The Art of Scraping Babbitt

SmokStak


| March/April 2003



Scraping Tools

A set of antique scraping tools.

The following comes from a recent topic on SmokStak, which can be found on the Internet at: www.engineads.com/smokstak.cgi. As ever, various individuals started, commented on and concluded the following bulletin board thread.

Scraping babbitt is something I have never seen or done, and I'd like to hear from people who have so I can learn how it's done. I have bought some tools I believe to be scraper tools -they look like files with no teeth. Let's see if we all can learn something new. - Kevin

I have seen it done by skilled craftsman, and it's not a process for the impatient. I have watched it done during the rebuild of a precision surface grinder, and there are no shortcuts. The craftsman uses a straight surface such as a granite bar or plate, and he covers the surface with bluing paste and slides the part on the plate. He then scrapes off the clean or high spots that show up on the part until he gets a desired number of contact spots per square inch. He may go back to the surface plate many times to get the contact area he needs.

With round shafts running on babbitt he uses the shaft that runs on the surface. For that process the tool looks like a three-corner file with no teeth. He puts the shaft in and takes it out many times before he gets the desired bearing contact area. This process takes volumes of patience, coffee or whiskey - and determination. Try it on a new set of cast babbitt main bearings and you will be amazed at how close you feel to your newly restored engine. Many of the large precision engines we see have had their bearings scraped, and most steam engines had the main guide box and bearings scraped. It takes a lot of time, but what fun it is. - Al

About 30 years ago I scraped the mains on an American LaFrance 570-cubic-inch T-head engine. It was fun, except for lifting the crankshaft into the mains about 100 times. My buddy on the project and I had sore arms and shoulders for about a week. My scraper was made from a half round file that I ground on a belt sander. It was so sharp I could peel the babbitt off like thin snowflakes. I also could cut the heck out of myself with the scraper. I've still got that scraper and it's wrapped up in an oiled rag so I don't cut myself when groping around in that particular toolbox. - Elden

I worked at a shipyard for 20 years and one of my jobs was on a wheel gang made up of eight workers. Our job was to fit the propeller wheel onto the output shaft. The shaft diameter was usually 34 inches and the taper was about four feet long. The propeller wheel was usually about 20 feet in diameter. After using about a half a pint of Prussian blue to cover the taper we would slide the wheel on by using four 75-ton chain falls, then put on the nut (thread size 24-inch by about 8-tpi) and tighten it. After that we would take off the nut, break the taper and remove the wheel with the four 75-ton chain falls. You'd stick your head in the wheel and grind the high spots with a 4-inch hand grinder, clean the shaft, clean the wheel, re-blue and repeat the whole process again. After about five tries we would have a fit the Coast Guard and chief engineer would approve. All of this took about 10 hours. I have done this so many times I lost count. Pretty soon I'm going to try the bearings on my Monitor -where can I find tiny chain falls? - Patrick