1987 Spacecab Turbo Diesel (C223T) new tapping sound

[cocheeze]

Hi everyone, long time no see!

I have been having very little trouble with my fleet of Isuzus lately, but I recently encountered an engine noise issue with my Spacecab that really has me scratching my head.

There is a rather loud tapping sound that starts at around 1500 RPMs and goes away (maybe it just smooths out?) at about 2000 RPMs. The new noise is accompanied by a pretty noticeable loss of engine power in general (regardless of RPMs) and the engine just generally feels less responsive.

If it wasn't limited to a band of about 500 RPMs, I would think it was an exhaust or compression leak of some sort judging by the sound alone. Here is a link to a pair of audio recordings that I made:

https://on.soundcloud.com/G6aeN

The "idle without tapping" shows the engine noise at idle (about 1000 RPMs because the engine was just started and high idle solenoid was engaged) and the "idle with tapping" is me holding the RPMs up at about 1500 RPMs to show what the noise sounds like.

I am hesitant to drive it until I figure out the source of the noise as it could be something serious like valvetrain or engine noise.

The only things I have checked thus far are the air filter (i removed the top of the air filter housing and filter to see if the noise changed; it did not) and I switched between the primary and secondary fuel systems (i have a secondary 50 gallon fuel tank/filter in the bed) just in case a clogged fuel filter was causing fuel starvation (no difference; the noise is the same regardless of fuel source). I also made sure immediately after I first noticed the noise that both my oil pressure dummy light and gauge sender was working and that my engine oil is at normal/optimal level.

Any ideas where I should start investigating first?

Thanks,
Casey

[Halden]

Sounds to me like valve train noise. Check all your valve lash. If that checks out, then check that your push rods are spinning when the engine is running. I think tappets can do some weird things if they are worn funny. They should turn a little every time they actuate a valve.

[cocheeze]

Thanks for the pointers, Halden.

I was able to tear everything apart and check the valve lash tonight. A few of the clearances were too tight. So tight that I couldn't get a feeler between them at all, in fact. I was a bit surprised by this as in my experience the valve clearances get loose over time, not tighter. Odd. Engine was fully cold and I checked to the cold clearance listed in the Isuzu shop manual.

I haven't had a chance to mark the push rods and verify that they rotate when the engine is run yet.

I also noticed the same issue that Siegfried posted about in his "C223 Rocker Arm Wear - Excessive?" thread. I haven't removed the rockers, but I did take an angled scribe and was able to feel the impressions on the underside of the rockers when I ran the scribe across the surface. I am not sure how big of a deal the indentations are reliability wise, but I will probably be ordering a C240 rocker set off of eBay tonight and will swap the rocker assembly out regardless.

I don't really know if the indentations in the rockers and the couple of valves being too tight could possibly be the cause of the new ticking sound or not, so I will probably do a bit more exploring while I wait for the new rocker assembly to arrive. How much more of the valvetrain can I inspect without removing the head entirely? Is it possible to inspect and/or replace the tappets without removing the head?

Does anybody have any suggestions where I should look next (aside from Halden's suggestion that I confirm the pushrods are rotating) in my search?

Thanks!
Casey

[lostkeys]

Casey,
I am not familiar with the pup turbo but check the wastegate cover/actuator (if any). I've had it make a rapid ticking noise on those before but that is usually a "rattle".

[Halden]

Thanks for the pointers, Halden.

I was able to tear everything apart and check the valve lash tonight. A few of the clearances were too tight. So tight that I couldn't get a feeler between them at all, in fact. I was a bit surprised by this as in my experience the valve clearances get loose over time, not tighter. Odd. Engine was fully cold and I checked to the cold clearance listed in the Isuzu shop manual.

I've seen both clearances loosening and tightening. Either is normal depending on what wears faster, the valve and seat; or the rocker and, if applicable, pad surface. They typically tighten, especially after a rebuild. They get looser on these engines I think because of the stupid design with no pads on top of the valve stem, but you can't get an accurate measurement... How long has it been since your last valve adjustment?

Depending on how tight they were you may have a decent amount of wear between the valve and the valve seat. Some sewage gas powered generators I used to work on would typically get pretty tight once the valves were getting ready to go out (Kind of a special circumstance). Just keep an eye on them and check it again in maybe 1500 miles or so a few times to see if there is any noticeable wear.

Make sure your rocker assembly is torqued before you check your valves, you are supposed to do this (even though no one does...) --- Isuzu says 9-17 ft/lbs. Break the bolts loose one at a time and torque them, or just check the torque.

[cocheeze]

Alright, I have an update. I decided that since I already had a new rocker assembly on-hand (a C240 assembly) that I would just swap it out to rule out the round indents worn into the existing rockers as the culprit. I installed the new assembly and adjusted the valves, and the tapping noise is still happening. I drove the truck around for a bit yesterday, and I noticed a couple of things:

First, the noise seems to happen as a result of me revving the engine and/or accelerating rather than within a certain RPM band like I originally thought. At idle, it doesn't happen at all. Once I get up to about 2500-3000 RPMs and cruise, the only way I can get it to happen is to hit the accelerator somewhat hard. I am hesitant to say that the noise only happens "under load", because I can make it happen simply by revving the car while parked, but the noise is definitely also very pronounced when I put it under load by accelerating hard.

Second, the noise definitely seems to be coming predominantly from the right side of the engine (viewed from the front) in the general vicinity of the turbo and exhaust/inlet manifold. The turbo is stock. I don't see any obvious signs of an exhaust leak, but the engine is really quite dirty so it wouldn't be obvious anyways.

Is it possible that the noise could be an exhaust leak? I haven't ever removed the manifold so I am not sure what kind of condition the manifold gasket is in. I assume if it was turbo noise it wouldn't be tapping at such a relatively slow rate, but this truck is the only vehicle with a turbo I have ever owned so I am pretty inexperienced with the difference between healthy and not healthy turbo noises.

Any suggestions on the next thing to check?

Thanks,
Casey

[JoeIsuzu]

Water pumps sometimes start tapping.

Jack

[cocheeze]

I replaced the water pump when I did the timing belt about two years ago, but the quality of remanufactured parts is pretty poor nowadays so I suppose I can't rule that out. Regardless, it would certainly be easy enough to check. I'll remove the alternator belt and see if the noise goes away.

[cocheeze]

I ruled out the water pump yesterday by removing the fan belt and confirming that the tapping noise continued. I suppose it was always a bit unlikely of a culprit since the tapping noise is accompanied by power loss and no water pump failure I can think of would make the engine lose power.

I could use a little help with my next troubleshooting steps. I have some ideas but I need to know if I am mistaken about any of my assumptions:

Exhaust leak: If it was an exhaust leak, it wouldn't just happen when accelerating or only in certain RPM bands, right? I assume that tapping would be fairly constant in that case?

Injector: I suppose it could be an injector going bad, but I am not sure how I would test that theory.

Turbo: Could it be the turbocharger? The tap seems pretty slow for a turbo sound, but I don't really know turbos.

Valve or valve seat damage: I suppose I would need to perform a leak-down test to check for this?

As always, thanks for any help!

Casey

[Halden]

Exhaust leak: If it was an exhaust leak, it wouldn't just happen when accelerating or only in certain RPM bands, right? I assume that tapping would be fairly constant in that case?

An exhaust leak would cause you to lose power so long as it's before the turbo and would be exacerbated depending on load.

Injector: I suppose it could be an injector going bad, but I am not sure how I would test that theory.

Just pull them out and have them pop tested (or do it yourself, you can get a tester for cheap, about $100). An injector fires every other rotation of the engine, and your audio clip seems to fit with this, seems like it's doing it about 300-350 times a minute. A failing injector typically either sticks open, shut or is completely erratic, but you definitely fell it. On a four cylinder it will run quite rough if it sticks open or shut. If it sticks open you should get a lot of black smoke. If it's missing it will be quite rough. You could crack injector lines as well when this noise goes away...

Turbo: Could it be the turbocharger? The tap seems pretty slow for a turbo sound, but I don't really know turbos.

Because this is perfectly in time with the engine speed I would rule this out.

Valve or valve seat damage: I suppose I would need to perform a leak-down test to check for this?

A leak down test isn't a bad idea. It's really the only accurate way to measure if something is going on. A cranking compression test can show you something if one or two cylinders are way off from the rest. An easy way to do this is to listen to the cranking, if it's uneven you've got something wrong. Or you can use an amp clamp on an oscilloscope and see if the current draw is even across the cylinders.... you just have to figure out a way to match each cylinder to each peak (It can be done)

My bet is something in the valve train, probably pushrod related. You can easily pull the push rods out and check them. Also make sure they are spinning when the engine is running.

[cocheeze]

Thanks as always for the extremely detailed reply, Halden.

You can easily pull the push rods out and check them. Also make sure they are spinning when the engine is running.

While I was swapping the rocker assembly for the new C240 one, I did remove all 8 of the pushrods and inspect them both visually and by rolling them on a flat surface to ensure they were still straight. I saw no obvious damage or defects, but I also didn't really know what to look for.

How exactly would I verify that they are spinning when the engine is running? Do I just clean and mark them with white paint along one side and then crank the engine for a few seconds and ensure they are rotating?

What sort of effect would non-rotating pushrods have? I suppose it would just be an indication of uneven wear, but could uneven wear on a tappet cause my issues of power loss and the tapping noise?

[Halden]

How exactly would I verify that they are spinning when the engine is running? Do I just clean and mark them with white paint along one side and then crank the engine for a few seconds and ensure they are rotating?

What sort of effect would non-rotating pushrods have? I suppose it would just be an indication of uneven wear, but could uneven wear on a tappet cause my issues of power loss and the tapping noise?

Pull the valve cover while running (it's kinda messy but not terrible for a minute), mark the push rods with a paint pen. They should spin, not fast but will turn a little with each actuation.

BUT since it's easier.... Do this first

Since you emphasize a loss of power, my mind is starting to go to a stuck delivery valve. Crack your injector lines at the injectors when it's making the ticking and see what you get. Pre-detonation can mimick valve train noise sometimes. I've heard it make starter fluid sounds and stuff that sounds like valve train.

[cocheeze]

Alright, it sounds like I need to understand what a stuck delivery valve is and how to fix it.

I did the injector crack test 3 times starting at the front of the engine (#1) and moving to the back of the engine (#4). On all three passes as soon as injector #3 was cracked the noise abruptly stopped, and as soon as I tightened it back up the noise returned. The #1, #2, and #4 injectors being cracked just made the engine stumble but the noise was unaffected.

I assume that the delivery valve is on the output of the injection pump, but I am not sure if it is possible to take it apart and clean it with the pump installed on the engine or if the entire injection pump needs to be pulled and rebuilt?

[Halden]

Alright, it sounds like I need to understand what a stuck delivery valve is and how to fix it.

I did the injector crack test 3 times starting at the front of the engine (#1) and moving to the back of the engine (#4). On all three passes as soon as injector #3 was cracked the noise abruptly stopped, and as soon as I tightened it back up the noise returned. The #1, #2, and #4 injectors being cracked just made the engine stumble but the noise was unaffected.

I assume that the delivery valve is on the output of the injection pump, but I am not sure if it is possible to take it apart and clean it with the pump installed on the engine or if the entire injection pump needs to be pulled and rebuilt?

You've probably got a fouled/stuck nozzle. After thinking for a few seconds, a stuck delivery valve probably wouldn't be the issue.

Pull your injectors and slap some new nozzles on them. You can get them fairly cheap. There are two options for part numbers

Here's a sped up video for disassembly.
https://youtu.be/yWfb-n4cV2A

Here's a sped up video for assembly.
https://youtu.be/7is1CgqNNx4

I don't have anything about setting POP but there's a bunch on YouTube about doing it. Just get yourself a cheap tester and do it outside.

Or I'm sure there's an injection shop around Portland that would do it for a good price. If it's never been done on your engine, man does it make a difference.

[cocheeze]

Halden, you are the man. Thanks so much for the help.

I actually have a set of spare injectors and a cheap pop tester already, so tonight I swapped out the #3 injector with one of the spare ones that I have (i tested it first to make sure it wasn't leaking and opening @ around 1920 PSI) and the sound is gone. It starts easier, runs smoother, and has a bit of its old power back to boot!

I put the injector that I removed from my truck on the tester and sure enough it was dribbling fuel and not wanting to build up pressure properly.

I still plan on getting a new set of nozzles and taking the failed #3 and my other 3 spare injectors to the local injection shop for rebuild and pop setting soon. I can only imagine that the other 3 that I left on the engine are worn out and/or maladjusted as well and it will be nice to have a full fresh set.

Does anybody know if the nozzle PNs are different for the C223t as opposed to the C223? I think I may even have a set of the C223 nozzles (DN0PDN121) around already but I am not sure if the turbo engine has different ones.

Thanks again!