Rear main leak fix

[Catahoula]

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

[Catahoula]

Sorry,

Left out the boring pic.

Jim

[Joe K]

Interesting. Rebabbitt without line-bore.

You're lucky. At least for now. It may eventually find it's "rotating center" - or make it - which may or may not be near where the cap centers to.

Keep driving - that is the point after all.

Joe K

[Catahoula]

Joe,
Since the bearing half had full crankshaft contact as indicated during lapping, I do feel confident that it is aligned with the last line bore.
Jim

[nkaminar]

Wow. Very impressive work.

To get the rope seal out, there are may seal pullers of different designs. Google "seal removing tool."

To get the aluminum rear seal out you may have to drop down the crank by loosening the main bearings and then push it out in an arc. But if you get the rope seal out you may not have to do anything else, assuming that the rope seal was just pressed into the aluminum seal.

[Catahoula]

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Thanks nkaminar,

Will look for a suitable seal removal tool.

[Chris Haynes]

There is an one piece aftermarket seal that you can install when the engine is torn down.

[Catahoula]

I just left the rope in the aluminum seal and removed it from the rear main cap. The Babbitt job has fixed my leak, so I will leave as is.
Thanks for the input.
Jim

[nkaminar]

There have been many people on the Forum that had a bad rear main bearing cap. Repairing them could be a business.

Many years ago, in the mid 1960's, while on a Model A tour, one of the cars developed a bad rear bearing cap. The Babbitt just came out in chunks. The problem was discovered by dropping the pan and removing the cap. A leather sandal was found on the side of the road and became a temporary bearing. The car was driven the 100 miles back home without further problems.

[Richard Knight]

Very impressive. Did you make any attempt to tin the cap. I used products made to do just that. Action tin, and tin tastic would did the cast iron cap. Also you can leave out the oil grooves and have a better bearings by not interrupting the oil film. Just cut the wells on the sides. The tool you where asking about is called a packing puller. But leaving it in and driving on is probably the right thing to do. Good job!

[Joe K]

Packing puller. The steam engineers friend. Especially friendly if you can "backseat" the valve.

Useful on Model A water pump packing too.

Joe K

[Richard Knight]

I have one in my tool box. I can take pictures. Being a steam locomotive engineer I am somewhat familiar with packing!

[nkaminar]

Can also be used to remove the cork on your wine bottle.

[Catahoula]

A friend disassembled a good running marine engine for restoration and discovered the connecting rod cap was replaced with a section of leather belt. Not looking to get into the rear cap restoration business, but posted for those with access to a lathe and mill what worked for me.

I did not tin the cap. It was already drilled to prevent the Babbitt from moving around. I didn’t know the groove isn’t necessary. I used to working on marine engines where the mains are grease lubed. I always put a groove or X in those bearings. The side wells are also new to me. I can see why the groove isn’t necessary.

No need for a seal puller pic, It’s all good for now.

Thanks for all the input,
Jim

[Gene F]

Originally Posted by Richard Knight

I have one in my tool box. I can take pictures. Being a steam locomotive engineer I am somewhat familiar with packing!

Licensed steam engineer here too. The ceramic seals became popular re4placmenets when I was younger, and are a lot less work.

[nkaminar]

Regarding the groove: The crankshaft is suspended by pressure built up in the oil film. This pressure can be very high such as 1,200 psi. The pressure is caused by a wedge between the crankshaft and the bearing. The pressure is zero at the edges and at the groove, so the groove reduces the area that supports the crankshaft. The pressure builds up away from the edges and the groove but does not reach full pressure until a little bit away from the edge or groove.

The grooves were put there starting with early engines to move oil into the bearing. There is conflicting opinions of whether it helps or not. With pressure lubrication it should, in my opinion, be left out.

[Synchro909]

Originally Posted by nkaminar

Regarding the groove: The crankshaft is suspended by pressure built up in the oil film. This pressure can be very high such as 1,200 psi. The pressure is caused by a wedge between the crankshaft and the bearing. The pressure is zero at the edges and at the groove, so the groove reduces the area that supports the crankshaft. The pressure builds up away from the edges and the groove but does not reach full pressure until a little bit away from the edge or groove.

The grooves were put there starting with early engines to move oil into the bearing. There is conflicting opinions of whether it helps or not. With pressure lubrication it should, in my opinion, be left out.

I stand to be corrected here but I think any grooves cut in the pressure bearing side of a bearing (the cap on the mains and rod side of the big end) will do as you say and therefore should be avoided because it destroys the pressure built up by the wedge you mention. (Hydrostatic wedge).
That is likely to be contentious but I am prepared to listen to any arguments to the contrary.

[Fullraceflathead]

In a pressure lube bearing any grooves actually reduce your bearing load capabilities if you think about it look at the connecting rod bearings in a modern engine there's no grooves many times the main bearings will have a main bearings will have a groove that's to provide full pressure lubrication to the rod bearings cause they're typically lubed after the fact from the main bearings this is strictly speaking of a modern pressure lubed engine.