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Has anyone used aluminum main bearings for the 4.0?

luby

New Member
Joined
Aug 12, 2019
Messages
7
Location
Wisconsin
Hello.
Want to replace main bearings in 4.0 engine.
The aluminum ones are cheaper and the write-up
describing them sounds okay.
Does anyone have any first hand experience with these
aluminum engine bearings?

Thanks for your time
 

Daryl

2004 Rubicon
Supporting Member
Joined
Apr 29, 2018
Messages
1,342
Location
Earth 🌎
Link? Here’s the different layers that a main or rod bearing are made of.

3E2F8BEC-D488-4AE3-8018-D21BF269C348.jpeg
 
Last edited:

astjp2

TJ Addict
Joined
Aug 22, 2018
Messages
2,954
Location
Utah and Alaska
Hello.
Want to replace main bearings in 4.0 engine.
The aluminum ones are cheaper and the write-up
describing them sounds okay.
Does anyone have any first hand experience with these
aluminum engine bearings?

Thanks for your time
Are you running an aluminum block hemi? if not a waste of time..
 

g.hayduke

TJ Enthusiast
Joined
Feb 19, 2019
Messages
289
Location
New Mexico
Your main (and rod) bearings are about a critical a part as you can find. The OEM bearings last 200K miles or more. If your el cheapo main bearings fail, your engine is probably completely destroyed. If the engine is not destroyed, a failure still leaves you stranded with a major repair needed.

Why would you risk using anything other than OEM? This is not a component to go cheap on.
 

astjp2

TJ Addict
Joined
Aug 22, 2018
Messages
2,954
Location
Utah and Alaska
Any of the big manufacturers will be fine, trw if the are still in business, and many other conventional manufacturers would be adequate.
 
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Jerry Bransford

TJ Guru
Supporting Member
Joined
Nov 9, 2015
Messages
12,545
Location
Escondido California
Similar flex and expansion. Aluminum bearings in an iron block, the aluminum expands and tightens up the clearances up to the point of possibly seizing the engine.
I don't understand why aluminum bearings would be used even with an aluminum block since the crank and thus the crank's bearing surface is steel. But then what I know about rod bearings is less than what I know about brain surgery lol.
 

GASnBRASS

TJ Enthusiast
Joined
Apr 6, 2017
Messages
420
Location
Minnesota
There is some misconceptions in this thread.

Bearings are typically either tri-metal using traditional copper lead and babbit construction, or bi-metal using aluminum alloy with tin and silicon.

For my stroker build I installed King aluminum alloy bearings. They have a more consistent surface thickness, resist seizure during brief oil film collapse, good particulate imbedibility, and longer service life. For the cam bearings I used DuraBond.

If you are not rebuilding the engine, or at least resizing/resurfacing the journals, you can't just slap in some new bearings and expect it to work. The factory mixes and matches slight undersized/oversized bearings to account for machining tolerances at the plant. You will do more harm than good if you just replace the bearings without checking the oil clearances.
 
OP
L

luby

New Member
Joined
Aug 12, 2019
Messages
7
Location
Wisconsin
There is some misconceptions in this thread.

Bearings are typically either tri-metal using traditional copper lead and babbit construction, or bi-metal using aluminum alloy with tin and silicon.

For my stroker build I installed King aluminum alloy bearings. They have a more consistent surface thickness, resist seizure during brief oil film collapse, good particulate imbedibility, and longer service life. For the cam bearings I used DuraBond.

If you are not rebuilding the engine, or at least resizing/resurfacing the journals, you can't just slap in some new bearings and expect it to work. The factory mixes and matches slight undersized/oversized bearings to account for machining tolerances at the plant. You will do more harm than good if you just replace the bearings without checking the oil clearances.
Thanks much.
I think I read that about the "mix and matching" in the TJ manual.
Is that practice used on all Chrysler engines? Or just this 4.0 engine?
Never heard of Chevy or Ford doing that.
Sounds like it would have been a problem whether I used aluminum bearings or not.
 

GASnBRASS

TJ Enthusiast
Joined
Apr 6, 2017
Messages
420
Location
Minnesota
I can't speak to other engines but the 4.0 will have various colored paint marks on the caps to denote what bearings were used. In mine the upper mains were standard but the lowers were .0005 (five ten-thousandths of an inch) undersized to tighten up the oil clearance. If I had simply swapped in standard bearings my oil clearance would have grown a half thousandth. When clearances are only 2-3 thousands that a huge difference. Factory fractional under/over bearings are not available, and aftermarket bearing companies only make then for the most common engines around such as small block chevy's.

In my case the #1 connecting rod was bent (hydrolocked?) and I tried to make an economy fix with a used rod and new piston and rod bearing. Then I discovered the pistons need to be a matched weighted set. That pushed me to just do a total engine rebuild.