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Crankshaft question

sunny67

sunny67

Silver Level Sponsor
I’ve torn down my old 1.7l out of my S5 and will be rebuilding with a different block. The only thing I’ll use out of the old engine is the crank and connecting rods and I’m trying to determine if the crank has been turned. I have a question about the crankshaft journal measurements. I saw the attached journal specs in another post but don't know what main journals “A and B” are. All my mains measure 2.374” using a $25 micrometer. The main bearings that came off only had the number A504X where X matches the journal type. None of the journals match the journal “B” size.
The rod bearing say STD which I assume is for standard size but they measure 2.115” and the spec sheet says it should be 2.271.
Can someone help me figure out what I have before I take it to a machine shop. This engine came from a 1969 Rapier so is this crank different from a S5 Alpine? If so, can I get proper bearings and where? Any help will be appreciated.
IMG_0143.jpeg
 
sunny67 said:
Can someone help me figure out what I have before I take it to a machine shop.
Click to expand...

The "A" and "B" are part of a grading system where "A" is the specified design size and "B" is for a crankshaft that for some reason needed to be machined undersize due to some flaw or damage. The machining probably would have only been on one journal and not the full set of journals. If machined under size beyond the design size, the crank should have been stamped "B" beside the affected journal. This system allowed the factory to use an "unperfect" crankshaft in production and gave any technician doing later service work a notification an undersize bearing was required for that journal.

For talking purposes, your mains are STD size but your rod journals have been reground to 0.010 inch undersize.

You state the mains are at 0.001 inch undersize. The main journals were probably polished instead of needing a regrind when the rod journals were reground. This undersize would affect the main journal running clearance, but could still be in spec - between 0.0025" and 0.0010."

The 2.271 inch size you are trying to match is the diameter of the big end hole in the connecting rod, large enough for the bearing shells to properly fit. The crankpin diameter listed with crankshaft specs is the crank rod journal size you're trying to check. Is there a "010" stamped beside any of the rod journals?

If you're doing your own journal measurements, you should measure the rod journals both parallel and perpendicular to the thrust axis and compare to check for signs of flattening.

BE AWARE, your question about crank differences leads me to mention this, make sure you check that the harmonic damper pulley markings ACTUALLY matches piston TDC. I'm not sure if the damper ring on the used pulley I compared to a new, unused pulley had slipped or if a change in the keyway position had occurred, but they were different.

Hope this helps,
 
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