I have a Pajero 3.8 V6 that has covered a little more than 180k trouble free kms. I recently drove it down from Namibia and had the 180k service done at the Mitsubishi Agent in Boksburg. Shortly afterwards I drove it to the Eastern Cape where a butterfly broke and where it was discovered that the bolt holding the inlet manifold in place next to the chamber where the butterfly broke had not been refitted.The vehicle had covered 1 347 kms since the service at that stage. Part of the butterfly was recovered but the other part has lodged itself in the valve in that cylinder. The dealer agent is claiming that this is a result of metal fatigue and not the fact that the 7th bolt on the manifold was not fitted as it can operate quite easily with only 6 bolts and even 5 for that matter. I find this very strange as why would something be engineered with 7 bolts if it only needs 5 ? I paid R16k for the service, had to replace the entire fuel flap set (housing with all six butterflies) for R19k and am now been requested to pay a further R34k to have the engine "repaired". I find it very strange that it is considered metal fatigue when the butterfly that broke is next to the bolt that was not fitted and the old fuel flap set has evidence of air being sucked into the chamber right next to where the bolt fits. Has anyone experienced this before?
Difficult to say without actually seeing the failed parts. However In my opinion (as both an owner of many pajeros, as well as having been involved with failure analysis in the aircraft industry once upon a time) I would fight them on this.
Metal Fatigue results from stress - typically causing the metal to repeatedly be distorted or bent backwards and forwards. This can occur during cycles of heating and cooling which engines are subjected to all the time. However engine manufacturers, particularly one like Mitsubishi simply would not design an engine where such a critical part as a butterfly in the inlet manifold could suffer the type of stress /distortion that would lead to metal fatigue at such a low mileage. In fact a part like this should actually NEVER suffer from the type of metal fatigue that would lead to failure... I would therefore tend to believe that come sort of ham-fisted workmanship occurred during the reassembly of these parts after the service, which then caused the butterfly and its securing screws to be abnormally stressed. This may have been the missing bolt, but could also have been some other incorrect assembly factor (eg; incorrectly placed shim or washer or gasket, or mishandling / dropping while the manifold was off the vehicle etc). The type of mechanic who misses putting back a bolt is often careless or badly trained and has made some other assembly error which may have caused the failure. It does seem "too coincidental" that the failure occurred adjacent to the missing bolt. My guess is therefore that the missing bolt allowed distortion of the manifold (when hot) in that area, which then resulted in "binding" of the closest butterfly against the inside wall of the manifold, and caused it to be be stressed in a manner for which it was never designed. I would start with a very careful examination of the inside of the manifold in the area of the failed butterfly for signs of scraping / polishing which would indicate that it had been "binding" prior to the failure. This may require special tools such as a boroscope. It may be worthwhile getting in the services of a professional, particularly a metallurgical or engineering laboratory to take a look to determine the failure sequence...maybe try getting the parts to a university...
Metal Fatigue results from stress - typically causing the metal to repeatedly be distorted or bent backwards and forwards. This can occur during cycles of heating and cooling which engines are subjected to all the time. However engine manufacturers, particularly one like Mitsubishi simply would not design an engine where such a critical part as a butterfly in the inlet manifold could suffer the type of stress /distortion that would lead to metal fatigue at such a low mileage. In fact a part like this should actually NEVER suffer from the type of metal fatigue that would lead to failure... I would therefore tend to believe that come sort of ham-fisted workmanship occurred during the reassembly of these parts after the service, which then caused the butterfly and its securing screws to be abnormally stressed. This may have been the missing bolt, but could also have been some other incorrect assembly factor (eg; incorrectly placed shim or washer or gasket, or mishandling / dropping while the manifold was off the vehicle etc). The type of mechanic who misses putting back a bolt is often careless or badly trained and has made some other assembly error which may have caused the failure. It does seem "too coincidental" that the failure occurred adjacent to the missing bolt. My guess is therefore that the missing bolt allowed distortion of the manifold (when hot) in that area, which then resulted in "binding" of the closest butterfly against the inside wall of the manifold, and caused it to be be stressed in a manner for which it was never designed. I would start with a very careful examination of the inside of the manifold in the area of the failed butterfly for signs of scraping / polishing which would indicate that it had been "binding" prior to the failure. This may require special tools such as a boroscope. It may be worthwhile getting in the services of a professional, particularly a metallurgical or engineering laboratory to take a look to determine the failure sequence...maybe try getting the parts to a university...