Chevy small block oil leak

This is really exasperating, and I need some fresh ideas. I did a
top-end rebuild on a Chevy 350 that's in a 1984 K-20 truck I recently
bought. It had a pretty good oil leak at the rear of the engine, so
last weekend I dropped the oil pan, cleaned everything out, and
installed a new rear main seal, high-volume oil pump, and pan gasket.
And it still leaks.

The two sender holes (one next to the distributor, which is connected
to the OP gauge, and the one above the oil filter) are properly sealed.
It *looks* like oil is coming from the back of the block, and anybody
would tell you at a glance that it's the rear main seal. But we know
it's not that because there's a brand new seal installed.

Is there an oil gallery plug or something at the top rear of the block?
I just gunked and pressure washed the whole engine, so presumably I
might be able to tell where the oil is coming from.

Did I miss something?

Thanks!

Jonathan Ward wrote:
> This is really exasperating, and I need some fresh ideas. I did a
> top-end rebuild on a Chevy 350 that's in a 1984 K-20 truck I recently
> bought. It had a pretty good oil leak at the rear of the engine, so
> last weekend I dropped the oil pan, cleaned everything out, and
> installed a new rear main seal, high-volume oil pump, and pan gasket.
> And it still leaks.
>
> The two sender holes (one next to the distributor, which is connected
> to the OP gauge, and the one above the oil filter) are properly sealed.
> It *looks* like oil is coming from the back of the block, and anybody
> would tell you at a glance that it's the rear main seal. But we know
> it's not that because there's a brand new seal installed.
>
> Is there an oil gallery plug or something at the top rear of the block?
> I just gunked and pressure washed the whole engine, so presumably I
> might be able to tell where the oil is coming from.
>
> Did I miss something?
>
> Thanks!

Rear intake seal ? Oil prewssure sending unit?

Jonathan Ward wrote:
> This is really exasperating, and I need some fresh ideas. I did a
> top-end rebuild on a Chevy 350 that's in a 1984 K-20 truck I recently
> bought. It had a pretty good oil leak at the rear of the engine, so
> last weekend I dropped the oil pan, cleaned everything out, and
> installed a new rear main seal, high-volume oil pump, and pan gasket.
> And it still leaks.
>
> The two sender holes (one next to the distributor, which is connected
> to the OP gauge, and the one above the oil filter) are properly sealed.
> It *looks* like oil is coming from the back of the block, and anybody
> would tell you at a glance that it's the rear main seal. But we know
> it's not that because there's a brand new seal installed.
>
> Is there an oil gallery plug or something at the top rear of the block?
> I just gunked and pressure washed the whole engine, so presumably I
> might be able to tell where the oil is coming from.
>
> Did I miss something?
>
> Thanks!
>
What shape was the crank and bearings in? If they are worn or there is a
groove on the crank a new seal may not do much.
It could also be a bad intake seal or a bad oil gallery plug or the
distributer seal Could even be that the sending unit itself is leaking
and causing problems. You have the engine clean now. Dust it with a
light layer of baby powder. Start it and run it for a while, DON'T drive
it since the air moving around the engine will move oil around a LOT.
Now look for the area that is wet with oil. Once you find it clean the
engine again, repair the leak and change the oil.

--
Steve W.
Near Cooperstown, New York

Jonathan Ward wrote:

> Is there an oil gallery plug or something at the top rear of the block?
> I just gunked and pressure washed the whole engine, so presumably I
> might be able to tell where the oil is coming from.
>
> Did I miss something?
>
> Thanks!
>

The only other thing I can think of is the rear of the intake can leak too.

Do what Steve said, run it without driving it. You may have to rev it
up a bit - it might not leak at 10psi (idle) but at 50psi it'll leak.

Possible leak points at the back of a SBC:
intake
distributor
oil pressure sending unit
valve cover
head gasket
oil pan
rear seal
oil filter

I'm not sure if it's possible to leak oil around the freeze plug behind
the cam?

Ray

Ray wrote:
> Jonathan Ward wrote:
>
>> Is there an oil gallery plug or something at the top rear of the block?
>> I just gunked and pressure washed the whole engine, so presumably I
>> might be able to tell where the oil is coming from.
>>
>> Did I miss something?
>>
>> Thanks!
>>
>
> The only other thing I can think of is the rear of the intake can leak too.
>
> Do what Steve said, run it without driving it. You may have to rev it
> up a bit - it might not leak at 10psi (idle) but at 50psi it'll leak.
>
> Possible leak points at the back of a SBC:
> intake
> distributor
> oil pressure sending unit
> valve cover
> head gasket
> oil pan
> rear seal
> oil filter
>
> I'm not sure if it's possible to leak oil around the freeze plug behind
> the cam?
>
> Ray

Yep it can very easily. Rear cam bearing also blocks the feed gallery to
the lifters. If the rear plug is rusted it can leak.
--
Steve W.
Near Cooperstown, New York