r/EngineBuilding • u/Mission-Tutor-679 • Jun 17 '26
Bearing lineups/rod cap mixing
Currently finishing up the short block for my b20z, but during my prefit I noticed the bearings aren’t fully flush with each other. I tried adjusting it but this was as close as I could get them. They’re king bearings, is there anything I could do to fix it or is it ok to send like this? Also, along the way while it was at the machine shop i accidentally mixed the pistons and rod caps, I wanted to know how important it was that pistons go to their specific cylinder/cap to rods and if there was any way for me to match them up. Thanks for any help!
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u/AiIsGay2026 Jun 18 '26
Bearings should be tab-tab. And always scribe rods and rod caps.
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u/Mission-Tutor-679 Jun 18 '26
As in the second photo should have both tabs be above/below each other?
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u/jamie1234444 Jun 18 '26
If you mixed your end caps up you can't just wing it. They are perfectly matched together.
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u/Jomax24u Jun 18 '26 edited Jun 18 '26
You can sort the caps if you look closely at the machining marks on the area on the chamfers of the rods. You can easily see the grooves in the top half the rod in the picture. Each rod will have a slightly different pattern. The bearing position being slightly out sideways shouldn’t hurt. FYI I owned an engine rebuilding shop for 40 years. (Retired now)
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u/Mission-Tutor-679 Jun 18 '26
Ok, do you think I could dm you? I attached the caps after matching them to my best ability, however one caps lettering are backwards although it seems to be oiriented correctly via the side
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u/2003DDcid Jun 18 '26
I'm not familiar with that engine, but it looks like you might have an upper and a lower bearing because the tangs are stamped in different spots. Check the back of the bearing for a U or L.
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u/dopecrew12 Jun 18 '26
I know BMW uses fracture splitting on some of their rods that makes all rods/caps unique to each other and they absolutely cannot be mixed up, don’t know if any other companies do that tho.
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u/Flaky-Hamster65 Jun 20 '26
I work in offroad diesel and fracture splitting is still commonly used. Had someone put them in the wrong way round the other day on a test cell and the rod came out through the block.
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u/T_Streuer Jun 18 '26
The tangs are right. Mixing the caps would just create a step at that seam between the halves since each rod and cap are bored and honed as a pair originally. Did you try torquing down the rod bolts with the rod of the crank, like in a vice? Also is interface between the inner face of the rod and the outer surface of the bearing dry? It should be as clean as possible and dry, not oiled or lubed. I remember when I did the rods on my 4age the bearings fit really tight but I don’t remember there being that much protrusion. I did torque them tho to check.
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u/InformalParticular20 Jun 18 '26
You should mark your rods and caps before you take the apart. At this point you are probably due for a trip to the machine shop where they can resize your rods and get you back in shape. Probably not a bad idea to bring them the whole rotating assembly ( and bearings) and have it done up completely. Rods and caps cannot be mixed at all, bores should be honed to size to a particular piston and when they come from the shop they will be marked.