Locating main bearings

[The_big_dill]

Hi all,

The main bearings on these engines do not have locating tangs.

How do you ensure that the installed bearing is centered in the bore?

In addition, the cradle does not have any dowels or aligning features, so it can be fastened in different positions... how do you ensure it is centered as well?

I can get close by eye, but I can't imagine that is acceptable when we have clearances to the thousands of an inch.

Thanks,

Phil.

[Jeff23spl]

For the bearing, you install them to clear the oil opening and i never heard of any that moved away. IT kind of seat into place and remain there....and unless you install them really off, it won't really matter if it is few mills more on the left or right, the crank is floating with some clearances.

You get the craddle aligned (intake to exaust side) by the bloc machining. It won't fall in place unless you push hard or tighten the bolts.....This is the main thing to make sure the top and bottom is aligned in that direction with the crank. (Line bore)

For the craddle left/right (Damper to clutch) the bolts alone will be enough to center it

[The_big_dill]

Originally Posted by Jeff23spl For the bearing, you install them to clear the oil opening and i never heard of any that moved away. IT kind of seat into place and remain there....and unless you install them really off, it won't really matter if it is few mills more on the left or right, the crank is floating with some clearances. You get the craddle aligned (intake to exaust side) by the bloc machining. It won't fall in place unless you push hard or tighten the bolts.....This is the main thing to make sure the top and bottom is aligned in that direction with the crank. (Line bore) For the craddle left/right (Damper to clutch) the bolts alone will be enough to center it

Thank you for the quick reply.

On the block side I Can use the oil passages as a guide, but on the cradle side its eyeballed.

Aligning the short side of the cradle (intake to exhaust) is not a problem. The cradle has room to move around in the other direction though. Maybe because I am using studs??

I discovered the bearing halve misalignment when I was checking clearances on the mains. I loosened the cradles, nudged it the other direction, fastened it and it was aligned to the eye.

[Jeff23spl]

You can compare diameter of bolts against studs but at the end, i dont think it should change your clearances.

even if the bottom is few mills far left and the top is few mills far right, it won't change the center line and as long as the bearing aren't exposed to touche the counterweights (except the middle one of course), i wouldn't worry much. At worst you lose few mills on the oil film diameter.

@MSMS3 may confirm ?

[Fstrnyou]

@MSMS3;

[MSMS3]

Originally Posted by Fstrnyou @MSMS3;

More and more manufacturers are moving away from the traditional main and rod bearings that had indexing tabs that fit in depressions or slots in the block or con rods. It’s a crush fit, anyway, with the mating edges of each half being pressed together when the main or rod bolts are torqued, tightly pressing the bearing backing into the supporting main saddle, cap or the connecting rod bore. It’s locked in that way.

So, simply make sure each oil hole in the bearing is centered in the oil hole in the main bearing saddle in the block before laying the crank in place. The center bearing has shoulders, so you can’t get it wrong.

With the crank in place, insert the other bearing half and position the main cap. Make sure the mating edge is aligned with the mating edge of the other bearing half in the block, so that the width matches as you close the gap and begin the crush.

Of course, follow Mazda’s sequence on tightening and final torque.

In essence, be sure to center the bearing oil hole in the block oil hole and get the other half to fully contact the mating surface (edge to edge full contact) to optimize crush as the two come together.

[The_big_dill]

Thank you very much for the replies guys.

I believe my confusion came from the fact that I was clamping the cradle to the block without the crank to measure clearances.

I think the difficulty was positioning the bearings into the cradle, I imagine it is easier when you position them on the crank. Either way, the alignment looked good.

Appreciate the support!