Tapping/knocking sound

[Lonestar10]

Cm871
I have a a tapping sound only heard with window down. I would compare it to marbles hitting each other or for some older generations a teacher tapping chalk on a chalkboard. Made sound before and after demandate though it seems less prevelent after demandate with the minor changes in timing.

Only happens under load I can't recreate it stationery it's about 1/2 speed of the engine so exhaust or powerstroke. My mechanic thinks possibly an overfueling injector. Truck runs strong but the sound makes my skin crawl. Passes cyl cutout runs on 1 cyl on cylinders the same, cyl perf test, and the 15 sec crank test.

Can't really move actuators if they are causing it as I can't tell location. And at about 500 an actuator or 600+ an injector I don't want to throw parts blindly.

Engine has 150k on overhaul only 1 injector was replaced during overhaul by the intl stealersh!t. Before I purchased.

Thanks in advance for any recommendations.

[Hammerhead]

Pop the rocker cover.
Check the Jake rocker arm's detent strength on each cylinder. It is the center rocker arm on each group of three. They should "snap" into ace, if they just roll into place, they're worn.
The Jake rocker's detent spring get weak over time, allowing the off center weight of the rocker to start sagging. This causes the jake rocker check valves to start to oblong the holes on the rocker shafts as well as making the sharp taper of the check valves wear in a radioused shape decreasing the ability of the Jake rockers to stay in the neutral position and they start to be "bounced" off the exhaust valve pins and then clang off the camshaft on the other end.
If you are jaking under high boost load and touch the throttle to interrupt the Jake's and you hear the clattering louder than normal with your window down slightly, then you can pretty much count on this being your issue.
The repair is;
New rocker shafts
Inspect the rocker bushings for wear, and replace if necessary (not likely)
Replace all 6 Jake rocker arm check valves and springs
Reassemble, and adjust overhead
It's not a difficult job, but it requires some specific tools.

[Lonestar10]

Sorry forgot to add just did overhead last week checked Jake's then engine off and engine on while reving couldn't get Jake's to make a single out of spec bounce. They showed how mine acted then took me over to some junk 871s in corner of shop and showed how bad ones move and act.

[Hammerhead]

You described the sound as "tapping, like marbles" that's why I went to jakes.

If the sound is more solid, like a small ball-pein hammer on steel, has the crank damper been changed? If the viscous fluid in the crank damper hardens, the inner steel weight ring bounces off the outer shell, but only does it under torque load so revving the engine while stopped reveals nothing.
If the damper has never been changed, I suggest you change it. If the viscous fluid has reached the end of its useful life, then the damper is no longer properly absorbing the harmonic vibrations from the crankshaft and these vibrations can and will play havoc with crank position and speed sensors, as well as lead to premature crank and main bearing wear. It's an 871, they haven't been made in nearly 10yrs. If the damper has never been changed, it is beyond its expected service life.

[Lonestar10]

I do not know on the dampener I'll have to have that checked out thank you very much

[Lonestar10]

Thinking of it now that I'm on the road today there is a vibration in the floor of my truck that seems to coincide with the tap

[Chamberpains]

This may sound far fetched, but, are you hearing the noise only when driving? I recently had a rear differential get water in it and it took out the carrier bearing in the rear assembly. This allowed the ring to slop around under load only. It sounded much like a teacher writing on a chalkboard and had a slight coinciding vibration on the floorboard. If I were you, I'd check all drive line components for failure and proper lube levels. I had to drain the rears to check the magnetic plug for metal, the magnets in the axle housing was doing a thorough job of catching the shavings from the failed bearings, so a simple finger dip in the oil didn't reveal any metal in the oil. Also make sure its not your clutch linkage or forks rattling around. Maybe they need grease or and end replaced.

I'd say does the problem go away if you push the clutch in but that takes the load off of everything. So you have to resort to checking everything properly in a static state (sitting still)

[Waterloo]

(10-21-2018 )Lonestar10 Wrote:  I do not know on the dampener I'll have to have that checked out thank you very much

Per Cummins, the damper should be replaced every 500,000 miles... I replaced mine at 700,000 miles and it made a world of difference. Just saying.

[Lonestar10]

I greased everything I could get to inside the bellhousing. But I did not get into checking the linkages so there's another thing I can check. I'll be parking in about 2 hours in Gretna Nebraska at the Flying J I'll check some stuff out then