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Rod Bearing Clearance

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1 month 3 weeks ago #231031 by sheddcanyon
Dealing with 80 year old engines, one usually would be concerned about too much clearance between a piston rod bearing and journal. My problem is the opposite. I am plasti-gauging the clearance on a D4600 crankshaft rod journal and using brand new after market aluminum bearings (made in Austria so quality should be good). According to the specs, minimum clearance for aluminum bearings is .0055" and I'm measuring .002 -.003. I had the journals polished prior to assembly. Main and rod journals have been turned .030" on a previous rebuild.

Can I run these as they are? My other options are: try the old rod bearings that I'm replacing (they looked reusable, didn't measure them), or remove the crankshaft and have the rod bearings turned down .002-003".

Thanks!

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1 month 3 weeks ago #231033 by kittylover123
Replied by kittylover123 on topic Rod Bearing Clearance
-what is the diameter of the rod journal? (rule of thumb is one thou clearance per inch diameter)
-do you have any pictures of the compressed plasti-gauge on journal you can post?
-you say .002 to .003", are they consistent, all the same?
-the compressed wax should appear very consistent all the way across the journal...and every journal should be the same..
-if they are, i would run with it

Caterpillar D6C 99j

Tax me, I'm Canadian:canada:

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1 month 3 weeks ago #231037 by sheddcanyon
Replied by sheddcanyon on topic Rod Bearing Clearance
Standard bearing journal on this crank is 2.625". These were turned down .030" on a prior rebuild and now measures at 2.585" . The rod journals showed no wear and probably 1 to 2 thousandths out of round.

The compressed wax was consistently closer to .003" than .002" and it was very uniform, all journals the same. It was placed on the rod end of the bearing, not the cap.

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1 month 3 weeks ago #231039 by edb
Replied by edb on topic Rod Bearing Clearance
Hi SC,
it helps us immensely if you give the model and Serial Number of the unit you are working on as these specs can vary over model ranges of engines as bearing metals changed.

Grab these for future reference.
Cheers,
Eddie B.
Attachments:
The following user(s) said Thank You: Mike Meyer, Mangoman

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1 month 3 weeks ago #231043 by Old Magnet
Replied by Old Magnet on topic Rod Bearing Clearance
If your reading the plastigage on the low side of the rod journal with 0.001 to 0.002 out of round then your clearance is going to be to tight on the high side.

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1 month 3 weeks ago - 1 month 3 weeks ago #231050 by trainzkid88
Replied by trainzkid88 on topic Rod Bearing Clearance
i know it might sound silly are you reading the metric or imperial readings. plastiguage is available in both units. and have you read the right line in the spec chart. i use a ruler as a guide when i do that sort of stuff so i know im reading the right info.

its a easy mistake to make.

also a family friend was rebuilding a engine yrs ago he bought 7 sets of bearings before he got a set that was correct. the bearings when checked didnt match what was printed on the box it does happen that they are mislabeled and besides not every single bearing is checked before being packaged as they are mass produced.
be aware they may be marked in metric units too.
 it doesnt hurt to check it can save you time and money.
Last edit: 1 month 3 weeks ago by trainzkid88.

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1 month 3 weeks ago #231051 by kittylover123
Replied by kittylover123 on topic Rod Bearing Clearance
-wondering how you know the rod journals are that much out of round? when they show no wear?
2 thousands is a lot...you might to touch those up to be safe..it would give you a bit more clearance too..

-what about the big end of the connecting rod? is it perfectly round? i don't know with diesels but with gasoline engines it is very common to have to resize the big end to make them round again (concentric) esp after the rods have many hours/miles on them and go thru torque cycles..

Caterpillar D6C 99j

Tax me, I'm Canadian:canada:

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1 month 3 weeks ago #231065 by sheddcanyon
Replied by sheddcanyon on topic Rod Bearing Clearance
"it helps us immensely if you give the model and Serial Number of the unit you are working on as these specs can vary over model ranges of engines as bearing metals changed.

Grab these for future reference."


Eddie, sorry about that. This is for a D6, 4R1143, 1942. I got my specs from the Cat Service Manual Form 30419, and the specs match the sheets you sent me. Thanks for these, though. Much quicker to scan.

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1 month 3 weeks ago #231066 by sheddcanyon
Replied by sheddcanyon on topic Rod Bearing Clearance
"If your reading the plastigage on the low side of the rod journal with 0.001 to 0.002 out of round then your clearance is going to be to tight on the high side."

I'm afraid of that being the case.

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1 month 3 weeks ago #231067 by sheddcanyon
Replied by sheddcanyon on topic Rod Bearing Clearance
Kitty lover, I know the out-of-round specs from measuring it and the mechanic who polished the journals confirmed. They are well within spec, but i guess it's not accurate to say the journals show no wear.

In any event, before I pull the crankshaft back out, I'm first going to first put the used bearings back in and plastigauge in multiple positions and see what it looks like. I really, really don't want to remove the crank and haul it 2 hours away to Fresno (no local engine shop can handle this crankshaft.

This time I'll take pictures.

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