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MG MGA - Sudden oil leak - advice sought

Seasons greetings all;

I have a ground up 1600 roadster. The engine is the original 1588cc unit that has been totally rebuilt by a reputable specialist (new pistons, bearings, reground crank etc etc). In the car’s first 12 months back on the road I have put 1,200 careful miles on the clock (600 of which was in one weekend) with the engine starting to bed in nicely. Between oil changes I’ve never had to add a drop of oil with the only leak being a couple of drops from the (usual) bell-housing drain hole.

That was until yesterday…..On the way home from a 10 mile run I noticed smoke coming from out under the car. Closer inspection sourced the smoke to the hole in the bell-housing for the starter motor bendix with a tell tale pool of oil under the car - emanating from the bell-housing drain hole. Both engine and gear oil levels still read full, however I suspect that the culprit is the engine rear oil seal (or lack thereof!)

Does anyone have any ideas or suggestions as to how I proceed from here? I’ve checked both the rocker cover and side plate vent pipes and both are clear. Perhaps I am running at too high oil pressure? …the car idles at 65 psi oil pressure when cold, 50 psi when hot, and cruises around 80-85 psi. Any feedback is appreciated.

Safety Fast

Steven
Steve

The rear crank oil retention system (can't call it a seal) could only get suddenly worse if a piece of metal got in and chewed up the end of the crank. Since you checked the breather it is possible the trans vent is plug and the oil is from it. My only other guess would be that the rear engine plate gasket sprung a leak in the area near the crank. Before you panic, check that the leak is not from the back of the head gasket or the oil lines. As the bell housing is not sealed, it is possible that the oil is leaking into it from above.
John H

Just a thought; have you overfilled the sump?

Steve
Steve Gyles

What color is the smoke. Could it be steam? A possible head gasket problem? Antifreeze with a small amount of oil mixed in can look like a major oil leak. I don't know of any part of the engine or transmission that would be hot enough to smoke when coated with oil. The only exception would be the exaust pipe or manifold. If some part of the engine or transmission is that hot, you have more than an oil leak to worry about!
Ed Bell

Also make certain that its not a leaky valve cover gasket running down the rear of the engine, into the bell housing and onto everything in its path.
Jeff Schlemmer

Thanks guys for your comments. Here’s what I’ve done so far. This morning I thoroughly detailed the engine and chassis. I then started the A and ran her in neutral for 5 mins or so. A couple of mins after switch-off a small but consistent drip of oil began from the bell-housing drain hole. I then took her for a 5 mile test run. Upon return I placed a glass jar under the bell-housing.

After about 20 mins I had collected about 4 teaspoons of oil (and still dripping). There was a small trace of oil visible around the rear head stud, so as a first cause of action I’ll re-seat the rocker cover gasket however I am still a little sceptical as whether this is the culprit. I also noticed a couple of drips forming on the clutch slave cylinder pushrod.

The leak aside I guess what concerns me at this stage is that after such a short road test I again noticed smoke (yes definitely smoke) coming from the starter bendix area (oil burning on the clutch plate perhaps? ... and suggestive of a sizeable leak?)

Thanks heaps guys. Happy new year to everyone.

…. Some pics of the vehicle in question can be found by clicking on the following link

http://au.pg.photos.yahoo.com/ph/nrswn1/my_photos
Steve

Just another thought--85# of oil pressure is over specification. Did you use an uprated release valve spring?
Paul Hanley

The smoke could be venting from the sump rather than burning on the clutch. But you would expect this more from an old engine - worn piston rings or valve guides. I guess you could eliminate some of the possibilities by doing a compression check, but as you say this sort of wear would be most unlikely after just 1200 miles. Did the problem occur immediately after an oil change?

Nice pictures.

Steve
Steve Gyles

Unfortunately I think that this is a crankcase pressure problem but I don't yet know why. You say that the breathers are clear so hopefully that is ruled out. Start the engine then remove the oil filler cap and race the engine. If you have blue smoke emitted then certainly it is a pressurising fault which can only be caused by blowby past the pistons and I suggest you take the car back to the engine builder and ask him what he intends to do about it.

With the oil filler cap on the pressure will leak out by the easiest means and this is obviously past the crank rear scroll and into the bellhousing. That's why smoke comes out of the bendix hole and oil from the bottom of the casing.

I sincerely hope that I'm wrong but it looks very likely this is the case.
Iain MacKintosh

Could be broken rings. I had a factory reman unit where too thin of rings were used and all broke in less than 500 miles. Would show low compression. Did you check compression? Chech oilpressure with a known good gauge seems abnormally high for any engine esp. an old English one I suspect your gauge reads high.
R J Brown

Gents,

Last oil change (both gearbox and engine) was 700 miles ago.

The result of a compression test was a consistent 140 psi on all 4 cylinders.

Iain, I ran the engine with the oil filler cap off and there were no signs of any blowby.

At this stage my thoughts are with excessive pressure in the sump or a leaking front gearbox seal.

I will contact my engine machinist tomorrow for his opinion.

Thanks again.

Steven
Steve

Hello,

Sounds like Steve and I are in the same situation. My oil pressure is very high as well and I tend to loose a lot of oil, most likely from the rear scroll area as it was damaged. If I could releive some of the oil pressure and crankcase pressure, I am sure I can reduce the loss to a more acceptable level. I am interested to discover the results.

Tom
Tom Baker

Steve, your crankcase pressure is high so you must have blowby when you remove the oil filler cap. You won't get it however at idle speeds. Run the car on the road for say 5 miles to get it thoroughly warmed up and then remove the cap. Race the engine up once or twice and see what happens because if there is crankcase pressure it must vent out of the rocker cover together with an amount of fumes. Until you confirm this or otherwise I don't necessarily want to specify what the cause might be as I don't believe that worrying about that will do any good. Your oil presure is very good if on the high side but this has little to do with the crankcase pressure or the leak which is aggravated by the crankcase pressure.

I'm pretty sure that the smoke emitting from the bellhousing is from the crankcase and if this is the case then you must be able to get it to come from the rocker cover.
Iain MacKintosh

Steve- Just a thought, if the engine oil pressure is excessive it may be delivering more oil to the scroll area from the rear main bearing than it is capable of handeling. A cheap trial could be done by using a different bypass valve spring to reduce the pressure down to 60-65 psi and driving the car to see if the leakage is reduced. Sometimes more isn't always better.
John H

John, this thought did go through my mind but there will be additional leakage through the other six bearings as well so the effect will be minimal. Don't forget that the smoke indicates blowby which looks like being the root cause of the problem.

You could also argue that because of the now tight tolerances between the shaft and bearings that less oil will be flowing across the journals and I believe this to be the case. This is therefore raising the oil pressure and the excess oil returns to the sump via the relief valve with no harm done.
Iain MacKintosh

Iain, can't argue with your logic, I was thinking that the oil smoke may have been caused by the leaking oil hitting something external that was hot, clutch, exhaust, etc. If it is blowby it should also be very noticable out of the engine vent pipe. A sudden increase of blowby makes you wonder about something that could cause the immediate change. I can only come up with expensive guesses that could cause this such as a bad head gasket, stuck rings, a crack in the head or block, or a damaged piston. You would like to think this couldn't happen to a fresh engine, but on the other hand, it is 40 some years old.
ohn H

Yes John that's right but I don't think that this engine would have had an open vent pipe. I'm pretty sure it would have vented to the rocker cover or the air cleaner. Head gasket/cracked head etc wouldn't cause this, it's definitely bottom end related i.e bores, piston or hopefully rings at worst. I still think that Steve should go right back to the engine builder with this one.
Iain MacKintosh

I think you will find that a 1600 B series used the open vent pipe from the tappet chest cover.
Bob (robert) I used to own a Morris Oxford

Iain, like Bob, my 1600 has the tappet chest vent pipe. I agree, I think it may be time for Steve to revisit the engine builder
John H

OK Bob & John I'll go along with that, now outlawed of course. What a pity but it does seem the best recourse as Steve is not really responsible for this. My opinion is that the sooner this is done the better to avoid any further damage being caused.

Good luck with it Steve.
Iain MacKintosh

Hi Guys, thanks a lot for your comments.

My engine builder is currently on leave but he's back monday morning and I'll be in his workshop first thing.

I have some good and bad news (well I think).

I went out to look at the car last night and in addition to a couple more drops under the bellhousing drain hole (minimal) there was a very small pool of oil under the engine near the oil pressure relief valve. Ah ha, I thought. Looking more closely I can feel a film of oil around the back of the head and the block. Not much but it is there. The problem is despite the engine being pristine, the oil is so damm clean that it's almost impossible to see.

The dipstick on the gearbox still reads full and from my best judgement is a slightly lighter colour than the drops under the engine so I believe I can effectively eliminate the front gearbox oil seal.

This has led me to think that my problem is just a leaking valve cover (perhaps exascerbated by high oil pressure?)

Now the bad news. I proceeded to take the rocker cover off. However when doing so the rear rocker cover stud came out with the cover. I don't think the 2 problems are related but is it possible that the head has now been disturbed? Can I just reinstall the stud and torque the fixing nut down?

The top end is very clean and well lubricated and there is evidence of gasket leakage from the back of the head (again not huge amounts).

I'm reluctant to do anything until I speak to my engine builder but I'm thinking that before pulling the engine etc I will (at a minimum) change the engine oil / filter and re-seat the rocker cover.

Finally, is it possible that the smoke is caused by clutch slippage. The 2 times I've noticed smoke have been after driving the car. I haven't been able to get smoke with the engine idling in the garage and both vent pipes are clean with no evidence of oil.

Here's hoping that it's just a rocker cover....

Cheers

Steven
Steve

Does have anybody have any experience with the dyes added to the oil? something like this:
http://www.amgas.com/tcpage.htm
It looks likte the answer to finding the source to many leaks on the MG. When added to the oil or any other fluid, it lights up with a "black light". i gues you wouldn't want to add it to al the fluids at once.

Chuck
Chuck Schaefer

There is a local shop by me that uses it. They say it works great. My leaks were way to obvious to need it.
Kris Sorensen

Steve, well at least there is now a hope. Refit the stud and torque it down. At the same time check the torque on all the other studs but don't tell your machine shop that you did it !! I think all will be fine here. Now rocker cover gasket leakage is a common issue so fit a new one but soak it in a pail of water overnight before you install and don't use any sealant. The other very important point is to fit new rubber sealing rings under the rocker cover retaining bolt caps because these go hard in time. A well sealing rocker cover relies on these to provide spring and nip on the cork gasket.

Now with a clean new engine as you say it is very difficult to spot oil leaks...I've been there, and a real difficult one to spot is the side covers. There could well be a leak there and this runs down on to the sump flange, round on to the backplate and down to the point where it drops off the bottom of the bellhousing looking like it came from inside. Please check this area very carefully before you you go any further. Make sure also that the O ring seals round the centre bolts are in place and sealing.

I'm still confused a bit by the smoke but if you can trace and eliminate the leaks first you can then deal with the smoke if its still there.

I run a couple of Bs and whilst access to this area is a bit difficult it really is far worse on the A and will be hard to spot the leaks. lets keep our fingers crossed.
Iain MacKintosh

Iain are you for real??
The stud fixing for the rocker cover has nothing to do with holding down the cylinder head so Iain's comments about torquing down and not telling anyone seem to be very strange? It only screws into the head and anchors down the rocker pedestal.
Steve
If the rocker cover has been leaking then oil can fall down to the area of the relief valve and also onto the exhaust when you are traveling. This creates a lot of smoke.

It would not be made worse because of excessive oil pressure, this is not the cause of your problem. I have often run engines at 80PSI without any problems.

When was venting an MGA block made illegal Iain???
Bob (robert) I used to own a Morris Oxford

Bob

I'm glad you said all that before I did. I wrote out a similar reply this morning about the rocker box studs, then had second thoughts that I may be totally wrong and cancelled out!

I have had fumes (possibly smoke) from oil dripping on the exhaust pipe. My instance resulted from overfilling the carb dashpots!

I don't think the MGA venting is illegal. Like all our regulations, very few are retrospective. However, I have converted my system to intake venting. Have a look at the picture from my website: http://freespace.virgin.net/stephen.gyles/hot_press.htm

I installed this on my 1500 in 1997 and ran it to about 2001 and it is has been on my 1800 since then.

Regards

Steve
Steve Gyles

Agreed Bob, but without questioning Steve further the easiest thing to do was to ask him to replace any broken stud whether it be head or cover fixing. If indeed he did replace a head stud and torque the rest then the last thing he should do is tell the engine builder as this could immediately invalidate any responsibility he may feel towards it.

We've already said that any cover on the engine including the side ones must be checked carefully as the oil will find its way down. On the B it is more likely to fall to the lowest part of the bell housing as Steve has found out, some could still of course land on the exhaust. We will wait and see as this will be obvious even after the car stops and by staining on the pipe.

Open ventilation systems were outlawed many years ago which is why cars went to a closed system where the engine burns the fumes and pushes them out through the exhaust. I did not say that they were illegal but outlawed in that after a certain date cars had to be manufactured with a closed system. There is no question of older systems being illegal and having to be modified.

And finally, yes I am for very real, some of us on this board pass on a lot of valuable information voluntarily on a regular basis and sometimes we do just get it right. This is based on lifetime experience and we should never sniff at it.
Iain MacKintosh

Nicely restrained followup, Iain. I don't think your critics understand you.
Tom

Thanks Tom, you may well be right.
Iain MacKintosh

Tom said it well. This isn't Flame Wars. Those of us helping and being helped need respectful correspondance. Remember we are here for the common love of our MGAs.
R J Brown

Couldn't agree more but we all know the expression "a little knowledge is dangerous"

The information about the rocker box stud was completely wrong as was the venting on the tappet chest cover and the suggestion that this practice had been outlawed.

is it useful to give mis information?

Perhaps I was harsh with my response but it was the correct reponse.

I suppose Ian's MGA may have been modified and perhaps the venting is not to atmosphere as in fact is my own, but contributors should be aware of the modifications done to their own cars to avoid confusing threads.
Bob (robert) I used to own a Morris Oxford

Guys, I spoke to my engine builder today and his opinion is that the presence of smoke is oil burning off the clutch plate which is indicative of a leak from the front gearbox oil seal (a leak from the rear main would be more likely to simply drain from the hole in the bellhousing).

He was also sceptical as to whether a rocker cover leak would be the culprit.

On the issue of oil pressure, he felt that my pressure is too high and suggested I change the relief spring.

So, on the balance of everything this is what I intend to do:

1. re-seat the rocker cover
2. thoroughly clean the block / gearbox
3. change engine oil / filter, gear oil
4. re-check vent pipes for blockages
5. replace oil pressure relief spring (reduce the
pressure)
6. degrease clutch
7. test car for leaks - both in garage and post a
brief road test
7. hope like hell that its not the front gearbox oil
seal !!!

Regards

Steven
Steven

Hi Steven. You state that you will be degreasing the clutch. To do this, you must pull the engine. If the engine is coming out, then the front transmission oil seal is actually pretty easy to change. Once the engine is out, you have access to the transmission front cover, which holds the front oil seal. The front tranny cover unbolts easily from the gearbox after removing the clutch fork and release bearing. The clutch slave cylnder would likely need to be unbolted from the gearbox, and the clutch pushrod removed also. Even so, replacement of the front transmission seal is not all that difficult a job, once the engine is out. Cheers! GLenn
Glenn

Sorry for the confusion. I simply meant following a technique similar to what is posted on Barney's site to degrease the clutch in situ (see http://www.mgaguru.com/mgtech/clutch/ct_105.htm) - the purpose being to try to get things as clean as possible so that I can re-assess the nature of any leaks. I'm still getting a few drops from the bellhousing which suggests to me that there is still a bit of leaked oil built up inside.

Glenn, are you suggesting that one does not need to remove the gearbox to change the front seal? Call me a pesimist but I'm now leaning towards a gearbox leak !

Steven
Steven

Steven, I've read Barney's article which is very interesting. What degree of success you will get will only be found out by trying it. However to try to determine conclusively where the oil is coming from without removing the engine have you thought of changing the gearbox oil either to Duckhame or using an ATF. Duckhams for example is green and has a distinctive smell and if this dripped out of the bellhousing you would then be left in no doubt. The bad news is that you will have to remove the engine to replace the gearbox front seal.
Iain MacKintosh

Hi Steven. The engine has to be pulled to change the gearbox front oil seal. If you leave the transmission in the car, it should be possible to crawl into the engine bay, and remove the clutch fork, release bearing, clutch slave cylinder, and transmission front cover. Once the front cover is out, it is a relatively simple job to change the front transmission seal. Cheers! GLenn
Glenn

Steve

I am still trying to get my head round your problem and am struggling with the assumptions made that the gearbox has suffered a 'major' instantaneous front oil seal failure. When I removed my gearbox a few years back I found the oil seal had almost disintegrated but it only became apparent when I rested the geabox almost vertically on its bell housing end. Previous to that I had the odd few drops of oil out of the 'giggle pin' hole but nothing like enough to burn on the clutch etc. Interestingly, early 1500 gearboxes did not, I believe, have a front seal, but instead a scroll, similar to that on the back of the engine.

I also think that at the end of your reported 10 mile run the gearbox oil would also still be relatively cold and thick. Any that escaped forward would probably seep slowly down the bell housing wall rather than be thrown forward onto the clutch.

For my 10 pennyworth I think your problem lies else where.

Hope all turns out well. It only takes a couple of hours to get the engine out. The likes of Dominic and Glen can probably do it in under an hour. I have had my engine out about 10 times in the last 8 years. Good excuse to spring clean the engine compartment and top up the steering rack!

Steve
Steve Gyles

Steve, A few points:-

1. If there is still doubt about whether the smoke,when driving, is coming from an oil contaminated clutch plate why not, in the comfort of your own garage try slipping the clutch. Start the engine and with the handbrake fully on and revs fairly high let out the clutch gently but not fully. It should take no more than 10 to 20 seconds for the lining to heat up and smoke if there's oil on it.

2. If the gearbox has been filled to between the high and low marks on the dipstick then the oil level will be below the front oil seal and shouldn't leak out if the car is level,stationary and with the engine off. However, if the box is overfilled to the top of the box inlet then the level will be above the bottom of the seal and should seep out at a rate depending on how bad the fit is to the shaft. So why not try adding another 2 or 3 pints of oil to the box and see if there is a constant drip over subsequent days: assuming you are not using the car now. I guess it's quite hot weather where you are so the oil should not be too viscous.

I have recently overhauled my 1600 box and it included replacing both the front and rear seals. When replacing the front seal I was a bit concerned at how easily the new seal slipped over the shaft. So I am going to try and overfill or tilt the box and see if oil leaks out before I put back in the car.

3. The smoke could perhaps be coming from oil on the clutch release bearing which becomes hot when the clutch pedal is down but this again could be checked in the garage with the engine on, box in neutral and clutch pedal depressed. This might seem irrelevant but it could have a bearing on whether you need to replace the clutch plate.

4. As several people have said replacing the front seal is easy with the box out but is taking the engine out absolutely essential I wonder? I've not tried but could not the seats/ floorboards/tunnel be removed and the box be withdrawn rearwards after decoupling the propshaft and gearbox mount? Maybe this is more time consuming but the thought of hoisting the engine over a nicely painted front shroud would fill me with dread!

Good luck Mike
m.j. moore

Much easier to pull engine than interior espesially if interior has been in a long time. Floor board machine screws tend to be quite rusty and need drilled out often.
R J Brown

RJ

I was just about to say the same! What with glued carpet sections and all.....
Steve Gyles

Steven, I agree with Steve Gyles here and have done all along. I don't think it's the gearbox front seal and neither do I think that the smoke is from oil on the clutch. If you look at your posting on the B board you have one reply from Chris Betson at Octarine services who is an expert in B series motors and also suggests you put another oil in the gearbox so that you can quickly identify where the oil is coming from. I cannot believe that the gearbox is suddenly leaking significant quantities of oil as this would be a gradual process. You must determine the source this way first of all and without any doubt and then it will be much more straightforward to decide on the course of action. If the oil proves to be engine oil then the builder will hopefully be more disposed to giving you assistance to rectify the problem. I'm not suggesting anything here but if I were the engine builder then it would be in my interests to prove that the gearbox was the culprit.

Hope this makes sense.
Iain MacKintosh

This thread was discussed between 30/12/2005 and 10/01/2006

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