Does anybody know the thread size of the brass radiator tap for a 140? I’ve just refilled with coolant and can’t stop it dripping, so will go to a solid plug.
Roger,
I understand from earlier Forum contributions (see below) that all these “radiator taps” are 1/4" BSPP (19 tpi). I assume yours is in the steel pipe at the bottom of the radiator, whereas the XK 120 has them in the bottom of the radiator itself.
The drain tap on the block seemed to have the same tap C.980 but I also see C.2354 mentioned which might have UNF 1/2" x 20 tpi.
If you don’t want to return to the original drain tap in your bottom steel pipe, you might consider to tap the hole slightly larger and fit a UNF 1/2" plug. See more below.
Bob K.
Thanks Bob - on the 140 the radiator pipe tap and the block tap are different. Confusingly the tap levers are 90˚ out with each other, so I can never remember which way they should point when the system is empty - one follows the usual convention of being in line with the bore when open, but the other doesn’t, and I can never remember which is which. Although very different in shape they are both basically a taper held against a tapered bore by a spring, but I have the original radiator pipe tap (brass), which has been very carefully rebuilt and the taper lapped in, but nevertheless still produces a drip. Given that I’m using Evans I’d rather seal this in a more reliable way as I don’t want to have to top up coolant a couple of thousand miles from home on a tour. Now that I’ve just refilled with fresh coolant following the cylinder head problems, I was toying with the idea of getting a replacement prepared and trying to do a quick switch, but I think a proper drain, repair and refill is a much more sensible idea, which will also give me the chance to check the thread properly. The pipe I have is actually a new aluminium one so drilling and retapping would be easy.
Roger,
I know exactly what you’re referring to: when the lever of my radiator tap is straight, it is closed! See pic below with the tap open…
The block drain works the other way round: see pic with tap closed
Bob K.
Radiator is BSPP and the side of the block is 1/2"-20 UNF. Same size plug as the oil galley plugs on the other side of the block.
Here’s mine, closed. It never drips.
You’re right, the convention is usually “handle to the side” being closed.
Yes, the convention is that the handle of the tap indicates the position of the pathway through it.
lots of good work getting done on your vehicle for sure
now I faced this issue, and racking my brains, but determined to overcome the issue after lapping failed, I recall there was some slack, possibly due to wear between the 2 main components.
I have an inkling that I slid a tiny metal washer or shim to take up that slack, and maybe magnified view of the sealing surfaces
It wasn’t a dream, as I recall fighting doggedly to get everything perfect.
It doesn’t drip so I must have done something right
always satisfying to restore an original 70yr old Jag part to working order if possible
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Roger,
I had the same issue with mine it continued to weep after laboriously lapping, adding spacers to increase spring pressure etc. so instead I got this;
Yes it’s 1/4” npt but it threads in by hand about half way and with some teflon tape and a quarter turn it seals perfectly without damaging the threads in the bung, it’s been in place for 2 years with no leak. I sweated a piece of tubing with a 90* curve to direct the flow and the nice thing about the npt is you can tighten it sufficiently to orient it correctly for directing the flow downward rather than having to rely on sealing washers of the correct thickness and hope it clocks correctly. An additional bonus is that the lever is perpendicular to the flow when shut off as it should be.
Roger, the radiator petcock for my 120 also leaked. I thoroughly cleaned and tinned the mating surfaces with low silver content metal work solder then worked the pieces together without abrasive until I could actuate the valve freely, then reassembled it. Cured the leak. Should last many cycles. Shine up the surfaces really well, apply a little flux, apply sufficient heat till the solder flows on the surface, wipe down with steel wool. Easy fix.
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