keyword = yield = they're purposely slightly stretched during install.

 

would not reuse.

 

as for tapping/chasing..... probably in no way necessary. if you were really adamant about it, it wouldn't hurt anything to make sure the threads are where they should be, but being an iron block, i don't think that will be a problem.

[Schurkey]

1993 GM factory service manual says to clean the bolts, and re-use if not visibly stretched (or corroded, or otherwise obviously damaged.)

 

I re-used the head bolts when I changed head gaskets on my '93 3.4L, and I plan to re-use the bolts when I do the same to the '92.

 

If you're concerned about removing metal when cleaning the head bolt holes with a tap, use a thread-restoring tap instead of a thread-cutting tap.

http://www.tooltopia.com/kastar-hand-tools-971.aspx

 

Cheapass alternative: Now you have a reason to keep the old, dull taps that don't work properly for thread cutting any more.

 

I've found that people's eyes glaze over when I try to explain how taps are sized for thread fit, and how some taps are ground to make the thread fit tighter or looser. Clearly, you wouldn't want to clean a female thread with a loose-fit tap, since the loose fit tap may pull more metal out of the hole. A tight-fit tap would be a hint smaller, removing dreck but not metal.

http://www.newmantools.com/taps/taptech.htm#cla

http://www.newmantools.com/taps/taptech.htm#gh

Edited August 10, 2013 by Schurkey