I was talking to a friend about torqueing the headbolts
he told me that when he was a young man an older timer was helping him replace a headgasket
the old timer told him a torque wrench is useless if you do not chase the threads in the block
and clean up the bolt threads
I was doing a headgasket job this week so I bought a 10 x 1.25 metric tap and ran it down all ten bolt holes in the block
some had carbon deposits
I wire brushed the threads on the bolts
lightly oiled the bolt threads and both sides of bolt washer
torqueing the head went like a dream
I did it in three passes 20, 35, 47 and every one felt the same all the way thru
that is one thing that never happened before
Headgasket Replacement Tip (headbolt prep)
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Headgasket Replacement Tip (headbolt prep)
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Re: Headgasket Replacement Tip (headbolt prep)
It was normal procedure when I worked for Nissan, that when we rebuilt a race engine to chase the threads in the block for the head bolts on each rebuild. I have not done that at home since I did not have a tap that large, but I do wire brush both the bolt threads, and use a wire brush in the bolt holes with lots of solvent, and keep cleaning the threads until the solvent comes out clean. Though chasing the threads with a tap is an important thing to do if there is any build up, corrosion or possible thread damage.
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'92 Mazda MPV 4wd (wife's daily driver)
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Re: Headgasket Replacement Tip (headbolt prep)
Have definitely paid the price when I was younger for not chasing head bolt threads. I've got an old head bolt with a couple of slots for gunk that I use to get the crusties, then a .45 caliber bore brush on a drill for final cleaning.