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Cummins NHC 250 HP ?

Posted By W921 Last Year
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grenfell34
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slow deceleration can be a few things 1 as steve said a restriction in the return line
also check for blocked breather in the tank
2 worn throttle shaft in the pump  creates exessive throttle leakage
3  damaged injector 'o'ring can cause return fuel and supply to mix
it also causes engine to run on after shutdown for a few seconds
from flight revs [max rpm] to idle should take 7 seconds
oil pressure hot at idle should be 25-30 on a good manual gauge    50-60 on the run
Tony Bullard
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"example decompression lever,turn over motor,let go of decompression lever,hit either button,let go of starter button, motor starts?"

Should read: hit either button, motor starts, let go of starter button.

The PT system on an automotive engine uses a limiting speed governor. It limits limits low and high speed only. When you set the throttle anywhere in between the speed will change with load. A cold engine has more load than a warm one.  A variable speed governor would be used on something like a drag-line where you might set it at 1800 and it will hold it there as the load changes.




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dieselsteveo
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How easily does the engine shut down??  If its slow to shut down, then your engine response issue may be due to a return line restriction.  Easy way to check is to remove the return line right at the PT manifold connection and put a new large line straight to a bucket.  If the engine works better going to the bucket, then you have a return restriction.  Not uncommon for lines to swell and harden over time, causing a restriction.
W921
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I really appreciate the info. I've trucked for years but most miles where on at the time new 80s and 90s trucks so this older stuff i don't really know about. When I bought this truck it sure smoked on the way home.It also leaked oil around the turbo exhaust connections. By the time i got it home. It stopped smoking I've cleaned up the oil on the exhaust connections and there doesn't seem to be anymore oil coming out of them. Another thing I noticed on the way home with it was when you let off the throttle it seemed to take longer than normal for your rpms to drop. Is this normal on these engines with a pt pump? I was told the diesel in the tank was at least 30 years old. I have since pumped it out but it probably still has a bit in it. Also what is normal oil pressure for one of these old motors after it is fully warmed up. Another thing I noticed was when you cold start the motor example decompression lever,turn over motor,let go of decompression lever,hit either button,let go of starter button, motor starts? I guess I'm doing it right? Anyway then I set the throttle lock cable to bump up my rpms so that it idles smooth. Well as the motor warms up I have to keep resetting the throttle lock because the motor keeps running away with more rpms as it warms up. Is that normal for one of these engines? Once its warmed up then its fine and doesn't do it anymore. Its kind of like an electric choke on a carb gas engine on a cold morning. You know how your rpms keep climbing until you kick it down. You wouldn't cold start one and leave it unattended until it was warmed up and the choke was off.

Anyway I'm hoping,guessing that it just needs to be driven hard under load to heal itself? What say you?
Thanks
grenfell34
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glenn akers (11/19/2019)
I like many others have install a few smoke kits and the goverment would pay for it if the fuel was not set up.However most guys came back a few days later and had the fuel set up on a different work order.

we never had the govt subsity here but     workin for cummins i could buy those kits cheap  n swap the turbo for a vt50
that and a tweak on the pump n squirtters    they would have a ntc290   lookin in the mirrors
but  with no piston cooling    a eye on the pyro was vital     !!!!


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I like many others have install a few smoke kits and the goverment would pay for it if the fuel was not set up.However most guys came back a few days later and had the fuel set up on a different work order.

Glenn Akers
grenfell34
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W921 (11/18/2019)
I have a 72 kenworth w 921s12 (2 axle full size w 900 cab). Truck came with the owners parts catalogue which has every part number for my truck listed. Its kind of neat because it was filled out at the kenworth factory in Canada in pencil just for my truck. Anyway my motor according to the book is a NHC 250 but there is no mention of a turbo. They have every other part and serial number for my engine except for the turbo. I'm wondering if the turbo was added later at a dealer? It looks factory butt I'm no expert on what a factory 72 should look like. But I'm wondering if kenworth dealers back in the day would modify or hop up a truck for you? Also what would be the HP of a nhc250 with a turbo? Was it common to add turbos to these engines?

needle nose is correct      altitude compensation kit aka smoke kit
small turbo gave about 5lb boost   
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I worked for a Cummins dealer in B.C at that time and in those days they marketed what was called a "Smoke -Kit", it's not what we considered a hop - up kit by any means.

Be careful when you follow the MASSES......sometimes the "M" is silent.


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I have a 72 kenworth w 921s12 (2 axle full size w 900 cab). Truck came with the owners parts catalogue which has every part number for my truck listed. Its kind of neat because it was filled out at the kenworth factory in Canada in pencil just for my truck. Anyway my motor according to the book is a NHC 250 but there is no mention of a turbo. They have every other part and serial number for my engine except for the turbo. I'm wondering if the turbo was added later at a dealer? It looks factory butt I'm no expert on what a factory 72 should look like. But I'm wondering if kenworth dealers back in the day would modify or hop up a truck for you? Also what would be the HP of a nhc250 with a turbo? Was it common to add turbos to these engines?


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