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Rear Main Seal for BN2


Staff member
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Looks like that nasty job of solving a rear main seal leak on a BN2 is about to happen here. What's the latest and greatest for solutions?

Last time I had one done for a BN2, the car was in the shop for 11 months and the price was several thousand dollars. That was for a concours car and so everything was done slowly and carefully, but I also remember that it didn't solve the problem and it went back for another six months and it still didn't solve the problem. I decided to live with some leakage as I wanted to drive the car before passing away. Oil is cheaper than the solution, and drip pans are not expensive.

That said, if there's a new kit or some other miracle cure - I'm a sucker for snake oil - please let me know about it.
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There's a couple different versions of the seals--at least there used to be--but IMO it's a wash. You'll have to get the crank machined and the rear engine plate crank opening enlarged. We did this on our BN2/100M, but still get some leakage. One thing that was recommended--in the BCS kit--was to drill an additional drain hole in the rear main cap; this would allow for more drainage and perhaps prevent leaking but we didn't do that (should have a machinist do it; I suspect there aren't a lot of bearing caps floating around). Have heard that removing the drain pipe on the rear main cap can help as well. Make sure the rear plate seals up well with the back of the block; the rear of the cam can be a leakage point.

The one thing that made a significant effect on leakage on my BJ8 was installing a PCV valve, but that would be trickier on a 4-cyl car with separate manifolds. I'm getting up to 3,500 miles on a quart in the BJ8, so I can live with it.

Healey 100

Jedi Warrior
I agree with Bob, I reduced the rear main leak by a ton on my BN1 by removing that drain tube off the rear main bearing. That tube is very small and restricts the ability of the oil coming off the bearing to flow by gravity back into the crankcase. That simple change reduced my oil consumption from a quart per 150 miles to about a quart every 600. The drip was also reduced from a major puddle, but it still leaks some. It is very reasonable now, leaves about a two or three in diameter spot when stopped after a hot run. I have been driving the car for about 5 years with the tube off with no problems from that.

I probably could have improved the situation more by grinding the crank and reducing the bearing clearances, but my crank is already ground to .030 and there are no bearings smaller than that. Tighter main bearings should reduce the leak by reducing oil flow through the bearing.

Blow by from worn rings/cylinders is also very important, just a small increase in crankcase pressure keeps the oil coming off the rear main slinger falling back into the oil pan so it all ends up on the ground. A pvc might reduce the pressure but it sure isn't obvious how to implement that with the four.

There is no way I would try the seal kit. It requires mangling the crank and some folks report that the seal doesn't stop the leak.

I played a lot with sealing the area around the rear bearing cap, especially around those cork inserts. I never found that to have much effect on my leak, I don't think a lot of oil gets past that area around the cap.

I have a number of old cars and they all leak somewhat. Unless you have a really serious leak, chasing after oil leaks usually offers more frustration than success. That's been my experience anyway.


Great Pumpkin
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OH! That Rick is ah :devilgrin: TOO :jester:


Jedi Warrior
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Not sure if it will work on a 4 cylinder engine, but I have been using Chev V-8 rear main seals on my 6 cylinder Healey race motors for the last 20 years. Yes, you have to do a bit of machining on the rear of the crank where that "scroll" is and massage the rear main bearing cap a tad to accept the Chev seal. It's not a big deal if your are already rebuilding your motor. And, it works great!


Jedi Knight
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Hey Bill and all,
Is that small tube you described accessible by dropping the oil pan ??? I too have built in Healey Rustproofing and that sounds like a simple fix if can get to it by dropping the pan. I have also have emailed back and forth with a fellow from New Zealand who fixed the majority of leaking he had by taking the breather pipe and basically adding a P trap like in plumbing to it. Seems a lot of the oil was being forced out through the breather pipe and the P trap would catch the majority of it but also not completely block it. I kinda took the same route as "if it ain't broke, don't fix it" and have left well enough alone but the fix with the small tube as described by Bill might be one to consider !
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Healey 100

Jedi Warrior

That tube can be easily removed once you drop the pan. It is threaded into the bearing housing, just unwind it with vice grips. Just make sure you don't cover the remaining hole with permatex when you replace the pan and gasket.

If the breather pipe is blowing oil, the engine probably has way too much blow by. Adding a restriction to the breather, like the P trap, will increase crankcase pressure and may increase the leaking past the rear main. My engine has never leaked significantly out the breather.

The 4 cylinder engine is not very generous with breather area, all it has is that little opening on the valve cover and the vertical draft tube on the side of the crankcase. I think this, plus the constricted drain path from the rear bearing slinger back to the pan is the root cause of the chronic rear seal leaks on these cars.



Jedi Hopeful
I first fitted a home made seal kit, similar to the DW kit. No leaks ,,,,, for about 1000 miles. Then I dropped valve and rebuilt the engine, fitting a new rear seal and kit from DW,,, no more leaks,, for about 800 miles, I'm finding cardboard on the garage floor resolves the problem, and makes an interesting art project! :encouragement:
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