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MG TD TF 1500 - Oil pan drain plug dilemma

Well I’ve been recommissioning a customers car after a 20 year hibernation. Oil had clean oil as the car had been parked shortly after its last service. After getting the engine running again and warming it up I began an oil change and to get rid of the obsolete filter system. When I put the wrench onto the drain plug to remove it, the weight of the wrench literally caused the pkug to fall out. Whoever worked on the car last had pulled the threads on the oilpan and globbed some sort of sealer on it and pressed it back into the hole. I’ve seen sketchy and bodged repairs but this is a new one for me. Can any tell me if an oversized fitting exists to adapt the original plug to the pan? Or an oversized self tapping plug etc? I would like to not need to pull the pan off to effect a repair. What have others done. What size is the original hole and thread. Was it metric? BSP? BSB? What have you done to fix this problem.
W A Chasser

Bill: I would assume you would have to have the opening filled by AL welding and then retapped for the drain plug. Sorry I don't have the specs on the threads for the drain plug.

The same is for rebuilding the missing fins on the sump too.
Christopher Couper

Hi Chris. Unfortunately this castings are very problematic to weld. To do TIG requires zero impurities such as oil, anti freeze JB weld etc. this is not possible with a used pan no matter how clean you think it might be. Plus given the crappy metallurgy porosity is a huge problem hi temps have been introduced.

Using 3/4-1/2 BSP bush can be done because there simply isn’t enough material at the bottom of the hole to go oversized. The same problem exists when attempting to use a 22 mm plug. A 20 mm plug is basically dimensionally the same as the 1/2BSP so no joy there either. I did manage to find a 1/2-14BSPP helicoil kit. Very expensive but it is the best option to try before a decision is made to swap the pan. I’ll provide an update once I get the kit.
W A Chasser

I knew the welding was problematic. Back in the 70's in SoCal we had a aircraft guy that somehow was able to overcome all of that and repair the sumps for us.
Christopher Couper

Personally I would pull it. A failed repair or patch could prove catastrophic. I've had sumps and bell housings repaired but it takes someone experienced, patient and just a little bit crazy.
Steve Simmons

I had an oil pump size and the parts thrashed around in the sump, the crankshaft throw pinned the piece between it and the pan. The pan lost. It banged a hole in the side. A friend of mine had a guy in his engine shop weld it.. afterward and now 18 yrs after you cannot find the weld. The pan does not leak and looks as original. Having said that, is there a heli -coil kit for this thread?

Regards, Tom
tm peterson

Many decades ago the threads failed on my aluminum sump and my shop repaired it for me with a threaded sleeve and a threaded plug. Has been working fine ever since but I do always use a thin wrench on the sleeve working against the wrench on the plug so as to not loosen the sleeve.

John Quilter (TD8986)

Tom, now you've scared me. A couple of years ago my dizzy destroyed itself resulting in the bottom gear (dog gear?) ending up down in the oil pan. I can grab it with a magnetic picker-upper but it's too big to get out through the drain plug. I've just left it in figuring it keeps the oil nicely stirred up and isn't doing any harm. Now I'm scared that it may interfere with the bottom end of one of the connecting rods or a counterbalance thingy and punch a hole in the pan. How scared should I be?

Thanks.

Jud
J K Chapin

I had that happen on my Y-Type once. I was able to get a magnet down the distributor hole and retrieve it. I don't expect that it would end up hitting a rod, but sometimes weird things happen...
Steve Simmons

I would want to get it out of there Jud. I bought a 82 Chevy years ago that was used by a salesman for the company I worked for. I knew it had a knock in the engine and I made the dealer who usually bought all of the cars know about it. They declined to bid on it once I told them about it and I picked it up pretty cheap.

It had a 305 V-8 and once I pulled the engine and took it apart I found the source of the knock was a broken piston skirt. In addition the block had a chunk busted out of the bottom of that pistons cylinder wall. The cause? In the pan was a single rod nut. There is only one way it could have gotten in there. When the engine was built the assembler had to have dropped the nut when putting in the rods and never removed it. It lived in the bottom of the sump for 30000 miles but the odds caught up to it and it got caught up between the rod and the block and bam. It was my first experience with a cylinder sleeve at a machine shop. A cheap rebuild kit and the car lived many years as the family car and when I sold it years later I got 4 times what I paid for it.
L E D LaVerne

OK, I'm convinced. I've got the head off to install new valves (see pic) so I might as well drop the pan. Thanks. Jud

J K Chapin

A piece of my distributor gear did just that when it let go and it pooched a hole in the side of the pan in the blink of an eye.

Regards, Tom
tm peterson

Well this got off topic. To answer someone’s question above the thread is 1/2 BSPP. ( Parallel Pipe). Yes I found a kit available they are extremely pricey but after receiving the kit it was understandable why. I do not recommend doing this in situ even though there is plenty of room to do the repair. The problem is it is impossible to drill the hole absolutely true. Also the oan thickness will only allow for 4-5 threats. I had to take a cut off wheel and remove several threads from the coil. Even with that I ended up needing to Nick more coil after installation so it sat below the sealing surface. I don’t not like the copper ring supplied by Moss as a seal. After installing the pkug I had a weep. I drained the pill and cleaned the plug and threads with Brakleen. I then applied liquid thread sealant and set the pkug back into the pan. I waited 4 hours to allow the sealant to cure per the package information before refilling the pan. It still has a small that I’m not happy about. Does anyone use a dowry washer for this plug and do they have a PN. I’m tempted to try a
Small rubber O ring on the plug that fits firmly in the groove behind threads

Bill Chasser
TD-4834
TD/c-8151
W A Chasser

try Dowty washers - the best
Michael Balahutrak

This thread was discussed between 29/04/2025 and 24/06/2025

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