Rear main options

[2speed]

I think I already know the answer to this. Car runs fine, not noises, only leaks oil when you shut it off. Pulled the pan, to check the rear drain tube and bearing. Drain tube is not great, where it screws in is damaged. Bearing has a crack.


Was planning on doing some long trips, but I think that's out of the question. Rebuild is not in the budget. Are there any other viable options?

[J Franklin]

The cap can be re-babitted, but the crack shouldn't be the cause of a leak. What was the clearance? If too much it might be the cause of both. That bearing is still there if you want to use it for a while.

[nkaminar]

As J suggested, check the gap. There are various ways to check the gap.

I would not worry to much about oil leaking out the rear. I little leak is normal. You can tie up a tray under the rear to catch any drops if you are worried about leaving a puddle in your garage or at the ice cream store.

Fix the drain tube. Depending on whether the damaged treads are in the bearing housing or on the tube, replace the tube or re thread the housing. You can use some JB Weld to epoxy it in, but clean everything in acetone first.

The bearing is OK for local trips, like to the ice cream store. Meanwhile look around for a new cap that can be fitted using Timesaver. Or save up for an overhaul. Or look around for a replacement engine that is in good shape.

[Marshall V. Daut]

I agree that the crack probably isn't the cause of the oil leakage from the rear. It doesn't help, but that's not why the oil is leaking out. Besides checking the clearance of the rear main bearing, just as important - if not more so - is center main bearing's clearance. That area wears faster than the other two main bearings because as the fulcrum for the spinning crankshaft, it takes a greater beating than the front or rear main bearing caps. The crankshaft flexes in the center as it turns, which causes a whipping effect with the center main bearing taking the brunt of this whipping action. That wears away the Babbitt bearing material faster than in the front or rear. Because of this, the center bearing will have more slop in it, which in turn affects the wear on the rear main bearing surfaces. Generally in an engine with a lot of miles on it, the center main bearing will need more shims removed to bring it into spec's than the rear main will. The front main bearing rarely needs more than one thin shim removed unless the engine is REALLY worn out. Get the center main into spec's at 0.0015" clearance first and then adjust the rear main cap for the same clearance. Double check the front, but I'd be surprised if you are able to remove more than one thin shim there. Let us know how many shims you have removed from each bearing.
Another thing to consider is crankshaft fore and aft play, meaning how much thrust surface is left on the rear main bearing. If the thrust surface is worn, the crankshaft will move back and forth while turning, which in effect causes a pumping action that sends oil through the place where there is least resistance to stoppage = out of the rear main bearing cap. You can actually see the crankshaft moving fore and aft while the engine is running if the thrust surface is worn away. Watch the crankshaft pulley's movement. If it moves back and forth more than a fraction of an inch, the rear main bearing thrust surface is too worn to keep the crankshaft centered in its bearing saddles. Even with the main bearing caps adjusted properly, this pumping action will still force oil past the rear main bearing. It's easiest to check the thrust play with the engine out of the car and upside down (preferably on an engine stand) where you can push and pull the crankshaft back and forth with the bearing caps in place. If there is too much slop and the engine is out of the car, you can install a brass thrust insert in the block sold by vendors, but the engine has to be out to do this. You have to sand/file the surface until the crankshaft can be spun with resistance. It's a pain to do this, but it will save you rebuilding the engine just to restore the crankshaft's thrust play. I have done it and the engine is still working fine with the minimum allowable leakage. If the engine is still in the car, use a long pry bar to force the crankshaft back and forth. If you can see or feel movement fore and aft, the thrust surfaces are worn.
As to the crack in the Babbitt, of course the best fix is to have the bearings repoured and align-bored, as already suggested. That doesn't seem to be an option for you at this time, so try the next best thing as a stop-gap measure until the bearings can be repoured. Take a small triangle file and carefully carve a "V" trough into the crack along its full length. Don't go any deeper than necessary. Once a trough has been filed through the crack, use an aluminum epoxy or similar tough epoxy and fill the crack with it, smoothing it out as much as possible on top to reduce the amount of sanding required after the epoxy cures. Then carefully sand the epoxy until it conforms to the rest of the bearing surface, checking occasionally with Prussian Blue. Sandpaper on a large wooden dowel or rolling pin works well to maintain the contour of the bearing. Reassemble between sandings and test the clearance, as well as resistance to turning. Be sure to oil the bearing surface before final tightening. I have made this temporary repair to a couple well-worn engines and it works a lot better than allowing the crack to get worse and maybe start losing chunks of Babbitt. Start squirreling away pocket change to someday afford a Babbitt job so that you can make those long-distance drives that this cracked bearing cap is preventing you from doing now.
Marshall

[Marshall V. Daut]

Here are photos of one engine I repaired with the brass thrust insert six years ago. Besides the miles put on the engine since then, the owner took a long tour with an antique car group two weekends ago and he reported back to me that the there is no knocking and virtually no oil leakage from the rear main bearing area. The bearing cap Babbitt had some minor pitting, so I smeared JB Weld over the surface and sanded that down to conform to bearing cap. Probably not necessary to have done that, but I feel better knowing the pits have been filled. Also, note that the bearing material was chipped out near the back edge. I filled that in, too, and it seems to be working well, according to the owner. Admittedly not the world's best fix, but the owner didn't want to spring for a complete bearing re-pour job. So....
Marshall

[nkaminar]

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Many many years ago (1960's) I was in a group tour of the Model A club at Cal Poly in San Luis Obispo. We drove north along Highway 1 through Big Sur. One of the cars developed a bad main knock and a bad leak out the rear main. The owner dropped the pan and took off the cap and the Babbett came out in pieces. He found a leather sandal on the side of the road and cut the sole to fit the cap. He buttoned it up and drove home with the leather bearing, about 100 miles.

[Marshall V. Daut]

Yup. I have heard of Model T owners "back in the day" doing exactly the same thing just to make it home - and probably for a while longer during the Great Depression when money was tight. I have also heard that a decent Model T engine could be bought back then from a junkyard for $5-10. But in 1933, $5-10 was a LOT of money. Tossed away leather belts on the side of the road were much cheaper.
Marshall

[2speed]

I pretty much just buttoned it up again, affixing the pipe better. I didn't check the bearings, because well...it's not long for this world anyway.


The engine runs well, has good power, but it's worn. While underneath I saw pockmark/fret on the cam lobes, some valves wiggle in the guides, etc.

[J Franklin]

Originally Posted by 2speed

Rebuild is not in the budget. Are there any other viable options?

You have been given a few good options. So if you don't even address the clearance while it is already opened up and can't afford any repair, what are you going to do when it completely fails?

[2speed]

Park it until the bank account grows or I find a better engine? This isn't my commute to work car, it can sit.

[oldspert]

You can also have the block align bored for insert bearings. There is a man in Waxahachie Texas that does this procedure.

[Jim Brierley]

I wouldn't worry about that crack at all. It is in the center of the bearing, and won't go anywhere or cause any problems.

[Dan McEachern]

Jim is correct- that bearing looks just fine. yea, its cracked but many are because with the later cast iron rear main caps, oil gets between the babbitt and the cap and causes fatigue cracks like this one. Next time, fit the bearing while you have the pan off and just drive it.

[2speed]

The front half of the crack will move in and out. I am/was planning on doing a 4,000 miles trip this summer, which is why I'm a bit hesitant about patches/running it.


I'm not sure about the crank forward and back movement pounding the crack wider, and I'm not keen on the JB weld against the crankshaft fix.

[nkaminar]

I would not chance it on a 4,000 trip. There are a couple rear bearing caps on eBay right now. Neither looks pretty but one may be serviceable. Or keep looking, perhaps at one of the Model A supplier.

Once you find one that can be used, fit it to the block with TimeSaver, see https://www.snydersantiqueauto.com/s...llow+timesaver You will have to have the engine apart to do this. It also helps to have something to turn the crank besides your arm. I used a right angle drill and made up a connector.

Or take out a second on the house and have the engine rebuilt with inserts.

[johnneilson]

Originally Posted by 2speed

The front half of the crack will move in and out. I am/was planning on doing a 4,000 miles trip this summer, which is why I'm a bit hesitant about patches/running it.


I'm not sure about the crank forward and back movement pounding the crack wider, and I'm not keen on the JB weld against the crankshaft fix.

If you are that concerned get your hands on one of Terry Burtzs' motors.

Just eliminate the worry.

J