Main bearings clearance

[jsfarmall]

I acquired a cub the bottom end was rebuilt. Motor was extremely tight. Never started just turned over by hand. Today I took the oil pan off to assess the situation. The no. 1 rod had .030 rod bearing where the rest are STD. With no. 1 disconnected it was noticably easier to turn. I plastigauged the front main bearing and was less the .002. with the cap removed it is really easy to turn. What's the preferred clearances on main bearings?

[tst]

.002-.003, look hard at the one with .030 bearing, most times the journals are ground the same size, not just one journal, I have seen that done so measure the journal to make sure it is correct, some one could have jammed the undersized bearing in to make up for a scored journal, I would be suspect of "rebuilt" with one bearing like that

[John *.?-!.* cub owner]

To what TST said, though it may have had a problem with the one rod, but I would be cautious.

[jsfarmall]

Will mic the journals, the .030 bearings do not fit. The only way I would be able to get the cap on enough is to use a hammer......not doing that.

Also is there a direction the main bearing caps need to go on? Like the rods and caps the numbers point to the cam. The main caps have a "bump" on one side. Does the bump go towards or away from the cam?

[Eugene]

The bump on the bearing fits into a recess/divet it connecting rod journal and the cap.

[jsfarmall]

I know how the bearings go into the cap, how does the cap go into the block?

[Eugene]

Anti-rotation tabs/bumps.

If you threw all 3 main bearing caps in a bucket - - - use machining marks to correctly place the caps.

[Ohiowoodchuck]

The same way they came off.

[tst]

the caps should have #s stamped in the side of them, 1-3, #1 at the front pulley, the #s on the main and rod caps face the cam, if you are using a hammer to put bearings in you have bigger problems, tear it apart, measure it all and start over, if they put in the wrong bearing I would not trust any thing else they did

[Slim140]

the caps should have #s stamped in the side of them, 1-3, #1 at the front pulley, the #s on the main and rod caps face the cam, if you are using a hammer to put bearings in you have bigger problems, tear it apart, measure it all and start over, if they put in the wrong bearing I would not trust any thing else they did

+1 on this.

[Eugene]

I check for stamped markings before I disassemble an engine. I have found only a couple of engines where the rods, main boss, rod and main caps were not marked.

No markings, prick punch to mark each matching part before disassembling the engine.

[tst]

that is what I do also, no #s, make some sort of id mark so they go back on correctly, many do not realize the main caps are bolted to the block then machined so they only fit one way correctly, if mismatched you can have big problems, tearing up bearings, the crank, vibrations, etc

[BigBill]

The main caps are bolted in place and they are line bored together. Some come numbered and some aren't. Before disassembly I stamp the bearing caps so a mix up can't happen.

Why one .030" under bearing.
Years ago if you had a rod knock you called the local auto machine shop and a machinest came out with a portable setup and he could grind that rod journal in the engine with the pan off.

[BigBill]

Funny but true.

I was taught by a engine guru in my teens. There's only one way to do something and that's the correct way. Mic everything and use plastic gauge as the final inspection for oil clearance. Don't trust what the bearing box says.

Fast forward to my first job at a dealer as a mechanic. I rebuilt a six cylinder engine. In the process I asked the head mechanic for plastic gauge he said we don't use that here. I said nothing. He hands me a handful of bearings loose in those little boxes. These bearing sets usually come packed all together in a larger box. I assembled the engine and noticed it was tight. He's the boss so I said nothing. I put the engine in. Note, I put extra sealant on the oil pan gasket. No leaks, no come backs. It's five o'clock and time to go to my second job. I come in on Monday he asked me why so much sealant on the oil pan I said no leaks. He told me one bearing was the wrong size. I told him the $1.50 plastic gauge would of caught that during assembly as I walked away.

[jsfarmall]

Well as far as putting main bearing caps back the way they came off does not.seem reliable given the way it was when I got the tractor. I could not find any marks on the main bearing caps.