Head bolt tap size

[Reptoid Overlords]

It might very well be that I'm using the search feature wrong, or Tapatalk and my phone are making things difficult.

 

At any rate, I've picked up my P79 head from the machine shop and am preparing to chase the threads on my block prior to installation.

 

Can someone advise me on which thread pitch to use in my tap set.

 

Thanks in advance.

 

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[zKars]

The head bolts, like ALL M10 female threaded holes in the block, are 1.50 mm pitch. 

Pretty much all other M10 bolts on the car are 1.25mm pitch, certainly all the suspension related bolts.

[Reptoid Overlords]

Thank you.

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[Captain Obvious]

I'm no expert, but I wouldn't chase the threads in the block with a tap unless you really really have to. I wouldn't want to remove any metal, and running a tap in there has the risk of cutting out metal that does not need to be.

I would use carb cleaner and a small round metal wire brush first before you resort to a tap. If, after wire brushing, the head bolt threads in easily all the way to the bottom, then you're good to go and it doesn't need to be chased by anything more aggressive than that.

IMHO.

[Reptoid Overlords]

Very well then. I will clean with solution and brush before sending the bolt in by hand. If no further action is required then i will move forward. Thanks.

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[Captain Obvious]

It's a plan.

You just need the correct brush. And I've found it most effective to stuff the brush all the way in and then rotate it in the direction that unscrews it. That tends to bring the gunk out instead of driving it deeper.

And then at the very end, give it a couple blasts of carb cleaner. Stick the straw down the hole and cover the hole with a rag while blasting And don't get any in your eyes.  

[Captain Obvious]

If that doesn't work, then maybe you'll need to try a tap.

Not denying that there are circumstances where it's necessary... Just saying that I think it's an overused and often unnecessary procedure.

[Reptoid Overlords]

I ended up using brake parts cleaner, I mistakenly grabbed it instead of my throttle body cleaner, hopefully this wasn't a mistake. At any rate I cleaned the threads with a wire cone brush.

 

It turned out that most had to be tapped. So I ran the M10 1.50 tap with some oil on it and ended up pulling a slight amount of crud out.

 

The one thing I'm not too sure about is the fact that some head bolts thread all the way to the end of their threads, and some do not. It doesn't seem right, but perhaps it is, and I just don't know.

 

Is this correct, or do I need to get in there and give it a bit more force? I am careful not to torque too hard on it, but at the same time give it enough force to feel like it's bottoming out.

 

Edit: I have all of the old head bolts, and compared them lengthwise to the new Nissan set. The old bolts are the same length as the new ones, hopefully removing the possibility that the tips of some are broken off and sitting at the bottoms of the holes.

 

 

 

 

[grannyknot]

4 hours ago, Reptoid Overlords said:

The one thing I'm not too sure about is the fact that some head bolts thread all the way to the end of their threads, and some do not. It doesn't seem right, but perhaps it is, and I just don't know

Don't force it! Some of those of the head bolt holes enter the oil gallery if I remember right, or maybe it is the coolant passage. In any case it is normal.

[Captain Obvious]

I don't think any of the bolts go down into any other cavity, but some of them are drilled and tapped slightly deeper than others.

And if you're really worried about the possibility of a tip of an old bolt being broken off down in the hole, you should be able to get a look down there with a good light. The bottom of the hole is cone shaped like the tip of the drill bit that created it. If you see a ragged flat bottom, you might want to do some more cleaning and investigating.

[grannyknot]

8 hours ago, Captain Obvious said:

I don't think any of the bolts go down into any other cavity, but some of them are drilled and tapped slightly deeper than others.

Every time I take apart an L engine there are always a couple of head bolts that are caked in thick old sludgy oil so I assumed that it was protruding into oil gallery.

[Captain Obvious]

I suspect that the oil seeps down the shanks of some of the head bolts since the tops of the bolts are constantly bathed in a violent flying oil bath. The washers under the heads of the head bolts aren't made to seal. I suspect that some of them do, but some of them don't.

Or... Depending on the head bolt in question, it could be leaking past the head gasket from one of the oil galleys. I had a couple exactly as you described on my engine, but the ones that were sludgy were nowhere near the oil galley holes, so I suspect the former.