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MG MGA - Valve Clatter

I have a noise that I have been unable to get rid of that I can only describe as valve clatter. I have an 1800 5-main with 28k on the rebuild, running approx. 9.5:1 compression with .030 pistons. It's a great engine and performs very well and I'd like it to stay that way, ehich is why I want to figure out the source of my clatter. This is not the normal B-series rocker noise. At a certain rpm- I can't say exactly what as I never switched over to an electronic tach, but it's right at the rpm needed for maintaining a steady speed- for whatever gear you're in. You know, not accelerating or decelerating, but lightly touching the throttle to maintain your current speed. Anyway, this is when the clatter happens. It will last as long as I maintain that engine speed. If I accelerate it will promptly cease, and the same will happen if I decrease speed. I also don't seem to notice it if I'm at a very high speed, like 70 mph+, but that could be because of the road noise. The noise is always the same, it doesn't get worse or better, it doesn't sound malignant like a sticking valve or a part failing due to lack of oil, but of course that's what I'm most afraid of.

For the past few seasons I've tried to tell myself that it was something vibrating at a very specific resonant frequency, but I've become convinced that it's coming from the valve train. I just reset my valve clearances and while that quieted the valves a bit (but not too quiet), that same old noise is still there at the same times.

I'd really like to figure this out so as not to cause any further damage to the engine. Could it be something like a fan blade or harmonic balancer starting to come apart?

Mark (I'm really envious of Dave Lieb's nickname schtick) Michalak
Mark J Michalak

I don't know much about 1800 engines, but it sounds more like your timing gear. Feathering the throttle is just when it would have the opportunity to misbehave.
Nick

Heres a possiblity. A number of years ago i remember an MGB with a clatter / rattle at certain revs or changes of revs. It turned out to be the fan being loose on the front pulley. It would move ever so slightly and rattle against the bolts. It might be worth a look. Best of luck.
DJ Lake

It may not be the timing gears but the timing chain tensioner is a possability. A rod knock also shows up at very light acceleration /deacceleration but the chance of that lasting for several seasons without getting worse is highly unlikely.
Pull the fan belt and see if it goes away, that could point you toward the water pump, fan, generator, as mentioned above.
J Heisenfeldt

This is a long shot but I experienced the same issue with my newly rebuild. At around 55 MPH I would start to get a clattering from what sounded like the engine. I could not for the life of me figure it out. After about 6 months I finally diagnosed it as the vent grill not tightly secured to the body! Go figure! Took it off and put a little silicon under it and re-secured it. Purring like a kitten since :)
WMR Bill

Is a clatter or more of a knock? I had more of a knock that started after a couple of thousand miles on my 1600.Same symptoms as yours.Sorry to say mine turned out to be the rods.The rod side clearance was too big,over the years the rods must have had been machined too many times.The side of the bearing must have started to wear,which then let the rod rattle.I could not find a set of rods that had not been machined,so the cure was to take the best rods and weld the crank.Hope thats not your case.
gary starr

No, definitely not a knock. I'll try pulling the fan belt and see if that eliminates any noise, that's a good idea. I just replaced the water pump pulley with one that is straight and true, so I'm sure it's not loose bolts, but maybe it's the fan itself. Or the alternator? I'll also double check my grille.

I haven't much experience with the timing chain tensioner. I'm assuming if the timing chain becomes slack it could prosuce the kind of noise I'm hearing. I don't have a manual handy- what's involved in R&R-ing the timing chain tensioner?
Mark J Michalak

To get to the tensioner you need to remove the radiator,fan and the crankshaft pully. You can then remove the timing cover.
J Heisenfeldt

This thread was discussed between 10/04/2008 and 11/04/2008

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