8.3 suddenly started knocking

[Joehop]

I have a M931A2 which I bought a few months ago from GL. It was overhauled at Ft Riley(not sure of the date) and is showing 1250 on the odometer. I believe the mileage is accurate based on the condition of the interior and rest of the truck. I drove the truck home and put another 150 miles on it since. It was started last week, moved in the yard, then shut down. About an hour later it was started again and started knocking pretty bad immediately upon starting. Now it will run with the knock but is puffing white smoke. I'm not a mechanic by trade but tried to do some testing which was suggested by a mechanic friend. I first checked the surface temp of the exhaust manifold with a IR thermometer, the front cylinder was reading a good 70 degrees cooler from the rest. I replaced that injector with another one and same issue. So now I am at a loss of what else I can do without having the motor taken apart which I'd rather not put the $ into. I think that parting out the truck might be a better option.

Any help or suggestions are greatly appreciated

 

[trooper632]

Im sure the oil level is ok, And have you changed the oil since YOU have owned it. If not drain the oil and check for metal in it, is so drop the oil pan and look inside. May tell you what the problem is.

 

[Csm Davis]

I agree with trooper but just drop the pan and remove the valve covers yourself and look to see what is wrong.

 

[R Racing]

Are you low on coolant. Or is there any oil in it ? Sounds like your front cylinder isn't firing. Could be lack of compression. Or your compressing something other than fuel ?

 

[Joehop]

I havent changed any fluids yet, that was the plan before the knocking started. I did check levels which were all fine. I wont be able to work on the truck again for another week or two. I'll drain the oil and see what I find, and take off the valve cover. What should I be looking for once the valve cover is off?

thx

 

[R Racing]

Look to see that your pushrods aren't bent and they are still under the rockers. Also that here is no damage to the rockers . Valves or valve springs.

 

[porkysplace]

I would get a oil test kit and have a oil sample tested .

 

[clinto]

If it was overhauled and truly has 1200 miles on it, there's no way I'd part such a truck out over a dead cylinder.

Pull a valve cover, see what's going on. If it isn't apparent, pull the oil pan. One way or another, if the valves are opening and the injector is firing and it's still 70° cooler than the rest, it's a dead cylinder.

Worst case, you put a piston and sleeve in it.

 

[Joehop]

Thanks for the input, I am a little short on time, and knowledge of taking the motor apart. Maybe the idea of parting out is jumping the gun. I would love to get it fixed and keep the truck. I will work on it the next chance I have and see what I can find out.

 

[porkysplace]

It will be a lot less work to fix it than part it out . Some parts sell quick and some sit forever.

 

[74M35A2]

Crack the fuel line open on #1 at the injector or pump, and see what happens. Do you know the condition of the replacement injector you installed?

 

[Joehop]

Crack the fuel line open on #1 at the injector or pump, and see what happens. Do you know the condition of the replacement injector you installed?

I used an injector from another truck that was in running condition, when I swapped them out the other truck ran as it should so I figured the injector was not the problem. I think that I cracked the line before I did the injector swap and there was fuel getting to the injector, Is that what you were going to suggest?? My plan next is to do a compression test starting with that first cylinder. The last time I worked on it, we took the roof, stack and boom off just to get it into the garage. Hopefully in the next month or so I will be able to do the compression test

 

[rosco]

Pull that front valve cover 1st, and start it - see what is or is not happening there. You can do that outside, in a few minutes. It won't be that hard to fix.

 

[porkysplace]

Any updates on what the fix was ?

 

[Joehop]

Any updates on what the fix was ?

I havent had the time to take anything apart yet, Its been sitting since my last post. I'll be sure to update when I do eventually get it apart.

 

[tnmegacab]

White smoke is unburnt fuel. You most likely have an injector problem, im almost positive. It could be a cracked or broken ring as well. Check and see if its making oil or has any diesel contamination.

 

[Joehop]

White smoke is unburnt fuel. You most likely have an injector problem, im almost positive. It could be a cracked or broken ring as well. Check and see if its making oil or has any diesel contamination.

Thanks for the reply, I still havent been able to find time to get it apart, I have 2 other tractors and a cargo which have put this truck on the back burner, once I get to working on it I will post anything I find out