Drain plug thread on engine block

[Ziggy]

Can anyone tell me the thread on the drain plug in the engine block on a 1972 MK4 1300 Spitfire?  Its not 1/4" BSP , that I know for sure, and its not tapered either.

[Pete Lewis]

here is a recent post about block drain plugs  read it and its  ..........edit  5/8unf   (  now under serious doubt )

tapped holes in the block are always parallel , in  general  it is the plugs are tapered not the holes but the block drain is a straight plug approx 5/16" deep/long  x 5/8"unf 

it does  use a fibre washer but thats 1/2"c  ????????????  now im puzzled 

 

[Roger]

I'm confused... I read the thread Pete refers to and I just happened to remove the drain plug from my early Vitesse 2-Litre engine. Correct me if I'm wrong, but is it not 1/2 inch? Did not measure TPI or if it's tapered or not. Have I missed something or are early Vitesse 2-Litre engines different? (HC-engine)

I assume 4-cylinders and 6-pots have the same threads?

Edited May 5, 2020 by Roger
Added info

[Pete Lewis]

Hi Roger  you say  "is it not  not 1/2"  "  as  thats what your vernier is showing  it makes sense youre right

i only said 9/16" as thats whats on  Canley's parts lists 

i dont have one to measure , this would make some sense of the fibre washer being 1/2"  

on that basis 1/2" unf  sounds a better clue   glad you have one to measure 

triumph  parts lists all show  129077

Pete

[Mad4classics]

Looks like 1/2 x 20 UNF.

Got a funny home made jobby.

Trouble is 1/2 UNF, 1/4 BSP and 1/4 NPT are all pretty close to each other.

David

 

[Pete Lewis]

weird  the canley site now shows 120077  so where did the HU805 pop up from its used elsewhere but at  5/8" its obviously wrong clues for the drain plug

has to be 1/2"   agree with the 1/2" x20

please ignore all other bright waffling  

Pete

[Roger]

20 TPI confirmed, see picture

I noticed (when reading previous thread) that my drain plug had different threads but I just assumed that some PO had ruined the threads in my block and drilled a new hole and made new threads with a new drain plug, hence my plug being different. My metric brain did not realize at first that 5/8 is a bigger hole than my own 1/2 thread which eliminate the logic... I'm still daft regarding fractions of an inch despite fiddling with these cars for 30 years. Dividing with 10, 100 or a 1000 IS a LOT easier than comparing different size of fractions 😉