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MG TD TF 1500 - Problem - help required.

I have a rebuilt XPAG engine in my TF that has only just been driven around the block.

The problem I have is that after a short time it starts to emit volumes of grey/black smoke.

On start up it is clean as a whistle. (??)

I thought I solved it previously by replacing the head gasket.

It starts OK and if I let it idle when it warms up this happens.

The head was pressure tested but I'm thinking this could be faulty.

However, the only oil going up to the head is via the pipe at the rear of the head which in turn goes to the rocker shaft.

Number 1 piston is down on compression but the rings are OK as I have previously taken this piston out to check, no broken rings, bore looks OK. This is why I suspect the head but where does the oil come from?

No oil in water, no water in oil!!

The valve guides checked OK and it has new seals.

Any solutions, guesses, clues, hints etc etc gratefully

Don TF 4887
Donald J Walker

Don could it possibly be oil in the muffler? A long shot I know but his happened to me with a dual cab that I once bought as a wreck. It had been knocked onto its side with the engine still running, which then seized. After the rebuild I had the same symptoms. The smoke only appeared once the exhaust system heated. After the prang oil had found its way down the exhaust & settled in the muffler. Cheers
Peter TD 5801
P Hehir

Thanks Peter, it has a new stainless muffler system.
This one has me beat.

Don TF 4887

Donald J Walker

Check the plugs when the engine is warm. I had a similar issue with no. 3 cylinder. There were scuff marks on the rings and piston although the bores were perfect.

Declan Burns

Thanks Declan, I am hoping for a solution before I go that far and remove pistons.

Don Tf 4887
Donald J Walker

Too much oil in the sump?
Dave H
Dave Hill

The sump level is OK Dave.

I'm beginning to think that maybe the oil draining back down the pushrod tubes there might be a crack in the head from this drain hole into the combustion chamber, hence the reason why it only does it when it's hot.

Don TF 4887
Donald J Walker

Don, maybe the bores have been glazed during the running-in process.
Been there, done that.

Rob TD11148
Rob Woodfull

That's a thought Rob, maybe go out and give it a belting along an empty road. In fact it's hardly had a 'run in' drive yet.

Regards, Don TF 4887
Donald J Walker

Black smoke is normally a sign of over rich mixture
If it starts up cold ok and plays up hot this could be the problem
--Choke not going off properly--?

Couple of things worry me though--
Why is No1 down on compression if it's a rebuilt engine,- and also are the valve stem seals fitted correctly just under the keepers in the caps and not further down the stems

How far below the other compressions is No.1

William Revit

Willy, the smoke is sort of dark grey-ish.

I will check tomorrow to see if the chokes are off after starting it up.

No 1 145lb, 2,3,4 175lb.

I have previously taken no 1 out and checked it OK.

The part that has me is it runs beautifully until it gets warm/hot, then increases until it becomes embarrassing.

Maybe it needs de-glazing as Rob suggests.

Rob, could you please expand upon your episode?

Don TF 4887
Donald J Walker

Does the smoke smell like oil burning or stinky rich -fuel

How many klm/miles since the engine rebuild
William Revit

Willy, the smoke has a rather acrid smell and until Sunday it hadn't been driven.

I had started it on a few occasions during the rebuild of the car so maybe the rings/bores have never 'bedded' in properly.

Donald J Walker

My TD has an "acrid smell" during hard acceleration go UP hills only! So much so that friends riding behind me pulled me over to report it. It is caused by the normal "normal" oil drip running down the hot exhaust pipe when going uphill. Running level or downhill the smell stops instantly. You can see the burned off oil stain on the exhaust if you crawl under the car.
Good luck.
efh Haskell

While the lower compression is suspicious, I would go for a long hard drive to see if it is oil in the exhaust, or some kind of coating or stuff in the new muffler. That would seat the rings if they were not. I would think if it was rings you would be blowing light blue oil smoke, not dark. If you have the original oil bath air cleaner, try removing it when the smoking starts- the tops can cave in, causing a rich condition which would be more dark smoke. George
George Butz

I think it's a cracked head or block. Color of smoke and that it only happens when the engine gets hot are my reasoning. Are any of the spark plugs unusually clean?

Tim Burchfield

It could be that the piston rings are installed upside down on #1.
Many moons ago I rebuilt an early volvo and the rings all had a dot on the side that I instaaled on top. Apparently that model ring was supposed to be installed with the dot down. I killed all mosquitos in the county till I reversed the rings. The TF does not have oil bath air filter but two seperate dry ones.

Thank you for your replies and hints.

So far my thinking is with the compression I'm getting on 2,3 and 4 the rings have bedded in.

I had this problem earlier on and removed the head and number 1 piston.

The head gasket was replaced and all seemed OK, compressions fairly even, although I hadn't taken it out on the road yet.

If I have to remove the head and pistons to check I don't mind but wouldn't want to do it unnecessarily.

What I'm wanting is to have a fair idea of what's wrong and know why, then fix it.

I am preparing a spare head to change over and hope that's the problem.

Regards, Don TF 4887
Donald J Walker

To start with retorque the head and see if there is a compression change.
W A Chasser

145psi isn't bad, 175 is better, but 145 isn't "bad."
Try redoing compression test, you may eliminate that #1 cylinder from the mystery.

Pull the plugs. If you're burning that much oil, one or more plugs would be blackened. Compare 1 & 2 vs 3 & 4. This might point to one carb dumping gas.

After running, pop the tops off the float bowls to compare that the fuel elevations are even, and the tops of both floats are well above fuel.

That oil line to the back of the head, the banjo bolt for the head has a much smaller hole than the block banjo bolt, right? Two large holed banjo bolts could flood oil onto the head.


Great ideas here but sounds like a problem I was faced with that drove me crazy. Check choke first but also check; float levels, jets centred and try adjusting the carbs a little leaner. Worked for me and all is now good.
Brian Smith (1950 TD3376)

I have just come back from taking the car around the block here a few times, could be getting better but on the over run then put the foot down, smoke, but it might be getting less.

Tomorrow I will go over to Hindmarsh Island and give it a squirt and try and dodge the errant kangaroos, the island has long straight, empty roads (except for the aforesaid fauna).

The float levels have been checked and the mixture adjusted lean.

One reply mentioned about being very over rich which does make sense.

Not much smoke when driven hard though........mmmmm?????

Regards, Don TF 4887
Donald J Walker

I just took the TF for a 10 mile run on fairly flat roads. It pulls really well and my observer behind said there was no smoke when driven hardish. However on the over run at slow speeds it still smokes. Sounds like valve guide seals but they are/were new. This doesn't explain why it smokes on idle when warm/hot. The compression is 145 170 170 170. Can't explain no. 1.
There does seem to be a fair bit of blow bye, not smokey though, out of the rocker cover at idle.

Don TF 4887

Donald J Walker

I think, at this stage, you need to do a pair of compression tests-
Firstly redo a dry test to see if your 145-170-170-170 has changed at all
Then a wet test-
With the sparkplugs out give each cylinder two good squirts of oil with your oil can
Try and squirt accross as far as possible rather than straight down so that the oil gets on the bore-Give it a slow turn over for one or two revolutions to get the rings nice and oily then redo your compression test
They should all read just a little higher because of the oil in there--but if there is an issue with rings on No1 the compression on that cylinder should respond to the better seal caused by the oil and bounce up to nearly equal the others If it doesn't respond then you have a leaking valve--
Seperate to that, are you sure the valve stem seals are fitted correctly--If you take the rocker cover off and squirt some oil onto the keepers it should stay there, if it drains off down through the joints in the keepers there is a problem with your seals

Hindmarsh Island, I had an interesting visit there years ago---Do they still run that barge to get over there--??
William Revit

Problem solved. After the oil burning episode I have fixed it. Previously I replaced the head with a reconditioned unit, still the same. I decided to pull the engine down and replace the rings after honing the bore. It now runs like a dream. All the problem down to what I believe was a faulty set of rings. Yippeee.
Donald J Walker

Congrats Don, just in time for Winter-ha ha ha
The old rings, could you see anything obvious
I put a set of chrome rings in a Mini once and they were smokey right from the start but replaced them with the exact same and it was good--couldn't see anything wrong with them at all--but
And by the way, thanks for reporting back with the results of your issue, It's been at the back of my mind wondering how you ended up with it all
William Revit

Hi Don,

Are you certain you fitted the valve stem seals correctly? Often they are not. To check them lift the rocker cover after a short run. You should see pools of oil in the recesses in the circular plates at the top of the valve springs. They ones that hold the valve collets. If the oil disappears after a short while your seals are faulty. This test only applies to the original type seals not the improved Mini version ones. May not be your problem but the check only takes five minutes.

Good luck

Jan T
J Targosz

Check also the end gap for the piston rings. New rings materials often require different gaps that originals.

Check how the rings are bedded in close to the gap.


LC Laurent31

I always ceramic ( thermal coat) the piston crowns & dry film coat the skirts & 140 per set. Ceramic coat prevents a burned piston if run lean, and dry film coat of skirts prevents piston scuffing. Also when re ringing use a ball type hone.
I like Hastings piston rings and they are still in stock for the XPAG in Hastings Michigan.
Abingdon Performance LTD.
Len Fanelli

This thread was discussed between 21/11/2017 and 08/07/2018

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