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MG MGA - 3H576 drain tap from Moss

I have just finished reinstalling my supercharger-spec engine and fired it up for the static run-in of the cam.

To make the swap as quick as possible, I obtained all ancillary bits and pieces like tacho drive, oil pressure gauge fitting etc etc and included only one brand new part - the drain tap for the rear of the block.

So tonight I filled the coolant system, and added 4.5 litres of Castrol Classic to the sump, primed the oil system, put the plugs in and started the car.

Where was the ONLY leak? You guessed it, from the brand new tap:- letting some fluid through it didn't help it seat, so it took an hour of taking dizzy out, removing oil pressure pipe, removing dizzy clamp and getting enough access to remove the tap and replace it with an old one that was lying in one of my drawers. The old tap sealed perfectly (I confess I had to give it a what with a hammer to free the taper to let it turn).

It's a bugger to fit (there's no space to get a spanner in and I ended up getting the angle grinder out and chopping the end off a spanner to achieve a result). Back in and now I am waiting overnight to see if there are any leaks on the floor tomorrow.

I bought the tap in April 2015, and I am unlikely to get a refund, so I have taken the split pin out to inspect, and the taper is a very sloppy fit in the body, so it looks like it is too poor a fit to seal as it should.
Dominic Clancy

You could try lapping the plug into the body with grinding paste, given enough time it should stop the leak - as a final "grind" use diamond compound.
David k Brenchley

I agree it is very fiddly, and in my experience not that effective as a tap.
I bought a cheap mini drain plug (53K2853)from mini spares. It just fits in easily with a socket set, and removal is just as easy for draining down

Graham V

Thanks for the tip. Will buy one with the next parts order
Dominic Clancy

I fitted a brand new Moss engine block drain tap last winter when I fitted my new engine.
It too was the only thing that leaked on my car!

When I examined the packaging later I found an extra tiny package containing a small threaded plug with a knurled end and a small printed instruction label inside. The plug is intended to screw into the inside if the tap before you screw it into the engine block!

The instructions said something along the lines of, "Due to manufacturing tolerences they recommend that you fit the extra plug to be able to ensure that the tap does not leak."

I was amazed and so I cleaned up and refitted the old tap like you did Dominic.

The instructions basically say that "This tap does not seal"!
Colyn Firth

Glad I read this post! I have just finished rebuilding a spare engine to replace the one in the car which has a tiny crack in the block that leaks a bit of coolant at start-up. I too bought one of the Moss block drain taps(which came with a reference to a note on the web site about the tap being prone to leak and a little threaded brass bung which renders the tap useless, i.e., the tap ceases to be a tap and becomes a large bung that looks like a tap!)to fit in my nice shiny engine. I thought they were probably kidding about possible leaking, or least just covering themselves but it would appear from previous comments they are not. So before I fit the engine, I think I may transfer the tap from the old engine to the new!

Lindsay Sampford

I took the new tap apart and found that the taper bottoms out in the body because there is a lip at the bottom of the body so a file would probably make it seal.

The washer supplied with the tap was a stiff rubber, and I stupidly reused it when refitting my old tap. It leaked again from behind the washer, so as the mini plug had arrived that has gone in with no trouble or dismantling needed at all, so a highly recommended mod with thanks to Graham

First outing with the new engine in glorious sunshine yesterday afternoon, but we were really glad of the heated seats!

Dominic Clancy

Your engine looks great Lindsay, looks like you have been busy over the winter, no wonder we haven't heard much from you.
I hope you used the same cylinder head in your rebuild because your "cracked" engine was surprisingly rapid.
Cheers x
Colyn Firth

Pleased it worked for you. I don't understand the point of the tap as it gets filled up with sediment so doesn't work anyway. You'll find it easy to flush out now.
Heated seats sounds a nicer mod though!
Graham V

Hi Colyn, engine was done in under a month, and we had a week holiday in the Canaries in the middle of it, engines don't take long to build once the parts are back from the machine shop. Barney can strip and rebuild an engine in an afternoon on the side of the road! I have plenty of other things to keep me busy.
The old engine is still in service but I may do the swap in the coming week if I get time.
The 'new' engine is a spare I picked up from a guy in Hull who had put, would you believe, an MGB engine in his MGA! Why would anyone want to do that? (Sorry, just poking a stick in a hornet's nest!)
The head on the spare engine was full of cracks round the valve seats when Ivor Searles checked it but fortunately I had a good head sitting on an old Magnette engine so that is on the new engine with new valves, hardened exhaust seats, springs, guides and a new rocker shaft.
Anyway, back to the new drain tap. I dismantled it and it looked pretty good. I spent some time lapping it with T Cut and it looks like a good seal when I try to blow through it or test it by leaving water sitting in the block-side of it overnight, but I am still debating whether or not to use it when I install the new engine. Has anyone had success with one of these new block drain taps?
Lindsay Sampford

The heated seats were an addition when I was recovering the original seats, I just put a set of these under the covers and added the wiring.

I have done a few others since I did mine, and can only say that the quality of the wiring in these chinese sets is really low, so check carefully before fitting. You will have to chop and extend the loom in any case.

There's a new set that allows a temperature setting (mine is just on or off, base or base and back)

I put the switches to emerge at the overlap of the carpets on the gearbox tunnel, and run the cables to the seats along the carpet each side of the tunnel. That allows the connectors to emerge in the void between the seat frame and the seat base.
Dominic Clancy

Blimey 26.50 - that sounds cheap for seat heaters! Hope they are safe.
Graham V

Lindsay, I did buy two of the Moss drain taps and the second one seems to seal and work just fine.

So a 50% success rate with them according to my own small sample survey.

(Sent you an email today Lindsay)

I havent got heated seats but I do appear to have a heated transmission tunnel! :-)


Colyn Firth

I have re-fitted the 'fettled' new drain tap to the block and filled the block with water to the point where it starts exit the water pump. So with a couple of inches of water over the drain tap I'll leave it overnight to see if I get any drips. Not pressure testing but the best I can do without fitting the engine and running it.
Lindsay Sampford

This thread was discussed between 14/02/2017 and 26/02/2017

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