M109 Engine Knock and rough running

My M109 has 27,940 miles on the odometer and around 1600 hours on it, got it from the SCNG. Usually runs like a top...except for today. Fired it up and backed it out of it's bay in the shop, heard a noise like a loud bang. Stopped thinking I might have hit something, but no.... Now it knocks and runs rough. Thoughts on how bad it is? It's got the 465 motor.

skuhler said:

My M109 has 27,940 miles on the odometer and around 1600 hours on it, got it from the SCNG. Usually runs like a top...except for today. Fired it up and backed it out of it's bay in the shop, heard a noise like a loud bang. Stopped thinking I might have hit something, but no.... Now it knocks and runs rough. Thoughts on how bad it is? It's got the 465 motor.

Click to expand...

Figure out which cylinder is dead causing it to run rough. Use a stethoscope on the injectors to ensure they are ticking and firing like they are suppose to. Or crack the injector lines while it is running to see which injector you loosen doesn't change the running ability. Temp gun on each of the exhaust ports also helps as well on which cylinder isn't firing off properly.

Also determine if the noise is top end or lower end related. Noises can echo bad.

simp5782 said:

Figure out which cylinder is dead causing it to run rough. Use a stethoscope on the injectors to ensure they are ticking and firing like they are suppose to. Or crack the injector lines while it is running to see which injector you loosen doesn't change the running ability. Temp gun on each of the exhaust ports also helps as well on which cylinder isn't firing off properly.

Also determine if the noise is top end or lower end related. Noises can echo bad.

Click to expand...

Thanks for the tips, once I figure out the cylinder what is bad, what then? The oil pressure is 60 at idle, making me think the crank is good. And there's quite a bit of smoke coming out the blow hose. What do you think, bad valve? push rod bent?

That sounds like a whole lot of trouble. I would NOT run that engine again.
Take off the sump and look for a fractured piston before any more damage ensues.
My 1/2 penne'th.

Lots of blow-by when running makes me think a piston has a hole in it. Did the truck have a large amount of blow-by from the draft tube before? There were a few bulletins advising to crank the multifuel over with the shut off rod pulled to the off position due to the older head gaskets leaking coolant into cylinders randomly while these trucks were in service. The idea being that since multi's fire off so easy, damage might be avoided if the engine rotated a few times with no fuel being injected to ensure the cylinders were clear. There was also the issue of the earlier engines with the 6 sided connecting rod bolts being inferior. There is an updated 12 point head rod bolt that does a better job of keeping the big end of the connecting rod connected to the crankshaft. I'm not sure when the change was made. I had a 71 year model Deuce with an engine manufactured in 1992 and it had the 12 point connecting rod bolts. I beat the mess out of that truck operationally but cared for it like my first child. It never let me down.

dmetalmiki said:

That sounds like a whole lot of trouble. I would NOT run that engine again.
Take off the sump and look for a fractured piston before any more damage ensues.
My 1/2 penne'th.

Click to expand...

Fractured piston would sure allow the blow into the crankcase. Do piston rods break?

It did have some blow by before, it looked like it would sit there and 'pant' at idle. This is also a 71 but I'm not sure of the date of mfg of the motor. A hole in the piston sounds like a good possibility, would it also create that banging knock I'm hearing?

skuhler said:

..........A hole in the piston sounds like a good possibility, would it also create that banging knock I'm hearing?

Click to expand...

Not if it was just a hole. Sounds like something else is there that the piston is hitting at TDC. Could be a fractured piece of it, stuck on top. Or something that got stuck in between valve and seat?