TR2/3/3A Help - Cooling system problem

[TR3-Stu]

Help - The new block drain on my '61 TR3A on the passenger side of the block stripped out, and left some brass (?) residue in the threaded hole in the block. Does anyone know what the thread is on that drain hole? It appears to be a 1/4" pipe thread, but I'm not sure and don't want to create even more problems for myself.
Thanks in advance,
Stu

 

[bobhustead]

The Moss rabbit hole seems to lead to 1/4 British Standard Parallel Pipe. Somebody who knows first hand will no doubt show up in this thread shortly. Your post indicates that you think the threads were sheared from the replacement valve. Chasing or repairing the threads in the block hole needs to be approached very carefully, preferably by one with experience, because you might only get one chance.
Bob

 

[Hamish Racing]

Revington’s suggest parallel 1/2"UNF thread

DRAIN TAP CYL BLOCK 1/2

There is another similar tap used in the bottom tank of the radiator part number 061864, this one having a similarly sized BSP tapered thread. Consider second hand part 061478SH

www.revingtontr.com

Is the brass just swarf or more substantial ,
If the former then just wire brush it out with a cylinder/round brush or run a fine “pick” around the thread.

 

[bobhustead]

Note that Harnish's quote from revington mentions tapered thread in the radiator drain. The Moss web site shows a copper sealing washer under the valve body in the block. This is confirmation that the threads are straight, or parallel allowing the valve body to snug up to the block. More like a bolt than a plumbing connection.
Bob

 

[TR3-Stu]

Thanks for all the advice. It certainly does look like it's a 1/4" BSPP (British Standard Parallel Pipe) thread in the block. I ordered a 1/4" BSPP tap to clean out the threads before moving forward. I'm not sure I'm going the same route with a new drain valve from my original supplier as the new brass (?) valve I previously ordered seems to be a very soft brass alloy. More research needed.

 

[bobhustead]

You want to get the brass swarf out of the block before you start the tap. A dental pick worked counterclockwise or a drill with a small diameter round wire brush rotating counterclockwise would help here. Gun cleaning brushes can be the right diameter.
Bob

 

[TR3-Stu]

You want to get the brass swarf out of the block before you start the tap. A dental pick worked counterclockwise or a drill with a small diameter round wire brush rotating counterclockwise would help here. Gun cleaning brushes can be the right diameter.
Bob

Great idea Bob. I'll try that before tapping the hole out.
Stu

 

[Graham H]

If the tape you have is a taper or starting tap you won't get it in very far, it's only a short hole and the last thing you would need is to snap the tap off. I replaced the original drain tap with an airline regulator tap that I can attach a fixable hose to direct the coolant away from the engine and chassis and it doesn't leak like the original, wont work if you want to go concorse.