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MG Midget and Sprite Technical - Engine oil leaks

I've decided that my winter task this year is to try and reduce the amount of oil that leaks from my midget. I got the car up onto ramps so I could see where the leaks were coming from, but as oil literally covered everywhere I've decided to totally clean the underside and then run the engine whilst up on ramps again, which may give me a better idea of where the leaks are coming from. I'm assuming from what I've seen already that it is leaking from the timing cover, and presumably the sump seals. I've checked my stock of gaskets, and note that as well as cork ends for the sump, I've also got a couple of rubber ones, one being about 5mm shorter on each end to the other. The larger one is marked as rear seal, so I'm assuming that the smaller one is for the front, or are they supposed to be the same size?
I also found a 58mm dia x 9mm rubber seal (with wire support on one side) which I'm assuming is to for the timing cover?
Then I found a rubber seal 70mm dia ribbed both sides. Any ideas what that might be for? (see attached)



Geoff Mears

Not sure of the engine size from your post. I don't know about 1500's but if its an A series then the larger sump seal goes at the back. Not sure what the larger seal is for.
Bob Beaumont

If the leak is from the timing cover end the most likely culprit is the crank pulley. I had to fit a Speedi Sleeve to cure mine. But as Bob says we don't know which engine you have so can't advise much further.

Les
L B Rose

Sorry. I should have said it is a 1970 car with 1275cc engine. Thanks for your replies
Geoff Mears

Geoff, the other critical thing is how you have the crankcase breather sytstem and matching oil filler cap set up.
GuyW

That is interesting Guy. My car is not happy revving over 3500rpm. It’s as though it has reached its capacity. I fitted an overflow from the timing cover cylinder to a plastic bottle with breather holes to try and help. The oil filler cap is a thick black plastic one. I’m sure you would want something more technical than that!! I expect if it won’t rev the pressure would put more strain onto gaskets etc.
Geoff Mears

The limit on revving is most unlikely to be anything at all to do with the breather system.

There have been volumes of BBS discussions about various breather systems on these cars! But briefly, the 1970's cars used a version of the breather system which extracted fumes by drawing air through the crankcase using the induction system at the carbs. At the same time air was alowed in but only at a restricted rate, via a special ventilated oil filler cap. This restricted flow in means that the pressure in the crankcase is reduced below the outside air pressure and this difference goes some way to prevent or reduce oil leakage, especially from the rear of the crankshaft.

To achieve this correctly it is important that the breather system is as originally designed, without addition of extra breather pipes or unrestricted openings which will allow air to be drawn in too fast, will upset this vacuum based system and lead to excessive oil leakage.

This is not to say that your oil leakage may well be to do with worn oil seals as well, especially that seal on the front chaincase cover.
GuyW

Thanks Guy. I assume the rubber end sump seals are fitted “dry”?
Geoff Mears

Geoff, follow the manual carefully. The semi-circular seals may need trimming back to allow the tag on the end of the flat sump gasket to fit over the end.
Also this is one place where a bead of gasket sealant in the groove before final fit will aid a good seal.
David Smith

Noted David. Thanks.
Geoff Mears

Hi Geoff, I wasn't really commenting on the seals at all, just reminding you of the importance of getting the breather system right when trying to minimise oil leaks.

You have the advice on fitting the seals. Only things not yet mentioned are:
1 Check the sump flange for flatness around each of the bolt holes, using a straight edge. It is very common for the metal to have been pulled up around each bolt hole and it is well worth gently hammering any back down flat again before refitting the sump. The ball end of a ball pein hammer works well for this.
2. When you fit the new chain case oil seal fit the chain case cover on with it's gasket but only just finger tighten the bolts. Then rotate the engine a couple of times by hand to centralise the oil seal before then tightening up the cover bolts. If you don't do this it will likely leak, or the deal will wear very quickly and then leak.
GuyW

Geoff,
sometimes the crank seals are (plasticy) rubber and cork, sometimes sets with two curved or straight lengths of cork (I could post you a couple of these). TAM1089 the plasticy rubber to the rear and LZB10005 cork to front.

http://www.leacyclassics.com/tam1089.html

http://www.leacyclassics.com/lzb10005.html

The vented and mesh filled oil filler cap you should normally have is the one below.



Nigel Atkins

Thanks Guy. Will act accordingly.
Nigel - I already have both types of sump seals, but thanks for the offer. I seem to have the same oil filler cap. Will make sure it has not becom blocked. Thanks to you both.
Geoff Mears

Nigel refers to the oil filler cap as vented, which it is in a way, but it is principally vented for incoming air being sucked in through the system rather than as a vent for breathing fumes to the outside. Though it very likely does both at different times if crankcase pressure gets too high from piston blow-by.

For the extraction system to work as intended, to minimise oil leakage, it is important that this filler cap is the ONLY vent. Everything has to be pulled one way and out through the chain case breather for it to create the partial vacuum in the crankcase. You can however add a sealed oil catch tank between the chain case and the extraction point at the carbs.
GuyW

Will change my vented catch tank for a sealed one Guy. Thanks.
Geoff Mears

Guy,
you have a good point, I've never been happy with my description but it comes easily to mind so I've continued with it, I'm sure (well, trufully, I'm not) originally I had a better description.

I changed mesh filter to mesh filler, but that clashes with oil filler cap, for venting I thought breather holes (dismissed air holes). I can't do crosswords or thesaurus as I can't spell but there must be a better description than - oil filler cap with breather holes and mesh filler.

Another thing I've wondered is, is it important to have the dipstick sealed to the dipstick tube?

Nigel Atkins

In a word Nigel, yes. It should be reasonably airtight.
Also the dipstick tube seal itself needs to be a good push fit.
Greybeard

Grey,
that's how I remember it but the seal you get now just had the dipstick sitting on the top of the tube, well the seal really. I said only today how I previously used a closed grommet but it went hard and I no longer have the size.
Nigel Atkins

Last time I had to replace one in a hurry I recycled a cork from a rum bottle. I forget now what engine it was.
Greybeard

Do you remember which rum it was?
GuyW

Hahaha! Lol, Guy!
Now I think about it, it was the only time I can remember replacing one. Spent ages whittling it with a razor blade to fit but it worked fine.
Greybeard

Geoff

Nothing to do with your oil leaks but you mention your engine is unhappy at high revs, I assume you’re referring to a feeling that it doesn’t want to rev any higher?

If this is the case what’s your distributor like? I’ve had had similar issues in the past and tracked it down to worn/stretched advance springs. This causes it to run out of advance at higher revs and makes it feel dead, once I cured this it would rev to the red line in 1st, 2nd and 3rd.

Bob
R.A Davis

There's definitely something wrong if an A-series doesn't want to rev. It should wind up easily to the red line. It could well be ignition timing as Bob mentioned, or carbs way out or even valve clearances all over the place.
Mike Howlett

Bob and Mike, I've got electronic ignition. The engine runs fine up to about 3500rpm, but then doesn't want to do any more. ( I can get more revs in 4th gear, but at 3500rpm I'm already doing 70mph - 3.5 diff, and I have taken it to about 4000rpm, but that's about 80mph and that is when my knuckles start to turn white!) I'm using a HIF44 carb and MG Metro big valve head. A few years back I took the car to Peter Burgess and he suggested I try fitting a catch tank which I did. At the time I did not consider it a problem and it wasn't the reason I took the car to Peter Burgess - I wanted the usual rolling road check. The engine was built by Geoff Mabbs (who used to race Minis at Autosprint with a mild cam 266 style' lightened, balanced etc..
Obviously it would be good to get to the bottom of it, and I might take it back up to Peter to see if he can sort it out for me.
Geoff Mears

OK Geoff, but what about in the intermediate gears? Can you run it up to the red line in second gear for example?
Mike Howlett

I'm following Mike's thinking here. With a five speed box (type 9?) and 3.5:1 final drive it may simply be overgeared.
Good call taking it back to Peter. A rolling road will give the game away and Peter might be able to find a few extra ponies.
Greybeard

3.5 diff in 4th direct with standard tyres of 145/80-13 would give 64mph at 3,500rpm and 73mph at 4,000rpm - this of course doesn't allow for errors in speedo and tach readings.

Depending on the power available it should pull at 4,000 revs, the acceleration wouldn't pull your face off but it should climb unless going uphill and/or against the wind.

Nigel Atkins

Mike - It doesn’t rev in any gears. 4000 is about the max
Greybeard - I have a standard 4 speed box. I purchased the 3.5 diff to replace the standard one to give me a more acceptable rev level at cruising speeds. The uprated engine compensates for the otherwise reduced power level.
Nigel - tyres are 155 x 13
Bob - reference the advance springs. Did you just get a new distributor or replace them? I’m wondering if my distributor is very old as I just replaced the contacts and condenser when I changed over to electronic.
Geoff Mears

First thing I would check is that the carb butterflies are fully opening when the throttle pedal is right down. Get an Attractive Assistant* to press the accelerator pedal right down (engine off) and check that the butterfly spindles are turning through almost 90 degrees so that the circular throttle discs are both fully open.

* other versions of Assistant may be available.

Failing that, I would think the best thing is to go back to Peter Burgess and he will get it set up right. With that specification engine it's a shame not to have it running as it should. Even if you don't need it's full performance day to day, potentially if it's something like incorrect timing you could seriously damage the engine.
GuyW

Guy is dead right. Take it to Peter. I'm sure he will sort it out. He's not so far away from you.
Mike Howlett

Geoff,
155/70-13 or 155/80-13 are sized either side of 145/80-13 but not that much that you'd notice on the needle of the rev counter (allowing for small inaccuracy anyway).

For the running, as many others have found, covering and re-checking the basics is essential, check and set tappets, points/plugs, timing and mixture in that order. Recently read where a B owner had a professional do some work and set his tappets at metric instead of imperial which he discovered because someone banged on about doing the basic checks before moving on to more sexy sorting.

A friend finally changed his spark plugs, even though they hadn't done the 30k-miles the Lotus WSM said they could do, cost £12, and for the first time in years lost the bad misfire - but a small misfire remained which another mate and I speculate could be engine damage. I'm not suggesting it's spark plugs for you just to check everything and get this issue sorted echoing what Guy has put about this potentially leading to serious damage.

Nigel Atkins

“reference the advance springs. Did you just get a new distributor or replace them?”

I come from a background of quantifying and measuring things so I built a test jig that allowed me to check it on the bench. This allowed me to plot the advance curve as a starting point. I was then able to adjust the springs and re-run the test, it took several goes to get a good match. It also allowed me to measure the dwell angle at various RPM as I was looking at variable dwell systems at the time.

If you look at the springs you’ll probably find they’re both slightly different with one of them having some slack in it, this is correct and it allows for an initial quick increase in advance as the revs rise, the increase then slows as the second (slack) springs takes effect.

If you’re thinking of buying a generic one size fits all replacement distributor be cautious, it may be correct for your car but there’s a greater chance it won’t.
R.A Davis

Thanks one and all for your very helpful comments. I'm going to get in touch with Peter when I have reduced my leaking situation. Having just come back in from the garage and put the car up on ramps, cleaned everything and started it up, in a short time I had several drips appear quite quickly. I'm pleased to say I have found the source of that particular leak. The culprit is the dipstick tube. It has completely lost its grip ability and just bounces up and down with the dipstick in line with the engine vibration. Will order a new tube ! Then I'll assess whether the other leaks are worthwhile bothering with at this moment. If not too bad, I'll go and see Peter..
Bob, ref the distributor, I jut bought an Ignitor kit from Min-its, so didn't touch springs. If carb is at fault, I'm sure Peter will find it, although I'm sure it was already fitted when I last went.
Geoff Mears

Geoff

Peter will find the issue whatever it is, let us know how you get on.

Bob
R.A Davis

Is it the tube not gripping in the sump or the dipstick not gripping in the tube?

If the problem is the dipstick not gripping in the dipstick tube, I'd be very wary of trying to remove the plastic tube from the block, as the plastic can get very brittle - hence it could easily break in an inconvenient way. If you want to stop the dipstick jumping up and down, you can easily fashion a hook with a spring to keep it pulled down. I did it on mine years ago (sorry, no photos), and I have a feeling the racers used to do that.
Jonathan Severn

Jonathon, the tube is loose in the sump. It just lifts out with no resistance. The grippers on it have worn out. I bet it is original so 50 years old .
Geoff Mears

Geoff,

The lack of performance and revving reminds me of a Caterham I had on loan, it was totally gutless and was eventually traced to the advance weights having been tack welded in place, once the tacks were removed it performed much better. Have you check to make sure the advance mechanism is working as they do sometimes seize.
David Billington

Geoff,
Wind some PTFE tape around the outside of the tube and push it back firmly into place. It will stay there.
If you don't have PTFE tape, then use some kitchen foil, but take care not to let any bits tear off it that might then get into the sump as you push it back into place.

If the dipstick itself is lose in the tube, then splay the two lower parts apart slightly more by pushing a flat bladed screwdriver between them.
GuyW

Have already ordered a new tube, but good idea ref the dipstick.
Geoff Mears

Bit worried about your oil catch tank.

I wouldn't expect oil to be thrown out of the timing cover breather. Not had that on three engines despite two of them suffering the blue smoke of death from the induction. Unless the engine is knackered.

The purpose of the tank in my opinion is to provide a settlement tank for oil to drop out the flow when induction breathing is added ie a pcv or carb connection. It must be sealed otherwise you will weaken your mixture but if you connect the carb and the timing cover towards the top of the tank, any liquid oil should fall out the flow as the velocity slows in the larger volume provided by the tank. Just remember to empty it.

My 1275 Frog passes oil like that while the oil is cold and was evident with some blue smoke at the first roundabout or traffic light stop (about a mile in each direction). The tank now separates out the small amount of oil and no smoke is evident.
Graeme Williams

Ha ha has ha--Graeme
Don't you start the oil sucking issue up again--If I remember correctly it's just a nature of the beast thing with cold oil and double row timing chains not giving enough room in the timing cover for the slow returning oil----------??
William Revit

Graeme
It isn’t throwing oil out of the timing cover breather. It looks like the timing cover gasket may be past its best and leaking a bit.
My catch tank had breather holes in it, which I have been advised is incorrect. I have changed it for a sealed one. The previous one just had a bare covering of oil splashes in it - not even enough to empty out. The HIF44 is not connected, it is blocked off.
Geoff Mears

"If you want to stop the dipstick jumping up and down, you can easily fashion a hook with a spring to keep it pulled down. I did it on mine years ago (sorry, no photos), and I have a feeling the racers used to do that."

Yes, that's what I did.

I made a small bracket and attached it to the lower mounting bolt for the dynamo/alternator rear bracket. Fitted a carb return spring.

Not too clear from the photo, as the king lead is partially obscuring it.


Dave O'Neill 2

Good idea Dave. If it proves necessary with the new tube I’ll fit a spring.
Geoff Mears

Geoff reading this it sounds like the car wasn't revving properly before (or after) you took it to the RR. Also that the HIF has been sealed off, so your current system is effectively plumbed open to atmosphere and feeding into a catch tank with breather holes. The reason some engines are kept open to atmosphere is to reduce the ingestion of oil must and because the standard positive crankcase system can no longer cope with the increased crankcase pressure. Either because the engine has been modified, or it's clapped - or both. Before you take it to the RR again I would do a compression and leakdown test. You may find sealing the catch tank may actually increase the other leaks.
f pollock

Regarding the lack of go over 4000, Cam timing and lack of advance are a couple of key causes which are easy to check.
Can timing could be wrong due to offset key (often used with MOD Cam) the wrong way round. Check by seeing where the crank is when valves on overlap are both the same amount open. Should be withing 4-ish deg of TDC. Key wrong way round would put it way out.
Advance could be seized or worn mechanism, right at idle but not going much further. Measure the actual advance at 4000. Should be 25-30 ish depend on on CR, fuel, etc.
Paul Walbran

Regarding the lack of go over 4000, Cam timing and lack of advance are a couple of key causes which are easy to check.
Cam timing could be wrong due to offset key (often used with modified cam) the wrong way round. Check by seeing where the crank is when valves on overlap are both the same amount open. Should be withing 4-ish deg of TDC. Key wrong way round would put it way out.
Advance could be seized or worn mechanism, right at idle but not going much further. Measure the actual advance at 4000. Should be 25-30 ish depend on on CR, fuel, etc. Anything under 20 would probably be a problem.
Paul Walbran

Bob - update as requested.
Changed my catch tank back to the vented one, as the sealed one started collecting oil. Changed filler cap to new vented one. New dipstick holder fitted. No leaks there now. Whilst watching it to check leaks I noticed seepage from oil pressure gauge fitting to block. Revved engine and soon had a pool of oil on the floor. Have now fitted new union / pipe and now no leaks from that. Cleaned underside of engine and ran engine. Now back to my normal small seepage from timing chain cover and rear crankshaft seal. Will leave these until engine needs to come out for something else.
Geoff Mears

Just caught up with this one. Geoff you need to get the air out of the catch tank! Either leave the exhaust side open (which is pointless even having the tank on a road car) or connect it to the carb or pcv.
Graeme Williams

Having read all this, I wonder again if my setup is optimal. On my 998 I have the 1098 rocker cover with breathing filler cap, 1098 front side cover with oil separator, additional oil separator connected to the redundant fuel pump point on the block, both Y-connected to the single carb upstream of the butterfly. No PCV. Over the years I have tried every possible permutation and the engine always leaks oil. I have sometimes wondered whether having 2 breathers connected together makes any difference - surely they are limited by the single pipe going into the carb? I suppose one thing I haven't tried is to stop air entering the rocker cover, but I imagine the cap has breather for a good reason.

Les
L B Rose

Les - If you need to check if the crankcase is indeed under negative pressure (as your set up indicates) just run the engine with the vented cap off and replaced by a beer mat. The beer mat should be sucked down and stay there. If it's blown off you clearly have pressurisation. In this instance you might be better off running 3 1/2" breathers to an open catch tank so the crankcase runs at atmospheric.
f pollock

I tried the beer mat test. No suction. I remember that the manual says to take the filler cap off at idle and the engine speed should rise, which is much the same sort of test. That's with the PCV valve fitted, which I don't have at present. Compressions are all good BTW. I will get the car in the garage once I have tidied away all the cylinder heads I'm working on, and investigate further.

Les
L B Rose

This thread was discussed between 26/10/2019 and 02/12/2019

MG Midget and Sprite Technical index

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