castirondude
New member
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- Austin,TX
Hi !
New member here. I've been reading the forum for a while now, as the big military trucks have always interested me, and I like the amount of real technical know-how you guys posess.
A few weeks ago I purchased an M925A1 - NHC250 (855) cummins, 5-ton, hydraulic winch, super singles. It is an '84 and was rebuilt sometime in the 90's with barely any miles on it since then. Looked great, ran great, so I decided to go for it.
However now it has been a bit of a lemon. When I bought it I went over the truck pretty carefully, checked all the fluids, including the axles etc, gauges. I got it home, test drove it about 20 miles, seemed to drive like new, with the minor exception that one of the rear brakes seems to be in need of adjustment (drum didn't get warm)
The second drive was different, I went to a friend's place about 7 miles away. After 5 miles one of the rear tires disintegrated. The tires looked like new with no weather cracking. I pulled over - noticed steam coming from under the hood. Shut down the engine - checked the gauge - HOT! OK I called my friend, he gave me a ride home and I came back with 5 gallons of antifreeze, tire changing tools. By now the engine was cool. It took all of the 5 gallons! The truck started and ran fine. It took us about an hour to change the tire, had the engine idling the whole time for compressed air. I checked the temperature regularly, did not get hot anymore.
OK after changing the tire I headed home. All seemed fine, I took it easy ~45 mph, carefully checking the gauges. After about 3 miles BANGRRRRRRRR some very harsh sounds coming from the engine, I was already looking in the mirror to see if there were rods and pistons rolling down the highway. Lots of smoke from the exhaust pipe.
I worked the throttle and the rattling was pretty consistent - so that tells me it is not the bottom end. After half a mile I had a place to stop but I that time the noise had become less. I could hear 1-2 dead cylinders though. Oil pressure & temp still good, so I drove the last 2 miles home.
The next day I looked again and found the heater core was leaking badly, but only when the engine was running. That's why I didn't catch it before. I am guessing it must have been leaking before and they just put water in the system, because I didn't smell antifreeze on the way down but I smelled it on the way back.
Thinking over the fateful events, I'm thinking that the failure is likely not related to the overheating, being that the engine ran flawless when I turned it off, and for an hour while working on the tire.
I did hear a bit of a popping noise out of the exhaust at higher RPM. I'm starting to think a valve was sticking open, or possibly the engine dropped a valve. I had a stuck valve on another engine once and after a while the valve was ground to dust and lodged in the aluminum piston.
Maybe somebody didn't assemble a valve keeper correctly, being that the engine had so few miles on it, it just now came loose.
After all I figure that they used these US based trucks to practice rebuilding, so they could do it flawless while overseas.
Well schucks....
no choice but to just deal with it.
The back cylinders are under the cab, how do you work on those?
I have been reading up on you guys' swap thread. I see a rather old looking 350 HP cummins with 10spd on Craigslist. Maybe I should see if I can pick that up for $1000 if it's any good..? But I wouldn't be surprised if that one needs work, might also have been sitting.
New member here. I've been reading the forum for a while now, as the big military trucks have always interested me, and I like the amount of real technical know-how you guys posess.
A few weeks ago I purchased an M925A1 - NHC250 (855) cummins, 5-ton, hydraulic winch, super singles. It is an '84 and was rebuilt sometime in the 90's with barely any miles on it since then. Looked great, ran great, so I decided to go for it.
However now it has been a bit of a lemon. When I bought it I went over the truck pretty carefully, checked all the fluids, including the axles etc, gauges. I got it home, test drove it about 20 miles, seemed to drive like new, with the minor exception that one of the rear brakes seems to be in need of adjustment (drum didn't get warm)
The second drive was different, I went to a friend's place about 7 miles away. After 5 miles one of the rear tires disintegrated. The tires looked like new with no weather cracking. I pulled over - noticed steam coming from under the hood. Shut down the engine - checked the gauge - HOT! OK I called my friend, he gave me a ride home and I came back with 5 gallons of antifreeze, tire changing tools. By now the engine was cool. It took all of the 5 gallons! The truck started and ran fine. It took us about an hour to change the tire, had the engine idling the whole time for compressed air. I checked the temperature regularly, did not get hot anymore.
OK after changing the tire I headed home. All seemed fine, I took it easy ~45 mph, carefully checking the gauges. After about 3 miles BANGRRRRRRRR some very harsh sounds coming from the engine, I was already looking in the mirror to see if there were rods and pistons rolling down the highway. Lots of smoke from the exhaust pipe.
I worked the throttle and the rattling was pretty consistent - so that tells me it is not the bottom end. After half a mile I had a place to stop but I that time the noise had become less. I could hear 1-2 dead cylinders though. Oil pressure & temp still good, so I drove the last 2 miles home.
The next day I looked again and found the heater core was leaking badly, but only when the engine was running. That's why I didn't catch it before. I am guessing it must have been leaking before and they just put water in the system, because I didn't smell antifreeze on the way down but I smelled it on the way back.
Thinking over the fateful events, I'm thinking that the failure is likely not related to the overheating, being that the engine ran flawless when I turned it off, and for an hour while working on the tire.
I did hear a bit of a popping noise out of the exhaust at higher RPM. I'm starting to think a valve was sticking open, or possibly the engine dropped a valve. I had a stuck valve on another engine once and after a while the valve was ground to dust and lodged in the aluminum piston.
Maybe somebody didn't assemble a valve keeper correctly, being that the engine had so few miles on it, it just now came loose.
After all I figure that they used these US based trucks to practice rebuilding, so they could do it flawless while overseas.
Well schucks....
no choice but to just deal with it.
The back cylinders are under the cab, how do you work on those?
I have been reading up on you guys' swap thread. I see a rather old looking 350 HP cummins with 10spd on Craigslist. Maybe I should see if I can pick that up for $1000 if it's any good..? But I wouldn't be surprised if that one needs work, might also have been sitting.
