Well sports fans, today is cooking class 101 here at The Old Motor. We are going to prep the bearing shells for the Thomas-Flyer that we have been covering in a special post and pour the new babbitt in them. They can be seen on the shop wood stove above, baking the moisture out of the furnace cement that we use for filling the oil holes in the inserts, so the molten babbitt does not leak out out when we pour them.
In case you are wondering, that weird device on top of the stove is our humidifier. It is an old copper still, that after restoring, works well for keeping the humidity level in the shop within reason, so wooden wheels and early wooden auto body parts, humans and the dogs don’t dry out over the winter here in the shop. The water boils inside and steam comes out of the spouts at the top. It works well when the stove is really roaring, but when we need moderate heat, we use a big old copper pot filled with water.
The reason for this whole bearing exercise, other than the one new insert that we had to machine, can be seen in the first photo below on the left. It shows a serviceable babbitt bearing, but the problem with all of the bearings in this engine, is that they are badly contaminated with all types of dirt and left over metal cuttings that were not cleaned out of the engine during the last rebuild. Look closely at the photo and you can see bronze, iron, steel and other assorted junk embedded in the bearing. If left this way, it will serious wear the crankshaft, so it must be replaced.
The second photo above shows an insert carefully lightly clamped between soft jaws in a vice to hold it while the old babbitt is melted out. The tip on the torch is an old tip that gives a very soft flame. This a tip we use for doing leading on body work and it only uses acetylene. With it we carefully and uniformly heat the back of the shell until the babbitt starts to melt and then we brush it out with a stainless steel brush into an old iron pot.
Before going any further, tinning the bearing needs to be discussed. Tinning is covering the inside of the insert, after it is totally clean and free of oxides or tarnish, with a tinning compound. Just before tinning in the first photo below on the left, you can see the parting surfaced covered with a yellow anti-tin compound that is brushed on. This anti-tin keeps the tinning off of surfaces that do not need it. In the second photo, the insert on the left can be seen covered with tinning compound which is a liquid paste of 50-50 solder and a powerful flux. The insert then gets heated up again with the torch until the compound melts, next it gets scrubbed with a wire brush and finally the flux gets wiped off with a rag. The shell on the right shows what it looks like after the tinning operation.
The last photo below shows the furnace cement dried out, after an overnight bake on the stove. Other ways of plugging up holes in the shells are taper pins and babbitting putties, but we have never had much luck with them. You have to be very, very careful that whatever you use to plug anything, cannot leak, as the babbitt is poured in at around 950 degrees. If any leak occurs, it will run all over you, burn you, your pants and your shoes and sometimes even go inside your shoes. None of the above is a pretty picture, we know, we have been there.
Next we heat up our electric babbitt pot and also turn on the hot plate under the bearing boring mold seen below that was designed and machined here in the shop. The round center mandrel is changeable for different sized bearings and the vertical plates on either side slide in a dovetails. The center of the mandrel is drilled in the lathe for a long-stemmed thermometer. The mandrel gets heated up to 225 degrees before we start, as it is the temperature that works best for bearing pouring.
One other BIG, BIG, CAUTION, is involved with any kind of metal casting operation, if there is any water or moisture on any thing in contact with the molten metal, it with instantly turn into steam and the 800 degree metal will blow up and out all over you, burning you instantly.
The babbitt pot is heated up to about 200 degrees over the pouring temperature, as we use a special bottom pouring pot that gives us totally clean metal. Most babbitt is heated in an open pot by a gas flame below it. The surface of the molten metal quickly oxidizes and forms a crusty layer. The ladle is used to skim this, but some of it always ends up in the bearing. Our bottom pouring unit (a customized lead melting pot with a special coating and valve) takes its pour from the bottom and away for the oxidization. The extra 200 degrees is factored in because of the time to fill the ladle and to get it to the pour, which causes it to cool off by 200 degrees.
The photo on the left above shows one of the new bearing halves that were machined in the last post clamped into the mold. Before doing so, the mandrel is coated with the black soot you see with a rich acetylene flame. The holes seen drilled in the flange, are anchor holes used to hold the babbitt which is cast onto this surface after the bearing fills. It is being heated up this time with a bigger torch, as we need a lot of heat quickly in this operation. The insert gets heated up to the point that the tinning we applied earlier is molten. Next our cast iron ladle is filled with babbitt and quickly used to fill the void between the mandrel and the bearing shell. The molten tinning on in the inside of the shell and the babbitt become one, and lock it all together.
The middle photo above, shows one half of the new bearing on the left already poured, along with the second half clamped in the mold. One of the other inserts is on the right hand side.
The last photo shows all fourteen bearing halves as poured (seven main bearings). In our next post we will show you the operations necessary to semi-machine these inserts, to get them ready of line boring.
Disclaimer: As they say on TV, don’t try this at home. It should only be attempted after much study, learning and practice and the acceptance of the fact, that if something you do goes wrong you can be badly burned. These methods have proven to work for us on numerous engines that have been run many, many miles, on both the road and the race track at over 100 mph without any failures. You assume all risks if you attempt to use our methods. Wear OSHA approved safety gear for any metal casting.