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MG TD TF 1500 - Intermittent knock

Happy Spring to all. Spring is finally here in the great white north. I pulled my '52TD out of its winter nest this morning, changed the oil and started it. All well so far. I then test drove the car about one mile and warmed it up. Oil pressure was about 60lbs.

Now starts the problem. I took the car out to the highway and at about 55mph, I began to hear a fairly heavy knock. The car also lost some power as if the fuel filter was a bit plugged, or there may be water in the fuel after the long winter hibernation. I stopped, and when the revs dropped to idle, the knock stopped. It returned when I raised the RPM and then stopped again when the revs dropped. I let the car idle for a few minutes and almost magically, the idle settled down as if the fuel issue had sorted itself out. Raise the revs, listen to the knock. Cool the engine down, restart, no knock even at high revs. ????

I think the sound was coming from the front of the engine, even the water pump, but I would have expected more of a screach from the water pump..???

Any ideas as to where I should start looking?

thanks

Glen Lucas
Glen Lucas

Twice after rebuilding the head I suddenly heard a scarry rapid knock with sudden lack of power, immediately shut down, that went away with restart after cooldown. We diagnoses a stuck valve- new bronze guides with modern oil seals were too tight. Maybe some rust over the winter on a valvestem? Otherwise you have something bad and expensive happening. The broken crankshaft knock doesn't stop and you also have no oil pressure.
George Butz

Glen, are you certain that it's eminating from the engine? Any chance at all that could be from a loose component that is hitting against something? A loose exhaust pipe/gearbox clamp once had me ready to tear things apart.
Bud Krueger

I would side with Bud except for the loss of power. Get the engine warmed up really well and then do a compression test, or better yet a leak down test of each cylinder. Your symptoms sound suspiciously like a blown head gasket. Good luck - Dave
David DuBois

Thanks, I did a compression test this afternoon. 120 across the board. The engine was recently rebuilt however, so I am hoping it is as suggested a stuck valve.

With reference to "something hitting", my wife and equally concerned helper, has been trying to tell me it is the fan striking something. I don't think that's it, the sound is too deep and slow for the fan. If it happens again, and please God make it stop, I will probe the head with a stethascope. I did not see bubbles or a rise in heat to suggest a head gasket. But, looking at the expensive things this could be, there will definitely be another look at each of these options.

Thanks again for the extra brain power. I really appreciate the help.

Glen
Glen Lucas

Unless your valve is intermitently sticking, you would know if it was a stuck valve... would run horribly and i don't think you wouldn't notice the misfire....

Your last sentence mentions that it was gone after starting up... has it continued or is it gone?
gordon lawson - TD 27667

I had the scare of my life when my short-reach-sparkplugged-XPAG started knocking when warming up, at revs and not when idling. It foolishly turned out to be the gunson Colortune, of which the hollow copper spacer rings compressed so much that it was hitting the piston when warmed up. It does get the pulse racing....

Willem van der Veer

Glenn, remove or loosen the fan belt. This will eliminate several sources.
w.g cook

your symptoms are exactly what i experienced after lead freeing my motor. as soon as the engine warmed up i would hear the noise and get a loss of power, when it had cooled down it woud be ok. it turned out that 1 ex valve guide had to be reamed out slightly. I think that your lay up probably caused your problem.
thankfully here in the UK i do not have to lay up.
r lee

When you rebuild a head for lead free fuel, always use Molybdenum DiSulphide lubricating paste on the valve/valve guide assembly as well as on the cam lobes and all over the cam followers.
The stuff in the little tubes supplied with some replacement cams is Molykote G-N Assembly Paste from Dow Corning. Available from bearing houses and catalogue stores.
S.R. Barrow

Thank you all for the help.

It seems after all the concern, (read mild panic), the problem seems to have worked itself out. After working through each of your sugestions, I became suspicious about the quality of the fuel after the long winter storage, so I added some alcohol to the gas and the noise stopped, power returned and we seem to be back on the road. Summers are so short here, I did not want to waste any of it fixing, just driving. Hopefully, tomorrow will not bring the horror back.

thanks again and best wishes to all.

Glen
Glen Lucas

This thread was discussed between 03/04/2005 and 06/04/2005

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