Datsun Roadster Forum-311s.org

I installed a cylinder head on our '67.5 1600 yesterday, but before doing so I did some prep work. Part of this was using a bottoming tap in the (10) head bolt holes in the block. I found that the majority of these holes had some carbon and trash in them. I had to tap most of them 4-5 times each to remove this debris. I'm guessing that several of them had more than 1/4" of debris removed, and so I'm certain that several of them were previously bottomed out as a result.

Four out of five on the drivers side were the worst, and I assume that this is due to additional carbon buildup being facilitated by the higher heat associated with the location of the exhaust manifold. I can't be certain of this, but it seems a reasonable guess.

Anyway, just throwing that out there for your consideration. If you aren't already, perhaps using a bottoming tap on the block prior to a head swap would be a wise investment of your time.

Cross-posting on the Facebook page.

I always run a tap down every bolt hole and try to clean out any oil that has seeped into them. I use head studs, and as I understand it they should be free floating (not bottomed out). Being fully clean may not be as important with studs as when using stock bolts as with bolts the torque reading on your wrench is more directly impacted by the resistance with dirty threads.

I think that the point that is missed is that there appears to have been sufficient crap in the bottom of the bolt holes that the head bolts could have bottomed out and given a torque spec, when in reality it was not clamping torque. Similar to the issue of having the longer head bolt in the wrong hole without the lifting hook under it.

AGREED! Clean em out!