You can do it!
Fixture for centering dummy shaft.
Anyone who has had the opportunity to watch an old-timer pour lead in a plumbing system or babbitt around a shaft knows that it looks deceptively simple.
But like any of the trades, years of practice and plain know-how are key to a successful outcome. While none of us will have the opportunity to gain years of practice, by reading the right resources, the craft can be duplicated well enough to bring an old engine or saw rig back to life.
For the last year I've been in the throws of a significant rebuild of a 5 HP hit-and-miss engine. Though the babbitt bearings looked good, once the camshaft gear and crankshaft were in place, a soft rumble of the gear set revealed that the bearings would have to be re-poured. The subject of babbitt pouring has been covered in the 40-year history of Gas Engine Magazine - November/December 1974, March/April 1979, September/October 1981, September/October 1983, September 1988, September 1990, December 1998, October 2000. But perhaps the readers will enjoy one more approach.
I decided to make a fixture to accurately hold a dummy shaft in the correct position, horizontally, on proper gear center, on the cylinder centerline, and in correct side-to-side location. I also decided it was best to pour the upper caps first, remove them and then pour the lower bed bearings. This was done without removing or repositioning the fixture.
First, a fixture (Photo 1) to be located within the cylinder bore was welded and accurately machined in a Bridgeport. The discs in each end of the bore (Photo 2) are 1/2-inch thick and have about a 0.001-inch clearance to both the bore and the piece of turned, ground and polished (TG&P) steel bar the fixture is made from.
The large end of the fixture is the correct width for the space between bearings. It is desirable to make the fixture as accurate as possible, as this will reduce scraping after the pour.
The flywheels and crankshaft on this engine are quite massive, and I decided not to try and pour using them, as it would be too cumbersome. Instead, TG&P stock was used as a dummy shaft to pour around. It is the same diameter as the crankshaft mains and has a ground surface, giving your babbitt bearings a great finish. The dummy shaft has been added to the centering fixture in Photo 3. Also visible are the shaft collars. These will be used later to form the bearings inboard of the saddles of the base.
In addition to positioning the crankshaft on cylinder centerline, it is important to correctly space the crankshaft to the camshaft centerline. All our old engines use diametral pitch gearing and a little number crunching will tell you the correct center-to-center distance required. I added 0.010 to that number for future wear of the bearings when making the 1-inch-by-4-inch spacer plate (Photo 4).
In order to seal the upper halves from the lower halves, I made tight fitting shims (Photo 5). You can make them whatever thickness you like, but I picked 3/16-inch because I could use standard 1/4-inch stock and surface grind them thinner, giving an excellent surface finish. The shims are made exactly as long as you want the bearings to be wide. Instead of drilling holes for the bolts, just cut slots so the shims are free to slide up against the dummy shaft creating a tight seal.
The notches in the ends of the shims allow the shaft collars to slide up tight against the bed saddles and bearing caps. This will mold the bearings in the space between the crankshaft and the bed saddles. It will also mold the bearings outboard of the bed saddles.
Now it is time to pour the first upper cap. The inside of the cap was sandblasted and lightly brushed with tinning flux. Then the top of the dummy shaft and shims were sooted with acetylene to prevent babbitt from sticking. Then the cap was placed on the bed, the shims slid tight against the dummy shaft, and the bolts tightened. Once the shaft collars were slid against the cap, Babbittrite was used to seal between the shaft collars and the cap (Photo 6).
While the babbitt pot was heating the cap and shaft were being heated with the torch. The babbitt is hot enough when a wooden stick dunked momentarily in the babbitt instantly blackens the stick. The shaft, cap and shims are hot enough when roughly 450 to 500 degrees Fahrenheit. I use an infrared thermometer gun for spot-checking temperature. You'll notice that an old greaser bottom is screwed in the cap. This needs to be heated almost red hot, as you want it to keep the babbitt hot. This is being used as a riser to keep feeding the bearing as the metal inside shrinks. This is crucial in preventing low spots in the bearing. As the metal cools, it will draw from there, keeping the rest of your bearing in contact with the dummy shaft you are pouring around. It is time to pour quickly until the riser is full.
Once both upper caps were poured, cooled and removed from the bed, it was time to clean the shims and dummy shaft and to prepare for pouring the lowers. Prior to assembling the pouring fixture on the bed, I wire brushed the saddles clean and applied a thin coat of tinning flux.
The shims were removed and a slot about 3/8-inch-by-3/8-inch was cut in the upper shim at the midpoint (Photo 7). This will be the gate that the babbitt will be poured into filling the lower halves. The underside of the shims and the dummy shaft were sooted and the shims positioned while being pushed up against the dummy shaft and tightened in place. The shaft collars were pushed into position against the bed saddles and sealed with Babbittrite.
Now it is time to begin the preheating (Photo 8), and once everything is up to temperature a small moat of Babbittrite is formed around the gates to act as risers (Photo 9).
Next it is time to pour the lower bearings (Photo 10). Pour until there is metal filling the riser above the bearing (Photo 11).
After all the pouring fixture is removed and the flux residue cleaned, the bearing should look like this (Photo 12). I rub the bearing surface with a little ScotchBrite to clean.
After a few hours of fitting, scraping and cutting radiuses, the crankshaft is in place (Photo 13). It is a little hard to see in this photo, but the pressure wedge chamfer has been added to the top edge of this bearing. The 45-degree chamfer is about 1/8-inch wide and stops 1/2-inch from each end. This draws the lubricant in and creates a pressure wedge and film of lubricant to properly wet the bearing.
A little squirt of oil and the flywheels are off and running (Photo 14). It's a good engine day!
Contact Curt Holland at: 209 Wynnchester Road, Gastonia, NC 28056; (704) 853-2992; firstname.lastname@example.org