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MG MGB Technical - Rear Main Seal Leak

Hello!

I'm considering the purchase of a fully restored '72 mgb roadster. I've had MGBs for 7 or 8 years now, so I'm pretty familiar with the car.

The car in question has been completely redone. It's beautiful, and I know the seller well. However, I have one concern with the car:

The rear main engine seal leaks a little oil. I know this is typical, but with the cost of this car, I'm not very pleased with the symptom.

Since the engine rebuild, the car has only about 500 miles on it. I seem to remember hearing that often a rear main will leak on a fresh rebuild until it gets fully broken in, then the leak will slow/stop. Is this true, or am I more likely looking at pulling the engine and trying to refit a new main seal again to correct the problem?

Thanks,

J

Jason

Hi Jason,
I replaced mine about 1100 miles ago and it leaked 2 or 3 spots after the first long runs. I was going to post asking what others thought was normal but it has now stopped, just a hint of engine oil on the joggle pin and the odd spot of clean gearbox oil on the drip tray. At the same time the OD had a new rear seal and brand new flange which was dribbling too and has stopped so I know it can happen but ideally you'd be safer checking again in a while before buying.
Rich.

Rich

Not sure I agree. A new seal should not leak especially considering that the materials used are improved now. If there is a groove worn in the sealing surface, then it needs a redisleeve or similar. And if the seal needs wearing in, then 500 miles should do it. Because the seal is a "rubber" item, wear, typically, will only make it worse.

Perhaps you can get some consideration for installing a new seal and whatever it takes to correct this. It may be the front seal in the transmission. Maybe the rear engine plate gasket.

Wayne
Wayne Pearson

Wayne, agreed, in an ideal world and on modern engines, a seal will be fine from the outset. That doesn't mean it cannot improve with running though if the shaft is less than perfect. If we think about plastic bushes running on steel shafts we know the steel may wear as much or more than the softer material. If the shaft is not a particularly good finish the seal may well polish it and the sealing may improve. Take a look at any good working shaft and seal to see this polish. How long it might take we can only guess, could be 5000 miles for all we know depending on the shaft, oil etc, but I'd think the level of leak at the moment may give Jason a clue as to whether he might realistically hope it to improve. Any more than a few drops after a long run would be a bit too hopeful I think. Rich.

Rich

Rich, I disagree. If the crank was properly finished, and the seal properly installed, it shouldn't leak. Although I expected mine to leak from all I've read here on the board, it didn't and doesn't. I know others whose seals also didn't leak with properly installed gaskets and seals. Maybe we're the exception?

Jeff Schlemmer

<<Rich, I disagree. If the crank was properly finished, and the seal properly installed, it shouldn't leak.>> Think you should read my posts again Jeff.

Rich

Thanks for the input, fellas. As it stands, it's only a few drops after a good run.

I'm of the philosophy that it "shouldn't" leak either if it was properly done, but I've also been around enough to know there's exceptions to every rule with these cars.

Forgive my ignorance, but what would be involved with repairing the leak, assuming it doesn't take care of itself?

Obvoiusly, the engine would have to be pulled, but beyond that I'm fairly clueless. Just trying to get an idea of cost should it be required. If I'm going to go to the trouble to fix something like this, I'm going to pay someone who can assure me they can do the job right the first time.

Thx,

J
Jason

Check for engine blow by this creates pressure inside the engine and also contributes on leaks.
luis rodriguez

Jason,

The symptom of oil appearing on the jiggle pin at the bottom of the bellhousing can be driven by oil escaping from either/both tappet chest covers, running down that side of the block, along the block/pan edge to the backplate then down, to be blown across onto the bottom edge of the bellhousing. I have found that situation on my 69.

Just a thought with, perhaps, less serious implications for a potential buyer!

Regards
Roger
Roger T

When I pulled my engine down I discovered there was no retaining plate for the rear seal. Apparently no problem. Is that piece of aluminum really necessary?
Barry
Barry Parkinson

Hi Jeff, Jason, Wayne, All, Firstly, sorry to go on about this, but I agree with all of you; ideally the seal shouldn't leak from the outset. There's nothing to agree or disagree about, I was just answering Jason's first question with my own exp and looking for a reason others and I have found this to happen.

Now to Jason's new question. I agree (!) with others who've pointed out the leak may come from elswhere or that the seal may be fine but blow-bye could cause a leak regardless. Things to be aware of.

<< Forgive my ignorance, but what would be involved with repairing the leak, assuming it doesn't take care of itself? >>

If you go for the seal, engine out, clutch, flywheel and backplate off (possibly backplate left on if you want to risk a screwdriver extraction). Change seal refit backplate with new gasket, re-install everything. The seal retainer stops the seal creeping out or being blown out if there's a backfire. Knowing bean-counters it will only be there for a reason. The parts will be £20 but the labour will be a day. The later black seal (earlier were orange) is different, it fits the shaft very tightly and may run at a slightly different point on the shaft. It's important to refit the backplate carefully working the seal edge onto the shaft with an eccentric movement without damaging the lip or turning it and dislodging the spring. I think there was a plastic guide available but I've not seen it. The whole assembly's quite heavy and the gasket will be in place all glued up so have everything to hand and don't underestimate the care needed here.

However, if the seal is leaking it may be the shaft that's damaged. Many have been cleaned up with emery in the past to lose the ridge of an old seal, mine had with quite a rough finish and may account for it improving with running in. If it's worse though it could be a lot more work with partial disassembly of the rear main to fit a speedi-sleeve.

I also think we have to keep in mind that this seal was never guaranteed 100% effective. It was a progression from the earlier scroll seal on the 3 bearing engines which nearly always leaked a little. Right into the 80's, after the MGB, they were still trying to get it oiltight with the Sherpa van application of the engine. It's simply not as good as modern designs and I think you may end up doing a lot of work only to find you still get a couple of drips from there or elswhere. Rich.

Rich

Firstly I think that you should be very sure that it is engine oil and not coming from the transmission because you don't want to change the seal only to find that the leak is still there. Is the oil dirty and the same colour as the engine or should you make sure by say changing one of the oils to Duckhams which is green and has a distinctive smell. Now Roger's point is a very real one, you can hardly see an oil leak from the valve chests especially if you have a spotless shiny black engine. Check this very carefully. I've been there and it was the valve chest, the centre bolt oil seal is prone to this.

I don't believe that a seal might leak when new and then bed in. I've designed many hydraulic rams and rotating shafts in the past and with the correct ground finish specified they will not leak. The shaft will also stand a slight groove and still not leak with a new seal. The backplate is probably dowelled so can't be fitted incorrectly. Genuine Rover new seals are supplied with an installer which fits over the end of the shaft and prevents assembly damage but the shaft should be smeared with engine oil to provide initial lubrication. When the installer is pulled off use a two thou feeler gauge very gently to ensure that the seal is contacting the shaft all round its periphery. I've fitted many of these and they don't leak. The later MG is no worse than any other car in this respect the same type of seals being used.

Now if you have a leak Jason I think you have a judgement to make. Is it leaving a puddle of oil on the floor or is it just a couple of drips. If it's the latter then think carefully about living with it until it becomes unbearable or you have some other reason to pull the engine or transmission and deal with it then.

Just one last thought is that if the engine was rebuilt "professionally" then the company might just be obliged to sort the problem out.




Iain MacKintosh

Sorry Rich - I didn't mean to come across as belligerent or insulting. Many times I just post a short snippet to get people thinking about a different viewpoint.
What I meant is that I, like Ian, don't believe that a crank should need time to "bed in" a seal. Any finish rough or irregular enough to create a leak has the ability to damage the seal that rides on its surface. Yes, deposits can build up to seal a small leak, but I've never seen a piece of rubber hard enough to polish steel. The biggest mistake made is not oiling the seal and crank during installation. That will cause a temporary leak, as will the seal drying out from extended periods of non-use. Sometimes this is cured by use. I still say that the only "real" fix is to have the crank properly ground and polished. Otherwise, you could be chasing leaks until the next rebuild.
More often than not, the crank leak is not the crank, but as others have suggested, something "higher up." read through the archive and you will find a variety of crank seal leaks repaired with valve cover and tappet seals.
Good luck!
Jeff Schlemmer

My son just had his rear main seal replaced and the shop told him that the cause of his leak was actually the end cap. His is a 302 motor so this may not apply. The point is, we thought we knew the problem cause and it was something else.
kids1

What's the end cap and what's a 302 motor ??
Iain MacKintosh

My guess is a 302 = a Ford v-8 and end cap would be the rear main cap? a little merican/British misss comm. Bob
RHT Thompson

Just goes to prove RHTT that engines other that MG can leak also.
Iain MacKintosh

Thanks again for all the feedback, gentlemen. Feel free to keep it coming. A few comments below...

"Is it leaving a puddle of oil on the floor or is it just a couple of drips. If it's the latter then think carefully about living with it until it becomes unbearable or you have some other reason to pull the engine or transmission and deal with it then."

As I've mentioned, it's a couple drips. Nothing alarming by any means that would cause me to want to jump in to pulling the motor.

"More often than not, the crank leak is not the crank, but as others have suggested, something "higher up." read through the archive and you will find a variety of crank seal leaks repaired with valve cover and tappet seals."

I will check this and cross my fingers. This would certainly be easier to fix than the rear main!

"Just one last thought is that if the engine was rebuilt "professionally" then the company might just be obliged to sort the problem out."

Understood. I know "of" the person who built the motor, but I don't know him personally. He's a semi-professional builder who has built race engines for years. He "should" know what he's doing, but of course one never knows. Again, I don't know him personally and he does not operate a formal shop to my knowledge, so how well he stands behind the quality of his work is unknown at this stage. I will inquire to the seller about this.

Thx

J
Jason

Seems this is a good car Jason. Let's know if you buy it.

Enjoy.
Iain MacKintosh

Another possibility - the rear bearing cap on the 'B engine can be installed without being exactly flush against the rear of the block - similar to the 302 example. Oil will run down the front face of the engine plate and blow around when moving, some ending up on the transmission side and that pin; the inside of the tranny will stay clean and dry.

Oil from the oil cooler fittings, the pressure sender, dipstick hole, oil filter fittings (or even when changing the filter), tappet covers, rocker cover and even front timing gear cover can follow the same path - down the side of the engine, along the sump lip to the rear engine plate.

Sounds like a good purchase to me too. You can afford a lot of cardboard for the garage floor before it's economical to pull the engine :). I'd only pull it if oil was getting past the rear seal and messing up the clutch.
Mike Polan

Jason, don't let this leak stop you from buying the car if everything else is in order. When you mentioned the engine builder is a semi-pro and builds race motors you said a lot. Race motors are usually built to close tolerances, but are also to be torn down much more frequently than a street motor. Piston and bearing tolerances are closely adhered to, but things like crank seals and balancer seals are typically neglected. I'm not saying they're ignored, just not treated with the importance of the rotating assembly. Either way, its probably a great car!
Jeff Schlemmer

<< Sorry Rich - I didn't mean to come across as belligerent or insulting. >> Jeff you didn't, I just thought you'd read me wrongly, no probs and I appreciate you posting.

Seems I'm the only one so far who's had this seal running in experience, memo to keep it to myself next time :-) Kind of reminds me of the arguement I had with my friend at school when i was trying to convince him big end bearings were made of lead and he thought I was crackers.

Jason, as you can guess, a couple of spots of oil wouldn't put me off buying it, I have a smart stainless drip tray under mine :-) Rich.

Rich

Jason, this is a common problem. Over the miles the lip of the rear seal wears a grove around the end of the crankshaft. Regardless of what you do it will always leak unless you fit a sleeve over the end of the crank. Napa auto parts sells something called a Redi-sleeve that is a tolerance fit over the end of the crank. I'd recommend putting some Loktite sleeve retainer on as well for good measure. Fit a new seal and no more oil leak. Also check the oil leakage from the first motion shaft seal in the front of the bell housing.

Andy
Andy Preston

Who suggested it might run in Jason? If it was the engine builder could you get in touch to get his view of the crank condition first hand? Rich.

Rich

A couple of observations about that rear seal:

I always fit the black viton "improved" version from the Sherpa engine.

Sometimes they are absolutely dry - sometimes they leak a little oil - sometimes they leak a noticeable amount.

Sometimes the leak improves with time, sometimes it stays the same, sometimes it worsens.

They are always fitted with care and the crank is always ground correctly.

I have no explanation - but if the leak is only a couple of drops then I would say that is normal for the design.

Chris at Octarine Services

Glad to hear your input Chris! I guess that means I got lucky!? ;-)

I've had many a gasket not seal properly, but over the years have refined my ways, but leaks still happen. Most are repairable, and some can be easily lived with. Jason, its up to you.

Andy has a great point. I just rebuilt my engine, but didn't immediately replace all the seals in the tranny. I was hoping for a new 5-speed. In the mean time, I had to remove the engine and tranny for body work and realized the front tranny seals were both leaking. I had also thought it was the main, and wondered why the new clutch wasn't working properly. Two birds with one stone you might say.
Jeff Schlemmer

A leak through the joggle pin hole can also come from the gasket of the gbox seal carrier esp if the bearing's been shimmed too tightly.
Thanks for the input Chris, I'm sure you have a lot of rebuilds to draw observations from. Seal running in is not surprising, uncertain maybe, but the evidence is there to see in that polish mark on a good shaft. Rich.

Rich

At 500 miles, the engine should be pretty well broken in if the driving was done under a variety of conditions and RPMs.

I will merely submit my experience:

I had the entire engine professionally rebuilt to Stage 1 specs, new HD clutch, lightened flywheel, reground, polished and balanced cranshaft. When I drove it into the garage for the work, there were no drips from either the engine or tranny and my mechanic guaranteed me there would be no leaks afterward.

I won't return the car until she's completed 500 mile post-rebuild, barring something major.

At 120 miles now, I have an oil drip that leaves a single spot when at rest, apparently from the rear main seal.

I have an apparent seepage coming from the tranny refill plug. The tranny was drained and refilled during the engine rebuild.

The OD plate maintains a single drop of oil at each of its four corners.

My mechanic did tell me that prior to the first start, he spilled some oil when he overfilled the oil cooler hoses, so I could expect some temporary appearance of an oil leak.

When I return the car for its 500 mile service, I expect that the defects I noted above will be history, or he will be pulling the engine again and rectifying the problems at his expense. I paid US$5500 for this rebuild and having a resultant leak where it was dry earlier is simply not acceptable.
Gary Kinslow '69B roadster Pale Primrose

Gooday all.
Just one more possibility..When i rebuilt my 69b,i filled the transmision with oil prior to fitting in the car.Next day before installing,i noticed oil on the floor and thought rear seal or front gear seal.After separating gearbox from engine,and much looking it turned out to be the front seal housing was cracked from the clutch throwout arm to the seal recess.Just a hairline crack but enough to leak when the gearbox was full of oil.I knew the previous owner of 30 years and he never picked it up.I think the oil level dropped below the crack and didn;t leak all that much.Replaced housing and seal and in 12000 miles not one drop of oil.
Cheers
cactus

FYI, this is Jason; I just logged in this time. :-)

Thanks once again for all your input.

So, what I've gleaned from all this is the following:

1) There are many possiblities that could be causing the leak. Start with the easy-to-get-to ones first, checking carefully for oil travelling along the block to the source. The last resort would be to pull the engine and check the rear main.

2) If indeed it comes down to the main, it's probably the crank/seal mating point, which may require a sleeve. I'll keep these notes, but if it comes down to that I'll be having an exeprienced 18V builder handle it from there.

3) As long as it's just a couple drips after running, it's not a big deal, and generally not a sign of anything catastrophic.

All these things considered, I'm going today to buy the car. I'll post some photos at my earliest opportunity.

Rich:

<< Who suggested it might run in Jason? If it was the engine builder could you get in touch to get his view of the crank condition first hand? >>

No one suggested that. It was just something that I seem to remember reading in a thread some time ago.

Nonetheless, I will get the contact info for the builder so I can at least have the opportunity to follow through with it if necessary.

Thx.

J
JFD Dutt

UGH! I should have made things more clear. My son's motor is a ford 302 and it is the rear main cap. Sorry. Doh!

kids1

Quick followup:

I did a thorough investigation of the leaking last evening. As many of you suggested, there are culprits higher up on the block, such as the oil cooler hose, and a few other erroneous plugs and entry/exit points. None of these are leaking much, but I figure with all of them combined, meeting at the rear base of the block, it has to account for at least one or two of the two or three drips!

My plan is to attack the "easier to get to" points first, and see how the situation improves. If I can get it down to a drip once in a while without pulling the engine, I'll be thrilled.

Regards,

J
JFD Dutt

Does anybody know where a person can get a
hold of one of those black Viton, double-lipped,
Sherpa Van rear main seals here in the
good 'ol USA?

There are folks here that list the part number
for the Sherpa seal in their catalogs - but the
actual seal itself is the OEM-type, red, MGB rear
main seal.

Maybe some enterpising fella in the UK can
make a small amount of extra pocket money by
offering them occasionally on eBay?

Just a thought.
Daniel Wong

Daniel, The later black seal is LUF10002 and I got mine from MGOC in UK who do export http://www.mgocspares.co.uk/contactus.html
They're still single lip btw but are tighter fitting.

Rich

In case anyone's still interested, I've posted a few pics of the car referenced in this thread on my blog, here:

http://jdutt.blogspot.com/

Regards,

J
JFD Dutt

Wow. Looks great!
Jeff Schlemmer

This thread was discussed between 09/06/2005 and 21/06/2005

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