LBZ Knock

henery97

henery97

Member
Apr 4, 2011
206
0
16
Nebraska
Cruising around town last friday night in my LBZ, lined up at a stoplight with a kid in a LB7, did a small 15-40 mph roll on the 125hp tune. Drove a half mile and I noticed a small tick. So I pulled over to check things out and my tick quickly turned into a faint knock. Pulled the truck into a parking lot and it developed a very loud knock on the rear drivers side.

Things I have checked

-balance rates are ok except cylinder 4 is at +6 in park

-tried turning injectors off using EFI and every cylinder caused the truck to have a misfire shake EXCEPT injector 4, made no difference in vibration or knock

-Little to no blowby

-no codes

-oil looks fine, no shine or metal chunks

-tested compression on what would be cylinder 5 on a sbc (idk what the dmax order is) and it tested 180psi so i pulled the motor and trans.

I suspect a rod? I don't think I have ever heard of a "stock" LBZ bending a rod with such a mild tune. Any ideas??
 
henery97

henery97

Member
Apr 4, 2011
206
0
16
Nebraska
Biggest tune the truck ever saw was 2900us at around 28* for 16 1/4 mile passes in April. Normally gets driven on a 40hp tune with around 8-9* of timing in the cruise area for fuel economy.
 
PureHybrid

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
3,538
526
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Central OH
Did you pull valve covers and check the overhead? I don't see how a tweaked rod would go from a tick to a knock in short time. How many RPMs was it turning?
 
henery97

henery97

Member
Apr 4, 2011
206
0
16
Nebraska
Got the heads pulled off and all the pistons look fine along with the heads.. Tear into the bottom end tomorrow night. Can't see any rods that are obviously bent or any other obvious problems
 
H

Hot COCOAL

May the farce be with you
Jun 9, 2012
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henery97 said:
Got the heads pulled off and all the pistons look fine along with the heads.. Tear into the bottom end tomorrow night. Can't see any rods that are obviously bent or any other obvious problems
Click to expand...

You turned the crank and watched to see all the pistons hit TDC? They all protruded slightly from the cylinder? The engine turned freely and you didn't hear anything while rotating it?

It's gonna be really crappy if it was just injector knock...

How about the valve train, did you rotate the crank and watch all the the valves open and close when the valve covers were off? And you made sure it's not just a pushrod?
 
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