Base Unit Fatigue Failure

SydneyRoverP6B

Well-Known Member
Staff member
#1
After changing the engine oil recently, I decided to have a general look around whilst lying underneath. Apart from the intention to drive to Newcastle, which is about 2 hours north of Sydney, there was nothing that prompted my decision.

As it transpired, I noted that the paint beneath the O/S shock absorber mount had a crack in it. Ringing an alarm bell I scraped the paint off to find what I feared, a fatigue crack in the base unit.



Inspection of the N/S revealed a similar situation. After scraping the bitumen paint off then sanding off the undercoat, it was obvious that there was no corrosion evident, so that was not the cause, rather the substantial mileage that my Rover has covered, around 313,000 Miles (504,000km) at the time being the initiator.



Some chassis stiffeners as they are referred to were ordered, and arrangements made for their fitment. It should be noted that this is a known point of failure, especially when corrosion of the base unit in this location is evident. The shock mounting can rip right out of the base unit, which could be very dangerous indeed depending upon the situation at the time.

I must admit that I have never seen this happen to another Rover, nor have I ever heard of such happening, but the fact that the stiffeners are available suggests that there have been other occurrences.

The cracks were drilled at both points of origin and termination so as to prevent stress risers and then all were welded up. The stiffeners were then welded into place.














After that, two coats of POR 15 were applied then the following day one coat of bitumen paint. There is one more coat of bitumen paint still to be applied.



I am very happy with the outcome, with the installation of the stiffeners in theory ensuring that the problem won’t occur again.

Ron.
 

rockdemon

Administrator
Staff member
#2
Glad you spotted it before anything bad happened.

It's interesting that this seems to be an issue in Australia and not in the UK to my knowledge... Is it something to do with the road conditions?
 

ghce

Well-Known Member
#3
Shonky Solihull cars!! I would be making a warranty claim on that if I were you lol.
Yes the only place you hear of this problem is OZ but I really think that Australian roads are little different than NZ or UK.

Graeme
 
#4
Good grief, UK has rear de-dion elbow failures, AUS has front shock mounting failures, NZ here I come! :LOL:

But good spotting Ron, and a fine repair and modification.

Curious though, were these stiffeners a Rover Australia available modification?, and how did you come by yours as you say you ordered some? thanks
Regards,
Scott
 

colnerov

Well-Known Member
#5
Hi, I am not sure that the stiffeners whether fitted before or now would have stopped the
crack. The crack started and ended between where the stiffeners are, so I would think if
left it would have turned and gone up the chassis rail and eventually torn the damper mount
out of the rail. Do you think welding a bar just above where the crack is between the
stiffeners and welding to the boss of the mount would be better?

Colin
 

testrider

Active Member
#6
The belt and braces cure for this would be for the shock mount to go through both sides of the chassis rail rather than just welded on the outside.

I seem to recall Ron that you have adjustable dampers wound up quite firm which would obviously transfer more stress into the mount, but your car has done 5 to 10 times more distance than most of ours so it's understandable that these kind of things might pop up occasionally.
 
#7
colnerov said:
Hi, I am not sure that the stiffeners whether fitted before or now would have stopped the
crack. The crack started and ended between where the stiffeners are, so I would think if
left it would have turned and gone up the chassis rail and eventually torn the damper mount
out of the rail. Do you think welding a bar just above where the crack is between the
stiffeners and welding to the boss of the mount would be better?

Colin
I would think the stiffener would stop a crack from developing in the first place. In the original condition, the shock mount flexes a long bit of the frame rail, which allows the deflection right under the mount pin to be quite large. Large deflection = lower fatigue limit. With the stiffeners in place, there is much less deflection possible for the same strain and the fatigue limit correspondingly higher. Pretty rarely seen failure here, though I've done it to one of my TCs as the result of driving the car very hard on gravel roads and I've seen three or four other cars with a hanging shock.

Yours
Vern
 

SydneyRoverP6B

Well-Known Member
Staff member
#8
Yes I was lucky to have spotted the problem. Given the cracks were covered with either black paint or bitumen paint, I am fairly sure that they would have passed by most people without receiving attention. It was only the fact that I looked around and saw a crack in the black paint that rang an alarm bell. Scratching it off revealed the crack that you can see in the first photo.

The main highways in Australia tend in the main to be fairly smooth, but many secondary roads are pretty rough. You can travel thousands upon thousands of miles even on dirt roads, although my Rover has not done that as yet.

westOz74P6B wrote,...
were these stiffeners a Rover Australia available modification?, and how did you come by yours as you say you ordered some?
Hi Scott,

There is a chassis stiffener that was produced by the Rover Car Club of Australia, which is based in Melbourne, Victoria. I don't know what their current status in terms of availability is. The ones that I purchased came from Classeparts.

colnerov wrote,...
Hi, I am not sure that the stiffeners whether fitted before or now would have stopped the
crack. The crack started and ended between where the stiffeners are, so I would think if
left it would have turned and gone up the chassis rail and eventually torn the damper mount
out of the rail. Do you think welding a bar just above where the crack is between the
stiffeners and welding to the boss of the mount would be better?
Hi Colin,

The crack on the O/S is the one shown in the photos, whilst the crack on the N/S was all on the face of the base unit, directly alongside the shock mounting, rather than beneath it. The crack was welded and the chassis stiffener then locates directly over the top of it.

The stiffeners are designed to prevent any flexing from occurring in this area as Vern mentioned, so I am certainly hopeful that they will cure the problem with no further cracks evident in the future.

testrider wrote,...
I seem to recall Ron that you have adjustable dampers wound up quite firm which would obviously transfer more stress into the mount, but your car has done 5 to 10 times more distance than most of ours so it's understandable that these kind of things might pop up occasionally.
Hi Paul,

I did indeed, but after I detected the cracks I set them just above the minimum setting, so as to reduce the load that the mounting would be subjected to. It seems entirely reasonable to surmise that the high setting that I was running with the front shock absorbers compounded the problem.

Ron.
 

unstable load

Well-Known Member
#10
Well spotted there!
I see that you did not weld the stiffener along all it's length, but only at the top, the bend and then all the bottom part.
Is that normal practice?
 

SydneyRoverP6B

Well-Known Member
Staff member
#11
billoddie wrote,...
A fortuitous find!
What has the end result of fitting the stiffeners been in terms of the how it feels to drive now?
It was indeed Brenten! Funny that you should ask, as before fitting them I never imagined that I would be able to notice any difference. The difference was subtle, but the front end felt tighter, more secure. It may well have been analogous to the placebo effect, but either way, the outcome was positive.

unstable load wrote,...
Well spotted there!
I see that you did not weld the stiffener along all it's length, but only at the top, the bend and then all the bottom part.
Is that normal practice?
Thanks John :)

The stiffeners are designed only to be welded at two distinct points when referring to the vertical section. The section between the top and the curve remains proud of the base unit, whilst the horizontal section beneath makes full contact along its entire length, thus promoting a continuous weld as opposed to a discontinuous weld as applicable to the above.

Ron.
 
#12
Ron replied,
Hi Scott,

There is a chassis stiffener that was produced by the Rover Car Club of Australia, which is based in Melbourne, Victoria. I don't know what their current status in terms of availability is. The ones that I purchased came from Classeparts
Thanks Ron, I saw the Classeparts ebay listing;

http://www.ebay.com.au/itm/ROVER-P6-200 ... 1c48a35c7c

and also noted their heavy duty damper mount kit, did you not consider this while you had welding being done with the stiffeners?? (again, just curious) looks like it is a larger diameter pin with smaller section bushes...

interesting that a UK supplier is aware of this potential, so its not just an aussie/rough road country thing...

Scott
 

SydneyRoverP6B

Well-Known Member
Staff member
#13
westOz74P6B wrote,...
Thanks Ron, I saw the Classeparts ebay listing;

http://www.ebay.com.au/itm/ROVER-P6-200 ... 1c48a35c7c

and also noted their heavy duty damper mount kit, did you not consider this while you had welding being done with the stiffeners??
Actually Scott I didn't give any consideration at all to the heavy duty damper mount kit. I have the tool to remove the shock from the original lower mounting, so that has never been a problem. I am not particularly thrilled by the nylon bushes that would replace the rubber ones. I would also want to be certain that they would work effectively with Koni Shocks.

Ron.
 
#14
Hi Ron,

We have the full strengthening kit fitted, including the pin part of the kit. Put simply don't fit the pin part of the kit!!!! The hard nylon damper inserts do not allow enough free movement of the damper "eye" which results in the damper "eye" fatiguing with time, we've broken 2 dampers so far. This part of the kit is very hard to remove once fitted so we've been left with no option other than leaving the nut looser than we'd like, this has stopped the failure but introduced a rattle, I think the other forum member with this fitted had a custom damper made with a larger "eye" and softer inserts, but I'm not sure.

We do use our car very hard but this failure would largely be unaffected by the type of use, as long at the nut was tight and the suspension moved through most of it's travel the fatigue failure would occur.

Tim
 

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mrtask

Well-Known Member
#17
My first set of the same standard-sized GAZ shocks on the front failed in exactly the same place, and for the same reason. As Tim mentioned, I then ordered one size larger shock eyes from GAZ. In actual fact the new GAZ front shocks are now the same size as fits a P5B, and I've fitted urethane bushes in preference to the hard-as-nails white Delrin bushes that came with the front shock mount upgrade kit. As Tim remarks, removal of the welded-in-place chunkier front shock mounts isn't an easy option, and in fact just fitting the new uprated gas shocks was a bit of a palaver. Two or three thousand miles of fairly regular use since the fatter shocks went on, and they're doing their job fine. I do have a lot of 'pinging' spring noise in the front suspension, as the coil springs are uprated as well as the anti-roll bar being uprated. That seems to have been the pay-off for improved cornering and generally taughter and more stable handling.
 
#18
I'm just bumping this thread as you don't always get the photos when you link to it.
I bought an anti roll bar from Colin Gould & he suggested the chassis stiffeners too so as they're only £20 a set l took a punt. We may or may not fit them to Bruiser 2 but Richard wanted a picture to see how they fitted.
 

jp928

Well-Known Member
#19
Can you advise where these bits might be ordered please? Cant see them at Classepart...
thanks
Found at Classepart - GBP 108!!! Where are the 20 quid units ?
 
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