Head Bolt Size?

[valdezhilander]

So I am starting to tear into this motor I am rebuilding and I'd like to clean out the head bolt holes with a tap. Thing is the head bolts don't match anything in my MAC tap set? It seems to be around 13mmX1.75, which I don't think exists? 14mm is too big abd 12mm is too small. I could'nt find anything in the FSM? Thanks for any help.

[valdezhilander]

Anybody???

[TrickyT]

Valdez,
I'm pretty much exactly in the same spot as you. I'm ready to re-assemble my 1989 3FE and before I drop my rebuilt head on I want to clean out the threads in the block. But I just discovered today that those head bolts are a very unusual size. I measure the bolt threads as ~12.7mm diameter with a pitch of 1.75mm. I can't find a tap anywhere near that, especially the 1.75 pitch part. I need to do some more searches in the 60-series forum, but at this point I'm thinking I'll just grind a groove lengthwise in an old head bolt and use that to chase the threads.

Edit: Link to needed tap (13mm x 1.75mm): MSC Item Detail

[John McVicker]

Sorry, don't know the size. But I remember that I had the same problem & this is how I solved it. I just used one of the head bolts as a 'tap'.

A) Start the bolt in the head w/your fingers. Make sure you're in there.
B) Then use some penetrating oil (not merely WD40) and your air gun. Run it down a few threads....back it out and repeat until you get to the bottom.

Use plenty of penetrating oil & each time you back it out, blow some air in the hole. Takes a while..plenty of holes....changing from air rachet to blow gun etc., but it did a really clean job.

John

[2mbb]

The parts microfiche says the bolt size is 13mmx1.75. e-taps.com has this size in a bottom tap.

Metric taps M10-M19

[valdezhilander]

Thanks for all the help, 13mmX1.75 it is, so I did measure it right I just had never encountered, or heard of that size. I'll have to order one, NAPA's never heard of that size either.

Thanks again everyone.

[Spike Strip]

It's an odd-ball size, 'cuz it's one-size larger than normally used.

Also available here: LINKY

[2mbb]

Originally Posted by Spike Strip

It's an odd-ball size, 'cuz it's one-size larger than normally used.

Also available here: LINKY

I saw that one at MSC, too, and I almost recommneded it because it's cheaper, but I think the bottom tap will work better for cleaning threads in a blind hole. A bottom tap has less or no taper and is used for taping blind holes. I'm guessing the head bolt holes are blind and that the holes are not much longer than the bolts themselves.