rear oil seal/thrower

[jddevel]

On the assumption I stick with the original cork gasket configuration in the rear bearing cap when assembling the crank. Is there any tips to try and get it "right". I`ve sort of decided this set up because of the mixed reviews on the conversion kit/lip seal.

[Steve Simmons]

John Seim wrote this years ago. Several people have done it with good results...

Recalling those words of wisdom, I took a hard look at both the Moss Oil Seal, and the GM rear oil seal. I looked at the MG engine block, and wondered, "Why would MG (Morris) put a seal in the back of the engine that didn't work?". Then it came to me. Morris put a rear oil seal (Thrower Plate) in the back of the engine. This design dates back to the mid-thirties, but probably was part of the Continental engine design, when the engine was initially designed, in the late tens. It worked well at that time (the tens), it just wasn't state of the art in the post-war years.

What they incorporated in their design, was an Archimedes screw to return the oil back into the block, that had worked it's way to the rear-most portion of the crankshaft. The Archimedes screw is at the back of the crankshaft, then an oil barrier (plate), then the large flange for the flywheel mounting. In the engine block, at the back of the rear main bearing cap, was a flange lip that would surround one half of the Archimedes screw. The thrower plate mounts directly to the rear of the block. It supplies the other half to surround the Archimedes screw. The thrower plate butts up to the bottom of the rear main bearing cap, and is secured by two pins and by three 6mm x 1.0 bolts. The design worked reasonably well, as long as the clearance between the Archimedes screw and the rear main bearing cap/ thrower plate was kept to a minimum.

What happens is that the crankshaft flexes. Remember, these weren't balanced crankshafts, or flywheels, or other moving parts. A small amount of unbalanced weight, over the years, moves the part in an elliptic, rather than a circular motion. Add the weight of the flywheel attached to the rear of the crankshaft, and you can either increase the unbalanced weight ( if both unbalanced weights are placed on the same side) or move the imbalance by installing the flywheel having a greater imbalance that that existing in the crankshaft, to the opposite side of the crankshaft's imbalance. In any event, the wear at the rear main bearing is greater than either the centre or front main bearings. This wear allows for the Archimedes screw to move outward into the circular surfaces of the rear main bearing cap/thrower plate, enlarging the opening. With a larger opening (clearance), the Archimedes screw becomes inefficient. No where in the workshop manuals does it mention to check clearance at this point. Jim Bigler, Jerry Felper, and others knew that the thrower plate had to be butted against the rear main bearing cap. In fact, they would advocate removing the two pins, and tap the thrower plate up against the rear main bearing cap, with the cap torqued to spec to the engine block. Bud Quist took this one step farther. So, what's the solution?

1. Have all parts of the engine balanced. Then, mount the rear main bearing cap to the block, torqueing the nuts to spec. Install the thrower plate, using the three bolts and the two pins (I would remove and discard the pins. D. DuBois), plus the gasket, and gasket cement. Do not tighten snug the bolts. Tap the thrower plate at the left and right pin corners, to butt the plate to the rear main cap. This also bends the pins, helping to keep the plate against the rear main cap. With this completed, now tighten the three bolts snug.
2. Smear a thin coat of J-B weld on both of the semi-circular surfaces.
3. Install new main bearings into the engine and main bearing caps.
4. Using Teflon tape, wrap two turns around the Archimedes screw portion of the crankshaft. Press the tape into the screw threads. The Teflon tape acts as a release agent, and helps to remove the J-B weld from the screw threads.
5. Lay the crankshaft in the block.
6. Install and tighten to spec the centre and rear main bearing cap.
7. Rotate the crankshaft in the direction that it spins, two or three complete revolutions.
8. Remove the centre and rear main bearing cap.
9. Remove the crankshaft. Pull the Teflon tape out of the threads. Use a dental pick, or other tools, and remove any remaining J-B weld residue.
10. Remove any excess J-B weld in the rear main bearing cap, oil thrower, or engine, not on the circular surfaces.
11. Let J-B weld sit for 24 hours.
12. Repeat steps 4-10.

This completes the repair of the circular surfaces. The Archimedes screw now has a minimum clearance to work with. When assembling the engine, place some gasket cement on the flat surface of the oil thrower. This seals the circular area. Almost all oil will now be returned to the engine. You will have a small leak, better than when the engine was new. The cost of this repair is about $5.00.

[stephen stierman]

When I rebuilt the engine in TC2911, I installed the modern lip seal conversion. It leaked, likely because of my installation not being exact enough. Ultimately I went back to the slinger. I read all the information I could find, ultimately I reduced the clearance of the slinger so it was in slight contact with the crank. Took the locating pins out, enlarged the bolt holes etc. I also enlarged the drain holes in the main cap to allow it to drain faster and removed the drain tube completely. On a long fast run upon parking, it may put a drop or two of oil down, but nothing more. Decreasing the clearance between the slinger and the crank evenly is what needs to be done.

[Duncan M]

Are you asking about the bearing cap to sump cork seal? #27 in moss catalog? https://mossmotors.com/mg-tc-td-tf/engi ... l-engine-3

If so, I cannot offer any fitment tips except to suggest when you figure it out to use a "gasket dressing" such as Hylomar blue. I am NOT talking any sort of silicone sealer, rather a very specific type of gasket dressing. It makes the gasket seal better, and also makes the cork seal last much longer than without. There is also a Permatex equivalent that is near impossible to find at auto parts stores, but can easily be found on ebay. Permatex 85420 (fuel resistant gasket dressing and sealant). Hylomar universal blue and the Permatex 85420 are the only 2 gasket dressings of this type. In addition to use on cork, they also great on paper/cardboard gaskets.

[Steve Simmons]

There are other makes and models in the British car world that offer modern materials (neoprene, etc) for this seal. I wonder why no one offers them for TC. I've considered making and installing my own. I put one into my wife's Morris without incident, although it leaks enough from other places that I can't say if it's oil tight or not, but I suspect it is.

[jddevel]

Thank you all for the contributions. I suppose it basically boils down to wear, flexing and driving "aggressively" and not the basic principle which held up to a certain extent against the times it was designed for and when there was possibly less interest in "that patch on the floor". The existing design does not really address our more concerned approach. Is the real problem the cork gaskets inability to absorb any flexing etc due to the absence of a spring? Also can it be guaranteed that the oil comes from there (the bottom of the crank) and not the top of the crankshaft? I suspect many hours of thought and discussion has taken place by those more skilled than I. I suppose like following the horse with a bucket a catch tray will at present suffice.

[stephen stierman]

Most of the oil comes by the bottom of the slinger if there is too much clearance between the crank and the screw threads. When this is mounted properly as the article that Steve posted suggests it works pretty well no matter what sort of driving you do. When I bought TC2911 it leaked a tea cup of oil at shut down, the Moss seal did not work for me, likely my installation problem. Upon reading those articles and installing the slinger properly it has worked well for almost 20,000 miles.

[Rob Zucca]

I too was concerned about the conversion on my recent rebuild and followed the procedure in Steve’s post. I set and torqued the crank numerous times applying engineers blue to the JB weld. Turning the crank a few times by hand would show a slight mark from the scroll. I’d then scrape the JB weld with a razor blade until the scroll made no contact. It is also a new crank with fresh scroll. I also followed the instructions carefully for sealing the sump. Carefully trimming the gasket ends and making sure the cork was centered. I used The Right Stuff sealant sparingly being confident I didn’t allow any to squeeze out on the sump side. The result is no leaking anywhere but a dime sized drip after a run at the jiggle pin. I’ve since installed a catch can under the jiggle pin. Before assembly, I also inserted a 1/4 inch piece of brass tube with a slight flare at the top into the jiggle pin hole along with a smear of JB Weld. Then inserted another jiggle pin through the tube. This directs any leakage into the catch can. Otherwise the proximity of the hole to the pan fins allows oil to creep past the catch can. It is all working very well.

[Duncan M]

A different article coming from a different viewpoint. https://www.mgccyregister.co.uk/technic ... -old-xpag/

What the two articles agree on is extra wear that occurs at the rear main bearing. Reading between the lines of the Cairns article, it would seem that careful attention to the drip on the floor over time could tell you when it is time to replace the bearing shells--with the original design

[stephen stierman]

Duncan, I think there is a good deal of truth to both those articles. Reality is that most of the Brit cars of the period used a similar arrangement to the XPAG, some working better than others. I think the adjustability of the XPAG seal can work pretty well. I recall reading an article about the MGA engine that had too much clearance built into the slinger with no adjustability. I believe they had a fixture to actually drill a couple extra holes in the rear main bearing cap to allow more oil to escape the trough before it went out of the slinger.

[Duncan M]

And as the wear on the rear bearing shells is allowed to become excessive, and the oil begins to puddle under the car, one might expect a broken crankshaft. Sound familiar? Crankshafts tend to break for a reason. I think Cairns article is more accurate, and the original excessive scroll seal leak is being caused by improperly done gasket seals, or, as an engine wears and the rear shells wear more, the added oil being pushed through the excessive bearing clearance overwhelms the Archimedes screw. The larger oil spot under the car is evidence the rear bearing clearance has become excessive and action is needed.

[stephen stierman]

I broke the crank in my 1500 MGA when I was in college. It would still run, but believe me the noise let you know that it was a catastrophic failure of some sort.

[Tom Wilson]

Most have their preferred way of solving the oil leaks. I'm a firm believer in using the Chevy 350 block split seal, putting forth the effort and detail for proper alignment and assembly.
My engine does not leak oil, except for one pushrod tube. I built the engine in 2009, drive the TC pretty hard, and it's still dry.
Tom Wilson
TC0273, TC0279, TC2040