The Ford Barn

Hoogah · 07-08-2018, 10:51 PM

My ‘29 motor is at the engine rebuilders after discovering white metal in the sump when chasing a rear main oil leak (see separate thread “Dropped sump, found metal”). He’s going to re-pour the main bearings, but is happy with the condition of the babbit on the con rods (the motor has been rebuilt once that I know of). The babbit on the rear main was mostly gone and what was there looked way too thin anyway - possibly a dodgy job to start with? Pistons and bores look OK with no ridge and just a light honing of the bores required. The motor has been bored out 80/1000”. We will replace the rings and valve guides.

That’s the context, now for the question! There are maybe four options for the rear main oil seal:
1. Original style
2. Brass replacement that requires modifications to the way the babbit is poured
3. Nitrile seal replacement that requires the rear oil slinger to be removed from the crankshaft
4. Nitrile seal replacement, as above but in two parts (although my parts man is having trouble finding these)

I hate getting conflicting advice, but I’m preparing myself for it! I have read of instances where the nitrile seal does not solve the problem, and the crank has been left permanently modified/ruined. I also don’t know what advantages the brass seal offers over the original style.

Is there any reason for me to do anything other than put it back as per the original design, and if not, what are the main considerations in ensuring that my rebuilt rear main has no leaks?

07-08-2018, 10:51 PM	#1
Hoogah Senior Member Join Date: Feb 2014 Location: Warrnambool, Victoria, Australia Posts: 800	Rear main seal options - which one? My ‘29 motor is at the engine rebuilders after discovering white metal in the sump when chasing a rear main oil leak (see separate thread “Dropped sump, found metal”). He’s going to re-pour the main bearings, but is happy with the condition of the babbit on the con rods (the motor has been rebuilt once that I know of). The babbit on the rear main was mostly gone and what was there looked way too thin anyway - possibly a dodgy job to start with? Pistons and bores look OK with no ridge and just a light honing of the bores required. The motor has been bored out 80/1000”. We will replace the rings and valve guides. That’s the context, now for the question! There are maybe four options for the rear main oil seal: 1. Original style 2. Brass replacement that requires modifications to the way the babbit is poured 3. Nitrile seal replacement that requires the rear oil slinger to be removed from the crankshaft 4. Nitrile seal replacement, as above but in two parts (although my parts man is having trouble finding these) I hate getting conflicting advice, but I’m preparing myself for it! I have read of instances where the nitrile seal does not solve the problem, and the crank has been left permanently modified/ruined. I also don’t know what advantages the brass seal offers over the original style. Is there any reason for me to do anything other than put it back as per the original design, and if not, what are the main considerations in ensuring that my rebuilt rear main has no leaks?