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Thread pitch ALL

I want to know the EXACT thread pitch for the oil line pressure hole in the side of a 1973 B-20 engine and the EXACT thread pitch for the temperature sensor hole in the right rear of a 1975 fuel injected head. Don't tell me what will screw into these holes (I already know that)tell me what the thread pitch specification is per the Factory Manual or? Thanks!

 





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    Re: Thread pitch ALL 60-75

    It would be helpful to most who aren't already aware of this

    to know that the vast majority of threads on Volvo cars and engines

    in the 122, 1800, 140 and 164 (and B18, B20 and B30) are of the

    Unified form, that is, inch sizes as used in the USA and Britain in

    the affected years. The exceptions seem to be items furnished from

    France and Germany, notably SEV-Marchal, Bosch and ATE.

    Some (but not all) of the threads on the 74 and 75 B20 are metric,

    notably the maincap bolts and bellhousing mounting bolts, which are

    M12 1.75 rather than 1/2" - 13 UNC and 7/16" - 14 UNC. On the bellhousing

    bolts it is deceptive because a pitch of 1.75 works out to about 14.5

    threads per inch, and 7/16" is mighty close to 11mm, so the 7/16" bolt

    screws into the 12 mm tapped hole pretty well, but is loose.

    In the Unified, American and British systems threads are normally

    given as threads per inch, so the pitch is the reciprocal of the

    threads per inch. Metric threads are normally expressed as pitch

    in millimeters, so a pitch of 1 is 1 mm per thread or 25.4 threads

    (millimeters) per inch. For rough calculations it is handy to remember

    that a millimeter is ABOUT 0.040" or roughly 2/3 of a sixteenth inch.

    At least in the oil industry (not sure about other plumbing) pipe

    threads are sufficiently standard worldwide that if you get a standard

    pipe thread almost anywhere, it will fit. Note that pipe threads

    are tapered 3/4" / foot or one in sixteen, so that they develop

    an interference fit as they are progressively tightened. That is how

    pipe threads seal. Extreme pressure lubricants like pipe dope, teflon

    tape, etc are helpful to guarantee that you can screw them together

    tightly enough to develop the required interference. If you mike a

    pipe fitting before and after making up a joint (properly) you can

    tell that you have expanded the outer fitting. On one occasion I

    used a LOT of teflon tape and was able to screw a piece of 1/4"

    (.540" OD) all the way through a tee and out the other side as a

    demonstration of, among other things, the fantastic lubricating

    quality of teflon tape.

     




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    Re: Thread pitch ALL

    To the best of my knowledge all of the oil pressure taps on

    B18, B20 and B30 are nominal 1/8" - 27 NPT. The pitch is therefore

    1/27" or 0.037037037.....inch. Like all NPT (Taper Pipe) threads,

    it is tapered 3/4" per foot. Note that pipe thread sizes are based

    on the nominal inside diameter of standard wall pipe. The outside

    diameter of 1/8" pipe is 0.405" or a little less than 13/32".

    I am pretty sure that they all have the same thread in the top of

    the head for the temperature sender. I took one out just now and

    measured it. It is a 5/8" - 18 NF thread so the pitch is 1/18"

    or 0.0555555.......inch. I don't have literature at hand (and the

    Volvo manuals do NOT give this info - parts drawings do, but they

    are not available.) but the temp sender seals on a tapered surface

    below the threads like a flare tubing fitting, maybe for 3/8"

    tubing or so.

    Just as a matter of curiosity, if you are so picky about the info,

    why didn't you measure it yourself?

     




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      Re: Thread pitch ALL

      Hi George,

      Thanks for the reply. The reason I am trying to "nail down" exactly

      what the thread pitch is that there are many thread forms that are very

      close to each other and difficult to measure accurately with a pitch

      gage (or optical comparator) even if the part has been sectioned. A

      good example of this is the 1/8 BSP (British Standard Parallel threads)

      at 28 threads per inch and the 1/8 NPT at 27. You can put these two

      together with a little teflon tape and they will function fine even if

      they aren't "correct". They feel like you would expect a 1/8 NPT to fit

      together. Racers commonly do this to the back of Smith gages to get the

      oil pressure gage to mate to an AN -3 fitting. In the case of the Volvo

      Block we have several possibilities that I can think of without really

      knowing the real story. The threads could be NPT or they could be some

      European variation of a pipe thread. The oil passage will certainly

      accept a 1/8 NPT male fitting. However, it doesn't feel to me like it

      has a normal amount of taper that I would expect which is a "red flag".

      Is this really a 1/8 NPT or something else. One possibility is that it

      is a 1/8 straight pipe thread, that is, without taper. Or it could be

      something entirely different. The hole in the head is similar in that

      it doesn't seem (to me) to have a normal amount of taper. I would just

      like to know what the correct thread for each is so that I can put the

      correct parts together correctly. In my particular case I have a Marcos

      car (Obscure British Car) which came stock with a Volvo B18 engine and

      M41 transmission. I have "uprated to a B20 bored and stroked to 2.4

      liters, dual Webers etc. mated to a M45 Ttransmission. So I already

      have a complete inventory of different thread forms from AN, SAE, BSP

      etc to keep track of. If I never actually find the answer to my

      question, the sun will still rise in the morning and life will go on.

      However, its stupid to do things wrong and not to ask questions if

      someone has the answer. In this case I realize that the question seems

      somewhat inane or anal. I wanted to avoid a lot of responses from

      people who really didn't know but would venture forth answers based not

      on knowledge but on what they forced into the hole successfully. Thus

      the use of the capitals for "EXACT". If you took offense, I'm sorry...

      none intended. I do appreciate your taking the time to respond and your

      thoughtful answer.

      Mike Denman

       




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      Re: Thread pitch ALL

      George,

      This type of technical info about thread pitch is something beyond my understanding.

      Would you mind giving us a little primer on how things are generally sized, and how to make such measurements?

      that kind of thing would have been very handy to me last Saturday after the test plug in the top of my new (aftermarket) catalytic converter somehow vibrated out!

      I wasted half a day running around to plumbing suppliers and auto parts stores looking for common pipe fittings, only to learn that a 3/8" plug, while large eough to screw into the hole, was still a smigeon too narrow to seal.

      It vibrated out in half the distance as it took the original fitting.

      Knowing something about these technicalities migh have helped me let my fingers do the walking by asking for a specific specification to my replacement plug.

      (Luckily, I went to the exact parking space 10 miles from home where I found the missing plug!)

       




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        Re: Thread pitch ALL

        Hi George,

        I'm afraid that a short primer on threads would be rather long. However generally speaking, threads are measured first by their diameter and than by how many threads are in an inch (SAE) or in a mm (Metric) etc. There are a lot of variations, some which are obsolete. So, if you have a bolt that you bought at you local hardware store in the USA it is probably an SAE (Society of Automotive Engineers) bolt. The SAE bolts are divided into two basic categoties (for bolts). Those categories are National Fine (NF) and National Coarse (NC). So, for example, a 1/4 in diameter bolt will come with two different threads, one is Fine and one is Coarse. The fine threaded bolt would be refered to as a 1/4 28 NF and the Coarse threaded bolt would be referred to as a 1/4 20 NC. The last measurement in the description refers to the length. So you might ask for a 1/4 20 bolt 1 inch long. The Metric system has a similar methodology except in mm. Aircraft bolts, which may be for all practical purposes, exactly the same, the 1/4 28NF bolts are referred to as a -4 bolt. A 4-8 bolt for example is a 1/4 28 bolt that is 1/2 inch long. There are also many many kinds of bolt forms and grades. The lowest grade bolt (in the SAE system)is a grade 2 which is ok for use on non stressed items. The next grade is grade 5 and then grade 8. If you look at the head of the bolt and it has no marks it is probably grade 2. A grade 5 will have 3 dashes arranged radially and a grade 8 will have 6 arranged radially. There are literally thousands of variations on each of the topics that I have touched briefly on in this message. Plugs (which you have had some experience with) pipes, tubing, instruments, plastics all have their own system but they are all based generally on measuring the diameter first and then counting the threads.


         




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          Re: Thread pitch ALL

          >However generally speaking, threads are measured first by their diameter >and than by how many threads are in an inch (SAE) or in a mm (Metric) etc

          Oh. I always assumed "pitch" had something to do with the *angle* of the threads. You say it's the number of threads per inch?

          Would not coarse vs. fine thread dictate differing numbers of threads, then, per inch? (1/4 28 NF and 1/4 20 NC)

          > The last measurement in the description

          > refers to the length. So you might ask for a 1/4 20 bolt 1 inch long.

          Do you mean the "20" in this example is the length? Or the Pitch and/or thread type (fine, coarse, etc.)?

          What kind of book would list these kinds of things? I'd like to read a threaded bolt "primer"

           




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    Re: Thread pitch ALL

    Well, the EXACT pitch for the oil pressure tap is 27TPI. Does that help?

     




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