The Ford Barn

motorvator · 10-04-2017, 10:22 PM

I have had a rear seal leak since I built my French block motor.i have changed the rope seals four times ,using the graphtite type .while looking at a crank the other day I noticed the scroll in the crank where the seal sits ,mine ,a Scat crank,does not have this .do you think this could be a problem? The clearances on the bearings are good and I'm running a pcv valve .thanks

Kurt in NJ · 10-04-2017, 10:42 PM

Have you checked that the seal surface is concentric with the mains,
By "scroll" do you mean spiral groove like a screw thread?

motorvator · 10-04-2017, 11:53 PM

Can I check that in the car? Maybe with a dial indicator ,and yes that's what I ment ,the spiral groove

flatheadmurre · 10-05-2017, 12:03 AM

My guess is that your PCV system can´t deal with the engines needs.
So with the now sealed up engine and positive pressure the blowby goes out somewhere...

scooder · 10-05-2017, 07:40 AM

As above, I'd be investigating the pcv setup, can you describe what was done and how it's fitted. There's a bunch of scat cranks out there that don't leak, hence investigating the pcv.
Martin.

Bored&Stroked · 10-05-2017, 07:48 AM

Sponsored Links (Register now to hide all advertisements)

The term 'leak' is relative . . . how much, how often? Also, how is your PCV plumbed? If you continue to have issues, you might want to do a 'leakdown test' to see how well your chambers are really sealing.

What oil pressure do you see, what weight oil and what bearing clearances on the rear main?

Due to the nature of the rear main system (rope seals) - I've seen many flatheads that leak a small amount - like a drip every once in awhile, not much more (you'll see it on the typical cotter key in the back of the pan).

Where I tend to see more oil "leaking" is with the 39-48 oil pans and the road draft breather in the front corner - I always tend to get a bit of blowby oil from that location (especially if I'm running it hard). I don't have a PCV and I do have the stock breathing system and baffle at the back on the intake (which is the intake side of the air flow - not the exit).

Bubsyouruncle · 10-06-2017, 09:13 PM

How many of you remember the black lines on the highway down the center of the road? The large black areas at stoplights?

These are all gone. Modern cars don't drip enough oil in 100K to fill a teacup. Our old girls could loose a quart in a thousand miles. Through leaks, not burning.

The old engines were not tight. They leaked.

And I suspect that they do not like being tight. So don't ask them to meet modern standards.

10-04-2017, 10:22 PM	#1
motorvator Junior Member Join Date: Nov 2011 Posts: 3	Flathead v8 rear seal leak I have had a rear seal leak since I built my French block motor.i have changed the rope seals four times ,using the graphtite type .while looking at a crank the other day I noticed the scroll in the crank where the seal sits ,mine ,a Scat crank,does not have this .do you think this could be a problem? The clearances on the bearings are good and I'm running a pcv valve .thanks

10-04-2017, 10:42 PM	#2
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,159	Re: Flathead v8 rear seal leak Have you checked that the seal surface is concentric with the mains, By "scroll" do you mean spiral groove like a screw thread?

10-04-2017, 11:53 PM	#3
motorvator Junior Member Join Date: Nov 2011 Posts: 3	Re: Flathead v8 rear seal leak Can I check that in the car? Maybe with a dial indicator ,and yes that's what I ment ,the spiral groove

10-05-2017, 12:03 AM	#4
flatheadmurre Senior Member Join Date: Apr 2015 Location: Sweden Posts: 3,045	Re: Flathead v8 rear seal leak My guess is that your PCV system can´t deal with the engines needs. So with the now sealed up engine and positive pressure the blowby goes out somewhere...

10-05-2017, 07:40 AM	#5
scooder Senior Member Join Date: Jul 2010 Posts: 2,593	Re: Flathead v8 rear seal leak As above, I'd be investigating the pcv setup, can you describe what was done and how it's fitted. There's a bunch of scat cranks out there that don't leak, hence investigating the pcv. Martin.

10-05-2017, 07:48 AM	#6
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,064	Re: Flathead v8 rear seal leak Sponsored Links (Register now to hide all advertisements) The term 'leak' is relative . . . how much, how often? Also, how is your PCV plumbed? If you continue to have issues, you might want to do a 'leakdown test' to see how well your chambers are really sealing. What oil pressure do you see, what weight oil and what bearing clearances on the rear main? Due to the nature of the rear main system (rope seals) - I've seen many flatheads that leak a small amount - like a drip every once in awhile, not much more (you'll see it on the typical cotter key in the back of the pan). Where I tend to see more oil "leaking" is with the 39-48 oil pans and the road draft breather in the front corner - I always tend to get a bit of blowby oil from that location (especially if I'm running it hard). I don't have a PCV and I do have the stock breathing system and baffle at the back on the intake (which is the intake side of the air flow - not the exit).

10-06-2017, 09:13 PM	#7
Bubsyouruncle Senior Member Join Date: Aug 2013 Location: Gurnee, Illinois Posts: 270	Re: Flathead v8 rear seal leak How many of you remember the black lines on the highway down the center of the road? The large black areas at stoplights? These are all gone. Modern cars don't drip enough oil in 100K to fill a teacup. Our old girls could loose a quart in a thousand miles. Through leaks, not burning. The old engines were not tight. They leaked. And I suspect that they do not like being tight. So don't ask them to meet modern standards.