Beck TD, Part 79: Radiator Tales

 In the last two posts, I detailed special tools I made to help with a big project on Beck TD: replacing the head and cam. That's all done and Beck is running very well, and someday I'll do a final report on that project. But for now, let me tell some "Tales" about my radiator. There's a new technique here that really helps minimize the mess of radiator work!

When I finished reassembling Beck's engine and refilled the cooling system, I thought I was ready for a test drive. That idea lasted until I noticed two tiny wet spots under the car. Two different coolant drips!

The first was easy to fix, but annoying because the radiator would have to come back out. The Volvo engine has a very odd design for the water pump, with two O-rings that fit into recesses in the cylinder head. Here's the pump off the car, with the O-rings in place:

The problem was that I had tried to drop the head in place without removing the water pump, and I managed to slightly dislodge one of those O-rings. Annoying, but an easy fix.

The other leak, however, was much more disquieting. It was at the radiator drain plug. Now, an MG TD came with a proper petcock at that location for easy draining, but the anonymous mechanic that converted Beck to Volvo power decades ago realized that it would hit the engine fan, and replaced it. The problem is that the threads for that drain were BSP - British Standard Pipe - and the mechanic just "forced" a standard coarse thread bolt in the hole, making some very loose threads.

I had used that drain to empty the coolant before removing the head, and I noticed that it felt "funny" when I replaced it. I had tightened it as far as I dared, but it still leaked. Sure enough, when I tried to snug it a bit more, the threads immediately stripped. Oh well, the radiator had to come out anyway. Here are the threads in that brass fitting in the radiator - what a mess!

As usual when I'm in over my head, I emailed Jake Roulstone and asked for advice. I had already determined that there was enough material to retap the hole as the next fine thread size up, 1/2-20. Jake suggested that the material was already so compromised, I shouldn't drill it further. Instead, he asked if I had a hand reamer to just barely clean up the edge of the hole before tapping. I said yes, but it was too long. He immediately replied, "Shorten it! They're cheap!" OK, 30 seconds on the grinder and now I have a custom short reamer:

I recruited Troy Nace to stabilize the radiator on the milling machine table (that's his hand in the photo) and then I carefully retapped the hole.

The threads came out very useable, although I'll admit this was the "best" side of the hole. Those old threads were pretty badly mangled.

Jake also suggested that I find a 1/2-20 oil drain plug with washer, and Amazon had just the one. It worked great, with no leaks.

However, Jake thought a bit more about that plug, and said that he was worried that galvanic corrosion might set in between the steel plug and brass radiator, and that might rip out the threads on removing the plug years later. He made me the brass plug below and mailed it to me. Like all of Jake's work, it is jewelry quality! He also told me that he would teach me how to replace that plug without draining the radiator, and without spilling a drop. 

The trick to removing drain plugs without spilling is to use vacuum to hold the coolant (or oil, for that matter) in place while the plug is removed and replaced. A neat trick! The TD's radiator actually makes it easier, because it has a big rubber O-ring right on top. I just needed something to seal to it.

My first attempt was to try to use my pneumatic brake bleeder as a vacuum pump. I modified a 3/8" bolt by drilling it through, and turning down a neck for the 1/4" hose size of my bleeder. Then I threaded a flat plate to hold it. The idea was that the vacuum would hold the plate tight to the radiator neck. It worked, sort of, but it was clear that my pump didn't create a strong enough vacuum. Round 2.

I returned to the lathe, and used a piece of Delrin rod to make an adapter for my shop vac. The lower diameter is a slip fit into my 1-1/2" vacuum hose, and the top just slips into the radiator. The adapter is drilled 7/8" all the way through, and you can see a "bleed" hole in the center that allows air to still flow into the shop vac. That was Jake's idea too - it allows enough airflow to keep the motor from overheating.

For the setup, I zip tied the shop vac hose to a ladder to take the weight off. The adapter would just be held together by vacuum. And it worked great!

I wasn't so cocky as to pause to take a picture of that hole with nothing leaking out of it, but I did indeed remove the steel plug and insert the brass plug without spilling a drop, just as Jake promised.

The story does continue, however. I need to shorten the neck that fits into the radiator a bit more. It didn't extend into the coolant, but it was close enough that it "misted" about a cup of coolant into the shop vac hose. I just moved the hose to the exhaust outlet to blow it out, but that still made a tiny mess that I'll avoid the next time I use the adapter.

I know that I will use the adapter again, because I actually used it twice today. When I first started Beck after the head work, I was checking everything out, ensuring that there were no leaks, and and that the running temperature was right. I even took a video, which turned out to be very useful later. I was able to extract this frame proving that my memory wasn't wrong, the temperature was just right.

The problem is, that's the last time that gauge worked! In several subsequent tests, the gauge didn't move and I was forced to use a non-contact laser thermometer to make sure the engine was still running cool. I had an older temp gauge of the same "bulb capillary" style, so today I used the vacuum adapter to hold the coolant in place while I installed it, just running the flexible pipe outside the car. I sat and watched as the engine warmed up, and it was gratifying to see the temperature rise to 180, and then drop as the thermostat opened.

So the next project is to replace that in-dash gauge, and if you've made it this far, I'd welcome your opinion. Do I buy another Bosch gauge so it matches the other gauges in the dash, or do I just install this one instead? The Bosch gauge only lasted two years, but I'll concede that maybe I damaged it when I unhooked it to remove the head. Either way, I have to spend some time upside down in the cockpit again... rats!

Continue on to Part 80...