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MG MGA - Exhaust Bracket
|Just back from the garage for my MOT test (1961 MGA) and when the car was on the ramp you can see that the front exhaust bracket that is welded to the pipe has fatigued off (both at the vertical and horizontal connections) This is where the two straps provide support off the engine backplate. I know there's been discussion on this in the archives but could not find it but basically some argued that it was OK to let the manifold support the pipe via its three flange connecting studs and others felt that the bracket support was needed. It's difficult to reach the bracket to weld it insitu so it would help me if owners could restate their views on this before I commit to a tricky welding job.|
|J H Cole|
Did it fail its MoT on that point? i.e. do you have the choice about whether the work has to be done?
For my part, I have never fitted those straps. All has been ok in 15 years of driving. I did speak to Bob West about it a while back and, if my memory serves me right, they don't fit them unless specifically asked to by (concours) customers.
I recall that there was a view that they can stiffen up the area to much resulting in increased stress levels from the more flexible lower exhaust system on the manifold. May be that is why the bracket on your car has fatigued, being weaker than the manifold?
|No it passed Steve because the garage accepted that the exhaust was still fairly rigid. I remain surprised that it fatigued off since the bracket and manifold connections did not allow movement for fatigue to come into play ie the whole front end was rigid. I can see that fatigue cracking could happen past the bracket.|
By the way thanks for the info on the boot lock.
|J H Cole|
|According to MOT requirements, Section 7.1 Exhaust System|
"The overall security of the exhaust system should be assessed; one or more exhaust mountings missing may not be a Reason for Failure."
Method of Inspection
1. Check the security of the exhaust system.
Reason for Rejection
1. An exhaust system not adequately supported.
|My bracket broke here 15 years ago, and it is still missing. The exhaust is still free from problems!|
|That point gets a fair amount of stress from vibration. I once had the L-shape bracket break loose from the welds on the tubing, but I recon it was a poor MIG welding job. I welded it back together with a 1/16" diameter rod in a stick welder, and it held up for more than 10 years to follow.|
More commonly it breaks the horizontal bracing strap, which is apparently too thin to do the job. After breaking a few of these I double up on the straps, after which they lasted for a few years (maybe 50,000 miles) before they broke again. I finally made one out of 1/8" steel strap, and is is still in use today, about 100,000 miles later.
The longer more vertical strap is apparently mot much use. I have never had an aftermarket exhaust setup where the stock strap waste the right length. Seems it was always too long (with a bow in it) because the "L" bracket we welded on the pipe a little too high. Three large studs in the bottom of the manifold take the weight of the pipe quite well anyway.
Omitting the horizontal strap runs a fairly high risk of breaking the flange on the bottom end of the exhaust manifold as the engine rocks about regularly. I have seen quite a few iron manifolds with one ear broken off, and I have repaired several of them.
I always find these discussions interesting. I understand exactly what you are saying and do not have any particular issue. My angle though is always to look at the circumstances of why, for instance, did the flange break. Were the cars in those cases fitted with the straps? I asked the question once before and no one was able to say. It is so easy to say that the leaving the straps off causes fractures, but has anyone any proof from a large sample of fractures?
Two of us (a very small sample) in this thread alone have been running quite happily for 15 years without the straps and have suffered no fractures. My car came to me without the straps so it was highly likely it was running in the late 60s and early 70s without them. I am a firm believer that sometimes making things too stiff causes metal fatigue. You only have to look at the aircraft industry to see how much wings flex these days, all in an effort to reduce metal fatigue. The industry learned this the hard way from aircraft design in the 50s - the same time the car industry was putting out its MGAs, TRs, Healeys etc.
|To add to Steve's point, I have been running MGA's for over 40 years including twelve years of racing without the strap, and not experienced any problems. |
|I'm with the "no straps" crowd. Over 40 years as well. |
|G T Foster|
|Thanks for the responses. I've taken off the bracket or to be more precise it fell off once the straps were released. It's in s.steel 0.0792 thick -a bit more than 1/16". The metal failed immediately next to the welds. It seems a bit thin to me and I suspect that if were to have been more like 1/8" there would not have been a problem.|
I will join the band of non bracket owners.
|J H Cole|
|Straps on mine are still the originals and have always been fitted. Only 85k miles though. The original manifold did have to be welded up but I recall that was because the stud and brass nut seized and I cracked the manifold flange getting the exhaust off and apart. Cast iron is brittle of course. Historically I got through corroded exhausts much more quickly when using mild steel, so perhaps the brackets did fail but I didn't notice. Stainless is generally much better in fatigue life than mild steel. John|
This thread was discussed between 26/03/2013 and 29/03/2013
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