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Max Main Bearing Clearance to Big

Practical Engine Building

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What are the options if the main bearing clearance is to big on one crankshaft journal. (video 2:45 min.)

Lets imagine that we HAVE to reuse the old crankshaft ...so not all journals are exactly the same after polishing each journal at your local machine shop.

One option would be matching and mixing shell halves from your set to get your numbers exactly where you want i imagine...

Would other option be to fit thicker shell half into the loaded side of the housing bore from another bigger set. with respect not to mix shell half of (+0.001-inch oversize) with half shell of -1 (0.001-inch undersize).

Please correct me if I'm wrong as this is really important for me.

Sorry for my English, i hope i explained it right.

I would mix bearing shells, and check the resulting clearance with Plasitgage.

Your english is very good!

As you think, depending on the supplier of the bearings, there will be a tolerance on how exact they are to the nominal size and some will be a tiny bit bigger or smaller and you can try selecting the ones that best give the desired clearances. Also as you suggest, the tighter ones should be fitted to the loaded side - the caps for the big end and the 'rods for the big ends.

there is another option, though, in that some bearing suppliers have off-the-shelf undersize (smaller clearance) for some popular engines or, for a little extra, will make up bearing shells to the exact size you need for the clearance you need. I understand KING bearings, for example have these options.

Just to throw a penny into the hat.

Personally I would use a small scribe and mark on the tang or inside the oil groove (if present) on the bearing where you have positioned that bearing (Not the running surface!) (Also possible time record the bearing ID if there is one one the shell itself)

As an example if you use a “yellow” grade (if your bearings had colours let’s say (Honda’s do) no two yellows will be the same. Also if you are using several yellows in one engine etc.

So on the bearing a simple 1,1c 2,2c etc where is is cap, this helps if you ever take the bearings out during the build process or even on the next strip down for inspection purposes.

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