What thread into block on 1975 DB 990 oil pressure switch?

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TIV
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Location: B.C., Canada

What thread into block on 1975 DB 990 oil pressure switch?

Post by TIV » Sun Feb 26, 2017 12:42 am

Hi, I've just registered for the Forum but have had my 990 about 15 years and put about 1100 hours on it in that time. I appear to have a low oil pressure problem now but it may simply be a defective switch for the "idiot light". The tractor runs well, in its normal way and no blue or white smoke or anything. Has never used any oil. ...I have no way of measuring the oil pressure, unless I can find out what the thread is, into the engine block, and get an adaptor to a common thread I can attach a gauge to. Can anyone advise on this? I really need the tractor back in service. Thanks!

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db2d
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Re: What thread into block on 1975 DB 990 oil pressure switch?

Post by db2d » Sun Feb 26, 2017 7:31 am

1/8 BSP. ( British Standard PIpe 28 Threads Per Inch )

TIV
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Re: What thread into block on 1975 DB 990 oil pressure switch?

Post by TIV » Mon Feb 27, 2017 6:15 am

Thanks very much, db2d! I had measured the threads at 28 per inch but didn't know the size & type of thread. ...Now to try to find an adapter from that to something more common that I can attach an oil pressure gauge to. Or, equally good or better would be a sending unit with that thread, if there is such a thing, for an electrical oil pressure gauge to put on the dash.

SteveCollett
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Re: What thread into block on 1975 DB 990 oil pressure switch?

Post by SteveCollett » Mon Feb 27, 2017 8:59 am

many back street garages will have a kit which will have a gauge and adaptors for virtually all known threads of this type. I had to borrow one from my local when the new switch I fitted gave some strange results . luckily the new switch was faulty which is apparently common.

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db2d
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Re: What thread into block on 1975 DB 990 oil pressure switch?

Post by db2d » Mon Feb 27, 2017 1:23 pm

I do not know of an electronic gauge but a normal oil pressure gauge kit is available that is similar to what was available as an optional extra when these tractors were new.
Try davidbrownparts.com

TIV
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Re: What thread into block on 1975 DB 990 oil pressure switch?

Post by TIV » Wed Mar 01, 2017 7:16 am

db2d: thanks again. On the davidbrownparts.com website I see only a gauge that should be fine but doesn't seem to be a kit and there's no visible evidence of a means of connecting into the engine block. I find that I can easily get ordinary mechanical (hydraulic) oil pressure gauge kits from automotive parts suppliers here but they all have the American 1/8 NPT thread into the engine (mostly come from the States). All I need, then, is an adapter from BSP to NPT and it looks as if I can get this from a couple of companies in Canada and a number in the USA. I may even be lucky enough to be able to get the adapter from an outfit in our nearest large city, Vancouver, that specializes in hydraulics.

I'm still bothered by one small concern, though. I suspect that the thread I need is BSPP; not BSPT (i.e., a "parallel" or cylindrical thread, rather than a tapered or conical thread) but I'm not sure. I think it is BSPP because I understand that this is much more common for this kind of application and also because I can't detect a significant taper of the threads on the old switch using my inexpensive micrometer caliper (the actual threaded length is only about 6 mm, though). On the other hand, the old switch has only some sort of fibre composition washer: no brass or copper or even urethane ring. Also, I've noticed that the switch turns out very easily (between two fingers) after it has been loosened only a quarter turn or less, which makes me wonder if it could be a case of a parallel male thread in a conical female one. ...In the absence of more knowledge, I plan to get a BSPP to NPT adapter and try it. Clearly, it will have to come with a sealing washer.

Steve: thanks for the suggestion. Unfortunately, I'm not lucky enough to live in a place that has back street garages here and there with knowledgeable and well equipped mechanics. I think I'm just going to have to buy a gauge and fit it. I'm hoping that my old switch will prove to be faulty like the new one you fitted!

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db2d
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Re: What thread into block on 1975 DB 990 oil pressure switch?

Post by db2d » Wed Mar 01, 2017 8:55 am

The thread in the block is BSPP

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