Diesel & silicon sealent?

Discussion in 'Diesel Engines' started by ted655, Jan 7, 2008.

  1. murdomack
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    murdomack New Member

    Ted,

    I'm almost certain that you have the same filter as I have on my own boat. It was originally a Duplex set, but when I re-engined three years ago I split them up and placed one bowl on either side of the engine space so that I could slide my body through easier (it gets more difficult as I get older, :D).
    Thinking back, I am sure it's a UNF thread and the fittings were union couplings similar to JIC. I'll be down there in the next few days and see exactly what I have.
    When you say that the 1/2" NPT tightens with 3 threads left that's what leads me to think that the bowl is 7/8"-14 UNF. The OD of 1/2" pipe is 0.84" which is actually smaller than 7/8" (0.875"), and the max finished thread dimension is 0.832" for NPT because of the flat crest. The female 7/8" UNF small diameter is quoted as between 0.814" and 0.798" so you could be starting to tighten up about this point but your thread will never be seated properly in the flanks.
    You could get a special oversize thread (to about 0.9" Max diameter) made as mentioned earlier, but unless you can get it made as a favour then you would be better getting the proper fitting as it will be cheaper and correct.

    If you have or can borrow a vernier caliper and measure the inner thread dia. of the thread in the bowl and if it is about 0.80" up to 0.81", then you can almost be certain that it is 7/8" UNF. Thread gauges will confirm the pitch and if it is 14 then all you need is an adapter fitting from male 7/8" UNF to 1/2" NPT or whatever your valve is. Try hydraulic hose suppliers for these threads as they are more likely to have them.

    I just got this link of fittings, what worries me is that the Racor 500FG max port size quoted is 3/4" UNF and there is no way you can put a 1/2" NPT up to its last threads in that. You need to get that vernier and get the true inside diameter. :D

    http://www.ftginc.com/distribution/Racor Fittings Applications.pdf

    My fittings are the sae straight and elbow types. How I adapt from that to pipe threads I will need to check as I can't remember right now but you can see that you can get connectors direct to NPT.
    I am begining to think that you might not be using a 1/2" NPT for your trial fit. Send me the lesser diameter of your filter thread and I should be able to work it all out,


    Murdo
     
  2. ted655
    Joined: May 2003
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    ted655 Senior Member

    :eek: . So sorry, reamy words as you have read them, I mis-spoke, The 1/2" NPT does not tighten up UNTIL it is complerely in and the last 3 threads of the taperfinaly have enough diameter to START holding..
    If I try a 1/2" straight thread fitting, it "almost" slips freely into the hole. The tips of the threads barley touch the tips of the bowl thread. Un fact, uf I rock it side to side, I can pass the fitting completely through, ubto the bowl, no twisting needed..
    Did I miss the 500 listed in your link? I saw it jump from 400 to 600.:confused:
     
  3. murdomack
    Joined: Jun 2007
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    murdomack New Member

    Hi Again,

    Directly below the table you mention is all dedicated to the 500FG. This is the road and plant model, the marine might be different, hopefully not. Try and get a measurement of the diameter as requested. You can give me an accurate outer diameter of the thread that just rocks through, it might give a pointer to what the bowl thread is. Fractional or millimeters will do for now if you don't have a vernier or a micrometer to hand

    Murdo
     
  4. murdomack
    Joined: Jun 2007
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    murdomack New Member

    Ted

    You mention the factory spigot a few posts back, so if you still have this then you have the thread and just need to ID it using the Swagelok website as a reference. Then you can order a connector to suit your valve.
    You could also take this spigot and your valve to a large diesel specialist or a large hydraulic hose and fittings supplier and see if they can get you the fitting that you need.
    It could be a time versus money decision

    Murdo
     
  5. ted655
    Joined: May 2003
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    ted655 Senior Member

    Murdomack, perhaps you can help with another problem.
    The inner (swwing) bolt holding my alternator was badly rusted. I finally got it out. I want to clean up the threads. The head of the bolt has 3 hash marks "BUFO, UNF, 88 on the head.
    .
    My M12-1.5 die "seems the closest, but something is a tad off maybe? I could have "pulled" the threads as I struggled to remove the bolt. Is a UNF a metric? This is a Volvo AQD40A. metric right? Bolt isn't that important but I sure can't mess the block threads up.
     
  6. murdomack
    Joined: Jun 2007
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    murdomack New Member

    Hi Ted,

    From what you describe about the markings on the head, The three hash marks and the 88 (look again, I think it will be 8.8) suggest that the bolt was manufactured in Europe/Asia, but has been threaded UNF, which is an American thread, Imperial not Metric. This would not be uncommon as UNF is used on a lot of engine threads worldwide. Conversely, my new US-built Westerbeke engine has a lot of Metric on it. It all depends on the donor engine that is marinised.
    8.8 is to do with the bolts steel strength. I think the American structural grade A5 is superior if my memory serves me right.
    The way I ID a bolt thread if I don't have my thread gauges handy is very simple, although I have had to have a few goes with some, my eyes are not as sharp as they were.
    Measure the thread diameter as accurately as possible then, using a rule or a measuring tape that has inches and millimeters find the thread pitch.

    If the thread is long enough try and place the zero and the 1" mark on the crests of two threads and if you can do that, count the number of threads between them. With a tape you would use two markings away from the end of the tape as the hook would stop you lining it up properly. You have to be certain that the markings are spot on the crests.

    If the thread is too short, try and place the 1/2" markings on two crests or on a crest and a root where the thread is an odd number. For example if the thread pitch was 13 you would be counting 6-1/2 threads in the 1/2" space. Sometimes you can match on the 1/4" marks and mutiply by 4 for the pitch.

    If you cannot get the marks to line up with the inch markings, then you have to suspect that it is metric. Try and line up groups of threads with the millimeters on your measure, if the pitch was 1.5 then you would have 2 threads at 3mm, if it was 1.25 you would have 4 threads at 5mm and so on.
    It's a bit crude compared to using thread gauges, but with care it will get you the answer.

    Compare your results to the tables attached,

    http://www.portlandbolt.com/technicalinformation/thread-pitch.html
    This one gives UNC, UNF and UNS. You are only interested in the collumns that say "Nominal size and Threads per Inch". The three sizes that I suspect could be your bolt are 7/16, 1/2" or 9/16" UNF. Note that 7/16" and 1/2" are the same pitch, so you will have to double check your diameter.

    http://www.engineeringtoolbox.com/metric-threads-d_777.html
    These tables are of the metric sizes, note that there are course and fine pitches.

    It's a bit long winded but I hope you can follow it OK

    Murdo
     
  7. ted655
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    ted655 Senior Member

    :D Will do, (rather my son will), I've tired eys myself.
     
  8. Landlubber
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    Landlubber Senior Member

    Murdo,

    No you must be right about the fule label instead if fine as I believed it to be, if the threads are the same pitch, that is the end of the discussion really eh, as fine does mean finer pitched threads, thanks for your reply.
    I will reset my brain.
     
  9. murdomack
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    murdomack New Member

    Ted

    I am begining to think that you are using a 1/4" NPT thread and assuming it is a 1/2" NPT. When you mention a 1/2" straight thread do you mean that the thread diameter is 1/2". If so, I would guess that your bowl thread is 9/16" UNF which is a size that Racor quote. It has the same pitch as 1/4" NPT,18 tpi, and would alow a 1/2" diameter to wiggle through.

    The nearest metric is M14-1.5, but I have only seen M16 mentioned by Racor. They could have used M14 in the past, so you will need to be carefull.

    When we say 1/2" NPT we are talking about a pipe thread where the 1/2" is the nominal bore of the pipe. It's thread diameter is almost 7/8".

    If I am right in my assumptions then you need a male 9/16" UNF to 1/4" FNPT adapter, 9040-6-4 in the Racor file I sent you earlier. You will also need a 1/4" NPT nipple from that to your valve.

    Just in case I am not right, why don't you obtain a 9/16" UNF bolt and try and screw that into your filter before you commit to buying fittings.

    An online chandlers here in the UK sells the metric versions of these adapters for about $6 each so I think they should be even less in the USA.

    Murdo
     
  10. TollyWally
    Joined: Mar 2005
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    TollyWally Senior Member

    The mystery of similar but not exact matches. This is just in time, as I am fitting out an aluminum diesel day tank for my new stove installation. This was a factory purpose built diesel tank. It has a standard 1 1/2 fill neck at the top, and what I thought were standard 1/2 pipe thread at top and bottom for vent and outflow.

    I have a double handful of misc. brass and bronze fittings and valves in the archives that I have tentatively dry fit into various assemblies trying to figure out a clean installation.

    I am barely literate in pipe thread trivia. I knew about pipe threads and machine threads and of course have some grasp of fine and course. I was completely unaware of a specific thread for fuel. I was work on the tank installation today but I think I will wait for a little more enlightenment and do some fiberglassing instead. The weather suits anyhow.

    On a related note, I had a hell of a time with the old bronze pipe cap that was used as a filler cap in the past. It was always a bit "sticky" in the past. Even though I put a bit of antisieze on it, it had been a year or so since I last opened it. ( with a new stove I decided to move the old tank to facilitate a few other engine room issues.)

    Since this is my boat and any maintence and repair in the future will be done by me I always design new installations for ease of service. What is the hot ticket for choosing and preparing (magic goop, tape etc.) the fittings that screw into the Aluminum tank?

    Thanks, I appreciate being able to tap into the wellspring of accumulated wisdom assembled here.
     
  11. murdomack
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    murdomack New Member

    The earlier discussion about threads for fuel does not mean that ordinary well made threads, with a suitable sealant will not do for diesel. The NPTF or the dryseal thread as it is known is used more in process plants, where pressures are higher, and leaks could develop through the tiny gaps in the threads. A lot of sealants will not withstand the combined effect of the hydocarbons and the pressure. Leaking hydrocarbons will explode, therefor the special thread. Diesel is very tame in relation to these liquids and gases, but you will see NPTF in the manufacturers specs for diesel equipment quite often.
    In case you are confused by my mention of FNPT in my last post, this simply means female npt.
    Running diesel from a daytank to a heater or an engine will not be subject to any great pressure, indeed it will be in suction at times in the case of the engine so as long as the threads are matched properly, Teflon tape should be fine. Check for leaks after the engine has been running for a while, the vibration will set them off if they are there. If the leak doesn't take up with tightening then you will need to either change the fittings or try using a sealing paste that is good for diesel.
    I am not sure that aluminum and brass/bronze are compatible metals. Aluminum is closer to steel in the tables. You could buy aluminum pipe fittings (www.mcmaster.com) to come off your tank threads then convert to tubing or use what you have. If the tank is much bigger than the bronze fittings and normally dry it should be OK. Was your bronze cap on an aluminum tank as well, maybe that's why it was siezing after a while.
     
    Last edited: Jan 13, 2008
  12. murdomack
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    murdomack New Member

    Ted

    Reading the spec for a 500 FG, the thread on the T-bolt that tightens the filter is threaded 9/16" UNF. See if this fits the inlet and outlet port threads

    Murdo
     
  13. TollyWally
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    TollyWally Senior Member

    Thanks for the info, I'll use teflon as per normal and maybe swap in a stainless or nylon nipple to start my manifold etc.
     
  14. seastalkercat
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    seastalkercat New Member

    Teflon Tape WARNING!

    Be cautious using it before any kind of pump as it finds its way into and can ruin pumps. It is best to use it only upstream of the secondary filter.
     

  15. ted655
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    ted655 Senior Member

    ;) Thanks. Actually it is up streame of both the primary (2 micron), and secondary, (10 micron), filters.
    It's been there awhile now. No problems yet, it seems to be doing the job. I have a "test" glob that is immersed in a tube of diesel. I check it reguarly also.
     
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