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MG MGB Technical - Parabolic springs - the report

I promised to let people know the outcome of the tests and the resolution of David's complaint.

The springs were found to be within the manufacturers' hardness range of 388 to 444 BHN.

They showed stress areas consistent with an additional spring leaf under the central portion of the parabolic, as seen in his photograph posted earlier.

Such an addition would interfere with the action of the spring and cause the springs to bend round the extended spring seat formed by the additional leaf, leading to the failure you see.

This clearly underlines the importance of not modifying parts as supplied, as this can be dangerous.

With MGOC's permission I attach the engineer's report - it is in 4 pages attached to this and three more posts

Chris at Octarine Services

page 2

Chris at Octarine Services

page 3

Chris at Octarine Services

page 4

Chris at Octarine Services

Chris. I have served as an expert witness in several court cases. I have, also, served on one jury which had to evaluate the testimony of several expert witnesses and decide which to base a judgment on. I am not impressed with this "engineer's report" for quite a number of reasons. Unfortunately, I do not seem to be able to copy and paste from the attachments you have supplied, so it is difficult to respond to all of the things mentioned. However, a few reasons worth considering are"

He notes that the springs are within the manufacturer's specifications of "388 to 448 BHN". One assumes he is intending to indicate that this is a Brinell hardness number, but the "engineer" does not seem to understand that it should be listed as either a "HBS"--Hardness, Brinell, Steel Ball, or "HBW"--Hardness, Brinell, Tungsten Ball. You will also note that the determined hardness is never mentioned by the "engineer". Thus, we are left to decide whether someone who does not properly notate the specific system used can be trusted to know what the factory used, then, properly duplicated the factory testing procedure. I would have expected, at the very least, for the "engineer" to note which penetrator ball he used and the actual Brinell valued found on each of the springs.

I note on page four that he states, in effect, that he has seen a photograph of what might be the springs in question, installed on a vehicle, and from that photograph has based a major portion of his "report" in favor of it being not a problem with the springs. The problems with this are obvious. First, there is no documentation that this is the actual vehicle/spring set under discussion. Second, there is no indication, based on that single photograph, at what point any "third spring leaf" was installed--it might have been installed after the springs were damaged to allow the individual to drive home safely. We do not know, nor is there any indication that this "engineer" knows when the third leaf was installed. Nor, do we know if there was any information supplied by the manufacturer or retailer of this spring set noting that there were any limitations on either the torque of the engine or the use of a "helper" spring (not an uncommon addition in some cases) with the new spring set.

If the report was actually written by an engineer (it does not read like it was)it is unfortunate. At least here in the US, a report like this would almost guarantee the plaintiff a win in any tort action. It is that bad.

Les
Les Bengtson

When I fitted the first pair of springs to the car, they gave a very low ride height leading to considerable contact between the rear tyres and the bodywork of the car. I should have removed them immediately, but since I had fitted them just prior to a holiday with my wife who suffers from back pain I decided to add the lower leaf from the standard MGB springs as reinforcement. This enabled me to use the car. It would appear that despite the initial excessively low position, it was my action that led to the damage to these springs. The replacement springs were fitted without this additional leaf since they gave the correct ride height when fitted.

So I wish to formally apologise to the MGOC Spares and Accessories for any prejudice that my actions and comments may have caused. I will ask the moderators of this forum to remove the thread to put an end to this discussion.

May I add my thanks to Chris Betsen for his support and patience thoughout.
D Balkwill

Why the sudden desire to delete what is a legitimate thread irrespective of the validity of the original allegation and subsequent 'engineer's' report?

God I hate bully boy tactics.
Mike

Just to note, this is obviously a recent report given it makes reference to David's forum post of 4 June 2010 and not the one he originally referred to in his post.
Mike

"The replacement springs were fitted without this additional leaf since they gave the correct ride height when fitted."

So the first set gave too low a ride height without the additional spring? And the second set gave the correct ride height, so had no additional spring, but still wound up (from what I can recall from the original thread? Neither of those situations sounds 'correct' to me.
Paul Hunt 2010

The "verdict" is............What? Faulty springs OR improper use??Rich O
rich osterhout

The "verdict" is that they could find no reason for the springs to have bent in the way they did except that the fitting of the third spring leaf would have caused local and severe stressing at its ends.

David says he only fitted the third leaf to the first set of springs, the club tested the second set (the first having been binned some while ago) - the second set have marks consistent with something having been fitted under them.

When is comes to modifying your car with any non original item, I would strongly advise anyone to talk to the vendor about fitting and use - do not assume that the item works or behaves in the same way as the original item.
Chris at Octarine Services

So can we be clear, David - did you, or did you not, fit (or otherwise modify) the second set of parabolics, which also went pear-shaped? If not, then there remains a valid concern, unless I too have missed something.
Curtis Walker

David says 'not' above. Hence my comment that as the two sets were very different, but the second set without reinforcing still distorted, there is something very wrong with them.
Paul Hunt 2010

Was thinking about getting new rear springs for my 1972 B ,HOWEVER,think i will just blast/and paint my orginial ones. Thats the verdict,as least for me. :) thanks,Rich O
rich osterhout

Springs shouldn't bend perminantly. Sprung steel. You can snap them. I pushed my V8 around with the factory standard springs for quite a long time. I tramped them allot, reverse S curved them and danced that axle around but they never looked like perminantly bending.
Peter Sherman

There are various threads on this subject on the MGC bulletin board. Views seem to be mixed on them. My own experience is that parbolics bend under load, remain bent and have reduced lateral stability such that tyres rub on the arches on mild cornering. Ground clearance was greatly reduced as a result of the bending. I junked the ones I had after a few weeks.

David B
David Booker

Rich, if your original ones aren't too worn and sit at the correct height I would maybe send them off for cleaning and for new interleaving material on them. There should be places around that can clean up and rebuild your existing ones. New springs seem very hit and miss. I got new, lowere dsprings for my roadster to make it CB height and they were still way too high so I used my originals but had them reshaped.
Simon Jansen

This thread was discussed between 11/06/2010 and 17/06/2010

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