Hey Guys,
Kind of new to Model A’s, bought two in August and another last month. Working on the best of the three to make it a safe reliable driver. Running good, fuel and electrical has been sorted, but had a steady drip from the rear main. Below is the steps I performed to remedy the situation.
Identified the leak to be the rear main bearing. Removed oil pan, and rear main bearing cap. Found babbit broken in cap. Without disassembly visually inspected other babbit bearings for breaks and looseness. Al others looked acceptable. Measured crankshaft and noted that it was offset toward the passenger side .015”. Turned up a 1 7/16” dummy shaft and two thrust molds for the babbit bearing pour and add a couple ramps to pour the babbit in the mold. The aft thrust mold was turned to fit tight in the slinger area to support the dummy shaft. Everything was siliconed in place to help support the front thrust mold and prevent babbit leakage. The assembly was placed in the BBQ and preheated to 450F, a torch can also be used for preheating. Poured the 800F high speed babbit as needed. Removed ramps shaft and molds. Trimmed excess with band saw and filed flat. Then lapped flat. The assembly was set up in a mill finding center between the mounting bolt holes and moving over .0075 from center to compensate for the crankshaft offset. A boring bar was used to machine bearing a few thousandths smaller than crankshaft. Bearing thrust surfaces was scraped to size. Medium grit time saver was applied to bearing and bearing cap assembly installed with shims that allowed some resistance when tightened and turning crank. With spark plugs removed, the starter was used to turn the engine for lapping. I would turn starter for about ten seconds, let cool, and crank again, for a total of about 40 cranking seconds. The cap was then removed and dark spots scraped with knife or bearing scraper. Repeat this process til bearing lapping shows full coverage on bearing and heavy black spots(bearing high spots) are gone. Took me five times. Cleaned everything up with solvent, supported crankshaft, reinstalled cap assembly with plastic gauge, removed cap and had even .003” full length clearance. Removed .003 shim from one side so I should have .0015 clearance now. Cut groove in babbit with dremel, filed little well areas at mating surfaces and reinstalled cap assembly and oil pan. Serviced, test drove and no leaks noted.
When tackling this job, I hadn’t intended on posting online but later figured it may be useful to someone. I do have a few below showing measuring crankshaft offset, set up, and finished product. And No I didn’t peen the bearing. Put a couple hours driving at highway speed on it last Sunday and still no leaks.
One question I have for you experienced guys is, can the rear seal be removed without removing the crankshaft? Previous owner had installed a rope seal and I was unable to remove it from the top half.
Hope this helps someone,
Jim
Kind of new to Model A’s, bought two in August and another last month. Working on the best of the three to make it a safe reliable driver. Running good, fuel and electrical has been sorted, but had a steady drip from the rear main. Below is the steps I performed to remedy the situation.
Identified the leak to be the rear main bearing. Removed oil pan, and rear main bearing cap. Found babbit broken in cap. Without disassembly visually inspected other babbit bearings for breaks and looseness. Al others looked acceptable. Measured crankshaft and noted that it was offset toward the passenger side .015”. Turned up a 1 7/16” dummy shaft and two thrust molds for the babbit bearing pour and add a couple ramps to pour the babbit in the mold. The aft thrust mold was turned to fit tight in the slinger area to support the dummy shaft. Everything was siliconed in place to help support the front thrust mold and prevent babbit leakage. The assembly was placed in the BBQ and preheated to 450F, a torch can also be used for preheating. Poured the 800F high speed babbit as needed. Removed ramps shaft and molds. Trimmed excess with band saw and filed flat. Then lapped flat. The assembly was set up in a mill finding center between the mounting bolt holes and moving over .0075 from center to compensate for the crankshaft offset. A boring bar was used to machine bearing a few thousandths smaller than crankshaft. Bearing thrust surfaces was scraped to size. Medium grit time saver was applied to bearing and bearing cap assembly installed with shims that allowed some resistance when tightened and turning crank. With spark plugs removed, the starter was used to turn the engine for lapping. I would turn starter for about ten seconds, let cool, and crank again, for a total of about 40 cranking seconds. The cap was then removed and dark spots scraped with knife or bearing scraper. Repeat this process til bearing lapping shows full coverage on bearing and heavy black spots(bearing high spots) are gone. Took me five times. Cleaned everything up with solvent, supported crankshaft, reinstalled cap assembly with plastic gauge, removed cap and had even .003” full length clearance. Removed .003 shim from one side so I should have .0015 clearance now. Cut groove in babbit with dremel, filed little well areas at mating surfaces and reinstalled cap assembly and oil pan. Serviced, test drove and no leaks noted.
When tackling this job, I hadn’t intended on posting online but later figured it may be useful to someone. I do have a few below showing measuring crankshaft offset, set up, and finished product. And No I didn’t peen the bearing. Put a couple hours driving at highway speed on it last Sunday and still no leaks.
One question I have for you experienced guys is, can the rear seal be removed without removing the crankshaft? Previous owner had installed a rope seal and I was unable to remove it from the top half.
Hope this helps someone,
Jim
