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MG MGA - RPM related noise could it be carb overflow pipes

Lately I've been hearing a noise that comes on at about 1800 RPM once the engine is warm. The noise continues at about the same "just enough to be annoying" level as the revs climb above the onset.

First thing I did was to check the fan and pulleys and ll seems tight and in alignment there. Next I swapped out the generator with a spare - no change. I next pulled out the heater air hose and all the clamps and checked for tightness around the heater box - no change.

Today I checked the heat shield and it's tight, but noticed some play where the two carb overflow pipes come close to touching as they head down to the tie down spots under the engine.

Has anyone had any odd noise that were traced down to the overflow pipes, and if so, what did you find was the best solution? I'm thinking of zip tying them together where the are closest - at about 6" below the exhaust manifold - but I expect the ties may melt away.

I know, noises are a wild goose chase but just hoping someone might say "I had the exact same problem and..."

Cheers,

- Ken



KR Doris

A common tinkling noise that comes in at that sort of RPM and above is a washer inside the the starter bendix. Took me quite a while to find that annoying one many years ago.

Steve
Steve Gyles

Ken. A "tinkling" noise is, most commonly, made by steel while a "tapping" noise is made by other metals. The steel rings more like a bell while the copper and aluminum make a duller sound. But, to isolate either I use an old stethoscope, one having the bell shaped end piece (or one having both the bell shaped end and the flat disk with the switch turned to allow the bell to function). When the open end of the bell is pointed at various areas, it tends to cut out the sounds coming from the sides and pick up the sounds directly in front to the bell's opening. Using this technique I have been able to focus on exactly where the sound is coming from and find the cause far more frequently than by using just the ear and eyes alone.

Les
Les Bengtson

Hi Steve,

Was your cure to simply replace the started motor?

I replaced the starter motor in the midst of all this. Had to as the old one was requiring a whack now and then to work. The noise remained. I guess it possible both old and new had a loose washer but I'm hoping I'll find a simpler/cheaper solution.

I was just on a chat line with old MGA friend Don Carlberg and he suggests splitting some fuel line and sliding it over one or both pipes. I'll root around in my spares boxes to see if I have some.

- Ken
KR Doris

Les,

Good idea for stethoscope - I think one of my car club friends has one.

As for the noise, it's definitely a tapping rather than a tinkling so the overflow pipes are a good suspect.


- Ken
KR Doris

Ken

It was nigh on 20 years ago I had the starter motor tinkling. I was able to buy a new bendix assembly from a local motor factor so I got away with keeping the original motor. I am pretty sure there is archive material on the topic. It seemed to be a common issue rather than a one off as I recall.

I think it was air disturbance caused by the speed of the rotating flywheel that got it tinkling, but I may be wrong and it was simply vibration.

Steve
Steve Gyles

Looks like the carb overflow pipes are the problem. Put a split rubber fuel line section over where the two are closest and the noise is almost completely gone.

I'll have to add some more and perhaps get underneath to see if I can completely eliminated it.

- Ken
KR Doris

Hi Ken
I just wondered if the float chamber overflow pipes have maybe become a little loose in their banjo connections at the float valve connection. This could explain the rattling noise.

I had this years ago when I ran with SUs, I had to remove the pipes and re-solder them.

Mine were steel pipes which looked like they had just been randomly pushed down through the manifold.

They were also pretty much unsupported below the float chambers, which is probably the reason that they failed.

Cheers
Colyn

PS. Hope you and Melon are both keeping well.

Colyn Firth

Hi Colyn,

The banjo connections up on top were the first thing I checked and they are tight.

The pipes are new copper from Moss - replaced them as part of the clutch and engine work done back in 2019.

The "originals" were very quiet as they were all bent so I had cut them back to almost the very top and slid rubber fuel line over them and routed it down to come out under the wheel arches (I may end up doing that again if this persists!)

Hope you and Chris are well and that all of you ("y'all y'all" down here in South Carolina) on the BBS are able to get back to some sort of pre-Covid normal soon.

Best,

- Ken
KR Doris

My pipes just dangle alone. Guess I should route them as per pic!
Art Pearse

Those copper overflow pipes should never rattle or need anything else other than a P-clip to hold them in place as the attached picture on Barney's site.
I have had Moss's copper pipes attached like this for the last twenty years - no trouble. As you can see the pipes are fixed on the same stud in the crankcase as the crankcase breather pipe. Just ensure the pipes are bent clear of everything. The pipes were a bit long so I simply bent them back a bit to the rear to look a bit neater - job done.
PeteT



PeteT

This thread was discussed between 19/04/2021 and 07/05/2021

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