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rotorwrench · 10-23-2020, 02:58 PM

A lot of folks that do Model A and T engines don't burnish them like Ford did. They peen the bearings after they are poured to get them to fit well against the block then they align bore them to size. Ford was manufacturing more engines in a day than most folks work on in a year. Ford found their best way of building them as quickly as possible. Ford also had equipment that is unobtainium in this day and age. It takes longer to peen each bearing and prep for boring or reaming of the bearings but that is a practical way of doing things in the current business scheme of things. Some crankshafts have less meat on them now days so that takes more bearing babbitt to fill that gap. The thicker the babbitt gets may make the job a bit more complex than having nice new standard size parts to work with. A person could also use Time Saver lapping compound with a turning machine like the aftermarket unit in the brochure. The Time Saver compounds have been around since the model T days and have always been guaranteed to leave no abrasive embedded in the bearing surface.

On the subject of burnishing, I mentioned before that I don't know what the fit was at Ford when they were ready to start that process but I assume that is is safe to say that there likely wasn't much clearance in any of the mains when they started turning for the process. That shaft is going to heat up a way lot more with little or no clearance than a shaft journal with 0.0015" clearance. A properly lubricated bearing with 0.0015" of clearance will run relatively cool. One with no clearance and even with some oil for lubricant will damn sure get hot. The hotter it gets, the more that shaft will grow in every direction. The growth of the shaft is what forces the bearing material outward against the block and the main cap. The heat would cause the increase in plasticity of the babbitt and allow it to gain more clearance. How much clearance could be gained that way depends on how hot it gets and how much plasticity will occur without damaging the bearing. I have no idea what they actually ended up with for clearance. Ford had something figured out for that since they managed to manufacture multiple millions of these engines in the four years of production and likely a few thousand more after production stopped since they were produced up into the 40s for ag and industrial applications.

10-23-2020, 02:58 PM	#30
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: Time lapse Model A engine build A lot of folks that do Model A and T engines don't burnish them like Ford did. They peen the bearings after they are poured to get them to fit well against the block then they align bore them to size. Ford was manufacturing more engines in a day than most folks work on in a year. Ford found their best way of building them as quickly as possible. Ford also had equipment that is unobtainium in this day and age. It takes longer to peen each bearing and prep for boring or reaming of the bearings but that is a practical way of doing things in the current business scheme of things. Some crankshafts have less meat on them now days so that takes more bearing babbitt to fill that gap. The thicker the babbitt gets may make the job a bit more complex than having nice new standard size parts to work with. A person could also use Time Saver lapping compound with a turning machine like the aftermarket unit in the brochure. The Time Saver compounds have been around since the model T days and have always been guaranteed to leave no abrasive embedded in the bearing surface. On the subject of burnishing, I mentioned before that I don't know what the fit was at Ford when they were ready to start that process but I assume that is is safe to say that there likely wasn't much clearance in any of the mains when they started turning for the process. That shaft is going to heat up a way lot more with little or no clearance than a shaft journal with 0.0015" clearance. A properly lubricated bearing with 0.0015" of clearance will run relatively cool. One with no clearance and even with some oil for lubricant will damn sure get hot. The hotter it gets, the more that shaft will grow in every direction. The growth of the shaft is what forces the bearing material outward against the block and the main cap. The heat would cause the increase in plasticity of the babbitt and allow it to gain more clearance. How much clearance could be gained that way depends on how hot it gets and how much plasticity will occur without damaging the bearing. I have no idea what they actually ended up with for clearance. Ford had something figured out for that since they managed to manufacture multiple millions of these engines in the four years of production and likely a few thousand more after production stopped since they were produced up into the 40s for ag and industrial applications. Last edited by rotorwrench; 10-23-2020 at 04:57 PM.