Small block chevy oil pressure take off thread size.
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  1. #1
    Rods 'n' Sods Junkie
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    marg is offline

    Small block chevy oil pressure take off thread size.

    Hi guys.
    I am helping a friend out getting a chevy powered rod going.
    This could be the simplest answer in the world.

    Old engine 305 had oil pressure take off at the top just behind the inlet manifold, where most of the Ones I have seen are taken from.

    On the new motor that take off has been bunged up and is not coming out.

    Correct me if I am wrong but there is also a threaded hole near the oil filter, is this an oil gallery and if so can I run the oil pressure switch from here, if yes,
    The thread is bigger than the one at the inlet manifold!

    Question 1 can I take oil pressure from here?
    Question 2 what size is the thread?
    Question 3 what size is the thread on the take of near the inlet so I can get a adapter from one to the other!

    Thanks for any help

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    Not sure about the oil filter location one but I think the top one is 1/8 npt.

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    I'm Not Jed Clampett stueeee's Avatar
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    The one near the filter is an oil gallery, so you could use it; but it will give a higher reading than the "proper" one a the rear of the block as it's a lot nearer the oil pump -unlike a hydraulic brake system where there is negligable flow there's a fair flow in a motor's oil system so you get hydraulic drag which has an effect on the guage pressure you would read at various points around the system.

    Thread of the one at the rear of the block is 1/8" NPT as said.
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    Rods 'n' Sods Junkie
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    Hi guys thanks for the help

    I'm still after the thread size for the hole near the filter so we can get an adapter.
    We will use the top hole in the future when the inlet is changed for a better one. However want to get the car running and on the road where it should be

    Amy one help with the thread size

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    Full Bloody Rebel! Mad Mark's Avatar
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    1/8"NPT is approx. 1/4" diameter.

    That hole will be NPT, so measure the rough diameter and take it down one size. 3/4" = 1/2"NPT, etc.

    If I remember correctly, on mine (I can get to it to measure!) it's 1/4"NPT. I had an oil take-off in there originally using the adaptor from the rear hole with a sleeve to up the size.
    If I wasn't meant to go that fast, the pedal would only go half way!

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    I'm Not Jed Clampett stueeee's Avatar
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    According to my thread chart, 1/8" NPT has a maximum OD of thread of .405" it's a taper thread so if you're measuring the the threaded hole it is likely to be a bit bigger than the 11/32 tapping drill size.

    1/4" NPT has a maximum OD of .540" also taper thread as above, tapping drill size is 7/16"

    I have a SBC motor in bits in my workshop at the mo' -I'll try to get a look at it later today and confirm the actual thread size.
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    I'm Not Jed Clampett stueeee's Avatar
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    Just checked the block, there are two holes above the oil filter on this block (early 350 high Nickel 4 bolt). From the dimensions in the previous post, they are both 1/4" NPT.
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    Official RnS Addict 35kid's Avatar
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    Quote Originally Posted by marg View Post
    Hi guys thanks for the help

    I'm still after the thread size for the hole near the filter so we can get an adapter.
    We will use the top hole in the future when the inlet is changed for a better one. However want to get the car running and on the road where it should be

    Amy one help with the thread size
    the inlet should have nothing to do with the oil pressure gauge hole? maybe ive misread what your saying...

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    Probably interference with sender Mark.....a tall spacer sorts it.

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    Official RnS Addict 35kid's Avatar
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    Quote Originally Posted by german8rcoupe View Post
    Probably interference with sender Mark.....a tall spacer sorts it.
    That's true, hadn't thought of that, it's easy to get hold of a spacer if needed.

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