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MG TD TF 1500 - Lack of Power

I consider myself a reasonably competent MG mechanic, but this one has got me going.

My '50 TD suffers from a lack of power - not a huge lack, but more than many other TDs I've driven. It runs well enough. Starts quickly, runs smoothly, good compression (135 - 140 on all cylinders). But it lacks guts - especially up hills. Even moderate grades cause a lot of downshifting. It's been that way for as long as I can remember. I've owned it for 18 years.

Here's what I know:
compression 135 - 140
oil pressure 35 - 40 cold, 25 hot
timing 5 degrees BTDC with advance up to about 15 degrees after
valve clearances .019" hot
valve lift .254" - .280" depending on cylinder

tends to run rich when first starting, but leans out as it warms
plugs tend to oil foul - plugs are usually black and somewhat oily
exhaust pressure (air volume at tail pipe) seems anemic

My theory is that the cam is worn and may not be an ideal grind. I don't know the specs. The valve guides (being silicon bronze) may be worn to the point that I'm sucking oil into the cylinders

Anyone have any other ideas or other things to look at?



Lew Palmer

I'm no expert on T series, but from what you describe other than the cam being retarded I don't think you have an engine problem. You said you had owned the car for 18 years and it has always been this way. Is it possible that at some time in it's past it has had a higher ratio rear axle gearset installed. This is a pretty common change and would definitely give the symptoms you describe as to having to down shift on hills and have slow acceleration. Hope you find some solution. Bill Young, KCMGCC
Bill Young

I should have mentioned that I replaced the 5.125 diff last winter with a 4.55. That gave me more top end, but compared with some of the other cars we converted to the same 4.55 diff, it still lacks power. Cruises fine, but lacks that edge in acceleration.
Lew Palmer

Just a suggestion...Sometimes we overlook the obvious! I had similar problems with my TD and after making myself crazy, I found that my origional oil filled coil was weak. Good Luck!
Steve Tobias

If you havn't already,make sure the throttle butterflies are fully opening. If not sure, remove the air cleaner, hold the carb pistons up, have an assistant floor the pedal, and make sure they fully open. While at this, try with the air filters off-restriction there can hurt power. Lastly, check the exhaust for restriction. Seems like there is a way to do this with a vacuum gauge, but don't remember exactly. Good luck!
George Butz

Hi Lew, as Steve says about the obvious, what about the air cleaner. If using a dry cartridge it may be blocked as you have weak exhaust pressure. Check the timing. You can't have 5 degrees before and 15 after. Maybe you have 5 degrees after which will give all the symptoms you describe. Measure down approx 20 mm from the TDC notch on the pully on the generator side and make a mark with liquid paper. This will give you a good starting point. This is before TDC. Set the timing to this mark at idle. As the revs increase the timing must advance away from the TDC notch not towards it. If the timing ever crosses the TDC notch there is something wrong. I have a 4.55 diff in my TD and can assure you that it handles this ratio very well. If the timing was OK originally I would suspect that The camshaft lobes may be excessively worn. Mine were at better than 200 000 miles and had to be built up and reground. There should be no great difference in valve lift between cylinders. The specified lift is .315 in my factory manual which suggests that there may be a problem with your cam. The cam followers are probably pitted where they contact the cam and this chews out the cam lobes. Remove the side plate and rocker gear and check out the followers. After all this, have a good weekend. Cheers, Paul.
Paul van Gool

Thanks for all the responses so far. I now have the engine bared to I can get at things and have checked to following.

I found the timing starting at 5 degrees ATDC advancing to about 20 degrees ATDC. I have now reset it to 5 degrees BTDC at idle.

I have not yet checked the throttle plates, but will do so once I take the intake manifold off. Someone else suggested that.

The coil is relatively new (I know, I know, even new coils are suspect). Spark is strong on all cylinders however. I can draw an arc of at least 1/2".

The valve lift is a few thou either side of .275" except the exhaust valve on #2 cylinder. It lifts about .256".

I am using the original oil bath canister, and have already reshaped the dome to ensure I have no breathing restrictions.

I have measured the valve timing. Although I can't EXACTLY find TDC, since the head is still in place, I have measured the following:

Intake opens 1 degree BTDC
Intake closes 38 degrees ABDC
Exhause opens 42 degrees BBDC
Exhause closes 2 degrees BTDC

The actual position in relation to TDC may be off a degree or two, but this seems like a very small degree of overlap around TDC. Any opinions from any of you automotive engineers?

Lew Palmer

Hi Lew. I will give you the specs for the cam timing out of the manual for the early TD. There was a change at engine # 24116 which appears to be milder but I am no expert on cams.

Inlet opens at 11 degrees before TDC.
Inlet closes at 57 degrees after BDC.
Exhaust opens at 52 degrees before BDC.
Exhaust closes at 24 degrees after TDC.

Here is the cam timing after engine # 24116

Inlet opens at 5 degrees before TDC.
Inlet closes at 45 degrees after BDC.
Exhaust opens at 45 degrees before BDC.
Exhaust closes at 5 degrees after TDC.

From this your cam appears to be a later one.

The new ignition timing will make a world of difference at an extra 10 degrees of advance over the previous setting. I think you may be a long way down the road to sorting your problem out. Keep us posted. Cheers,
Paul.


Paul van Gool

Thanks for all the input.

Just for the record, I check the butterfly valves last night and found thet they are wide open on full throttle. No problem there.

The most likely cause so far seems to be ignition timing. We'll see how she performs after the snows melt.

Now if I can ever solve the pesky engine oil leak....
Lew Palmer

It sounds like you have gotten sage advice, hopefully your problem will be solved! With regard to the "pesky oil leak"; that seems to be a signature of T-series MGs. I am going to have my TD's engine out for a bottom end rebuild this winter, and I have acquired a Moss rear seal modification. I am hoping that this will allow me to park on friends' driveways without sufferring embarrasement!! Any one have any experience? I'll post my experience with it when I have gotten a chance to evaluate it.
Steve Tobias

Steve,

I have a number of friends who have tried this seal. The most common opinion is that it is VERY difficult to get seated correctly so that it seals properly. Those few who have had enough patience to do so (remember, it means taking out and reinstalling the complete engine for EVERY attempt) seem to be happy. I only know two people that have succeeded out of the eight I've talked to about it.

I know an equal number of people who have had good success aligning the original oil thrower. I, for one, feel that I can achieve the same result, now I understand the principle of the original seal.

It is written up in a number of places. The most recent I've read is in Horst Schach's book. That plus sealing leaks around the starter, engine number tag, oil pan, and timing chain cover, will probably take care of the worst of my leaks.

Good luck,
Lew
Lew Palmer

Although I have yet to run my spare engine, I used the Moss oil seal when I rebuilt it. I checked the location of the seal position on the crankshaft flange by coloring the flange with a black magic marker. Then I installed the seal and rotated the crank one revolution. The seal wiped the black color off in the location where it was contacting the flange. I found it was riding on the forward edge of the flange and not by much. I installed a speedi-sleeve (not sure of the name anymore) on the flange and repeated the test. Eventually, by gradually tapping the sleeve farther forward on the flange and rechecking with the magic marker, the seal began to ride on the sleeve at a point where I felt it had a chance to do its job. Actually, the sleeve wound up extending slightly beyond the forward edge of the flange but at least the seal had a good smooth surface to contact. It may not work but I think I will be far better off with the sleeve than without it.
Jim Merz

This thread was discussed between 14/01/2000 and 17/01/2000

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