I'm ready to chase the head bolt threads. Is it okay to use a regular tap for this? Do I need to be careful not to cut new threads?

 

http://www.garagejournal.com/forum/s...d.php?t=138020
http://www.practicalmachinist.com/vb...er-tap-237679/

A chaser is designed to not cut new threads. I'm not a fan of using a tap unless the threads are already severely messed up. But a chaser is a fair bit of money to only use once.

 

I usually just wire wheel the bolts and run a tap in the block threads. I also give a shot of compressed air to blow any other garbage.

Just make sure that your tap is chasing and not cutting new threads.
You can cheat and use an old head bolt or another bolt with the same diameter and pitch, just take the threads to a grinder linear wise and create your own chaser.

Pat

 

Shouldn't be a problem if you're careful, though. Use some grease to catch any grit or shavings.

- Eric

 

You can use a tap carefully, just don't force it too much. Be prepared to pull it out multiple times and restart after cleaning it.

 

Sounds good guys, thanks for the tips. I have some experience cutting new threads so I know how it feels. Grease and clean often. Got it.
don71, love the sig.

 

After I'm sure I have the right tap, I put it in my Dewalt Cordless and turn the clutch down to about 3-4. Then just forward and reverse a few times and the threads are clean and shiny. I clean the gaps on the tap on a wire wheel. With the clutch set low, it won't even try to cut a thread. Works for me.

 

Randy S
Good call
If you have more than 1 or 2 to do, get a power tool.

CSB*:
I once had to chase/ reform threads on an aluminum insert at work. Spending $1000/hr on the test chamber, so it needs to be done efficiently. I asked for a 3/8 tap and they said, sure, but how you gonna turn it with that housing in the way? I said, I can probably figure out how to turn a tap, thanks. Having done this once or twice on engines, I chucked it in the cordless drill and had the hole fixed in 20 seconds. They were amazed.

* Cool Story, Bro

 

 

I recently asked for advice on fixing internal threads on my crank and received a lot of good suggestions . if its external threads they do make chasher or restorers. for my situation I could not find a big enough as the thread size was 3/4 I was told my a local machine shop that as long as I could start the bolt to use another bolt then use a plug tap which worked well I was carefull and slow and made sure to back it out a little for any material that build up all went well and botl tightened and torqued well

 

http://www.pts-tools.com/cgi/CGP2SRI...75700140220904

Stores vary.

Kind of expensive for a single use, but you can always pay the machine shop to use theirs. Me, if I need a tool like that I just buy it. Can always find a use for it later or sell it.

For a single use on not too mangled threads, you certainly can make your own thread chaser out of the original bolt. Rather than a bench grinder I prefer to use the Dremel and a fibery cutting disk. Form a tap-like cutting tooth [or three], with a sharpish leading edge. Usually works, and takes less time than running to the store or ordering a tap.

Also, there is NO reason that bolt would not still serve as your crank snout bolt.

 

As it turns out I don't have that size tap. Anyone know off hand what size bolts these are for the '71 350?
Octania? Crank snout bolt? Are you saying I can modify one of the existing head bolts and still use it to bolt the head on? Sorry if I'm off base here.

 

I would suggest using a flat bottom tap.... Unless you are very careful using a starter (Taper) Tap, you could possibly cross or start a new thread....

 

The head bolts are 7/16-14 nc. I would not cut a head bolt to chase threads and reuse it for torqueing the head back down. The crank bolt 3/4-16 nf .

Shaun

 

I would think that if I'm trying to clean all the crud out of the threads without damaging the steel, then maybe modifying a brass bolt would be best.
Thanks for the specs 70vert.

 

No problem I would just get a bottoming tap and be done with it. It will clean the threads out the best just be careful starting it. If you were near me I would give you one I have a bunch lol.

 

Very generous vert but I doubt we're anywhere near close enough. I don't know if you all got the wrong idea, my threads aren't damaged at all, just thought I should clean out any crud before I bolt the heads back on.

 

Just go to the local hardware and grab a bolt per 70vert's specs. I would take a small screw driver to measure the overall depth of the hole and grab something with full thread is possible. Standard GR5 is ok just make the serrations as described earlier

Pat

 

Sorry that was a tangential reply to the crank snout thread issue and the use of a crank snout bolt to chase those threads.

For a head bolt, no, I can't recommend making one into a chaser then using it as a head bolt. Head bolts are exceedingly common from dismantled engines. Although, if you disturb only the bottom 3-4 threads, I argue that would have absolutely no effect on its ability to serve as a head bolt. The part that matters is from the head to about 3-4 threads closest to the head, the rest is just along for the ride.

 

No problem Octania, after I reread the thread I understood. I think I'll do as 1970cs advised. Hardware store will be a open in a bit. I've modified gr5 bolts like this to cut threads into hard wood. Although with those I usually taper the end. Anyway, this should work just fine.