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Terry Burtz, Calif · 12-21-2018, 12:33 AM

Dave in MN,

You are correct that having the seal rubbing surface ground at the same time the rear crankshaft journal is ground is the best method for concentricity. This method also provides a good surface finish for any seal to rub on.

Compared to modern engines, Model A and B crankshafts are more expensive to grind properly because the fillet radii on Model A and B engines are larger which requires dressing (removal of material) from the grinding wheel, and if the grinding wheel has to be narrowed for the seal surface, even more material has to be removed. Crankshaft grinding wheels are expensive and removal of material shortens their life.

To save money, you may need to find another machinist, or a machinist that does not have a worn out lathe. Most any lathe built in the last 70 years has preloaded back to back bearings in the headstock with almost zero runout. If the crankshaft to be machined is in a lathe and the rear main journal is dialed in for minimum TIR runout, machining of the seal rubbing surface will be concentric.

The likely problem of short seal life (worse for packing type seals, but will also happen with radial lip seals) is wear caused by the rough surface finish of the seal rubbing surface.

After lathe machining, the seal rubbing surface should be sanded to provide a surface finish similar to grinding. A wooden paint stirring stick wrapped with progressively finer wet or dry sandpaper can be pressed against the lathe machined seal rubbing surface while spinning to obtain the required surface finish.

There is a lot of conflicting information regarding rear main seals, and for the education of all, I ask BRENT in 10-uh-C in post 2 of this thread to explain how thrust (I assume fore and aft movement of crankshaft?) needs to be adjusted. The Burtz seal was designed for the crankshaft to be in its original location. The following is copied from Brent's post.
"If you use the Terry Burtz seal, then you need to be able to adjust the thrust (-again, machine work by the machinist) to set the proper thrust."

12-21-2018, 12:33 AM	#14
Terry Burtz, Calif Senior Member Join Date: May 2010 Location: Campbell,CA, USA Posts: 319	Re: Best Rear Main Seal Dave in MN, You are correct that having the seal rubbing surface ground at the same time the rear crankshaft journal is ground is the best method for concentricity. This method also provides a good surface finish for any seal to rub on. Compared to modern engines, Model A and B crankshafts are more expensive to grind properly because the fillet radii on Model A and B engines are larger which requires dressing (removal of material) from the grinding wheel, and if the grinding wheel has to be narrowed for the seal surface, even more material has to be removed. Crankshaft grinding wheels are expensive and removal of material shortens their life. To save money, you may need to find another machinist, or a machinist that does not have a worn out lathe. Most any lathe built in the last 70 years has preloaded back to back bearings in the headstock with almost zero runout. If the crankshaft to be machined is in a lathe and the rear main journal is dialed in for minimum TIR runout, machining of the seal rubbing surface will be concentric. The likely problem of short seal life (worse for packing type seals, but will also happen with radial lip seals) is wear caused by the rough surface finish of the seal rubbing surface. After lathe machining, the seal rubbing surface should be sanded to provide a surface finish similar to grinding. A wooden paint stirring stick wrapped with progressively finer wet or dry sandpaper can be pressed against the lathe machined seal rubbing surface while spinning to obtain the required surface finish. There is a lot of conflicting information regarding rear main seals, and for the education of all, I ask BRENT in 10-uh-C in post 2 of this thread to explain how thrust (I assume fore and aft movement of crankshaft?) needs to be adjusted. The Burtz seal was designed for the crankshaft to be in its original location. The following is copied from Brent's post. "If you use the Terry Burtz seal, then you need to be able to adjust the thrust (-again, machine work by the machinist) to set the proper thrust."