JD 350B... not the oil pump

The old gal, a delightful 1971 John Deere 350B Diesel Crawler Bucket-Loader, had a bit of a heart attack recently. Before delving _too_ deeply into her inner-workings, I'm wondering if anyone might have thoughts as to where to focus my attention.

The story goes...
A few months ago, after letting her rest for a couple of weeks, I started "Scoop" to do some work around the yard.
While I busied myself removing the backhoe, I heard a fairly loud "bang" accompanied by an engine slow-down (from around 18,000 to a loapy, barely-running 8k).
Thinking that my troubles might be fuel-pump related (I had rebuilt it a couple of years ago, getting rid of those pesky, fibrous washers), I busied myself investigating throttle-position, etc.
After just a few seconds I realized that the oil pressure had also fallen (to near-nothing, as far as I could tell).
I raised the bucket, to facilitate engine hoisting, and shut her down.

Draining the fluids, I found the engine oil black, instead of its usual honey-color, but am pleased to say that the engine still turns. After dropping the pan, there appears to be no obvious lower-engine anomalies, either. The trouble, affecting the oil pressure as it does, and the oil pump being prominent, prompted me to investigate the oil pump first. In keeping with the local John Deere dealer's insistence that he's "never seen a diesel's oil pump die", I realized that there was nothing apparently wrong with mine, either.


Would any of you, seasoned equipment-doctors, care to share insights?
Most 350B "bangs" seem to be attributed to the drivetrain springs, but in this instance, this is not the case.
The patient awaits, on her engine-stand down stairs, and I anxiously await any opinions.

Thanks for your time, and consideration.

Welcome to YT.
If your engine oil is normally honey colored what type engine oil do you use? Is oil spec'd for use in diesel engines? Did you check condition of all rod & main brgs? You could check condition of engine oil relief valve in RH frt of engine block. Below is relief valve spring spec's..

I hope you meant 1800 rpm down to 800 rpm ?

Because if it truly was 18,000 than that is a problem.

You may just have a bad governor ring in your injection pump causing the rpm issue. Oil pressure may be unrelated issue of just a worn out engine ? or wrong type of oil ?
Keep an eye out for antifreeze in the oil as sleeve cavitation (pin holes) is a common problem on wet sleeved engines like this.

I just got done with a 3'164d with oil pressure problems. I took an hydraulic tank filled with oil and plumbed it into the line that comes out of the oil pump. found that someone rebuilt the engine left out the piston oilers. couldnt see them from the bottom of the engine sure found a lot of oil coming out of there LOL.

(quoted from post at 08:52:03 04/29/16) I hope you meant 1800 rpm down to 800 rpm ?

Because if it truly was 18,000 than that is a problem.

You may just have a bad governor ring in your injection pump causing the rpm issue. Oil pressure may be unrelated issue of just a worn out engine ? or wrong type of oil ?
Keep an eye out for antifreeze in the oil as sleeve cavitation (pin holes) is a common problem on wet sleeved engines like this.

Click to expand...

You're _absolutely_ right...
pesky decimal points!

1,800 normal running speed
~800 barely running (when I shut it down)

Working close to a John Deere dealership, I was fairly good at frequent oil changes (using the grade recommended by JD).

The Hobbs shows 3564.3 Hours, but having the tractor for only ten or twelve years... who knows.

Thanks, everyone, for the input.
I'm re-configuring the engine stand before knocking about too much more
(the previous stand collapsed, and I'm a bit leery).

Any personal observations, forthcoming.

Thanks again!