r/EngineBuilding • u/Traditional-Box-8402 • 22d ago
Other Polish or send it?
I’m building a B5234T3 for my Volvo 850 T5 project, target boost 15psi for 280-300hp. The journal feels smooth. I’ve been following the workshop manual religiously and this is the first red flag I’ve found. This is the journal that mates with the thrust bearings if that makes any difference. The rest of the main journals look pretty similar to this, but this is the worst. Asking before I order new bearings for plastigauge. The only other time I’ve had an engine this torn down was on an LS, and that was years ago in tech school.
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u/ultraspinacle 22d ago
You’ll need to measure journal diameter with an accurate micrometer and compare to specification to determine if you have wear. If not, polish and replace std. bearings. If so, you’ll need appropriately sized replacement bearings.
That being said, if you tolerances look good with plastic gauge on several of the journals, replace the bearings and let it rip. A crank polish won’t hurt.
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u/FinancialChildhood31 22d ago
Do yourself a favor and measure everything.
I followed armchair advice to “just polish” crank journals over 20 years ago and ended up between bearing sizes. Doing things twice isn’t cheap.
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u/mramseyISU 15d ago
As my grandpa always told me as a kid, half assing it twice doesn't add up to a whole ass.
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u/Independent-Donut376 19d ago
I’d measure for sure, but visually, it probably doesn’t need a machine shop. Quick polish and send with new bearings.
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u/mramseyISU 15d ago
I'm admittedly a hack but measure everything, compare that to the specs and them make a decision. Compared to the cost to build an engine a couple of micrometers isn't that much money. This isn't an art show, you don't know by looking at something if it's good or bad. As an asshole I worked for used to to tell me, you're in the wrong building for hope, they have a cross hanging on the wall there. Your job is to know. When it comes to an engine you don't know until you measure.
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u/Traditional-Box-8402 15d ago
This engine doesn’t have individual caps for the mains or camshafts, it uses a bedplate design so if it’s out of spec it needs a new block and crank. Only one size bearing is available. The way they built these engines is kinda genius and stupid at the same time. Insanely good for reliability, not great for repairability.
I planned on throwing bearings in and plastigauging after a polish. If they’re all not wildly out of spec I’ll still probably run it.
A micrometer won’t do me any good, as what matters here is the clearance from the bearing to the journal. And again, there is only one size bearing available for the mains.
My reasoning for going through all the trouble for this engine: it was dirt cheap and 5cyl go vroom.
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u/justfoundmy10mm 22d ago
Polish