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MG TD TF 1500 - Engine Drain Tap

I bought an engine drain tap from LBCar Co and even though it looks the same, the threaded length is the same and there are the same number of threads, the tap is loose in the block and when it starts to tighten it suddenly becomes loose again. Has anyone else experienced this?
Ron Coates


Is that the reason that you bought a new one??
Sounds like the threads in your sump are stripped..

Steve
SPW Wincze

Ron,
I measured the drain cock on my TD XPAG Block and it comes up on the thread portion as 3/8" dia. - on an electronic caliper.

Thread size is harder to determine - It looks like a toss up between a 0.9 metric and 28G Whitworth on my thread gauge.

The Nut measures at 29/64" but has some wear marks so not sure of the actual "new" original size. Somewhere very close to it.

If it helps at all.

Hopefully the thread in your block is not damaged?

Rod

Mine has been around the block - literally :)

R. D. Jones

Same issue, David DuBois told me the tap/helicoil size, fixed years ago and is still fine. It is likely a BSP thread (?), find his chart on T-talk or wherever it is. George
George Butz

Ron
Also Found at http://www.ttalk.info/engine_fasteners.htm

SIZE LENGTH WRENCH DESCRIPTION/USE QTY ORIGINAL ABINGDON MOSS
(INCH) SIZE P/N P/N P/N

1/8-28 BSP N/A 3/16W BLOCK WATER DRAIN TAP 1 3H2724 3 - 14 434-240

looks like 28 BSP

Might be of more help.

Rod
R. D. Jones

1/8 BSP is the correct thread. Cheers - Dave
DW DuBois

I am replacing it because the original was leaking through the tap. I tried grinding it but to no avail.

The new one is just very loose even though the old one still tightens. Jeff Zorn at LB Car is sending me another one to try. He thinks the old one is not an original maybe. They look the same to the naked eye. If the second one is loose also, I will plug the old one and put it back and use it as a plug in the future to drain the block -- that is if it holds.

I would have thought that the threads on the brass tap would have stripped before the iron ones in the block. The engine is still in the car so if the treads are stripped I will be looking for something like a self tapping plug or goodness knows what to seal up the hole! I will be asking for suggestions.
Ron Coates

Ron - It could be that someone ran a tapered tap through the threads in the block - that happened to the block in our TD. About the only thing you can do is to heli-coil the hole (difficult due to how thin the block shell is ) or you could go a step up and use a 1/4 BPS drain tap. (I found a rather unorthodox method of dealing with the oversized hole in the block of our TD - I put a rod through the side of the block at 4000 RPM and got a new block - not recommended. Cheers - Dave
DW DuBois

Sounds like you may have a mix of BSP threads, there are two types BSPT(tapered) and BSPP(parallel). BSPT are used with a thread sealant, BSPP are used with a buttress washer. I believe the tap I purchase was the latter and required the washer to provide a seal.
G Evans

G Evans: Interesting point. I don't have a micrometer gauge, but it does look like the old tap maybe a half mm bigger at the one end. That would suggest that it is a tapered thread! It has been holding, whereas the new one does not. Were these taps made with a tapered thread at all?

Dave: You suggest maybe a 1/4 BPS drain tap. I would still have to drill a hole and tap it for a bigger drain tap. Are they available? If I have to drill and tap, I could put in a helicoil. Is this a reasonable thing to do with the engine in the car. There is not much room down there.

I am thinking of Loctite thread repair paste/liquid or whatever it is as a quick solution with the new tap. Is this any good?
Ron Coates

Ron, you have a number of options. Fortunately, any machining is into the water jacket, not the crankcase. Bud
Bud Krueger

I should have paid more attention to Rod Jones' note. I measured the outside thread diameter of my old tap and the two new ones that I received from the supplier (actually O'Reilly Auto parts kindly measured them for me with a digital caliper). My old one has a smaller diameter than the specification for 1/8 BSP, and that is not surprising after 60 years, but it is still big enough to tighten. The two new ones are identical to each other but even smaller outside diameter than my old one. This small difference(0.54 mm smaller than the 1/8 BSP spec) stops them from tightening. Of course the threads in the block may also be larger than original after 60 years of use. The upshot is I have plugged my tap and replaced it - and it holds. I have returned the two taps to the supplier and informed him of my measurements. He is going to talk to his supplier.
Thanks for your help. Ron
Ron Coates

The final reply from LBcar Co is that they have no other complaints, and neither do Moss, so it must be a problem with my engine block threads. It doesn't matter that the product does not meet spec I guess. The business model is to send them out and let the complaints decide whether they are any good or not. Not a good business model. I would have thought they would want to measure the product and see if it meets spec.
Ron Coates

I totally agree with you Ron!!! I like CC's approach. Before he mentions an AM part on his site he inspects, compares & tests it BEFORE it cracks a mention. LBC sells mostly Moss stuff & because of the embarrassing quantity of their poorly designed & ill fitting parts, it's obvious there is no quality control or vetting of suppliers. The real killer is that when the dud item arrives you get to pay the shipping both ways! I'd love to be a fly on the wall watching Glen Adams, the Moss CEO, trying to restore a TD/TF using his parts. I'd pay BIG money to see that! Maybe then we might get a change in the Company ethos. Glad you got your problem sorted Ron. Cheers
Peter TD 5801
P Hehir

Yes, Peter, I paid shipping both ways. Another issue is that I had to pay $7+ for one tap to be shipped to me and then it only cost me $2+ to ship two of them back to LBCar! I also have to pay a 5% restocking charge. I guess they make money on every step whether the product is good or not.
Who is CC?

The thing that irks me is that the product did not meet spec and after 60 years there is bound to be some wear on the block threads. If the product had met spec it would have been fine because my old one still holds and it is smaller than spec, again, probably because it is 60 years old. There is clearly no quality control. All Jeff Zorn kept saying is that he and Moss have had no problems (hard to believe) but no mention of any measurements versus spec.
Ron Coates

Bit concerned about some logic being applied to this issue. I question how a threaded tapping in a block could wear, how many times would a tap have to be screwed in and out to wear the thread? I know the brass component would abrade prior to the cast iron block. Yes the block female thread could become corroded.

There still is no clear indication if the block thread is BSPT or BSPP. I am of the opinion that it is BSPP because the new block tap that I purchased required a sealing washer fitted at the thread buttress to achieve a seal.

Interesting exercise would be to source the major and minor thread dimensions for the two BSP thread types, this might shed some light. It would be doubtful if the tooling used to cut the tap threads was not to specification.
G Evans

CC is Chris Couper the author of the Original M.G. TD site. Cheers
Peter TD 5801
P Hehir

If a sealing washer is used (as in this case) it is a parallel thread. Bud
Bud Krueger

Try checking with Doug Pelton of www.fromtheframeup.com

Doug carries all the parts and if there's a problem with any of them he sorts it out.
Gene Gillam

That's what mine looks like as well Bud,
It is definitely not a tapered thread.
A washer would certainly help.
Rod.

R. D. Jones

The SPL AKD834 definitely shows the tap as attaching through a washer. A/S and Moss show this configuration. Bud
Bud Krueger

The thread diameter I used was for BSPP. There isn't much doubt that it is a BSPP if you read D DuBois' note and look up his table on bolts and threads.

I am not sure why G Evans doubts any logic. Yes it is unlikely that the female threads will wear much but if the product had met spec, it would have held even better if the female threads had not worn. The new tap threads were too small!! Even smaller than my old tap. No logic needed there.
Ron Coates

The thread is 1/8 BSPP. As far as I know all suppliers, to include myself, use same item as Moss, I have not had issue with this.

First chase the threads, if it does not hold then repair threads with insert. I do not have the insert in stock but they are available, check on line for 1/8 BSPP insert.

I have had to do this on 2 engines (actually my engine shop did this). Not a big deal so "do it correctly" and don't JB weld, plug, or other one off repair.

Doug Pelton, From The Frame Up
Ron Coates

That last contribution was not from me but from Doug Pelton. I don't know how he did that! It looks like I will not be able to resolve the issue. Doug gets his supplies from the same place as the others and there is no mention of measurements versus spec. It is a mystery to me. I am satisfied with the plugged tap holding like it is.
Ron Coates

This thread was discussed between 23/06/2015 and 13/07/2015

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