Isuzu 4BG1T vibration: Eating Hyd pump coupler and speed sensor

[Pigpen]

My 2005 LBX 160LX, SN K2J4 8450 (160Q3-1351) has an Isuzu 4.3L (4BG1T variant) engine that has a sharp vibration that I suspect is causing the flywheel to rub the housing and hit the engine speed sensor.
It seems more pronounced at lower rpms. The engine runs fine.

I removed and replaced the Hyd pump coupler, cleaned the area then reinstalled. I didn’t feel any movement on the crank and as you can see, the rear seal is tight with no leaks. The flywheel was checked by a machine shop who found no issues. The motor mounts look good too.

I checked the front pulley with my digital boroscope tool and I don’t see any damage to the big rubber dampener.

Are there balancing tabs or weights on the crankshaft Washers? Could the thrust washers have play that maybe I missed?

I don’t want to just willy nilly take the engine out but I’m kinda stuck. My next thought is to pull the oil pan off, assess, and then find an engine guy

Has anyone had this issue with the Isuzu 4.3L? Good motor but I’m not finding a lot of literature on the engine. Last pic is the new coupler.

Thank you in advance.
Pigpen.

 

[Lagwagon]

How many hours on the engine? What do you mean by ‘variant’ ? Is it a crate engine? Idler pulleys can slip internally but look normal, unless you marked the steel flanges when it was good, there’s no way of knowing how far or if it has slipped at all. I had the same issue on a 4jb1t, horrible at idle but smoothed out the higher the rpm, rebuilt injector, rebuilt pump, new plugs, checked all timing chain etc…. Turned out to be the pulley

 

[Pigpen]

How many hours on the engine? What do you mean by ‘variant’ ? Is it a crate engine? Idler pulleys can slip internally but look normal, unless you marked the steel flanges when it was good, there’s no way of knowing how far or if it has slipped at all. I had the same issue on a 4jb1t, horrible at idle but smoothed out the higher the rpm, rebuilt injector, rebuilt pump, new plugs, checked all timing chain etc…. Turned out to be the pulley

It has 5800 hours and by variant I was referring to the different models. Mine is a DD-4BG1T and it’s the original motor.
Good idea, I should probably pull my front pulley and check that too.
Thanks for the insight

 

[Lagwagon]

Pulling the oil pan first would be a good idea and cheaper. if your taking the pulley off then replace with a new isuzu genuine, not cheap. Obviously if there’s chunks in the pan you have issues but no chunks isnt a clean bill of health. By washers do you mean bearings?

Did the vibrations start all of a sudden or gradual ?

 

[Lagwagon]

Another thing, were you looking at the engine mounts while engine was vibrating or off?

 

[Pigpen]

Doesn’t the thrust bearing sit on a concave washer/sleeve? I’m guessing as someone told me it’s a possibility.
I believe the vibration has been with the machine since I’ve had it and graduated a little. In the cab I don’t feel anything abnormal.

 

[Pigpen]

Engine off. I took my big pry bar to them but it didn’t move. Maybe I should take another look at the front mounts.

 

[Lagwagon]

I believe we are taking about the same thing just different terminology, typically any of the wear bearings that straddle the crankshaft will make a rattling/ knocking noise if damaged, the thrust bearings more so at the point of engine load/unload.
if any of these items have disintegrated then they would likely end up in the pan.
i would remove the pan, inspect, if good move on to compression if you can get hold of a compression tester. If you have a cylinder 30+ psi different to the other 3 then this could cause engine to run rough. If they are good pull injectors and have tested, if they are the originals then they could do with a service anyway. Check your valve clearances while you’re at it.

 

[STEFANO]

Motore spento. Ho portato loro il mio grande pry bar ma non si è mosso. Forse dovrei dare un'altra occhiata ai supporti anteriori.

Ciao Amici, Vi invio Manuale di servizio per ISUZU 4BG1T .

Regards

 

[Pigpen]

Ciao Amici, Vi invio Manuale di servizio per ISUZU 4BG1T .

Regards

Ciao Stefano, grazie mille, lo apprezzo!

 

[Simon C]

Would be very easy to pull the engine oil filter apart, as anything that has been slowly grenading would leave cuttings in the paper pleats.
Have seen a couple of failed dampeers before. One was on a car and made a horrible racket but was not visible to the eye. So I watched it with a timing light and there and behold the damper was jumping back and forth. When I shut it off and with a punch could with no effort turn the damper 2 hours on a clock I knew I had found the clunk.
If you did find anything in the filter, then pan off would be wise.
Would start at damper myself .
Simon C

 

[Miller1990]

Just curious if you found out anything yet? We are going through kind of the similar thing at low idle there is a weird harmonic vibration that is cracking the suction hydraulic line from the tank. Once you read the machine not pass about 1200 RPMs, the vibrating line dissipates. I’ve put new motor mounts on my machine and also pulled the hydraulic pump to check the coupling and everything is fine.

 

[Miller1990]

Just curious if you found out anything yet? We are going through kind of the similar thing at low idle there is a weird harmonic vibration that is cracking the suction hydraulic line from the tank. Once you read the machine not pass about 1200 RPMs, the vibrating line dissipates. I’ve put new motor mounts on my machine and also pulled the hydraulic pump to check the coupling and everything is fine.

@Pigpen

 

[Universal Parts]

50H connecting glue, the steel flange looks badly worn and vibrates noticeably at low speeds.

@Pigpen

 

[Universal Parts]

@Pigpen

Could it be that the engine shock pads of your machine are worn out, causing the cab to shake at low speed?

 

[Pigpen]

Just curious if you found out anything yet? We are going through kind of the similar thing at low idle there is a weird harmonic vibration that is cracking the suction hydraulic line from the tank. Once you read the machine not pass about 1200 RPMs, the vibrating line dissipates. I’ve put new motor mounts on my machine and also pulled the hydraulic pump to check the coupling and everything is fine.

Miller,
Check the rubber dampener on the front pulley at the water pump/fan. As Simon says above, they may look fine but can have just a little play, as in my case, to cause a vibration at low RPM. That was my issue too. My oil was clean so I ruled that the lower part of the crank eating itself. Therefore I didn’t remove my oil pan.

Is yours a 160LX as well?

 

[Miller1990]

Miller,
Check the rubber dampener on the front pulley at the water pump/fan. As Simon says above, they may look fine but can have just a little play, as in my case, to cause a vibration at low RPM. That was my issue too. My oil was clean so I ruled that the lower part of the crank eating itself. Therefore I didn’t remove my oil pan.

Is yours a 160LX as well?

Yeah it’s a 160lx 2003-2004.

Did you pry on yours to see if it had play or what did you go?

 

[Simon C]

On older John Deere 6068 the manual said to change the vibration damper at I believe it was 6000HRS but may of been at 4000HRS.. I did one for a guy and you could tell it was getting tired as the rubber between sections was starting to degrade. How many hours on your machine?
On the Deeres it would eventually break the crank from what I was told. Necessary maintenance at whatever the manufacturer decides.
May not be your problem, but need to rule out.
Simon C

 

[Universal Parts]

If you need to replace the hydraulic pump damping glue, you can consult me. There are various regular H glues, 25H, 35H, 50H, 110H. If I am not mistaken, your machine is 50H glue. If you have high quality requirements, you can choose Taiwan Bogeng YCC, which is well-known in the industry.

 

[Miller1990]

If you need to replace the hydraulic pump damping glue, you can consult me. There are various regular H glues, 25H, 35H, 50H, 110H. If I am not mistaken, your machine is 50H glue. If you have high quality requirements, you can choose Taiwan Bogeng YCC, which is well-known in the industry.

I’ll have to do some looking I’m not too familiar what you’re referring to.