Crankshaft grub screws

(Jim XK140 FHC) #1

Can someone help me with the thead size of the grubscrew plugs in the crank ? Are they eeadily available ?
Thanks Jim

(peter balls) #2

!/4 BSP, ask at a plumbers merchant.
Peter B.

(Robert Wilkinson) #3

Just for my reference…BSPT (I suspect) or BSPP?

(Jim XK140 FHC) #4

That was my next question , would the plug be tapered and the hole straight ?

(Robin O'Connor) #5

A vernier will define if it is tapered or parallel and engineering supplies would be a better place to source from I think.

(Jim XK140 FHC) #6

Here they are .
I will need to drill out one of my old plugs and re-tap , so I still need to find a correct tap , straight or tapered ?

(Paul Wigton) #7

Either, in this case, can work.

(peter balls) #8

Robert, BSPP

Jim, plug and hole straight, think about it! if the hole and plug are tapered one turn
and the plug would undo easily, did they?

Robin the plugs are standard plumbing fittings. If “engineering” the threads would
most likely be UNF/UNC or Metric

BTW I allways Loctite them.
Peter B

(tony) #9

tried to remove some, with the aid of a long pipe, but the internal hex within the plug began to distort, so I desisted.

Is it normal practice or helpful to relieve the 3 stake marks by drilling them slightly ?..or is that a waste of time?

Is it normal practice to apply heat via oxy as the next step ?

I did not even try impact gun, as the needed torque was way too high for mine
(and I didnt have the right size bit)

(Jim XK140 FHC) #10

I relieved the staking and got 4 out with a socket type key and a long breaker bar . I used propane heat on some , I thought oxy ac would be too fierce… One screw distorted and I broke the key off in another which put me in a load of troble. I got the bit out do have to drill 2.
Video to follow !

(Jim XK140 FHC) #11

Thanks Peter
if they are both straight what stops the plug disappearing into the void inside the crank ? Surley the plug must "bottom " out somehow ?

(Robin O'Connor) #12

Check that the threads are not right into the void, they are probably not tapped through.

(peter balls) #13

Exactly Jim !! the plugs “bottom out” as they voyage into the void and
reach the end of the galactic thread…
Peter B.

1 Like
(peter balls) #14

Tony I use a number 7 or above oxy nozzle and direct it into the hex of the plug,for 30/45 secs…
Let the plug cool then repeat as required.
The continual expansion/ contraction of the plug I find does the trick.
I prefer not to heat the crank metal around the plug.directly with the torch.
Peter B

(Jim XK140 FHC) #15

Thanks for the replies . Am I still missing the point ? I still think the plug is tapered ?

(Robert and Darlene Stevenson) #16

If it wasn’t how would it seal?

(Phil.Dobson) #17

jim i get replacement plugs from the machinist who does the block and gets the crank checked and ground where necessary. i believe they are tapered. i put them back with loctite as has been previously recommended. you can buy the plugs from most of the usual parts suppliers.

(Jim XK140 FHC) #18

I got some new plugs today and measured them , definitely tapered.

(peter balls) #19

Oh Well !! Humble pie tonight. Will you run a tapered tap into the crank?
Peter B.

(Jim XK140 FHC) #20

Is there such a thing as a tapered (finishing) tap? I know there is a “tapered” 1st tap but isn’t this to be used with a 2nd and bottoming tap for blind holes and not intended to be a usable thread ? I presumed the hole was a straight thread .