[How do I?] Whitemetal Casting Question

GCM

GCM

Self Trained Hobby-Machinist
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May 20, 2014
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Any yesteryear guys around that still remember about white metal casting ?
I am about to try my hand on white metal casting on bearings for an old 1930's throttle governed engine. I have machined the crank, but the bearings made by previous owner are a bit oval so I align bore it. I want to cast white metal to get everything up to standard again ;-) As an amateur machinist/engine builder so many question comes to mind while working on this project.
What is the ideal thickness I should push for on the white metal after casting and align boring?
How big "gap" should I try for between crank and white metal to allow oil to lubricate and conrod to freely turn on crank ?
If I can get info on the gap for lubrication, the ideal thickness of the white metal, only then I can do my final cut on the bearing face :) The engine only runs at about 600 rpm max so in my mind I think maybe I can get away with a few thousands here and there but it would be nice to know what is ideal tolerance.
Any ideas would be highly appreciated.
 
Keith Rucker at vintagemachinery.org has several videos on pouring, scraping and adjusting Babbitt metal bearings. You use the crankshaft and the crankcase as the mold for pouring the bearings in place, with the surfaces protected by a soot coating for easy separation. Then you scrape the bearings to fit the shaft, spotting them in and removing shims from the caps as needed to make the fit correct. Then you cut oil grooves in the bearings so the oil can reach all points of the bearing surfaces while running.

Edit: removing shims from the cap joints is also how those bearings were tightened in service when they would wear loose.
 
Thank you for the replies but I think I need to do a better explanation. I have some pics I want to show you and maybe there would be more method to my madness. This is the bearings that came out of the motor. Also note the thickness of the copper bearing and the scratches. The crank has been cut and polished and runs true again.

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I then made these two molds and the idea is to first tin the brass bearings and then place the bearings in the molds ready for casting. You will notice that the thickness of the white metal will be close to 2 mm or more.

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I have mounted the conrod on the mill bed and align/level check and rechecked alignment and level. The bed and head are locked centered and will stay that way until after final cut. Here you will see the bearings on the conrod and I have align bore them and they are smooth again. After casting I plan to place bearings with white metal hopefully nicely "attached" to the brass back in the conrod. Then align bore it again to the correct thickness. When done hopefully it will sit nicely on the crank and do its job ;-)

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Hope with the pics and the one I mussed to upload you will understand better my questions :)
What is the ideal thickness I should push for on the white metal after casting and align boring?
How big "gap" should I try for between crank and white metal to allow oil to lubricate and conrod to freely turn on crank?
If I am barking up the wrong tree feel free to tell me. I will be using white metal bought locally in South Africa which is almost the exact within 1 or 2 % of the original babbit metal combinations.

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Look up using plasti-gage for measuring crank gaps.

Also look for the use of same in rebuilding searches as the gaps are usually less than a couple thousandths as the oil needs to stay in there to be the bearing as th r metal never touches so to speak.

Gap depends on oil viscosity and how well it can get in the gap.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 
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