I've been reading with interest threads by guys whose opinions I value ('Ol Ron, Bruce L., & many others). Here is my question- If running a tap into the threads of a flathead block before ***embly is a big no-no according to these guys, why do all of the major flathead books say to do it? I have at least three books that I can recall that say to do this before any ***embly or you will not get accurate torque readings. I understand that you what to leave the threads "as factory" as much as possible, but if most of the guys I mentioned above agree that you need to chase the threads and NOT run a tap (contrary to what the published books say) what gives? Like most things flathead, you ask three guys, you'll get three different answers. Curious on this.
yeah, me to. I don't do flathead Fords, but the motors i do, I sure chase all the threads when I get them back from cleaning.
There's a difference between a tap and a chaser. A tap will be slightly larger than needed, that's how it cuts the thread. A chaser is slightly smaller and will clean existing threads but not cut into them. If you have well worn taps of the size threads you need, you can use them but a new tap may damage the existing threads and cause a loose bolt or stripping out of threads under torque.
This makes me wonder, if the hole was made with a tap in the first place, why would chasing it with a tap make it larger? I know hex nut thread chasers will normally cause a male thread to be undersize after clean up, but the tap shouldn't be oversize.
Threads wear, iron rusts... The holes will be larger after a bolt has been run through them. The deck on a flathead is thin, so the threads on the bolts don't get alot of bite as it is. The looser the holes, the weaker the hold. My opinion anyway Flatman
All good points. I've had a selection of well used taps that I use for chasing the thread on every engine I've built for the last 30+ years. They are no good for tapping fresh threads but perfect for cleaning threads to get the proper torque while ***embling an engine.
I rarely use taps anymore for most work. I use chasers whenever possible. I'd only use taps for new holes or when using something like a heli-coil. This is the chaser set I own.
When a tap is run into a hole there is some pressure exerted on the surrounding metal while the tap cuts. After the tap is removed the hole shrinks in diameter. Each successive p*** with a tap will press against the diameter of the hole removing material until that pressure is gone. Keep in mind that this pressure is minimal but it's enough to make a difference if a tap is run through too many times. Then you have a sloppy hole and nobody likes that. After the tap cuts the threads a chaser can be run through to clean burrs out of the threads but not cut them any deeper.
I do know that if you try to chase a heli-coil hole the coil grabs the tap and you ,or in this case, me, are in trouble. Again I fine that hex, nonadjustable dies (rethreading dies) will cut undersize and remove the bottom of rolled threads where the grain is most compressed. I think if you use "J" series taps you will do OK.
I've got a F1 in the for sale section with a flatty that you guys can buy and ream all you want. Make me an offer.
I make thread chasers out of the proper bolts, example a head bolt. I put it in the vise, take my triangular file and make 3 or 4 slightly angled cuts in the threads. Making it look like a tap. The grooves are deep enough to collect any crud in the threads, and it is not a hardened cutting tool, so it does not cut much if at all. I've been doing this for years on late model ****, and dont see why it wont work for a flatty.
If your REALLY serious about engine re-building; ARP makes a beautiful set of thread chaser taps. (longer than the Craftsman chasers) To add to oldcarmike's reason for NOT chasing a threaded hole with a CONVENTIONAL tap. Once a fastener - stud or bolt - has been used in a threaded hole and loaded (torqued), the "peaks" of the cut thread "bend" in the direction of the load. (very slightly) So, if a conventional tap is run down the threaded hole - AGAIN - it will cut the "peaks" - that are "pulled" very slightly and produce a sloppy fit.
The big thing to remember with ANY engine is to clean the threads so you get the proper torque on the bolt. For example, if you have a threaded hole that the threads are bad, you won't get the proper torque on that bolt. A good rule of thumb is to chase all threads prior to ***embly. I prefer to chase the threads with a tap. But, like you mentioned, 3 different people= 3 different answers. Just my $.02
Taps...there are cl***es of fit controlled by the design of the tap. The real dope is in the Carroll Smith Bobolt book, in the various little macinest pocket books, in posts by people who have checked out the prints in Ford archives. This stuff in my post is from memory, and may be a bit addled but is essentially right I think: Two known areas, by the way...'28 up deck holes for studs, banjo to axle housing bolts. Studs and bolts for each are normal hardware sizes. Cl***es from memory are 1 (all thread from K Mart), 2 (prctically everything on a car), and 3 (tight threads). The tight kind was made with a type 3 (or whatever it is) cl*** tap, DIFFERENT thread for, I think key part is threads go deeper into grooves of fastener, flanks of said thread also rub tighter on flanks of female part of fastener threads. I don't know if the Fordage was done to this standard or some other...lots of bolt designations are postwar, but same ideas were in use back to Isaac Watts or whatever. S0...normal cl*** 2 tap, the onliest kind you can get locally without hitting industrial supply places, will shave down the threads in block, loosening up the fit. I am not sure if a worn tap or chaser could be fully expected to have desired form to avoid this... If you can find an unmolested block, damn hard nowadays since I already ran taps through all of them (sorry), screwing in a good original stud by hand til solid will result in a stud that is vertical and free from wobble. A tapped hole will give some degree of wobble, and likely you will have to hand tighten your fasteners against a temporarily installed head to get them all set up vertically after you apply your favorite goo. Incidentally, studs go in just a bit beyonf hand tight, maybe a 10 ftlb MAXIMUM. Tapped banjos, by the way, leak 90 weight. Good ones usually don't--you can tell because bolts are hard to turn in by hand with good threads on banjo. Tapped holes (***uming good tap) work OK, but are obviously a bit weaker than stock due to diminished thread mesh. I'll dig in books and see if I can put proper designations and numbers on what I said. Also--somewhere in my rat's nest I have a NOS KR Wilson tap supposed to be the right one for this job...I would love to check it out, but I don't know whereinhell it is. Found the original Ford stud puller, but tap wasn't there... I've been seeking out this stuff, bringing it home, and losing it since the '60's...
Chasers made out of good bolts as above should be very safe. My current useage is gun cleaning brushes rotated through threads with copious spray solvent, followed by close eyeball inspection with powerful light. Obviously if metal has been distorted by some violence or threads are rusted, chasing will be necessary. There is indeed an issue here, and you need to be aware of original form of thread before making your choices. I think close reading of the thread spec section of machinist's book might illuminate use of normal chaser safety. I'd say make one from a bolt.
Now--I need to find books with thread descriptions...and are modern cl***es same as Henry used?? Gotta dig through the Fordschool meallurgy and machining books...I know modern Grade 5 and such postdate Ford, so Henry worked from his own version of 5 and 8 and 10 there...many Ford critical fasteners are tougher than 8's, more like aircraft than SAE bolts. Anyhow, somebody older than you probably ruined your threads in 1959... Just got hold of a book on British wartime flathead production...shows a gigantic Ford machine apparently tapping at least head, exhaust, and pan area bolts ALL AT ONCE...possibly even more, maybe all the holes in block. Wild picture...tapping oil and chips flying in all directions...
Every one who works with mechanical stuff should go out and buy the "Machinery's Handbook" mine is the 18th edition I think it's up to about 27 by now. Everything thing you will ever need to know about taps to treads to linkages to material selection is in this book. It is the Bible of the metal working business. Mine was required from Engineering school days. It is expensive at about $70 bucks but you will not find the amount of information contained in this book anywhere else.
Also, IMHO, a used one of almost any age will do the job for most of us. It seems to me that most of the newer huge additions are only of much use to those using modern high-tech shop equipment with CNC and lasers and aliens... I also like little pocket books for engineers/machinists containing only the bits I need continually, like drill sizes for taps and decimal equivalents. Some of this basic stuff can be found in very nice charts online. My favorite is one I think was probably ripped out of an old Poular Mechanics and installed between two sheets of plexigl*** with aluminum rivets around the edge--I'd bet money it came out of some sort of WWII airplane factory! Folklore: Machinery's handbook fits into a special odd-sized drawer built into all machinist's tool chests; I've been told that the publishers have to continually make binding and paper grade changes as practices change and multiply so it will continue to fit with a zillion pages that didn't exist in the '42 edition...
In addition to the nominal size and pitch of a tap, there is the "H" limit or number to identify how much a tap will cut over basic. Each "H" number equals .0005" and a tap marked as H1= .0005" over basic. A tap marked H3= .0015", H4= .0020 and so on. You can buy good and less good taps from Rutland Tool. rutlandtool.com
Bruce, a used book is a excellent idea, besides saving money it already comes with patina (sp) that is in so much demand today.
FWIW, I was working on a "C69A" - the Canadian equivalent of a US "59A" - block a short while back. The main bearing stud holes - sometimes used bolts - have an UN-TAPPED area from the block surface to where the threaded area in the block begins. I had purchased a new set of ARP studs that have a slightly longer threaded ends than the original Ford studs - block end - and decided that it would be wise to "clean" the threads a bit. (to allow the stud to sit further down in the un-threaded area) When I went to start a CONVENTIONAL tap into the un-threaded area; it STARTED TO CUT THREADS!! Knew something was wrong after one turn! I stopped immediately; got my THREAD CHASER SET - Craftsman - out and started again. Because the Craftsman thread chasers are SO SHORT, I couldn't reach into the bottom of the stud holes to clean the existing threads. (the Craftsman chaser DID p*** through the un-threaded area) Make trip to my friendly ARP dealer and purchased THEIR thread chaser set. (a bit expensive) Their chaser taps look EXACTLY like conventional taps; especially the length. THEY p***ed through the un-threaded area, and didn't even leave a scratch. Cleaned out a lot of "junk" at the bottom of the hole threads. So ... for what ever reason; for cleaning existing threads, I use THREAD CHASERS - ALWAYS!!
My Machinery's Handbook is seventeenth edition. Bought it new in '65. A give away that i use more often is the Machinist's Practical Guide that Morse gives away, or used to. maybe not today.
The Jalopy Journal
