Cummins 444 vibration...

Hi, my name's Josh and I've been reading on here for years and have ended up with a ton of info from OLDSKOOLERnWV, SmokinCAT and everybody else, so I need to say thank you all for that!

I have a 1990 Cummins NTC-444 (CPL 1280 and Serial 11580979) that I've ran as my daily driver for four years, but I'm starting to have an issue with.

I got the engine as a good used unit that I converted to high flow cooling, rolled Cummins bearings into, added a second fuel line, ran the overhead, re-sealed and slid it in the truck.

It works in the hills all day, five days a week at 82k and has been super reliable. The pyro stays right at 800 degrees or less on a long grade and coolant temp has never got to 200 in the time I've owned it.

Over the years it has developed a slight "miss" that comes and goes and usually clears up with a bit of RPM, so I resealed the STC valve hoping that it wasn't providing quite enough oil to switch an injector, but no change. About a year and a half ago the next step was a set of injectors from Premco (figuring that there's nothing else that could cause an intermittent miss like that), but no change...

It has never really had the miss show up until after oil temp has come up, so if it's a little "off" when I shut it down for the evening, it's good in the morning.

Well yesterday it wasn't so smooth on fire up and when I got it out on the road it didn't go away. I brought it back home, ran the overhead on Outer Base Circle to find maybe another quarter turn at 90inlbs on the injectors and only a thou or so than spec on a couple valves. After that I road tested it without any change. It has a little bit of a vibration under power and shakes on decel, but it doesn't change with the key on or off, so I can rule out fuel system.

I'm going to check to see if any valves are tight under the bridges and potentially hanging open or tuliped and open the oil filter to see if there's anything in it and if everything's good there I'm going to pull injectors and scope the cylinders for burnt pistons or valves.

I guess the point of this thread is to see if anyone else has dealt with a similar situation and also to ask about the reliability of non-Cummins piston and liner kits. Interstate McBee is a brand I've used for other parts, but I really don't know if the reliability is there with those or PAI or something like that.

Also, if anyone is familiar with swapping an earlier/larger oil cooler onto a BCIV, I'd love to hear about it!

Again, thank you all for your time and have a great day.

 

I tore into it the other day after it started acting up to replace the o-rings on the plastic oil jumpers (on the injector side), but hadn't realized how the plastic pieces were laid out before I tore it down, so I only did one seeing as I hadn't ordered enough o-rings to do the inlet and the outlet of the oil jumpers, BUT I feel like I can rule out fuel system because if I'm coasting and key it off (killing the fuel) the vibration doesn't change.

The valves weren't out of adjustment enough (only a thousandth or so on a few valves) to lead me to believe that I'm losing the cam or any followers.

Oil pressure hasn't changed and is still plenty good, but I'll pull the cooling nozzles to check them and run a bore scope in to see if everything looks decent on the lower side of the pistons and cylinders.

It hasn't had any significant changes in blowby, so I'm not EXPECTING a scored cylinder, but once I get the o-rings for the inlet side of the plastic oil jumpers I'll scope the bores and look for any valve issues when I have the injectors out. I'm going to make sure that I don't have any valves that are tight on the crossheads and holding a valve open.

I had two people say that it could be a clutch, so that's going to be where I go if everything else checks out.