Can someone tell me where my oil leak is?

[TroonSprint]

Thanks again Rohan. I have ordered a 1/4" - 18 NPT bottoming tap.

Mike

[Craven]

Hi,
NPT & NPTF are not the same!!
NPTF (Dryseal) pipe taps have the same basic dimensions as NPT except the crest and root flats are norrower. This insures an interference fit when the part is assembled, the crest and roots are crushed to bring the flanks of the internal and external threads in contact with one another.
Ron.

[englishmaninwales]

TroonSprint
As Rohan states, that plug has not engaged fully, I have 1.5 threads showing with my 1/4 NPTF plugs from the same supplier, in that same rear oil gallery end.

Gas tight 1/4 NPTF is the correct plug as we discussed in April:
lotus-twincam-f39/nptf-oil-gallery-plugs-t33835.html?hilit=nptf

Malcolm

[TroonSprint]

OK Ron, so which is it? NPT or NPTF?

Mike

[ort]

the block is threaded !/4 NPTF and the plug is NPTF. the thread form is only gas tight when the components are fitted together for the first time as the deformation of the crest and root of the thread form the full metal to metal seal. If the plug is removed it must be replaced and the female thread recut within tolerance. In practice NPT will be fine with sealant as the oil system is not high pressure at approx. 3 bar max. I use these fittings at 300 + bar

[englishmaninwales]

Mike
Have a look at the photo of the original Ford blueprint on the 2nd page in the thread linked in my last post. If you download the photo and open it will be less blurred. Shows 1/4 NPTF as the correct thread.

Malcolm

[ort]

the difference between NPT and NPTF is the crest and root truncation
for 1/4 NPT both crest and root truncation is between 0.0018" min and 0.0049" max
for 1/4 NPTF crest truncation 0.0026" min 0.0043" max
root truncation 0.0043" min 0.0061" max

as can be seen NPTF can fall into NPT tolerances. we used to select from NPT stock for small orders if we were out of NPTF stock and remark

Mike
to give you an idea how far the tap should go in

be careful run the tap in by hand then max of a 1/4 of a turn less if possible otherwise the thread will be oversize and the plug will go in too far

Iain

[TroonSprint]

Iain, thanks for that guidance and photo. It's exactly what I need to know. I have now ordered a NPTF tap as I want to get this right. Hopefully with the right tap, the right plug, and a little thread sealant, my oil leak will be a thing of the past.

Mike