Advice on Worn Bearings (Long Post)

Wed Dec 22, 2004 6:15 am

Guys, I need some advice on my '50 Cub:

1. The oil pressure on my Cub barely stays above the red when mowing during the summer, so damage can't be far away. I am thinking that the cam bearings are worn because the rods aren't making any noise YET.

2. The Cub only smokes a little at start-up and has a little blow-by when hot, but doesn't use a full quart of oil during a mowing season. So, I think that the rings are at least acceptable.

3. Since I am retired and disabled I have to be really careful with my money.

4. My questions:

a. Should I just run the tractor until I hear the rods knocking, or should I plan to go ahead and have the bearings replaced?

b. Can the cam, rod, and crank bearings be replaced with the motor still in the tractor?

c. How much can I plan to spend on the bearing set?

d. Will the crankshaft have to be turned/trued?

e. How much labor can I expect to pay (broad ballpark) to have the bearings replaced?

5. Thanks for any feedback and advice. I really don't want to damage the tractor and have to sell it because I can't afford to have it repaired.

Wed Dec 22, 2004 9:12 am

Hi Rick,

I have just finished the re-build on my '50. Here is what was done:

bored to +.020
new pistons/rings
new rod wrist pins
turned the crank
new main and connecting rod bearings
4 new valves/the remainder was honed
all new valve guides

The bill on all that was $522.00 Also, I went ahead and replaced the
oil pump grears. All of the gaskets and seals were about $75.00

I know that this may sound expensive. however, it should last a long
time and still be worth it.

I am sure others will come on board and give you some other ideas
as to cost and other options for re-build.

I hope this helps some.

Wed Dec 22, 2004 9:16 am

First of all, running ANY engine with low oil pressure is a bad idea. Fix it now before your engine suffers damage that you don't want to see.

Getting by cheap is something I've had to do all my life so I'm all too familiar with it. Before you do anything else, make sure you really DO have low oil pressure. It would be a shame to replace expensive bearings when a bad gauge is lying to you.

Sounds like your engine is tired. A good rebuild would be best, but it would be expensive. For now, If your pressure is low, I'd change the rod bearings and try it again...that's by far the cheapest thing that could be causing the problem. Just because they aren't making noise doesn't mean they're good, and they're more likely to be the culpret than cam bearings.

A list of possible problems would include main bearings, cam bearings, rod bearings, oil pump, contaminated oil (I'm assuming you changed it), blocked passages, loose parts or cracks extending into an oil gallery somewhere. None of these are good, and most would require tractor disassembly.

Your rings are probably usable for a while longer.

Wed Dec 22, 2004 9:27 am

Cam bearings worn enough to cause low oil pressure on a cub are pretty rare. The crankshaft bearings on a cub (both main and rod) are pressure lubricated rather than splash lubed as they were on many old tractors. They will get pretty badly worn before they start knocking. More than likely the low oisl pressure is from the crank bearings rather than cam. You can get plasti-gauge from auto parts store to check them. You use it by dropping the pan, and removing a cap, then place a piece of the gauge between the bearing and crank and clamping the cap back in place. Do nto turn the crankshaft while doing this. You then remove the cap and compare the width of the plastigauge with a chart included to tell how much wear you have.

Wed Dec 22, 2004 12:18 pm

Rick, I highly recommend you make sure your oil pressure gauge is reading correct. A while back my buddy made a gauge tester where you could test 4 at once against a known good master. We found no gauges including new ones that were accurate. We were thinking rebuild also untill we installed a good gauge and then realized the engine wasn't as worn as we thought.

Wed Dec 22, 2004 8:35 pm

Check the simple, cheap things first. When you pull the pan to check the bearing wear, check the oil pickup tube that runs from the pan to the pump. If it is loose, the pump could be pulling in air.

If you find you need to change bearings, I would change both the mains and rod bearings. Then, if it doeasn't "need" new rings too badly, go ahead and put new rings in anyway. Reface the valves too, as it is just a labor cost. That should leave you with an engine that will not need to be messed with for a long mime.

Thu Dec 23, 2004 11:09 am

Jim Becker is right, and I have to agree...the main bearings should be changed also because they're a good possibility, and changing them now would make it a one-time trip through the bottom end. I didn't suggest the mains in my earlier post because they're considerably more difficult to change than the rods with the crankshaft in the block, they'll add some to the expense and the man is working on a tight budget. My suggestion was basically just a "Winchester maintenance" approach, based on the most likely and least expensive scenario. Can the main bearings be changed without removing the crank? How about the thrust bearing? Somebody help me out here!

There's no question that the rings should be changed and the valves ground (or at least lapped), but I didn't suggest that either for the same reasons. The head must be removed for those jobs, and we all know about the possibility of head bolts being frozen in their bores if they weren't sealed properly when they were installed before (they're "wet" bolts). It sounded to me that the man wanted to cure the oil pressure problem only, nothing more...and at minimum expense...until he can afford to do more later.

I'll stand by Jim's suggestions. That stuff really needs to be done, and it can all be done without splitting the tractor apart if the crankshaft doesn't have to be removed. Hopefully, his oil pump is's behind the flywheel.

One last suggestion...don't forget to check the oil pressure relief valve. It's behind a large plug near the lower right front of the engine, and it limits the oil pressure if everything else is good. There is a spring and a piston in the machined bore, and it can get stuck sometimes. Not very likely, but it's easy to check and costs nothing.

Thu Dec 23, 2004 1:26 pm

Many thanks, Guys, for all of the very detailed suggestions. I think that I will begin by ensuring that my oil pressure gauge is correct. I just installed a new one, but that doesn't mean that it is correct.

If that checks out OK, I will have to start with the rod and main bearings as I can afford them. Then, I can proceed to to the rings and valves.

It's no fun being too poor to afford to do things the right way the first time, but I do enjoy my Cub and hope to keep it running as long as I can.

Thanks again, and Happy Holidays to all.

Thu Dec 23, 2004 1:28 pm

I don't know if they are still available but auto parts stores used to sell a little tool for rolling the upper half of the bearings out. It looked like a very short nail with the head crooked. You put it in an oil hole in the crankshaft and turned the shaft. The nail head caught the end of the bearing and rolled it around the shaft so you could remove it. Note if you have a later block that has the notch at one end of the bearing to keep it form spinning you have to roll it in the direction pushing the block away from the casting. Thrust bearing removes the same way.

Thu Dec 23, 2004 8:11 pm

One of the "Blue Ribbon" service manuals I have suggests useing a cotter pin in the oil hole of the crank to turn out the main bearings to do a "roll-in". It said to flatten the head of the cotter pin in a vise before using it. :wink: