Cleaning threaded block holes

[jkeesey]

If it is labeled as a tap its not correct. It should be a chaser or thread restorer. The edges of a tap are sharp and designed to cut anything out of its way, a chaser has more rounded edges designed for straightening existing threads. Unless the tap is very old and worn out I wouldn't use it for cleaning. A flat bottomed tap is simply for tapping closed end holes.

[Ian NZ]

I removed all the studs on my V8 engine tapped the holes out with a bottoming tap and I then placed antiseize on the threaded bolts when I fitted the aluminium heads, tightened the bolts down to the correct torque, and I have had no problems with water leaks. I am not using antifreeze.

[HCO41]

I'd like to open this subject again. Earlier in my career I worked for a large cutting tool manufacturer. One of my jobs was creating the specs. For "special taps". We manufactured Carbon, Cut thread and ground thread taps. Since 7/16-14 is the thread size this thread is addressing, I can tell you that our blocks would have been tapped with a ground thread tap. Tolerances are much closer. I don't know what class thread Ford originally used, but I suspect GH-2, possibly GH-1. The ground taps we stocked in this size were GH-3. Carbon and Cut thread taps were tooled to this dimension, but tolerances were not as stringently controlled as the ground taps. (Carbon and cut thread taps are generally roll formed). Ground thread taps are classed higher or lower than nominal size and designated by GH (above nominal), GL (below nominal). Each limit (GH-1,2,3,4etc. and GL-1,2,3,etc.) has a tolerance range measured to the 4th place (ex. .0001-.0003). The taps purchased at our local hardware store or even industrial supply store would likely open up the threaded hole more than originally intended. I took a look at the rethreading taps on the link posted above and noted that there was no class specified. I would have to trust their intended use and would definately use them before a hardware item. If I still had access to special overruns, I would be looking for a 7/16-14 GH-1 bottoming tap.
Hope this helps for the future

[TStiles]

This site is a nonstop education. Thanks all for your contributions. HCO41 shared details not commonly known to the shade tree guy. Great information!

[Ross F-1]

A question: are the specs in the Ford workshop manuals for head bolt torque on 8BA-style engines assuming dry threads, or oiled? All these sealers undoubtedly reduce friction while sealing, I would assume. Some reduction in stated torque values would be in order if the specs assume dry (which is my experience on other engines).

[Bruce Lancaster]

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Here's an old Model A forum post on the threads...
model A used same threads as V8.Marco came up with blueprint, grade 4 fit in early standard, a later print showed 5 I think. I found 1930's thread specs from Ford sources, don't really know translation to modern class 3 or whatever.


http://www.fordbarn.com/forum/showth...lass&showall=1

[rotorwrench]

I think the classes have remained unchanged from the opriginal SAE classification. This chart goes into some detail about taps.
http://www.newmantools.com/taps/tapclass.htm

This stuff hasn't changed much over the years but only a few industries worry about bolt hole and nut fit to a fastener. Aviation still uses them for the older equipment like the Radial engine cases where a lot of studs are used in aluminum castings. My Rex suply catalog has taps in every fit but they have pages & pages of taps to poor over till you find what you want. Most machine shop suppliers have these types of products.

[Marvin/TN]

There is a GM product that works very well as a thread sealer. You can get it at any GM parts dept, may have to order it at some dealers. It is pipe sealant with PTFE P/N 12346004. Good for any bolt that goes into the water jacket. It also makes the bolts and pipe thread plugs etc easy to remove. It isn't cheap but nothing good is.

[HCO41]

I looked at both links above and recognized the taps listed as "stock" items. These sizes and class limits are what is the more popular fits used in general industry. "Stock" taps (ground thread) may have been used in Engine blocks, but I doubt it because these taps, on an average, will produce 75% thread. The only thing that seems somewhat ironic about this discussion is the point brought up by rotorwrench. The quality of the bolts we might use as replacements might not be of the highest quality since so many fasteners are made off-shore now. A tap other than stock whether it be for tolerance, shank size, flute configuration, point type or flute hook is considered "special". I felt the 7/16-14 GH-1 would be a good choice for rethreading since it would have a slightly smaller major and root diameters, yet would effectively clean the stock threads. Previous attempts to rethread blows this all away since most would use the "Hardware store" tap.
Here's a couple of examples of Ford taps we supplied as "specials" and their use in production. We made a special short projection pipe tap (NPT) used to tap the intake manifolds for the heater hose fittings. Short projection was needed so that tap wouldn't bottom out in the manifold before full thread was produced. This was in the late '60s, so I can't say I ever saw special tooling for our flatheads. The other taps we supplied were those used in a set-up to tap the pan rail. Ford was having trouble with sloppy set-ups in this area, breaking taps because the taps weren't aligning with the drilled holes. Instead of paying a little more attention to setting the station up probably, Ford asked us to come up with a solution. The solution: Anneal the tap shank so they could bend a little and "find" the hole. This significantly reduced breakage, however I suspect that some of the pan bolts may have gone in a little crooked?
I still think a GH-1 tap would be a good rethread size. Do any of the above posters have a better suggestion?

[HCO41]

This is a heads up! I went to the link 19Fordy posted above. You will notice that there are 3 taps shown but 7/16-14 was the only description. The link showed several suppliers of this (these?) items. I went to Jegs sight and the same group of three taps was shown. I specifically asked (Larry) if they were offering three taps or just the 7/16-14. He assured me that a 3/8-16 and a 1/2-13 were included. I ordered the taps.
When I got my confirmation it only showed the 7/16-14. I sent Jegs an inquiry via email and got a call from them. Guess what; "Larry made a mistake". I was then offered a five piece rethreading tap set for over $100.
Watch out!!!

[jack orchard]

How about these?

http://www.summitracing.com/parts/sum-900200/overview/

[Ross F-1]

Originally Posted by jack orchard

How about these?

http://www.summitracing.com/parts/sum-900200/overview/

Not sure if those are the same ones I have, but it appears to be. Mine are made in USA, they work well. They take out lots of crud but no metal.

[V848 Ford]

Look for for a Gh1 class tap . That is a cuts tighter threads you will have to probably have to special order it from a tool supply co . Go to a parts house and they will give you dumb looks . It dosent hurt to use a thread sealer

[HCO41]

I've got a set like that shown on Summit link. I first used them to clean 5/16-18 and 3/8-16 threads in a 78 transmission case and cast iron clutch cover. Even with cleaning the tap after each hole, by the time I got to the last couple of 5/16 holes used for top cover the chaser was showing signs of wear. I finished up with a worn plug tap that I cut the end off. I don't know if the 7/16-14 will reach bottom head bolt threads.
Follow up: I received the 7/16-14 chaser from Jegs. It looks to be a highend product that I believe is made from hss (M-1?). Still seems a lot ($26) for one tap and their ad is deceiving. (See my post above)

[Tim Ayers]

Thank you all. I've used both the old head bolt with notches and gun brushes in a drill with cleaner. Both work well.