Slow Oil Leak on Brand New Engine, Help!

I am new to the forum, sorry if I ramble incoherrant...
Ok, I bought I new (well new to me) Rebuilt, 83' 305 marine block through AutoZone's marine vendor, after it was installed (not by myself, but my father-in-law, who has worked on boats/cars for about 30 years now) there is a slow drip oil leak in the rear of the engine. It was hard to tell exactly where it was coming from, the rear main has been replaced, the plugs have been checked and are not leaking, the pan gasket checked, sending unit etc. After looking close while it was running with a mirror in a couple of very uncomfortable positions, we could see the slow drip, dripping straight off of the shaft in between the block and the fly wheel.

Does anybody have advice on what it could be? Do you think I was sold a cracked block? Is there anyway I can repair this without pulling the motor again?

Thanks for the help

Re: Slow Oil Leak on Brand New Engine, Help!

Could be gear oil leaking from the front seal on the outdrive........

Are you sure it's motor oil?

Re: Slow Oil Leak on Brand New Engine, Help!

The only shaft that I know of that is between the block and the flywheel is the crank shaft. Your rear main seal is probably leaking. On an 83, you have a 2 piece rear main seal.

Re: Slow Oil Leak on Brand New Engine, Help!

Gotta be the Rear Main. That is the onlything there. If it is indeed a two peice like Don said, are you sure it was installed correctly when it was replaced? The two peices can be tricky to install sometimes and get them right...

Re: Slow Oil Leak on Brand New Engine, Help!

BoatNFool,

You mentioned the rear main seal had been replaced - are you implying replaced as in new given the reman through Autozone or did you/father-in-law change it?

As mentioned, an 83 SB had a two piece seal yet it is rubber thus not real susceptible to leaking.. If it was installed correctly and still leaks then I would worry about my rear main bearing tolerance as well.?

It could just be the rear pan rubber/cork seal where it mates to the rear bearing cap. I've seen these leak and look just like a rear main issue. And on that note, if it actually "drips" while running then it's most likely not the rear main seal because a main seal leak would tend to be "thrown" from the spinning crank etc.. As in typically will coat the inside of a bell-housing and then drip off of that...


If it is the rear main/seal and you have enough room to drop the pan "and work", the rear main can be replaced without pulling the motor. But i'm sure the "and work" issue will prevent that...

Good luck!

Re: Slow Oil Leak on Brand New Engine, Help!

Could also be the core plug in the rear cam bearing area.

Re: Slow Oil Leak on Brand New Engine, Help!

KJSmitty said:

If it is the rear main/seal and you have enough room to drop the pan "and work", the rear main can be replaced without pulling the motor. But i'm sure the "and work" issue will prevent that...

Click to expand...

Very very doubtful that would be a sucessful way to do it.

Re: Slow Oil Leak on Brand New Engine, Help!

bruceb58 said:

Very very doubtful that would be a sucessful way to do it.

Click to expand...

I've done several with SB and BB chevy's while still in the car/truck - actually, quite the easy/common job back in the 80's.... A rope seal in a pontiac however was a pain...

This was with the vehicle up on a hoist and room to work. As mentioned however, even if the pan was easily removed, in a boat it would be quite the PITA...

Cheers

Re: Slow Oil Leak on Brand New Engine, Help!

I have replaced a pan in a boat. After I completed the job...never again. Think about it...in a car, you can drop the pan...boat not so easy...bottom of the boat is in the way. Would have taken me far less time pulling the engine completely. I can't even imagine doing the rear seal.

Re: Slow Oil Leak on Brand New Engine, Help!

bruceb58 said:

Think about it...in a car, you can drop the pan...boat not so easy...bottom of the boat is in the way.

Click to expand...

Concur - as I eluded to above, twice.

Re: Slow Oil Leak on Brand New Engine, Help!

KJSmitty said:

BoatNFool,

You mentioned the rear main seal had been replaced - are you implying replaced as in new given the reman through Autozone or did you/father-in-law change it?

As mentioned, an 83 SB had a two piece seal yet it is rubber thus not real susceptible to leaking.. If it was installed correctly and still leaks then I would worry about my rear main bearing tolerance as well.?

It could just be the rear pan rubber/cork seal where it mates to the rear bearing cap. I've seen these leak and look just like a rear main issue. And on that note, if it actually "drips" while running then it's most likely not the rear main seal because a main seal leak would tend to be "thrown" from the spinning crank etc.. As in typically will coat the inside of a bell-housing and then drip off of that...


If it is the rear main/seal and you have enough room to drop the pan "and work", the rear main can be replaced without pulling the motor. But i'm sure the "and work" issue will prevent that...

Good luck!

Click to expand...

Yes, it was replaced by my father-in-law. When we dropped the pan and got in there the 2 piece rear main was set flush, he was convinced it was because it wasn't installed with the offset, it didn't look bad, but we went with a new one just to be safe, and installed at a slight offset (he said you always apply the 2 piece with a slight offest). Also, there was nothing on the bell housing, really nothing even on the back of the block. It's dripping straight off the crank down, leaving no trail.

I just figured if it was the rear main it would be spitting a lot more than the slow drip we're getting. I am at a loss, it seems all variables have been considered and replaced / repaired and this haunting drip is always back...

Thanks for the help.