5 Ton 290 Big Cam Swap

[davo727]

You said dichotomy.... thats too big of a word for around here.

 

[Lukes_deuce]

Looking forward to your detailed results. Hoping to one day turbo my 250 or drop in a big cam.

 

[Jakelc15]

I see no reason not to turbo the non turbo nhc250. It should actually make the engine last longer by keeping it cooler.
I have put thousands of miles on my truck since adding a turbo along with many others on this site. The truckers had been doing the same thing for years with the low HP nh motors.
I heard once that the reason the piston cooling nozzles were never installed in the military version was because they are prone to breaking. The plastic nozzle doesn't like the harsh ride a military truck is put through. I think it's crap, a lot of offroad equipment has piston squirters and they don't seem to break any more than the ones in trucks. It was probably a price point, as is most government purchases.
It's easy to tell if your engine has nozzles. They are installed from the outside, just below the exhaust manifold. There are 6 cast bumps where the nozzles would go. If you motor does have them please list your cpl #.
Nozzle

This motor has the holes drilled

 

[Vintage iron]

I agree with Mechanic. As much as the small cam 855 block is the same they are just as different. I know I put a big cam 290 in my M936. I love it.

 

[ryanaubra]

I was all for putting the 290 in there. In the interest of time and to see what happens..... I went with the 250 conversion. I still have the 290. It is an excuse for another project....
Just left the parts store buying fluids - dang. With new-in-the-can 654 Allison trans, new motor, PS fluid, coolant - I will be putting around 22 gallons of fluids in this thing. Here is what i found:
Engine - 27 Quarts
Transmission (dry) - 23 Quarts
Coolant - 8 to 10 Gallons
PS Fluid - 3 to 5 Quarts

 

[Jakelc15]

Good deal. Hold on to that 290. Good mechanical motors are getting harder to find.

 

[WillWagner]

The reason there are no piston cooling nozzles in the NHC is purely cost. Less machining equals less money, uncle sugar bought lots of these engines. The small cam, no piston cooled engines were used heavily in the refuse industry also.


Just a tidbit on the flywheel hsg swap from small to big cam. The small cam one will fit, but the hole for the mounting capscrew above the cam bore needs to be enlarged due to the bolt hole moving up and outward slightly. I have a jig for that somewhere.

 

[ryanaubra]

I have the flywheel and everything for the big cam motor. If/when it goes in, it would have a 10 speed RoadRanger behind it.
The 290 is going back in the engine can for now......

 

[Stevepala]

Big cam swap is easy. Get the right front mount, cut and reinforce the cross member. Your front Coe mount is not. Everything is a direct swap. How do I know? I put a 400hp big cam in my 929.

 

[ryanaubra]

Last night was more of the same, prepping everything for getting the motor back in the truck. I checked to small ports in the rocker box that lead tot he intake and mine were open. It was strange though because 1-2 and 3-4 had a small plug in them that still had a hole through it, it was just restricted. 5-6 was wide open. Since i also added jakes, i had the rocker boxes loose to install the new studs. This helped in the drilling and tapping process.

With the rocker box loose, I slid a piece of cardboard with adhesive spray applied to the surface (stick side up of course), between the head and rocker box directly under the port i had to drill and tap. Then i placed a small piece of paper towel in the hole as well. I the smallest plug i could find was 1/8" npt, so i had to open the hole up to tap. I used some blue tape around the hole and a shop vac while i was drilling to catch any aluminum particles. It worked really well.

After I finished drilling and tapping a vacuumed out the hole and used a seal pick to draw out the paper towel. I applied a little locktite and inserted the plug.

 

[rangereter]

ryanaubra, you may have to cut out some of your cowl for the rear brake housing to fit under. stevepala would know for sure.
Regards, Bob

 

[ryanaubra]

We were able to raise the cab a few inches and get the motor in. Had at least 4 millimeters to spare!

 

[ryanaubra]

So the motor is in now and she is running well. i will have more pics and updates soon. I had to get back to "work". been playing with the motor too much. Next starts the bobbing process.

 

[ryanaubra]

After

 

[Vintage iron]

Can't wait to see the pictures.

 

[ryanaubra]

Here is one from my phone. Heading back up tonight to make a relocation bracket for the coolant reservoir, tie in the aftercooler, and run the intake and exhaust pipes. Note to all - when you add the fuel line tap to the rear of the head, make sure the pressure and return lines are in the right spot. Motor won't crank if you don't........

 

[Csm Davis]

Here is one from my phone. Heading back up tonight to make a relocation bracket for the coolant reservoir, tie in the aftercooler, and run the intake and exhaust pipes. Note to all - when you add the fuel line tap to the rear of the head, make sure the pressure and return lines are in the right spot. Motor won't crank if you don't........
View attachment 609933

Oops how many days did that set you back?

 

[ryanaubra]

2 days and lots of head scratching! What a difference in throttle response though!

 

[ryanaubra]

I was able to take all of the venting and relocate to the passenger side of the motor. I "reconfigured" all of the parts that were on the original configuration and made it all work. I even had two pieces left over. All I did different was put a plug in the hose that went to the valve cover. I dropped the metal blow-by hose and replaced it with a flex hose and ran it down the driver side firewall right in front of the pedals.

 

[ColtRice17]

Great looking truck and looks like your doing a really good job. I can't wait to hear a video of it running. Please keep up the good work. As soon as I get my transfer case to work right I plan to follow along your exact footsteps. Not 100% sold on bobbing mine tho.