396 oil leak [Archive] - Team Camaro Tech

: 396 oil leak

Sep 29th, 03, 09:17 PM
It's actually a 1970 402 engine, but anyway.

The "396" engine currently in my 68 (originally an SS350) runs strong, but has this nasty oil leak coming from the back of the block inside the bell housing somewhere. It only leaks while the engine is running, pressurized. I inspected the best I could around the rear main seal from under the car with the tranny, clutch etc. all in place and it does not seem to be coming from there. Where else could it be comming from back there? The oil tends to get onto the flywheel and then gets slung all over the inside bell housing. I was wondering about the rear cam plug. How hard are these to repair? Can they be repaired reliably without disassembling my top end?
I want to make this engine last until I save up enough for a 454 or 502, and aside from this leak, it's up to the task.


Sep 30th, 03, 03:38 AM
I'm not as familiar with eth BBC but on the small blocks I have never seen a rear cam plug leak. Usually its either the rear oil pan gasket or the rear main.

A valve cover or intake gasket can leak and run down in that spot too. On a SBC there are a couple 1/4" threaded holes on top of the bell housing that if left open could allow oil from the intake etc to drip into the bell housing. Kind of a long shot though.

There are a couple oil galley plugs that I suppose could leak too but that is also a long shot.

Sep 30th, 03, 08:43 PM
Yup. I checked all the usual suspects like the back of the valve covers, intake, head gaskets, but those are all outside the bell housing and the back of the block outside the housing is dry, so this leak is definitely under the bell housing.

Around the rear main and pan appears too dry also. Leaks from either of these spots would typically result in a lot of drip off the bottom pan, but the pan is not that wet either.
This leak seems like it is originating up higher than the rear main which is why I suspect the cam plug or maybe some other oil galley opening that might be present.

I'm like you in that all my experience is with small blocks. I bought the car with the 396 already in it so I haven't seen the backside of the engine above the rear main yet.

With the way the oil is scattered around the inside of the bell housing, it almost seems like it leaks forceably when the system is pressurized as opposed to a drip. I'm also wondering if maybe this is gear lube from my 4 speed leaking from the transmission input shaft seal as the tranny is pretty wet. I relly gotta crawl under there and lokk at this closer.

Still curious about the difficulty of replacing/repairing the rear cam plug without pulling the top end off the motor.

Oct 1st, 03, 06:31 AM
If it is gear lube, it will smell like gear lube.
I know that may sound extremely simple, but you can tell the difference between motor oil and gear lube with a simple sniff test.

Oct 2nd, 03, 05:48 AM
There are oil gallery plugs back there as well as the cam plug.

It's either the rear main or a plug..


Oct 2nd, 03, 09:43 AM
There's no seal of any kind on the 4-speed input shaft; any lube that gets through the front bearing runs down the inside of the bearing retainer and drains back into the case through a drainback hole. graemlins/thumbsup.gif

Oct 2nd, 03, 08:37 PM
Thanks for all the feedback, guys. The news that the 4 speed input shaft has no seal helps to narrow it down further.
I suspect it must be one of the oil galley plugs or the rear cam plug...won't know until I get the engine out or drop the trans and flywheel out of the way.