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Rod Bearing Clearance

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1 month 1 week ago #231236 by sheddcanyon
Replied by sheddcanyon on topic Rod Bearing Clearance
I've decided to go with the used bearings. After talking to my engine guy in Madera, CA, he said that trying to grind a crankshaft .002" can be more difficult than grinding them .030". He also thought that honing the piston rods to give more bearing clearance might cause additional problems, as well. On his advice, i reinstalled the used bearings and plastigauged them. And they were still on the tight side .005" to .006" clearance. And I'm assuming the engine was at least a mid-time engine, based on overall condition. I looked back in my notes to when I oriignally measured the crankshaft, and I did measure in some places that in some places the journals were on the bigger side. I didn't think too much about it and wrote it off as being due to my inexperience with a mic.

Thank you everyone for your input and information. And if anyone is looking for a new set of D4600 aluminum rod bearings, .030" under, pm me.

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1 month 1 week ago #231242 by edb
Replied by edb on topic Rod Bearing Clearance
Hi SC,
from the specs for the 4600 engine your aluminium big end bearings should have a clearance of 0.0055" to 0.008" so 0.0005" under the stated minimum I would think should not be an issue for one of these old low stressed slow revving engines and using today's much improved slippery oils.
The difference could be a micrometer zero error.
Just my thoughts.
Cheers,
Eddie B.
The following user(s) said Thank You: sheddcanyon

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1 month 1 week ago #231263 by trainzkid88
Replied by trainzkid88 on topic Rod Bearing Clearance
round surfaces are difficult to measure as you may not be perfectly centred over the shaft and you can get a false reading.

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1 month 1 week ago #231270 by sheddcanyon
Replied by sheddcanyon on topic Rod Bearing Clearance
I discovered early on that being able to measure accurately with a micrometer is a skill that takes practice. I'm not there yet.

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