39 B Kaboom

JD39B

Member
I have been working on my 39 B for a couple years. It ran great up to yesterday. I got it out this weekend to do some cleanup and paint prep. I let it run for about 5 minutes and all of a sudden it had a metallic ping and smoke started rolling out of the crankcase breather. I tried to shut it down but I was too far away before it ground to a stop. I pulled the crankcase cover and let the smoke go out. I checked the oil pump and it was spinning. The valves were working correctly and the rods were tight. The motor spins freely and has great compression. I don't feel any resistance when spinning it over by hand. I changed the oil and no pieces or chunks of metal came out. Long story short is I have no oil pressure and one heck of a knock coming from the pulley side of the engine. I don't see the part AA824R on the top of the oil filter housing. The parts book and service manual don't explain how the spring is installed. Any insight on what it could be? I'm thinking mains.
 
Ok, but you just said the motor spins freely. So is freely after the fact? Perhaps after you worked it back and forth some? Just cooled down and was found to then be free? These are the things that connect a timeline to what the issue is and they are missing. Stop doing that - take the time to reread your typing please. What you are leaving us with is not making too much sense. Especially conflicting statements one right after the other. Good compression followed by feeling no resistance. I'm sorry but no, not unless removing the plugs was in between there.

"I checked the oil pump and it was spinning"
Wow it must have really been wound up to still be spinning...
So I actually read that to mean instead you turned the oil pump drive shaft with thumb and fingers and it spins fine.

But it's not supposed to, it's supposed to be captured by the oil pump coupler which might be missing in action and in two pieces under the oil. Did you even look while you changed the oil with the lid off? Why did you change the oil? Has just doing this fixed a lot of stuff for you before?
Is the main issue resolved at this point? Who could ever tell if it's not you? And even if you told us, I'm not banking on a single word until I see some coherent typing.

I know Kaboom - my own tendencies would be in half panic mode too, but it doesn't really help us.

Alternative to missing coupler is twisted off oil pump drive shaft where you can't see it. I would drop the oil pump before going after mains that simply can't cause these symptoms. There is a metering hole thru the oil pump drive shaft that would be a weak point and possibly twist in two here. I would also not put any more oil back into it until some actual reason for this episode is found guilty as charged and has been corrected.
 
You might be able to remove the oil gauge fitting at the governor to inject shop air into the 1/8 pipe fitting and notice where there is a large unauthorized amount of volume getting away at. Sounds like something holding oil pressure let go and massive amounts of oil bypassed the engine bearings. Had a 39 B decades ago but can't possibly remember what was on top of the oil filter can now, sorry. Any of those oil line fitting ends might have come unsoldered too and only leak under pressure. Right side noise might be pointing at that main bearing supply line? Number two rod noise from lack of suitable supply there? Only wish I could be of more help, best of luck figuring this one out.
 

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