Continental Z134 engine

Hi to all and hope all had a happy and safe 4th...
My question is about a connecting rod bearing that spun.
Bought this 1965 MF202 with the Z134 gas engine and knew it had a spun bearing, just didn't know which one. Dropped the pan, and found the #1 connecting rod bearing had spun. Pulled the rod cap to inspect the crank and rod journals, discovered the rod and crank in bad shape. So, I'm going to have to do a major overhaul with a new crank and another rod. all the other rods and main journals look good.

Now the question...
Is there anything specific I should check for to determine why the rod bearing spun?

I have the mauals, and have been reading to try and figure it out, but no luck so far.

I appreciate any and all input.

Thanks,
Roger

Several factors can cause bearing failure depending on when it failed.

If the engine ran for many years, then failed, it was probably caused from lack of lubrication, either ran low/out of oil, oil contaminated with fuel, lack of maintenance (dirty oil), or low oil pressure.

If the failure occurred shortly after a repair or rebuild, it could have been caused by all the above conditions plus the possibility of improper machining of the rod journal, the rod itself, or the bearing, in other words, the clearance wasn't properly set. It could have also been caused by improper assembly, (rod cap installed backward, improper bolt torque, assembled dirty).

At this point, what happened is not as important as making sure it doesn't happen again! As you said, the crank is probably not worth saving. They can be welded up and turned, but they're never the same. A used crank will probably be higher quality than a new aftermarket. Just have it checked, turned if necessary. Same for the rod, it can be reconditioned or replaced with a used one. I would still have it checked.

One huge concern is finding a reputable machine shop. I trust none of them! If at all possible, double check everything, mike the journals, check the rod ID, take no chances. If you can borrow the measuring equipment, or get a second party to measure everything, it will be a great reassurance that it was done right, it can be assembled once, and will stay together for a long time!

Also keep in mind, when the rod bearing failed, it shed a lot of fine shredded metal that got picked up by the oil pump and circulated through the engine. It's in there, hiding in the most inaccessible places. The block and head should be hot cleaned, then solvent, soap and water, compressed air, and brushed inside every oil galley.

To stay in place and last, the rod bearing needs the proper clearance against the crank, proper crush on the OD of the shells from the rod and cap, oil pressure, NO water in the oil, round crank journal, and a round rod-hole on the big end. The latter seems to be one thing often neglected in rebuilds. The big end of the rod (where the bearings go) should be checked for size and roundness. High hour machines sometimes get slightly oblong to a point the bearings no longer fit tight. If out - it can be resized most times. That by shaving the end of the rod-cap and rehoning. That is standard procedure in any good shop. Finding an automotive machine shop you can trust with the job is another story.
In regard to repairing crank journals? If spun - you might get lucky and be able to clean up the journal with emory cloth and install a .001" or .002" undersize bearing. If real bad - I would no be afraid of getting it ground undersize or having one bad journal spray-welded and ground back to standard. We had many high power diesel cranks spray welded with no failures. A little Z134 is less likely to be a problem. Now -if it's cost efffective?

Get the rest of the rods reconditioned too. Get that block & head striped down and hot tanked to get all the fines cleaned out or you can start over.