MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Blue Smoke on Idle.

TF 6688 has developed an issue of making gobs of blue smoke on idle. But not all the time.

The engine is original as installed.
45,000 actual miles. t has never been apart.

Compression test shows (1-4) 105#, 85#, 110#, 107#

Plug 2, shows evidence of oiling.

Oil pressure 75# on start,50# running and 25# on hot idle.

Engine starts and runs well.

Possible diagnosis
Stuck or broken oil ring
Burnt exh. valve
Worn Cyl.

WHAT DO YOU GUYS THINK?




colin stafford

I think it's time to pull the engine and do a rebuild.
MG LaVerne

Colin,

I doubt the valve guides would be worn in 45,000 miles, but one never can tell. Perhaps some acid may have formed over the years, but that's likely a long shot.

Possibly too, gum has formed behind some of the rings causing some to break.

My guess is that the seals and glands in the carbs have simply deteriorated and you're just pumping raw gas.

It makes economical sense to rebuild the carbs first and see if that makes any difference. If a complete engine rebuild is in the cards, why not start with the carb rebuild on the remote chance that this is your problem.

Gord Clark
Rockburn, Qué.
Gordon A Clark

Collin-
THAT GERMAN TF DOESN'T NEED A REBUILD!!!!

Get your butt to the next meeting and we'll do a real compression test that shows good results! We'll show you!

Jim Northrup
JRN JIM

JRN JIM has some good advise. I always run at least two compression tests before I trust the figures. Also make sure your gauge is accurate. I think that just maybe, pulling the plugs dislodges some carbon that sticks on the valves giving an erroneous reading first time through.
John Quilter (TD8986)

Colin,
That sounds like rings to me. I had the same smoke problem recently, similar compression values and an oily plug.
It was embarassing moving off at the traffic lights when cyclists were around. It was the rings in the end.
The bores were fine when we measured them.
Regards
Declan
D Burns

Blue smoke=oil
Black smoke=gas
White smoke=water
Paul S Jennings

I usually break the plugs loose, fire it up for a number of seconds, then shut down and pull plugs. Have seen bad compression reading miraculously jump up to normal after rerunning. Helps to prop carb open, too. A little squirt of oil and rechecking can identify ring issues vs valves. Good opportunity to check plug color, and verify the right plug length, too.
JRN JIM

I agree that blue smoke is usually oil, and most often comes from one of two causes - bad rings or leaky valve guides.

Although a compression test can be useful. I find it more useful to individually pressurize each cylinder, using a fitting and an external air pressure source, and then listen at the oil fill, tailpipe and intake ports... rushing air at the oil fill will tell you it is most likely rings; air at the tailpipe tells you it's exhaust valves; similarly, air in the intakes tells you it's the intake valves. Applying heavy oil to the cylinders can then help lock down if it's just worn rings or if it's a cracked ring.
Kevin McLemore

If it is all of a sudden, I would also consider valve seals, as the o-rings break, and then there is a slot for oil to drip down, when in the right position. In any case, I would pull the head and start there. That gives you a chance to survey the rocker gear, the valves, seals, guides, springs and seats.

Tom Lange
MGT Repair
t lange

take the rocker cover off after a run.If any of the spring caps have no oil resting on then then 'O' ring has failed. They can be replaced without removing the head.
Ray TF 2884
Ray Lee

Number 2 doesn't look good with an oily plug and low compression. If it was mine, I'd pull it and rebuild the whole engine. You can guess all you want, but until you pull it apart, you'll never know if anything else is wrong. The oil could be caused by a few easy fixes, but the low compression, that's another story. JMHO. PJ
Paul S Jennings

I missed the low compression in one cylinder - thanks, PJ. No valve seal will fix that!

I would pull the head and see if you can see what is going on, you may have a broken ring, stuck rings, etc. IMHO it really has to come apart. Photograph EVERYTHING so you can get all the points of originality back again (like the lockwire on the left side of the engine, in 2 places, usually forgotten).

If it truly has only 45k, you may be able to get away with new rings, cylinder hone, rocker rebuild, valve job, oil pump check and a thorough clean. But this is also the time to balance the engine, and the hip bone IS connected to the thigh bone, the thigh bone IS connected to the leg bone, the leg bone... It,s a slippery slope, but only one way to do it right.
Tom Lange
MGT Repair
t lange

I agree that it probably does need to come apart, but as I say, I'd do that pressurized test first. If most of your leakage is through the intake or exhaust then you may get away with just pulling the head instead of the whole motor. For example, you could have a burned or simply leaking valve on that one with low compression - it may not be a ring issue at all. But once you pull it apart you can no longer run the pressure test to find out.

I made a simple pressure device by taking an old spark plug, knocking out all the porcelain guts (so all you have left is the hex-shaped threaded bit), then tap the insides for pipe thread. Screw in a pipe of whatever length you like, then screw a valve to that pipe and, finally, screw an air fitting into the valve.

To use it, put the cylinder's piston at top-dead-center (easily found by placing an 8-10" piece of 1/8" dowel in the spark plug hole and as you rotate the engine you feel the piston top coming up)... then remove the dowel, screw in your pressure device, pop on the air and open the valve. Listen for the leaks - this will give you a wealth of information.
Kevin McLemore

This thread was discussed between 19/08/2014 and 20/08/2014

MG TD TF 1500 index

This thread is from the archives. Join the live MG TD TF 1500 BBS now