I have bad hearing. Noises are sometimes elusive and are not what you think. I pulled my oil pan a few months back expecting a knocking rod and all was well. Ended up being a bad belt tensioner pulley bearing. I'm not suggesting that's your problem, just that it's hard to diagnose till it actually blows......I highly suggest one of these to help you find the source of the noise before you start tearing stuff apart:
Amazon product ASIN B004KEHGZY
Put your hands on every single rod and shake it around. If you have a knocking rod you will feel it being loose. A spun rod bearing/knocking rod will change sound as you rev and let off not under load and may not make noise when you have a load. If you have 1X spun rod bearing you can likely polish it out on the crank with emery cloth and a boot lace(google for instructions, or ask me) measure the journal and get a new bearing. You can drive for a long time with a knocking rod before it blows. If you unbolt your rods be aware that when you bolt them back up you need a good correct torque wrench or you may stretch and break the rod bolts, and no you can't just go buy new ones easily. PM me about this if it happens to you and I'll tell you what I did to fix this problem.
Piston slap can happen from broken rings. It's more of a tick than a knock sound. It can be a slower tick only happening on 1 of 4 strokes vs. a rod knock at double that tempo. You can run a long time with broken rings. Broken rings happen from high temperatures. Rings swell and don't have the end gap to take it and crack/break.....At least thats what I was told by someone I believe to be more knowledgable about diesels than I am here on the forum(apologies for not remembering the name at this moment). We've talked about my in-frame rebuild before. It's not that expensive or time consuming.
Not sure what to tell you about a dropped/swallowed precup other than a new out of china head for a 3B is about $600ish and may get here in less than one month from Ali express. Perhaps DHL in 2 weeks if lucky. You can grind smooth a "diveted up piston" but you really need make sure the edge isn't smashed diveting it and pinching the ring. If it is you can fix this with a dremel tool and go awhile longer. It's really important to get any chunks of iron/steel out of the top of the aluminum piston as it will at some point come loose from the piston it's embedded in next time it gets too hot. It's not rocket science. It's a tough diesel engine, not a formula one motor spinning near 15K rpm. I found 3B pistons on Ebay for $140 a set. Full price is around $450+.
@OGBeno as much of a perfectionist as his work is responded to me once that "people in pakistan rebuild 3Bs on the side of the road with sticks and rocks"... YOU CAN DO IT
Good luck!
