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MG MGB Technical - Irritating rear end noises

I have two sounds coming from the back of the '79 B that I wonder if someone can diagnose for me. When underway, I hear a noise that sounds like an exhaust pipe rattling. The sound does not change in volume or tempo at any speed. I have checked the usual culprits such as exhaust pipe/muffler and shocks and took everything out of the trunk. Have not looked at drive shaft, u-joints or tried rotating wheels/tires. The second sound is a ticking noise coming from the exhaust that a friend of mine said might indicate a valve problem. I did remove the center muffler and am currently running only the stock rear muffler. The valves are noisy and have been adjusted mamy times. The engine was rebuilt by teenagers of the automotive engine rebuilding class at the vocational school that I work at...so I can sort of expect something to not be right! One more problem I may as well throw in...whenever I start the car, black smoke (I am told) shoots from the exhaust along with moisture (water) and always leaves a sooty, black spot on the garage floor/driveway. These are my last major problems that I am having after a long rebuild to make this car a daily driver. Thanks for any advice or help.

Larry
Larry Youngblood

Have you checked the fuel pump? An airleak in the pickup pipe will make the pump run faster.
j soutar

the rear of the mg is a weak part of the mgb .ive had many noises,first being worn bushes and the hardest to find was the fixing which bolts from the anti roll bar to the chassis .the rubber wears in the eyelet cheers big ears
daren

do you have spax or lever arm shockers
daren

J: I removed the stock fuel pump and have installed an aftermarket pump so don't think that is the problem.

Daren: Stock shocks...did not think about the sway bar. Will check that next time I have it jacked up.
Larry Youngblood

Larry - "I removed the stock fuel pump and have installed an aftermarket pump so don't think that is the problem." If you installed one of the little square, run all the time, make a lot of noise Facet pumps, that may well be where the rattle is coming from. This is particularly true if the pump is hard mounted to the chassis as the sound is telegraphed all over the car. If you have this kind of a pump, try unbolting it from the car and just let it hang from the fuel lines (or tie it up with some twine) and see if the noise goes away. If it does, get some sound mounts for the pump and remount it on them. If you have a Carter rotary pump, this doesn't apply. Cheers - Dave
David DuBois

David: yes, I do have a facet pump on the car and it works fine with a lot of noise. I did isolate it with rubber feet and that helped quite a bit. I did install a rotary type pump also and the facet is not hooked up right now but will be in the future as a backup.
Larry Youngblood

Larry-
The black smoke on startup is usually caused by oil leaking down the intake valve guides and puddling atop the intake valves. Were the valve guides reamed after installation? The noisy valvetrain can have several causes: Worn rocker shaft and/or worn rocker arm bushings, worn thrust faces on the rocker arms, and/or worn tappets. You said that the engine had been "rebuilt". Have these items all been replaced?
Steve S.

Is the exhaust ticking up by the engine? It could be the manifold gasket failing.
Martin Layton

Often wear on the valve train components makes accurate setting of the valve lash nearly impossible as the mating surfaces are no longer flat and parallel. Use of a dial indicator positioned above the rocker tip is one way to set it, and some will adjust it down when running until the ticking just stops. If you do this, be sure to verify that you have some play left afterwards.

Jim
Jim Blackwood

A burst of wet 'soot' is normal as far as I'm concerned and is caused by cold-starting. All three of my cars (only two of which are MGBs) do it, always have done, and as far as I can recall all previous cars have as well. So much so that I had to fit a tail pipe trim to the V8 to stop splattering the front door, and prop a bit of board up against the tumble drier in the garage to stop the roadster splattering that!

A rhythmic ticking or beat in the exhaust does indicate a possible burnt exhaust valve or seat (or in the intake if an inlet). When removing the HT cables from the distributor cap one by one, if one makes noticeably *less* difference to the idle speed it is likely to be that one. However a rhythmic 'splashing' sound is a symptom of a rich mixture, or over-choked, which will worsen the wet soot situation.
Paul Hunt 2

Nothing much to report back on. The last two days have been beautiful...sunny and in the 50's so spent time outside in the yard, walking, etc. Did go back to work today after the holiday break and the automotive engine rebuild teacher asked me to bring the car in and he would check it out. I did lean out the carb some more and that did seem to help with the sooty crud coming out of the tailpipe. I now am seeing a bit of coolant around the #3 sparkplug hole...not a lot but enough to puddle in the recess. The head was cracked, I forget where, exactly, but had it welded at a good repair facitlity for cracked blocks, etc. So anyway, the instructor is going to check for problems along that line and the valvetrain for the ticking noise. I have another engine in the garage so may have to swap out the heads. Have not had the time yet to get under the rear of the car and check for the original irritating noise! Maybe I'll just sell the MGB and get a new Pontiac Solstice!
Larry Youngblood

This thread was discussed between 31/12/2006 and 04/01/2007

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