Isuzu 4jb1 knocking sound

[John V]

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My engine has a pretty constant knocking sound that I need help diagnosing. I tried one-by-one loosening the fuel injector lines to see if it was one cylinder making it, but I didn’t isolate it to one. I did a valve clearance adjustment and that didn’t fix it. Next I’m thinking a leak down test. Any suggestions appreciated.

The engine is smoky for the first 2-3min when cold, eventually it clears up.
Thanks,
John

 

[John V]

This is a video I took last month, sound wasn't there https://photos.app.goo.gl/bmzTgF4bnSXr1AUa6, and engine hasn't been run much since then. I've since fixed the leak in that video.

 

[Coaldust]

That sounds bad. I would probably check check exhaust port temps and verify that every cylinder is contributing. You already attempted that with shorting the nozzles, but it’s quick and easy. It sounds 1/2 crank speed to me in the video, but you said the valve clearance was fine. I would remove the oil filter, cut it open and look for debris.

Is the oil pan accessible to easily remove?

 

[John V]

I’ve got an infrared thermometer, do I just point it where the exhaust manifold and head meet for each cylinder?

Just finished a leak down test. All cylinders tested about 42-44psi when 50psi was applied. I found a small exhausted leak where the manifold bolts to an exhausted pipe, but I doubt that’s where this sound is coming from.

 

[John V]

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Took the pan off. Pistons 1-3 seem fine, piston 4 has about 1/32-1/16” of play at the crank. Would that be causing the sound? Can I just remove the connecting rod caps to inspect?

 

[John V]

Spun a rod bearing:




What are the chances I can throw new bearings in that rod and carry on

 

[Vetech63]

Your rod journal is already undersized from the spun bearing.....your connecting rod too i bet. A new bearing will last about 30 seconds

 

[John V]

Good point. I mic'd the spun journal and it was about 52.08mm, unspun journal was about 52.90mm.

 

[John V]

When a supplier says the rod bearings are .25 or .50 oversize, do they actually mean undersize?? If they were oversize, wouldn't the OD grow and ID stay the same? If you were going to get anything but standard size rod bearings, wouldn't it be after the crank was ground smaller, necessitating undersize bearings?

 

[Nige]

When a supplier says the rod bearings are .25 or .50 oversize, do they actually mean undersize?? If they were oversize, wouldn't the OD grow and ID stay the same? If you were going to get anything but standard size rod bearings, wouldn't it be after the crank was ground smaller, necessitating undersize bearings?

To cater for all eventualities there are generally various options in crankshaft bearings.
If the crankshaft is ground then undersize bearing shells would be required.
If the connecting rod or main bearing caps are bored then oversize shells would be required.
If BOTH the crankshaft is ground and the rods/main caps are bored then undersize-oversize shells would be required.

From what I can see on your photos the crank will need grinding (so undersize shells for the big ends at least) and if you want to re-use that rod it will have to be bored oversize. The other option would be to only grind the crank and replace that one connecting rod. That would require undersize rod bearing shells.

You haven't removed any main bearing caps yet so the possibility exists that the mains may also require grinding.

 

[John V]

Is there any hope in replacing that con rod and inserting the piston from the bottom (so as to avoid top end disassembly)? If not I might as well get to pulling the engine from the excavator

 

[Nige]

Dunno, never worked on one but FWIW with it being such a small engine you might be better off pulling it and getting it all apart. Who knows where metal shrapnel from that bearing failure might have ended up.?

 

[Coaldust]

Ouch. The piston won’t clear the crankshaft counterweights. Good diagnosis, BTW. Sorry about the mess.

 

[John V]

the crank has to come out anyway to get reground. I was thinking 1. Remove crank, 2. Pull piston out bottom, 3. Insert piston with new rod to tdc, and lastly install the crank. But I’ve never gone this deep in an engine before, so I don’t know if is possible

 

[Nige]

Unless I’m missing something surely the engine would have to come out of the machine in order to get the crank out.? If you’re going that far you might as well go the rest of the way and disassemble completely. As I mentioned above I would be worried about where the particles from the failure have ended up and for all we know some of them could have found their way into places that will only be cleaned out with a complete disassembly.

 

[John V]

I took the engine completely apart. My first time going this deep in an engine. Fortunately no spun main bearings! I ordered a new crankshaft as the nearest shop said it'd run about 500-600$ to grind the crankshaft, whereas I found a new one for $225. Also the Isuzu manual says due to the Tufftride hardening process the cranks shouldn't be reground. The main bearings all show wear similar to this one:

So I'll be replacing all of them. Going to replace all the rod bearings as well, as well as the one wallered out conn rod.

Beyond that, I'm not sure what should be replaced or reused. The top piston ring on all 4 pistons was broken. 3 out of the 4 cylinder liners have one or two of vertical lines like these:

I can't feel the mark with my fingernail, so I don't know if it's a cause for replacing the liners. I have a bore gauge on order so I can't measure the liner diameters until tomorrow.

Cylinder 4 liner was very easy to remove, it actually came out with the piston. The manual describes using a special tool and press to remove the liner, as well as a different tool and press (or dry ice) to insert the liner. Should I be concerned with how easily it came out, and what would cause this?