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Discussion Starter · #1 ·
So I have finally started to install the replacement bearings in my 4BTA CPL 0986 that I got from CrewCab59 a while back (thanks!) and I have run into a bit of an issue.

When I pulled the old main and connecting rod bearings they were all basically worn out, and the #1 Upper and #5 Lower Mains looked terrible and there was visible but immeasurable (with an indicator that reads 0.001") damage to only the #1 and #5 journals. I could barely even feel the damage with my fingernail and it felt more like low spots than high spots. Every other journal including the ones for the rods was perfectly smooth, but the bearings were starting to look like crap, though none were worn through as bad as the #1 here in the picture.

When I was inspecting the caps, there was the shadow of the date codes of the previous bearings and it seems as though bearings were put in the motor in 1989 (build date), 1993, 1998, 2000, and now in 2011 (the motor went out of service in 2004). And I have the actual odometer from the vehicle which reads 100755.8 miles with a tag that says "Add 41,816 for odometer miles" meaning it was re-zeroed at re-power. Also, it means the bearings were changed every 20,000 miles.

When I started the engine before removing it from the bread truck, the oil pressure gauge (with no numbers, but only a L and H) pegged on H and then came down into the upper end of the green as the motor warmed up.

I don't think it is a low oil pressure issue, but are there any thoughts on the cause of the issue?

Is the weight of the flywheel and the tension on the belt causing the issue?

Could the engine have been built with the wrong oil pump by mistake?

Were the new bearings improperly lubed during assembly?

Did they not turn off the engine while doing an oil and filter change?

I think I am going to remove the new #1 and #5 bearings and polish the journals a little bit, but I would really like to get to the bottom of this. Some of the other threads talked about too much oil volume washing out the bearings, but I haven't found any other reliable information on this problem.

Additionally, the crank end play was near the upper end of the tolerance band which started this whole process. The engine had the one piece thrust bearing in it and the new genuine Cummins kit came with the three piece thrust bearing. Should I somehow try to get a one piece thrust bearing as well? I understand the three piece logic, because it removes all bending stress from the corner of the bearing to prevent fatigue failure but there must be some flaw in the logic because Andre and some other people have had them come apart.

I am a bit stumped, and any help would be much appreciated.

Patrick
 

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Discussion Starter · #2 · (Edited)
So, my friend Don seems to think that if the oil pressure and / or volume is too high, combined with a crappy oil filter, the filter will just operate in bypass mode, and then dirty oil will circulate through the engine and wear out the bearings. He thinks the #1 upper may be the worst because of this and excessive tension on the belt followed by #5 lower because of the weight of the flywheel. That correlates exactly with the wear I have.

This may be why you're not supposed to interchange 4B and 6B oil pumps...

What do you all think?

I wonder what my camshaft bearings look like.... Is there a way to check them without removing the camshaft? I doubt it.
 

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possibly an issue with the oil pump....most likely they changed the bearings and never pulled the crank for pollishing.
a bearing set every 20,000 to 40,000 is incredibly low number of miles for mains.by not polishing or checking the crank in any way,the destruction of a new bearing set was guaranteed.

i suggest you pull the crank and make sure it isn't bent (highly unlikely),and get it ground true and polished.bsically re-man the crank.the block could also be trouble...get the block measured and make sure the mains run true to each other...they may need to be align honed.your new bearings will live a happy life after that.

the cam only has one bearing insert,at the front.you'll need to pull the cam to see it.the other bearing surfaces ride directly on the block.use copius amounts of assembly lube...a-lot of builders use lubriplate for the mains.lube everything...bearings,cam lobes,rocker assembly's etc.the works.
 

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i should also mention that if the crank needs ground...you'll need a new bearing set to match.
 

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You may want to pull the crank out [and using a dedicated 3 point contact micrometer that measures outside diameters] recheck the journals for being out of round. Also check the main bearing line bore of the block for straightness.
 

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Discussion Starter · #7 ·
Oh, that would make some sense too. The motor was from a bread truck in Maine, and the corner of the motor mount by the oil cooler was cut with a torch to remove the oil cooler at some point.

So I'll get the crank cleaned up, check the oil pump, perhaps pull the oil cooler and check for leaks, and check if the filter bypass valve is stuck.

Thanks everyone!

Cold starts , coolant/ water in oil , alot of miles before oil change.

The cam has a bushing not bearings.

Scott
 

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Oil pressure isn't oil flow, so there could be a restriction somewhere. Maybe core shift or a clump of sand & iron from when block was cast. Not sure here if oil passages are rifle drilled or cast on 4BT's. But a simple restriction could cause this recurrent problem. I've seen pop-off valve problems in oil pumps too, not maintaining pressure continuously.
 

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Oil pressure isn't oil flow, so there could be a restriction somewhere. Maybe core shift or a clump of sand & iron from when block was cast. Not sure here if oil passages are rifle drilled or cast on 4BT's. But a simple restriction could cause this recurrent problem. I've seen pop-off valve problems in oil pumps too, not maintaining pressure continuously.
There could have also been an issue with "lugging" the engine....along with constant idling...
 

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When I was inspecting the caps, there was the shadow of the date codes of the previous bearings and it seems as though bearings were put in the motor in 1989 (build date), 1993, 1998, 2000, and now in 2011 (the motor went out of service in 2004). And I have the actual odometer from the vehicle which reads 100755.8 miles with a tag that says "Add 41,816 for odometer miles" meaning it was re-zeroed at re-power. Also, it means the bearings were changed every 20,000 miles.


Seems pretty strange to have to rebuild a 4BT every 20K miles? Instead maybe the re-man mechanic went to the parts window and the parts guy grabbed several individual boxes of bearings to make a set, hence the different date codes. I can't imagine 5 rebuilds in only 15 years on a 4BT? Naw....
 
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