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MG TD TF 1500 - Alice&Alex, Stuck valve?

Hi, I had a new total head engine rebuild (50 TD) and a valve stuck. The mechanic thought that he had it sorted out and after about 50 miles it stuck again. Same one, exhaust. Now the darn thing just wont run right it sputters and pops and backfires and has no power. The valve is unstuck now but still no power. We timed it, set the valves, changed the gas, cleaned the plugs, set the points but still no luck. How could an engine run so good and after a stuck valve run so badly. The valves are bronze maganese (sp). The exhaust valves had been reemed to spec. Please help, Neal Turner
Neal Turner

Neal,
Just some things that can cause a sticky valve.

The engine's operating environment and design causes valves to stick. Many factors influence this environment, including engine temperature, engine design, operational technique, oil, fuel, and frequency of oil changes. Even ambient temperatures have a great influence on valve sticking. Valves stick more in the hot summer months than in the cold winter months
High temperatures in the exhaust valve guide oxidize oil and forms carbon deposits on the valve guide and these deposits cause the valve to stick. The most frequent reason for elevated valve temperatures is valve leakage. All of the combustion gas must pass around the valve face as it goes out the exhaust port. The large heat-absorbing surface of the exhaust valve face must conduct heat away from its surface. A valve that is not contacting the seat properly cannot conduct as much heat into the cylinder head as a valve with good seating. Elevated valve stem temperatures may then cause the valve to stick.

Do not use Marvel Mystery Oil or other solvents to un-stick a valve. Solvents may un-stick the valve in time but not immediately. Eventually the valve may un-stick, but not before your camshaft lobes have been damaged.
I am sure you will get a lot of good advice on this issue.

Good Luck.

Don
Don

Check compression- you may now have a bent valve- if stuck open it could hit on piston, or stuck closed the valve or pushrod could bend. I recall the bronze guides need more clearance than the factory spec for steel guides. Also way too lean with minimal clearance can cause this- how do the plugs look color-wise?
George Butz

I think George hit on the head. Did you have the new manganese/phosphor bronze valve guides installed? They need to be reamed slightly larger than the original ones did.
Gene Gillam

Thanks Don And George. I will check the compression tomorrow. The plugs are black with some sooty-oily looking stuff on them .I did remove the valve cover and rotate the valve assembaly and all valves seemed to move like they are supposed to. Why would it not run as good as it did after the valve became un-stuck. If the valves adjust up properly and move properly it should run properly. I don't understand. It seems to idle pretty well but runs rough at any increase in revs. Thanks again, Neal Turner
Neal Turner

Neal,

Had exactly the same problem last week. I fitted a reconditioned un-leaded head with phosphor bronze guides. The engine ran well for about 5 mins and then started miss firing. I found that various plugs were fouling up with black sticky carbon. If I cleaned them everything was OK for about two minutes only for the mis fire to return. Eventually cleaning number 2 plug was having no effect so tested the compression and was zero. Took the rocker cover off and the valve was stuck down. Returned the head to the machine shop and they took out all the valves. The black sticky goo was on the stems and in the guides. This was cleaned off and the gides opened by a couple of thou. Now runs fine. I think Gene is spot on you need extra clearance with bronze guides and if they have started to stick the goo will now be on the stems and the only solution is to dismantle. Don't think bent stems will be a problem - I believe a fully open valve will miss a piston but am open to correction.


Jan t
J Targosz

Hello again, I have just done a compression test and all cyl are very close to 149,150 ppsi. The exhaust valve guides have been reamed more than the intake but don't know how much. Is it possible for a tight guide to seat or will it have to be reamed a bit. Thanks, Neal Turner
Neal Turner

Good compression is good, still possible something slightly bent or gunky that hangs at high RPM. However, you "cleaned the plugs"-throw them out and put new ones in. Then try the simple cheap stuff-check for major air leak carb side, change the rotor (lots of failures recently),change points/condensor, coil, check carbs, try without the air cleaner (because the tops can crush in and smother the air flow, etc.) Do this one thing at a time so if you are lucky you will know what you did to fix it. If not, off with the head and they will have to disassemble and find the problem.
George Butz

Thanks for all your comments but nothing seems to help. I've changed the points, condenser, rotor button, Ive even changed the gas in the tank! Gosh-a mosey, I do not have a clue as to whats wrong. I called John Twist and he said to change the points cond and rotor button and the same thing happens. Alas and alac. Neal Turner
Neal Turner

Neil, I think I would regroup and start over - First with a meticulous check of the timing, comparing the notch with actual top dead center,etc.
Dallas Congleton

Having spent many hours trying to start engines with the ditributor 180 deg. out over the years and other stupid things like that, I suggest a clean fresh start and look at the simple basic things one more time. If you find nothing, if it ran perfectly until the valve stuck, then there is no other choice- off with the head. You will not doubt find the problem there.
George Butz

Neal,
I assume that the head has been milled a bit for dead flat. Did you fit shorter pushrods or shim up the rocker assembly? If the rockers are pushing the valves "sideways" instead of straight down, I would think that there would be the possibility of sticking a valve. Just a thought.
Craig Cody

Thanks for your comments, I know that I will have to remove the head but it still worries me that this machine worked so well and then this mess. What the hell, Off with her head! Thanks, Updates soon, Neal Turner
Neal Turner

Hi, My problems have been solved By George who suggested to throw away the old spark plugs and install new, Thanks, George and all who contributed. When installed the new plugs just made the engine purr like a kitten. So simple. Thanks again, Neal Turner
Neal Turner

Spark plugs, in most cases,can be cleaned with a propane torch. As previously stated, (when all else fails) go back to the basics.
Len Fanelli

This thread was discussed between 01/10/2003 and 04/10/2003

MG TD TF 1500 index

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