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Main Bearing Part Number??

IowaRV9Dreamer

Well Known Member
I want to assemble my engine core so I can work on the cowl. My plan was to use the old/trash bearings to hold up the overhauled crankshaft. The nose bearings seem OK but the middle and rear bearings do not fit the case. I think the case dowels may have been changed. This is what the dowels look like:
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This is an OLD wide deck O-320-E2A. I'm having trouble finding the correct bearing. The latest PC203-3 (dated 2011) lists 18D26098M003 (I need the M003 for my crank). I'm not sure that is correct. The picture on aircraft specialties doesn't look right with the oil hole not in the center.


I have a sheet from Superior Air Parts that tries to decode 4 different dowel types into Lycoming engines. If this is a "Straight" dowel, it seems to indicate that I need SL11020 bearings (superior part number). That seems to at least look right on Aircraft Specialties.

Any idea how I can find a solid cross reference for these bearings? It seems that in the 50 years or so since this engine was new Lycoming has changed part numbers and dowel designs a lot.

Also, would it be OK to buy new bearings, assemble them into the case with crank, and then remove and re-use them later after the case has been overhauled? My goal at this point is to just temporariliy build up the lower end to assist in cowl mounting.

If anyone has 4 old used bearings that I could use for testing, I'd be happy to buy them!
 
Dave, just make sure you goop the bearings and journals really good and make sure you don't trap any grit when you test assemble. Just use a few perimeter bolts to hold it together.
 
Main Bearings

Dave: I'm with Gil, a engine shop is a good place to look for scrap bearings. If you can find a standard size set that should work for what you want to do even if crank is .003" undersize. I don't think you could tell the difference from the outside. And if all else fails I would use the new bearings for this temporary assembly but not put any serious clamping pressure on the thru bolts.


Don Broussard

RV-9 Rebuild in Progress
 
Thanks guys - I wish there was an engine shop around here to get the old bearings. Since my crank is 0.003 under, I would love to have used full size bearings to increase clearance. My plan is to clean everything really well and lube it up with 100W I won't be spinning it.

Edit: Wow Don and I think (and type) at the same rate!
 
bearings

I have a set of STD bearings you could have! Send me your address. M03 is just a worn out STD so you shouldn't see any difference since your using it as a mock up.

Jesse
970-874-7575
 
I have a set of STD bearings you could have! Send me your address. M03 is just a worn out STD so you shouldn't see any difference since your using it as a mock up.

Jesse
970-874-7575

For reference, an M003 bearing is .003" THICKER than a standard bearing, not thinner. While some refer to the bearing as undersized, it is actually the crank journal that is undersized, requiring an oversized bearing. When people mention a 3 under bearing, they are referring to the application of the bearing and not the actual bearing itself.

Larry
 
Last edited:
For reference, an M003 bearing is .003" THICKER than a standard bearing, not thinner. While some refer to the bearing as undersized, it is actually the crank journal that is undersized, requiring an oversized bearing. When people mention a 3 under bearing, they are referring to the application of the bearing and not the actual bearing itself.

Larry

Thanks Larry! I understand what you are saying. I was referring to the crankshaft sizing and not the bearings in that case.

Jesse
 
Thanks to Jesse my crank and case are test fit together. It came out good enough so I can go hang it for cowl fitting.
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The bearings are LW-11021. I think the hole in the bearings are "stepped" in that the bottom is larger than the surface near the crankshaft I'm still not sure they are right, but I'll get that sorted out when I have the crankcase overhauled by Divco. Something doesn't look right in there to me.
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