Hi Jag Folks.

In the re-commissioning of my 1989 5.3 HE V12 Coupe . . I've discovered that a previous owner has partially stripped the original brass bleed screw (probably by over-tightening) at some point.

In preparation for a full "warm-up", I took the bleed screw out in prep to topping-up and was amazed at what little force was needed. My suspicions were confirmed when I saw blue thread loc present on its threads. When I re-threaded it, it was barely hand tight before the thread "jumped". OK . . . I knew it was going to need a better fix . . and sure enough, coolant started leaking from the bleed screw at warm-up today.

And so Jag folks . . . the question is . . . Is there an easy or best fix?

My initial thought is to get a slightly bigger (and better material?) bleed screw ready and tap the thread up to a new (metric) size. Is this the way to go and any tips on best replacement parts?

Cheers . . Jag Folks

 

Do they make a helicoil in that size?

 

Are you certain the hole is a NPT thread?
Some times straight threads are used with sealing washers or O rings.
The plug or valve that was used might not be the correct threaded piece.
I don't think Heli-coil etc are very good at sealing.
My recommendation would be to use the next higher size NPT tap and try that.
Tap slowly with plenty of lubricant, removing tap after a few turns do a clean-out of the threads.
Rinse and repeat.
I have done this a few times to rescue bad pluming jobs.

 

It is most likely BSP thread, read "British standard pipe". Comes in both parallel and tapered. I had to find a thread chaser as well as a heli coil kit for the banjo bolt on the radiator. Mine was alloy.

 

That will be best and easiest. I also suggest using a fibre washer on it, rather than a copper one.

 

I think the tread is 1/8” BSPP. Or British Standard Pipe Parallel. Helicoils are available, but I can’t see you wanting to spend $84 on the special tap for them.
I think you can drill it out and then tap it for any suitable fine thread. The washer seals it anyway. A fiber washer may work, it may even be better, but a copper one is the official way. There are also metal clad rubber gaskets.

 

Hi Greg et al. Thanks for everyone's thoughts.

It's not too much of an issue at mo as not running her for very long. Last time, just long enough for a full warm-up and to spin the rear brakes free after a bit of TLC to pads and disks via some 2x2 and a lump hammer!! The rad drain plug I took out didn't have any washer, so that's a definite for a final fix.

Another thought is to maybe line the threads with some liquid metal epoxy mix and then thread cut with a tap of same size/thread etc of the original plug. Amazingly, I think there are helicoil kits as small as the plug size (6/8/10mm I'd guess) but not too keen on that route as lots of drilling, dumping the final barb/tang into the rad . . . and not altogether sure how watertight under pressure that thread would be?

She did run for years in her "thread partially stripped and coated in gunk" state . . . so a decent repair should be possible.

I'll update "this" thread when I decide on a fix for "the" thread. Cheers Jag folks