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MG MGA - exhaust muffler incident
|I was driving down Interstate 680 yesterday (on my way to a great day at the "MGs by the Bay" get-together in Danville CA), minding my own business, when my muffler fell off.|
Once I got home and was able to take a closer look under the car, the cause was obvious. The rear muffler hanger consists of a couple of overlapping pieces of metal, with a block of rubber or some other sort of vibration-absorbing material sandwiched between. It appears that the material simply separated from the metal, leaving the top half of the hanger securely fastened to the frame and the bottom half to the muffler. At this point presumably there was enough stress and vibration on the clamp between the exhaust pipe and the muffler that the muffler separated from the clamp, and hey presto, it's merrily bouncing down the interstate while my eardrums are being assaulted by the now (very) free-flowing exhaust.
So it's time to buy a new muffler, rear hanger, and front clamp. But I'm wondering if there's some sort of fundamental bad design about these hangers that makes this failure likely to happen again. This hanger was only on the car 6 years, and driven maybe 2000 miles.
|The muffler was probably misaligned to cause the failure. The open tip should point upwards at about half way between 1 and 2 o'clock. Then nothing is under stress and nothing will fail.|
The hangers are very long lasting (mine is 20 years old, I know of originals still in service), but not designed to take a shearing or twisting force that comes from the exhaust being mounted with the tip pointing down....
|Alas the tip was in the correct position, exactly as you say. So I'm still scratching my head about it...|
|Interesting thread this. Question :-|
Which way round should the tailpipe (i.e. the rear) hanger , face ?
I have two parts catalogues -- Moss , and Brown and Gammons.
Moss show the hanger facing forward and probably therefore clamping onto the straight part of the tail pipe where it comes out of the muffler.
B and G shows it facing backwards which seems , as per my 1600 roadster , to position the clamp either on or just outboard of the bend in the tailpipe and therefore possibly under some load.
|D C GRAHAME|
|It is important when installing the exhaust and its 4 mountings that there is no "pre-stress" introduced into the system. The trick is to bolt up the pipe to the manifold, using the right donut, first, but leaving the 2 stays and 2 exhaust mounting rubbers and brackets loose. Then tighten the 2 stay straps on the bellhousing and the exhaust bracket. Next tighten the mount ahead of the muffler, and lastly tighten the rear mounting.|
That way you will not stress the rubbers and they should last for years (unless the Chinese QC man had an off day!)
|The mounts available recently are not of the same quality as the old original mounts nor of ones supplied twenty years ago. Additionally, some suppliers substitute an earlier MGB rear mount for the MGA mount. The MGA mount is longer--make sure you have the long one.|
This thread was discussed between 11/05/2009 and 14/05/2009
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