S1 V6 auto back on the road at last!! - Problem solved!!

[xmexclusive]

In inspecting for cracks in these quite thin components ultrasonic or eddy current detection are probably a bit of an overkill.
Ultrasonic is good in solid metal contact but very poor close to the surface boundary.
Eddy current is better for surface cracks but needs a bit of signals seen interpretation.

Internal flaws in the steel are the least likely cause of failure in these components.
Clean steel making was a major success achieved in the 1960's.
In my opinion machining marks, rough handling marks, surface breaking imperfections or rust pits are the most likely crack initiators.
A very good clean and then careful visual examination should identify any areas that need detailed examination.
First stage of the detailed examination just requires good light conditions and a very strong magnifying glass.
A dye penatrant test will reveal the full extent of any surface cracks.
I consider the dye test can be carried out by someone used to working in a clean environment.
The test item surface needs a full clean.
It is then sprayed with the red dye and the surface wiped clean.
The area is then sprayed with a white powder and left for a few minutes.
If surface cracks are present the red dye will leach back out and appear as red lines in the white powder.
Kits can be bought but a little hand sprayer of red dyed penetrating oil and a talc puffer does work.
For those that want very detailed visual examination a USB microscope (50x to 1000x magnification) can be had on ebay for £20.

John

[Dieselman]

Good advice there on the dye penetration testing, John.

[MTXM]

Thanks for your further comments and sympathies chaps and yes I have not given up on her yet! Slightly better news today as the replacement starter plates arrived and are looking good. I decided to take both those in stock as I think I was lucky to find the parts and the price was reasonable.

I am going to start pulling bits off on the weekend and there is just a chance the engine might stay in the car! The replacements appear sound and undamaged, although I shall arrange further checks before fitting. As to why the problem occurred, I mentioned before the ring is only under load when starting and I cannot personally see how even a slight imbalance could cause shear cracks around the centre fixings, other than through age and natural fatigue.

Any thoughts/suggestions would be most welcome and the steel plate is approximately 1.5mm thick by the way.

With regards,

Matthew T.

PS. Another thought of mine is that the starter ring is attached only to the crankshaft, therefore any imbalance problem would have to come from the engine, although the ring obviously sits alongside the flex plate and shares the same centre fixings, with the latter connected at each outer corner to the torque convertor.

[MTXM]

A number of the gearbox specialists I have spoken to point out not unreasonably it is a odd coincidence that the flex plate and then the starter ring have failed within a short time and there must be a linked cause, eg. an imbalance and/or misalignment issue. On the other hand, even without additional mitigating factors, there is a link in that both parts were of the same age and subject to the same past use and abuse! I know that the car was not looked after well and driven hard from the generally poor state of the engine and box. What does everyone think!

I also wanted to put out that the examples of failed starter rings shown earlier are actually combined with flex plates, so the situation is slightly different to what I have.

With regards,

Matthew T.

PS. In answer to Dean's earlier query the mileage is 135,500.

[xantia_v6]

I imagine that when the first arm of the flex plate failed, it would put unbalanced strain on the starter ring, perhaps causing localised fatigue, leading to later failure?

[MTXM]

The flex plate did not fail completely Mike and the component when removed was cracked under all three corner fixing bolts, which I assume allowed some further lateral movement and I was alerted by a slight chaffing noise as the nut heads grazed the engine casing.

As also mentioned above, the starter ring is only under load when when the starter motor is engaged and the two items are completely separate, therefore no unbalanced strain could anyway be imposed.

With regards,

Matthew T.

[Dieselman]

I was alerted by a slight chaffing noise as the nut heads grazed the engine casing.

There is only one way that can happen, the starter plate was being flexed. I suspect this is what has led to it's demise.

[MTXM]

That comment was actually in relation to the earlier cracking of the flex plate Will, although the subsequent failure of the starter ring created a similar if slightly more dramatic noise before it eventually broke! As you suggest the starter ring is also designed to flex, so perhaps it is just due to prolonged used and age that it has failed and no other factors? With regards, Matthew T.

[MTXM]

Well I got the car blocked up in the garage this weekend and started to strip of the engine! The good news is that the failure of the starter plate does not appear to have done any damage that I can see and the bad news the engine must come out yet again!! I shall take my time over dismantling and rebuilding and there is some consolation in that I know exactly what is involved. While the engine is out I shall also change the steering ram as the operation was not as smooth as I would like. Watch this space for future updates! Regards, Matthew T.

[MTXM]

Here is a further picture of the starter rings that I have been fortunate to acquire! Regards, Matthew T.