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MG TD TF 1500 - Expert input sought on my engine issue?

Yesterday, after a nice drive, fumes were pouring out of the engine compartment from around the rocker cover. Took the oil filler cap off and it was like a steam engine smoke stack. Turn off the engine and it basically stopped.

A few weeks ago I did a compression check and all 4 were around 115. Did the same check today and 2-4 are in the 115 range, 1 is very low and only creeps up a few pounds.

I pulled the rocker cover and valve gear is all moving so not a broken spring.

Fumes are clearly coming up from below via the oil drain between 2 and 3.

So obviously something mechanical has failed on 1. I am leaning towards ring failure.

Thoughts? and next steps?

Thanks much
Simon
S Griffin

Before you tear the engine down, you might consider doing or having done a leakdown test. The testers are available for under $100. (Don't buy one from Harbor Freight. They are junk.)

The tester is hooked up much like a compression tester. Air is injected with the piston at TDC. It will then show you how much pressure is being lost. If it goes down significantly, you can listen for air escaping. Where it is escaping will tell you what is wrong. For example, if the air is heard and seen as bubbles in the radiator, it's a head gasket, out the tail pipe - it's an exhaust valve. From the crankcase, it's rings. Etc.
Lew Palmer


Simon, I'd suspect a failed head gasket allowing some coolant/water into #1. Low compression is usually cased by head gasket, valves, or rings.

Suggest you remove the head and begin to eliminate the obvious. If its a head gasket as I suspect, check the head and block surfaces, and clean everything well. Its common to find the original head studs stretched from previous torque and marginal material strength. After I've personally used the ARP studs sold by Tom Lange, I fully recommend them for their improved material strength. They permit a solid even torque setting across the head.
Richard Cameron

Richard is almost certainly correct. No other source for the steam expect the coolant. But if you want another check for low compression squirt some oil into the #1 cylinder. If the compression goes up you know you have a ring problem. But I'm sure it the head gasket as well.

Tim
TD12524
Tim Burchfield

I have no idea about the internal history of this engine, if it has been rebuilt or had any other work done over the years. Time to investigate further and pull the head I think. Thanks for the suggestions. Much appreciated,
Simon
S Griffin

what comes out when you drain the oil?
T W Moore

I'm a little wary of a broken piston - Simon didn't mention actual steam, just the fumes pouring out. A gasket would have to be pretty much all gone to have only a few pounds compression. Even broken rings would show more than that, usually. Anyway, pulling the head is the first thing I'd do - anything that far gone is not going to respond to adjustment.

No tapping noise? I've got a piston on the shelf with a valve head stuck sideways halfway thru it.

Best of luck, fingers crossed. David
D A Provan

If it's steam the coolant level will be down
If it's still full then it could be smoke
willy
William Revit

I could not hear any strange noise from the engine. I am going to pull the head today and see what I can see. Thanks for the additional input.
S Griffin

Hi Simon,

Another good teaser to keep our brains alive. Do you mean steam as in a kettle or were you using steam engine as an example of a machine that generates oil fumes? I don't see how a broken ring will cause steam. The head on my TF was warped but not along the long direction but rather across the short length. I tested it with a long straight, metal ruler and it appeared OK but you can't check it this way. You need a long flat block about 1" wide.

Jan T
J Targosz

Simon - we're all eager to hear what you found.

Tom Lange
MGT Repair
t lange

Tom. I bottled out! I decided to step back and contemplate what needed to be done, rather than tear right in. I don't have the best environment for this and not being all that experienced I don't want to make anything worse. I am going to take it to a local pro for assessment and repair. I will report back what is found.
S Griffin

Simon - OK, we understand. But we can also walk you through what you need to do/look at - many of us have found ourselves in the same position of doom and gloom.

All can be fixed, as they say, with a few common hand-tools!

Best, Tom Lange
MGT Repair
t lange

Tom, with more time on my hands and better space to do the work I would tackle this in a heart beat. I have a really heavy work travel schedule over the next 2 months and know that this will just sit. I want to be able to enjoy the car this summer when I am in town so will get it done. What I probably should do is clear out the garage to make it a more pleasant place to work!!
S Griffin

Simon, since I think you did not mention steam, just fumes from inside the motor, I'm led to believe there's a leak in the lower end - i.e. a piston, ring or block failure. The latter is highly unlikely, so at this point I'd look to rings or piston failure. And, given the pressure held is so low, it's a pretty major failure.

As far as a leakdown tester, I made a very simple one that you could easily construct. I took a spark plug, removed all the ceramics and the electrode assembly (effectively hollowing it out) and then threaded the upper end of it for a pipe-tread to insert a small bass in-line valve screwed to an air-hose adapter.

After screwing in the spark-plug-leakdown-tester, I connect the air hose to it, set the motor for TDC on that cylinder, then open the valve and listen for where the air is escaping. Works very well! Plus, the frugal me loves that it only cost one used spark plug and a couple of cheap air fittings.

Kevin McLemore

I'm at work so I can't upload a photo of my home-made tester, but I did just find a YouTube of one being made that's very similar to mine (though I'd like to think mine is a bit more tidy that this one!). Here you go:

https://www.youtube.com/watch?v=ohB1osh5pNk
Kevin McLemore

Thank you Kevin, that is a nice idea. I appreciate the additional input as well.
S Griffin

Thanks, Simon. I'm home now and found a photo of my easy-make leakdown tester. See below.

Listen at the intake (through the carbs), exhaust (at the back pipe) and in the engine (open the oil fill)... where you hear the air flowing out will tell you your problem area.

I pray it's not too serious.



Kevin McLemore

Kevin,
While your leakdown tester will certainly work, it cannot show you how much air is escaping. Some air will always escape, usually past the rings and up the valve guides. The trick is knowing how much leakage is occurring and whether that indicates a normal or fatal leak. Thus most testers include 2 gauges, one to show the initial air pressure and the second to show the amount of leakage.

Just my $0.02
Lew Palmer

"All can be fixed, as they say, with a few common hand-tools!"

Or even just one. As we Armourers say, 'When in doubt, get a bigger hammer.'


David
D A Provan

This thread was discussed between 10/06/2017 and 13/06/2017

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