Since making the film I have tapped the firts hole and rather satisfied that the tap found the old thread and cleaned it out . One more to go.
Now that its too late to stop you…
I got to wondering if that black goo could have been flushed out with a steady stream of pressurized solvent? That’s what I did, but mine were not solidly gunked up, I had flow initially.
I did wonder that , but all the engine people I spoke to told me they have to come out . Even with them out it will be hard to get in all the nooks and crannies.
From memory, I believe that the hole is BSPP (not BSPT), hence the staking around the edge.
Mine was defiantly BSPT for plug and hole .
No, a tapered thread in both the plug and the hole makes sense to me, in that you don’t want any leakage. The staking makes sense in the disastrous consequences of the loss of a plug.
I was just surprised that they were not 1/4-18 NPT because the British were moving towards unification with the US and Canada at that time, ANF threads on new designs being the preference, and a new part like an XK crank has ANF threads at the ends.
In my experience of other makes, British manufacturers moved gradually to UNF from Whitworth during the fifties and sixties, with many engine fasteners being the last to change. British pipe threads endured for a long time, though. I don’t recall coming across NPT threads in a British car, although they’re obviously very common in anything with a US V8, 4bbl carb etc.
Y’all have not convinced me yet. The plugs are not long enough to be tapered thread. You can’t control the exact depth of penetration with a tapered thread like you can a straight thread. Makes no sense to stake a tapered plug. Any kind of leak there would be inconsequential.
I agree with this. Between the block, intake and radiator, there are lots of BSPP and BSPT fittings on XK’s. You still see BSPP/BSPT fittings on all manner of modern industrial and earth moving equipment hydraulic systems.
Plugs measure 12.58 / 13.28 diameter x 12.85 long . That gives an angle of 1.56 ° which is about right for 1/4 BSPT at 1.47° .
I have an unusual item, a BSPT die. It is about 12mm thick, so is only capable of cutting a tapered thread about 12mm long .
Minimum useful thread length for 1/4"-19 BSPT internal threads is 80% of 7.25 threads, or 5.8 threads. 19 tpi / 5.8t = 0.305", or 7.75mm, so the length of the thread engagement needs to be at least that long for tapered thread.
1/4"-19 BSPT left, BSPP right
Sorry Mike but what has to be shown to convince you that the plugs are tapered?
The staking has nothing to do with sealing the possibility of a leak, that’s the purpose of the taper, staking is just a mechanical means of keeping the plug from creeping out.
I don’t know. I can tell you one thing, I am consistent. This same question came up in 2004 and 2011. My response was the same.
And in 2011:
In reply to a message from wardell sent Tue 19 Jul 2011:
3.4L and 3.8L plugs are 1/4’’ BSPP, parallel thread. I have never
seen brass ones, only steel. They are fairly soft steel.
They are generally staked in 4 spots around the perimeter. I just
removed a bunch of them. In my experience, it is futile to attempt
to remove these using any type of hex driver and muscle alone. You
will certainly strip the hex on one or the other. I have never
taken a torch to a crankshaft.
I use a 1/2’’ diameter carbide ball mounted in a die grinder to take
out the as much of the top of the plug as I can, removing the plug
head and staking, but leaving the crank metal untouched. The top of
the bore for the bungs is not threaded, so there is little danger
in damaging the threads. I then drill out the center with a 12’’
long 1/4’’ drill bit followed by 11/32’’. I drive in a square EZ out
and use a 14’’ Crescent wrench to turn it while simultaneously
tapping on the EZ Out with a hammer. Sounds like a lot, but it only
takes about 5-10 minutes per plug in practice.
I recently tried a different type of EZ Out, one with a hex head I
could put a 1/2’’ drive socket on. I thought I had discovered sliced
bread all over again. Thought I could skip a couple of steps and
pass GO. Wrong. It sheared off in the plug and I spend the next 4
hours drilling out the nub with a carbide bit.–
The original message included these comments:
In reply to a message from Bishop13 sent Mon 18 Jul 2011:
I think these plugs have a BSP thread. ( British Standard Pipe).
This is a commom plumber’s thread here in the UK. and available as
blanking plugs for all kinds of engineering applications. (
Why the 12" long drill bits? Not cheap…
With a short jobber length bit, there was an interference between the drill chuck and the adjacent crank throw counterweight. I couldn’t get the angle right. Using the long drill bit moved the chuck back and allowed me to drill right down the center of the plug, avoiding damage to the female threads in the crank.
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Did this job today, not nice but now it’s done. Thanks for the advice Mike - I tried the first with a nice Snapon hex key socket, which duly broke off in the hole. It came out easily enough but I took your route for the rest. I used a ½" tungsten carbide ball grinder bit to take out the first bit including the staking, then went up through 6 drill sizes gradually to 5/16" before using a rectangular stud removal tool with a large adjustable, tapped with a hammer. Got all 6 out intact apart from the drilling through the centre, threads intact as I didn’t get near them.
I didn’t need the long drills, though. There was plenty of room for my chuck (Makita cordless) so an ordinary HSS size worked fine, with the hole through the plug being nicely concentric.
Looking at the plugs that came out, I’m afraid I really can’t decide if they are BSPP or BSPT. If they are tapered, it’s a very, very slight taper, which could easily be down to the effect of the tapered stud remover opening them up slightly on being hammered in. I can’t help thinking the staking makes sense for parallel plugs - I need to take some careful measurements.
On replacement, would you re-stake them, or use a thread locker?
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I prefer thread locker…no hammering involved and the high-strength stuff can be removed…with HEAT, that is. The medium-strength requires plenty of torque to remove, but no heat.
I staked them, but can’t say that an appropriate thread locker would be a bad thing.
IMO, it takes more skill to run an oxy-acetylene torch than a grinder, so I stick to the grinder.
What do you use to stake them, Mike?
I used a center punch.