'74 Cummins NH 230 TOP END ADJUSTMENT

Truck Shop · Nov 4, 2022

You need to start somewhere so find which cylinder is running cold, then remove the rocker cover to
that cylinder, check that the adjuster screw jam nut/nuts are tight and check the push tubes. It also
could have gotten a piece of dirt in the fuel system and found it's way to a injector. Or injector failed.
But check the push tubes first, if you have a bent one then something isn't right with your overhead
adjustment.

Best I can tell you from where I'm setting.

charles walton · Nov 4, 2022

Thanks,I'll try thats. If everything seems good and I need to pull an injector,how should I proceed? I did check some of the cylinders at the exhaust manifold today with a temp gun. How much difference should there be on the bad one?

mekanik · Nov 4, 2022

You did not miss tightening a lock nut on one of the adjustment screws? I have seen adjustment screws snap off from the lock nuts being over-tightened over the years. They failed after the engine went back in service after a top end adjustment not while being tightened.

Truck Shop · Nov 4, 2022

Normally that engine would idle at hot coolant temp of 180* and exhaust temp of give or take a few
degrees {300*} at idle. So if you have one running 250* and less.

Bar engine over till injector rocker lever is up on injector. Loosen injector adjuster jam nut, remove the
injector lash screw and nut {careful not to drop in engine}, slid push tube to the side, flip rocker straight
up. Remove the two 5/16 bolts on the injector hold down clamp {use magnet to remove screws} remove
clamp. Use a heal bar/lady foot to catch lip of injector, rock the bar back lifting the injector. Reach in
and lift injector out. You will need a injector copper brush to clean the injector copper in the head.

Truck Shop · Nov 4, 2022

mekanik said:
You did not miss tightening a lock nut on one of the adjustment screws? I have seen adjustment screws snap off from the lock nuts being over-tightened over the years. They failed after the engine went back in service after a top end adjustment not while being tightened.

I noted a loose jam nut above but that does happen to the adjustment screws, those can snap.

charles walton · Nov 4, 2022

mekanik said:
You did not miss tightening a lock nut on one of the adjustment screws? I have seen adjustment screws snap off from the lock nuts being over-tightened over the years. They failed after the engine went back in service after a top end adjustment not while being tightened.

I might not have gotten one tight enough but I'm not usually guilty of over torqueing.

charles walton · Nov 4, 2022

Truck Shop said:
Normally that engine would idle at hot coolant temp of 180* and exhaust temp of give or take a few
degrees {300*} at idle. So if you have one running 250* and less.

Bar engine over till injector rocker lever is up on injector. Loosen injector adjuster jam nut, remove the
injector lash screw and nut {careful not to drop in engine}, slid push tube to the side, flip rocker straight
up. Remove the two 5/16 bolts on the injector hold down clamp {use magnet to remove screws} remove
clamp. Use a heal bar/lady foot to catch lip of injector, rock the bar back lifting the injector. Reach in
and lift injector out. You will need a injector copper brush to clean the injector copper in the head.

Will the injector lever be up at the same time the valve rockers are loose?

Truck Shop · Nov 4, 2022

charles walton said:
Will the injector lever be up at the same time the valve rockers are loose?

Not necessarily, it's just going to make removing the adjuster screw easier with sliding the push tube to the
side.

charles walton · Nov 7, 2022

Truck Shop said:
I noted a loose jam nut above but that does happen to the adjustment screws, those can snap.

mekanik said:
You did not miss tightening a lock nut on one of the adjustment screws? I have seen adjustment screws snap off from the lock nuts being over-tightened over the years. They failed after the engine went back in service after a top end adjustment not while being tightened.

That’s exactly what I did, that explains why it was running good for a while and then started running erratic.

charles walton · Nov 7, 2022

Truck Shop said:
Not necessarily, it's just going to make removing the adjuster screw easier with sliding the push tube to the
side.

Now I’m looking for advice on the order which I should get the lever straightened up.

Truck Shop · Nov 7, 2022

Remove the adjuster for the push tube slide push tube to side, tip rocker back and remove the crosshead.
If it has no damage put it back inplace. Check the tops of valve stems, valve locks valve springs for damage.
Reassemble in reverse, go back through the firing order that I posted to adjust that cylinder. But I would
remove the push tube to make sure it's straight and no damage, putting it back in cam follower socket
below. You can get this done, it's not hard you have already been through adjusting, and mistakes happen.

charles walton · Nov 7, 2022

Truck Shop said:
Remove the adjuster for the push tube slide push tube to side, tip rocker back and remove the crosshead.
If it has no damage put it back inplace. Check the tops of valve stems, valve locks valve springs for damage.
Reassemble in reverse, go back through the firing order that I posted to adjust that cylinder. But I would
remove the push tube to make sure it's straight and no damage, putting it back in cam follower socket
below. You can get this done, it's not hard you have already been through adjusting, and mistakes happen.

Thanks, It was running great at first,it actually was even smoking less.

charles walton · Nov 9, 2022

Truck Shop said:
Remove the adjuster for the push tube slide push tube to side, tip rocker back and remove the crosshead.
If it has no damage put it back inplace. Check the tops of valve stems, valve locks valve springs for damage.
Reassemble in reverse, go back through the firing order that I posted to adjust that cylinder. But I would
remove the push tube to make sure it's straight and no damage, putting it back in cam follower socket
below. You can get this done, it's not hard you have already been through adjusting, and mistakes happen.

One thing that I have noticed while rolling the engine around is that the intake valves on the cylinders that I'm checking I can barely get the.14 feeler under and they are not loose enough to feel anything when I try to shake the rocker,I can shake the exhaust a little. I was wondering if that's optimal adjustment or a tad too tight on the intake?

mekanik · Nov 9, 2022

The feeler gauge should slide through with a slight drag you should not have to force.
It sounds like they are a bit too tight.

charles walton · Nov 9, 2022

mekanik said:
The feeler gauge should slide through with a slight drag you should not have to force.
It sounds like they are a bit too tight.

Thanks,while I'm spinning it around to get 6 fixed I'm going to readjust them.

charles walton · Nov 10, 2022

charles walton said:
Thanks,while I'm spinning it around to get 6 fixed I'm going to readjust them.

mekanik said:
The feeler gauge should slide through with a slight drag you should not have to force.
It sounds like they are a bit too tight.

Well,I cranked it up while ago and it was skipping so I pulled that valve cover back off and the intake rocker was not moving and it looks like the valves are closed. I checked everything yesterday and couldn't find any damage,don't know where to start.

Truck Shop · Nov 10, 2022

Did you make sure the pushrod/push tube was seated in the cam follower?
And did you remove the intake push tube to inspect for damage?

charles walton · Nov 10, 2022

Truck Shop said:
Did you make sure the pushrod/push tube was seated in the cam follower?
And did you remove the intake push tube to inspect for damage?

I removed the tube and it looked fine but I must not have gotten it back in right,not sure how to do it without pulling the rocker box I thought I had it in right but I guess not

kshansen · Nov 10, 2022

Not sure this will help or even make sense.

But if you put a bit of oil on the ball end of the push rod and then lower it into the cam follower. Then try lifting it up easy just a little bit. If you did hit the socket of the cam follower you should be able to feel it kind of stick when trying to gently lifting it.

It take a little trying to get so you can feel it but once you get the feeling it should be easy to know if it is seating in the socket and not some place else.

Truck Shop · Nov 10, 2022

Shine a light down in there while installing, when push rod is in the cam follower
socket it will spin smooth with two fingers.

'74 Cummins NH 230 TOP END ADJUSTMENT

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