I had a 390 rebuilt by a local engine shop that has been around for 25 years and has a good reputation. The motor was run on the engine stand for almost 4 hours as part of a break-in they do. I was there and saw the motor run. No oil leaks and it ran great. I took the motor home on an engine stand.

The motor sat on the stand in my garage for almost a year until it was ready to go into the truck. No oil leaks; everything was good. I connected the bell housing and the automatic transmission; still no problem. After the motor and transmission was tilted to be put in place I noticed oil leaking out of the bell housing. I took off the inspection plate and there was engine oil in the bottom of the bell housing. In all I would guess about 1/4 cup, including the oil on the ground. I cleaned it up and there was no more oil on the ground or in the bell housing.

The motor than sat almost another year in the truck until I got to the point that I was ready to start it. In this time there was not one drop of oil on the floor or in the bell housing. I primed the oil pump with a drill and guess what I found; oil on the floor that was coming out of the inspection plate on the bell housing.

The first time it happened I went to the motor shop to ask what could cause this and the guy I talked to (it was a saturday) was not sure. It did not leak in the motor shop and a year later of storage on a motor stand there was a leak. He said something about the rear seal and having to run the motor and it should be good. Sounded like BS to me, but the motor was already in the truck so it was no more work to pull it out later than sooner. Looks like later is here

Does anyone have any idea what is the cause of this oil leak and what I can and should do to fix it? It looks the rear seal to me, but it does not make sense to me how the engine could be run with no problem and then the leak developed.

 

Rear oil seal and I agree with the mechanic. Run it and give the seal a chance to seat in. Worst thing for anything with flexible seals is just sitting. Good chance it will seat and worth the try since it's in.

 

the rear mainseal and cap on a fe seem to be a rain pain to seal and keep sealed, i have tryed several different tactics.

 

I agree with 69cj. I have never had this happen but the only thing I can think of is a year of sitting where all the oil is down in the pan and not sitting on the seal to keep it moist and sealed. It sounds weird but depending on the climate, a year of just sitting can really play with stuff, especially soft parts.

 

I feel your pain brother. I just rebuilt mine myself got it in the truck broke in the cam after a year, all is fine so far. And then while running about 20 min or so to get all tuned shut down to see oil on the ground from inspection plate area. So i spent sunday tearing apart (while still in the truck) to find that i forgot to put sealer in the corners of the cap. Nothing like experience.lol

 

I have always heard that if you are going to store an engine that you should drain the oil, doesnt seem to make sense but something about it not being good for the seals.

 

If it ran out of the engine without even running, it's not the "rear seal" I'd bet. Probably more likely it's the pan gasket, OR, those funky end seals on the main bearing cap where you put rubber strips in the holes and drive what looks like a long skinny nail into them.

 

The pan gasket and end seals should not be under the stationary oil level unless it is over filled.

 

If I read this correctly, when he was installing the engine into the vehicle, w/tranny on it, and tilting the engine/tranny to get it installed, the oil ran out the back of the engine.

Then, once running, it's still leaking. Did I get that right?

 

He actually never stated that he sterted it if I read it correctly. He does need to do a run in to see if it seals. And yes, the seal, gasket could have been under the oil level during the install if I read that correctly.

 

After rereading this part, I'm going say it could be: crank oil seal, cam plug, or even the galley plugs.

Disconnect from the tranny and remove the flywheel and see where the oil is coming from when priming.

Something is not right.

 

Cam and galley seals are hard parts. I would have to put my money on the crank seal. Wouldn't be the 1st bet I've lost however.

 

Although a seal can develop a flat spot if the engine is not run for a long time (which usually goes away once it's run for a time), I think Krewat is on to something.

The OP stated that the oil would leak out when he spun the oil pump with a drill, so a leak from one of those rear plugs or cam plug does seem more likely. I forget if any of the rear plugs (other than the cam plug) are pressed in. Threaded ones would be less likely to develop a leak, but sealer is used on press-in ones.

On the thought that the oil might be high in the pan with the level above the bottom of the rear seal, would one expect constant seepage (even just sitting and not running) in that case?

I'd also check the back of the block just below the intake manifold gaskets. The oil drain from the heads is nearby and oil may be leaking down into the bellhousing from higher up. And the valve cover gaskets. Although it sounds like an immediate leak, which indicates pressure. So it's more likely one of those rear plugs is leaking.

Annoying, but so far it doesn't sound like the engine has to come back apart, and that's a good thing. About the same annoyance as knowing you have to change the clutch, although perhaps more-so as the engine rebuild should have prevented this.

 

Good points John...I knew you were smarter than you looked !! lmao..Just kidding Buddy !

 

The original poster hasn't been back since about 3 minutes after he started this thread

I assume it's fixed

Or he's in jail for assaulting his machinist