Stripped sump plug thread

[Freddie116]

I am doing an oil change on my 4.2 series 1 and the sump plug has come out with all the thread from the sump! Do people recommend heli coil or retapping kits to repair? Any in particular? I think it's a 5/8 plug is that right? Any other tips?

[Mikael B]

I did mine with heli coil one year ago and yes it’s 5/8” UNF tread. A tip is to make sure the heli coil drilling in done in a correct angle, otherwise you will have a leak.
I got mine just about right and could tighten it to seal properly.
Mine was done in situ but I would recommend removing the pan for better access, however that is a big job.

[Freddie116]

Thank you. Was there a particular kit you used or you would recommend?

[mgcjag]

This could be an option... https://www.coolcatcorp.com/Merchant5/m ... y_Code=Oil dont rush into anything yet im sure you will get a few options given...Steve

[Tom W]

Mine stripped shortly after I got the car. Someone had used a similar metric bolt and cross threaded everything! I got my local classic car engineering place to drill out the hole to the next size up and tap a new hole. Means I have a non standard sump plug, but at least it’s not bringing the threads out with it each time I change the oil! There’s plenty of meat on the sump for a bigger plug. They removed the sump when they drilled and re-threaded it so as not to get any swarf in the engine. Having removed the sump once from under the car on axle stands, I can confirm it’s not a fun job.

[Mikael B]

I used the kit in the following link:
https://rover.ebay.com/rover/0/0/0?mpre ... 3125091337

I also used this drill:
https://rover.ebay.com/rover/0/0/0?mpre ... 1398696734

Good luck.

[johnetype]

The Coolcat option won't work for you, it's too small if as you say all the thread has come out from the E types' aluminium sump.

Taking advantage of the fact its an aluminium sump and the hole size you are now left with is very close to the size for a 3/4 UNF tap, I chose to buy a 3/4 UNF sump plug and 3/4 UNF tap. Cheaper and easier than the helicoil route.

As an interim, you'll find that your old sump plug suitably cleaned and degreased along with the sump drain hole and refitted coated with silicon sealant will give a surprisingly durable temporary repair if you need it.

[mgcjag]

Hi...Just befor you start drilling have a look at the thread.....just been looking at a couple of old posts and one says that the thread extends much further into the sump than the actual length of the plug.....so could be there is quite a bit of good unused thread still availabel......you then just need a longer sump plug....worth a look....Steve

[johnetype]

That's a good thought in which case I'd start with a 5/8 UNF setscrew with a backing nut on it so you can wind the bolt in as far as any remaining threads will allow and then use the nut to wind down on the copper washer to seal.

[Freddie116]

Thanks everyone. There is a tiny bit of thread left but I have deliberately pulled as much as possible out so it doesn't go in! Not enough to put a longer 5/8 back in. Will examine 3/4 kit but drawback is lack of originality.

[JerryL770]

I'm not 100% certain but very much doubt the thread is either 5/8" of UNF!!

I think it is not even UNC but 3/8" Whitworth comes to mind as the original size.

You can of course change to a UNC thread but UNF is never used in aluminium, I believe, it is too fine and easily stripped.

[tim wood]

On one of the old e type club magazines there is an article on this very topic. If I recall correctly the thread was replaced with an 18mm and a suitable plug used. The operation including drilling (by hand) and the re threading was all done whilst the sump was in place.

I will see if I can find the article we can’t reproduce it here.

[JerryL770]

I was a bit wrong. The original thread size would have been 5/8" Whitworth which is 15.875mm OD. So 3/4" BSW (Whitworth) is the next size up which is more easily obtained. This is 19.025mm OD so an alternative of an 18mm metric could do . . . . . if you allow metric threads in your Imperial car!!

Metric coarse threads are based on Whitworth profiles.

[Freddie116]

Thanks. I'm going to try to heli coil and get the original back in. Doesn't seem to be much difference between unc and bsw on 5/8 - both 11 turns per inch so a tap for either should work right?

[Mikael B]

Hi,
Tread is not BSF or UNC
Right tread for original oil plug is UNF 5/8 x 18.

I tested with old oil plug and new purchases from one of the usuals also rechecked with my other S1.5 E-type all was the same.

Agree that UNF are not perfect for aluminium sump but I guess that’s why we have this problem.
Helicoil insert is stainless steel and will be more durable.

As I said previously take care drill and tap in correct angle suggests that you put extra effort into this.

Good luck

[Freddie116]

Thanks. May I ask how you checked so I can check mine? Is that 18tpi?

[chrisallen01]

I fitted a sprung loaded valve from the following https://www.quickvalve.co.uk/ once fitted no need to worry about the sump plug threads again - ever.

[mgcjag]

Hi Freddie...you can check a thread with a thread guage....https://www.ebay.co.uk/itm/Sealey-AK72S ... ect=mobile
Specified here as 5/8 UNF https://www.terrysjag.com/product//C23435X.html Note they also have an oversize repair plug 3/4 UNF...others also sell them https://www.terrysjag.com/product//C23435OS.html Steve

[Mikael B]

Tread on sump plug was checked with a standard feeler gauge and yes 18 treads per inch.

The same tread for the sump plug is also quoted in other topics here and on JL forum.

You could maybe also use a standard 5/8 unf bolt to check your plug.

[Freddie116]

Thanks all