Engine noise

[clevend]

I bought my 1974 300D 14 years ago from the first owner. It had 14,000 original miles. The engine started immediately, didn't smoke, had great oil pressure and would take the cart past 100 without breaking a sweat.
But it had a knocking noise coming from the front of the engine. That would go up and down with the rpm. Checked valve clearances, replaced injectors. Nothing changed. Replaced the vacuum pump. No change.
Over the years various mechanics have suggested piston slap, worn wrist pin or rod bearing and sound of the piston hitting the head.

Thinking it might be heavy carbon buildup I have used diesel purge a number of times.
I have tried 50 weight oil. No change. 50 weight with Lucas. No change.
Every few years I get curious, find a deserted road and run it over 100 for some miles. No change.
Now it has 144,000 miles and I am getting it ready to sell. This is my last attempt to isolate the noise without tearing the engine down. Any suggestions would be most appreciated.

Thanks

[vstech]

Where did you get the injectors that were new?
Most common is injector nailing.
And poorly balanced injectors, even new can be an issue.

[vwnate1]

Also very common is the front lower pulley on the crankshaft gets loose and knocks.....

[JHZR2]

Originally Posted by vwnate1

Also very common is the front lower pulley on the crankshaft gets loose and knocks.....

BTDT, had the failure 30 miles from home…

OP, the lift pump makes some ticking sound too. These engines make lots of noises that are hard to isolate to a specific location.

Is it like this?

https://youtu.be/0jS6PFSPviM

I have a rythmic tapping that’s not the injectors. Can’t tell exactly what it is.

[vwnate1]

Okay, I was just offering a S.W.A.G for you to worry about .

Thanx for the video / audio clip, it sounds better than most of the old Diesels I see .

[BillGrissom]

I think a loose rod bearing would give a deep sound. I had a ticking when the alternator fan blades were barely striking the bracket. Nothing a pry bar couldn't fix. Combustion sounds can sound like tapping. If in CA, try filling w/ renewable diesel (Propel or Union 76), as my cars idle noticeably smoother than on fossil. In other states try B20 in summer and/or pour in a quart of veg oil.

[vwnate1]

Rod bearings typically don't knock at idle ~ lightly rev the engine and when you release the throttle a bad / loose rod bearing will rattle a few times the instant the engine begins to slow .