MG-Cars.info

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

Recommendations

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 - Burnt valves ?

I parked up a month ago,last week decided to go on a run. It it would not start so I went through all the usual things Ignition, fuel etc, and found nothing wrong. I asked a friend to turn it over on the crank to check spark occurring at the right time. He told me I have no compression !!!!!.
I put each cylinder in turn at firing stroke TDC
and used 120psi airline to pressurise.
Air leaked into carb manifold on all cylinders, maybe exhaust too.
All valve clearances still normal so no stuck valves,
Engine was running slightly rich before this but I only expect valve damage with a weak mixture.
I have had this car 50 years,300000 miles and this is the first time it has let me down,besides losing a piston crown 48 years ago.
Ray TF 2884
Ray Lee

No way the valves burned. Possibly surface rust preventing sealing? Pull the plugs and peek into cylinders, look for rust or debris. Buy an inexpensive fiber optic camera and inspect. You could also squirt some oil into cylinders , crank a few times and try again. Next step would be pull manifolds and look at valve stems. Very strange deal. George
George Butz III

This might seem silly, but is it possible the timing chain or drive sprocket broke, so the camshaft isn't turning? I could see the probability that any of the valves would end up fully closed to be unlikely if that's the case, so you wouldn't have any compression. Of course if you checked the valve clearences with the valve cover off and witnessed valve train movement, then that negates any broken valve train components. Just a thought.

Jim
Jim Rice

Can't see how every cylinder would have an open valve.

Do a regular compression test and see what you get.
Bruce Cunha

I tried oil into the bore, no real change.
Camshaft is turning, valve clearances normal.
Cranking compression test just 20 Psi !!!
When I pressurise I can clearly hear air(and smell petrol) blowing through carbs at each TDC position.
So there is no doubt I have a valve problem at least.
The head has to come off to investigate.Hopefully that is all as engine removal on a TF is horrible.
I will report what I find

PS don't forget handbrake on and wheels chocked when pressurising If you forget, the car runs over you foot and ruins your day further.
Ray TF 2884
Ray Lee

Hi ray,
I had similar symptoms once. And I was not the first one. The valves were only stuck close to up position but no perfect seals.
Read this and you may avoid to take the head off.
https://mg-cars.org.uk/cgi-bin/or17?runprog=mgbbs&access=&mode=archiveth&subject=8&subjectar=8&thread=202103291928208262

Laurent.
LC Laurent31

Hi Laurent,
the head is off,massive carbon build up.
Too knackered to carry on today.
Over the weekend I will make a bore plug to check ring blow-by. I don't want to put it back together only to find I have to take it out.
The strange thing is that I did a 100 mile run on New Years day and it ran sweet before parking.
Ray TF 2884

PS I just noticed I posted on yours. Sounds very similar. Just shows brain fade as you get old
Ray Lee

Right ! You gave me the trick 4 years ago.
LC Laurent31

Been unable to do anything for a week,did back in lifting head off.
Nothing nasty with the head apart from carbon deposit,Seats just needed a slight fine grind.
Made cover plate and rubber gasket to blank bores one by one, minimum compression on any cylinder. Bores not scored can see slight hone marks on non thrust side of bores. (13000 miles since new pistons).
I either have stuck piston rings through over rich carbon or rings in hundreds of pieces.
Until my back is OK I can't get the sump off to drop the pistons out the bottom.
I am happy there is no damage and the worst outcome is new pistons
Ray TF 2884
Ray Lee

back still not good enough to risk getting under the car.
Head done and ready to fit. I nay have passed this tip on before.
To fit valve "O" rings, Cut a cartridge nozzle off at the same OD as valve stem and chamfer the inside slightly.Cut off remainder of nozzle so it will slide over stem.
Put "O" ring on first bit,place it on valve stem and push on with the other piece.
No broken finger nails or cut "O" rings.
I will update when I can move properly again.
Ray TF 2884
Ray Lee

I read Lurent's link to an older post about stuck valves after winter lay up. Was thinking might be a good preventative measure to once a month go out and give the engine a 3-4 second spin over on the starter to move things around a bit. Thoughts?
John Quilter (TD8986)

I am lucky enough to live in a area where I can use my TF every day except for the 2/3 weeks we get snow or ice,
Circumstances meant my car was outside and not started.
Ray TF2884
Ray Lee

Me as well so I can use the MG at least every 5-6 weeks I got it out of the garage today for the grocery run, since the 1 inch snow has melted. And then there are two Morris Minors that need to be used and an Austin 1300.
John Quilter (TD8986)

I found Lazarus (TD10855) in 1988. Got him driveable come summer of 1995. Said that I will have him on the road at least one day of every month of every year. This was in Plymouth, Massachusetts. Serious projects were started on the 1st of a month and planned to be finished by the end of the following month. Continued for 20 years. In mid-January of 2015 it began to snow in Plymouth. Didn't quit until Mid-March. I couldn't get into the garage to get him out. That was our signal to get to a warmer climate. In 2016 we moved down here to Marrietta, Georgia. Drove him down here and the series has continued ever since. Also, have only missed driving in 3 July 4th parades since 1995.

Bud Krueger & Lazarus
Bud Krueger

Yep that is what they are for. Mine has 360,000 miles, not bad for 51 years in Britain plus a few in France & Spain,
Ray
Ray Lee

You can't see my TD because I'm leading up there around the bend. This is Highway 215 in NC just approaching the Blue Ridge Parkway. Like Bud, we get our cars out at least a couple of time a month all winter. We're lucky to be where we can do that.

Jud
The group included two MGs, an Austin-Healey, two TR-6s and a couple of modern sports cars.

J K Chapin

Ray Lee's earlier post:
Over the weekend I will make a bore plug. What is a bore plug? Never heard that term.
John Quilter (TD8986)

John, a bore plug is just a general term for a blanking plate or similar to plug up the top of the cylinder so that it can be pressurized to check for cylinder leakage/blow-by from badly sealing rings.
In a later post Ray mentioned-"Made cover plate and rubber gasket to blank bores one by one"
Cheers
willy
William Revit

Hey Ray,

You are my kindred soul. Like you, my TF has over 350,000 miles. I am the original owner - a true, one-owner car. I drive it at every possible opportunity, and mostly with the windscreen folded. But not today. We’ve just experienced 43cm (17 inches) of snow.

Re your cyl head ... Before you removed the head, was the compression equal for all cylinders? 20 psi is seriously low; and the others are ??

One item not mentioned, is the issue of the guides. Doesn’t take too long to lose compression with worn valve guides. With the head off, good time to removed the valves and re-seat them. Of course, check the guides. Not big job to replace them ... only down-side is that a new head gasket is £50.

Anxious to see how this plays out.

Like you, my back too, is shot. The days of doing all my own work has come to an end. My daughter (owner of 2 MGs) does a lot, but local guy does the meaty stuff.

In closing Ray, I want to make a suggestion to you of an improvement I made to my TF. About 3 yeas ago, I installed a set of deClan Burn clutch rods (Google ‘deClan Burns clutch rods’). These come with 4 sealed, Heim joint's ... everything in stainless. Combined with changing the gearbox oil to Redline MT90 lubricant, absolutely transformed how the clutch and gear changes work. You will be impressed.

Gord Clark
TF 4592
PA 0921
Rockburn Qué.
Gord Clark

Gord, I am not the original owner, it was 20 years old when I bought it.After 4 rebores and a re-sleeve it owes me nothing (I do tend to thrash it)
It is definitely a ring problem. I took the sump of and pushed a piston out the top of the bore and the compression rings stuck in grooves.
I had thought of cleaning grooves and fitting new rings. Decided not good as I need to re-hone the bores. I will pull the pistons out the bottom and
do it properly.
About £130 should be all it costs ans I cannot complain after the service and fun it has given me.
As to the back, if I knew I was going to live this long I would have looked after myself a bit better
Ray TF 2884
Ray Lee

!0 minutes each to wiggle pistons 4,3 and 2 up past the crank 1 hour to get no1.
Going to have a sit down and relax now before fitting top rings.
Ray TF 2884
Ray Lee

Ray if you drive it on long runs & keep the rev's up the A/F mixture is too rich IMO.
Len
Len Fanelli

Hi Len, I run a 3.9 diff (19mph per 1000 revs so no high revs.
I have been running and tuning this car for over 50 years and never had a prob like this.
It was extremely carboned up 3&4 and a bit in no2.
This happened after a run just above freezing with high humidity. I am wondering if the back carb
iced up and went full rich. Any though anybody?.
It will be going for a rolling road tune up when I get it back on the road.
Ray Lee

Hmm
It'd have to be something over a longer period to gum up the rings etc. Just running rich for a little while would be more likely to wash things out a bit rather than clog it up.
Maybe run some upper cylinder cleaner through it occasionally might be a good idea.
Usually if it's all carbon'd up it's because of poor quality fuel ,old fuel that has gone off,or fuel that has a way to high octane rating for the application and not burning off properly but that'd be rare . -Valve stem seals maybe but you would have noticed the smoke.
A bit strange really if it just went suddenly.
willy
William Revit

Willy - which upper cylinder cleaner do you use and how do you use it?

Merv
M Hyde

Merv- I'm a fan of the Subaru one, It's a little silver/grey spray can. I've used the Nulon one as well and that seems to be very similar.
The Subaru can is called "upper engine cleaner" and comes in a silver/grey spay can with a blue cap. It's very potent so keep it away from your skin and it eats paint so you need to be super careful using it.
To use it, if you have a vac. hose on your manifold you can go in there, otherwise it's aircleaners off and spray direct into the carby mouth(s)
Best done at operating temp so idle strength is good.
Start the engine and hold the revs just above idle as this stuff will stall the engine at normal idle. take it in turns spraying into each carb while maintaining a slightly raised idle speed-The can comes with a little plastic hose so you can get right into the carby without spraying everywhere else.-keep spraying until you've used roughly half the tin then let it settle/idle normally then a decent spray in each carb. and it'll stall out. Leave it sitting for 5 mins or so for a soak then start up and continue using the rest of the can with raised idle then try and judge it when the can is nearly empty for another stall. leave it sitting for another 5 mins. then startup and up the road to blow the rubbish out.

WARNING--this stuff is potent -dangerous, DO NOT breath the fumes-- DO NOT use it inside

Best to find a good spot out in the open and point the front of your car into the wind so that the smoke (yes there will be smoke) blows away from you. After you've been through the process take the car for a blast/blow out up the road to get rid of the fumes, again - DO NOT BREATH the FUMES
William Revit

Thanks for the detailed explanation Willy. Most interesting and I will give it go before long.
M Hyde

This thread was discussed between 29/01/2025 and 27/02/2025

MG TD TF 1500 index

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