We’ve seen this as well and have made it a routine check ANY time we remove a coil extension. At some point during commissioning Wartsila went through and changed out any coil boots that did not have the “Wartsila” emblem on them. Some brand other than altronic manufactured these and our Finnish team deemed them unacceptable. At any rate we had a lot of the kits for coil extension rebuilds minus the boot and therefore a lot of extra springs etc.
We chocked it up to an installation issue at first and thought maybe we had some heavy handed mechanics working on the units but after the initial inspection and replacement of these springs we’ve had more than a handful subsequently fail. They seem to break right at the point where the spring diameter and coil rate reduces from the electrode connection to the insertion portion of the spring.
No REAL remedy to this, though we did make a warranty claim and were sent new kits to replace the broken springs. What we have done is take the boot off of a brand new unused coil and get a ballpark measurement for insertion depth of the spring. We were not provided the special tool “846 704” for inserting the spring which I’m guessing has a pre set depth machined in it. *shrugs shoulders* What we have found that works is just a straight pick and rotating it clockwise into the coil extension. We’ve seen less coil spring failures after replacement but still find one or two and sometimes more broken when we go to do valves or anything that requires all the coils and extensions to be removed. Bottom line: inspect them every time and replace them if they look questionable.
It could be that the spring protrusion is too great and is causing a bind when pressed on the spark plug. That combined with vibration and heat and, you guessed it, you’ve got a broken spring.
If you do any measurements and find a good sweet spot to set them please share. Or we’ll just eventually but that $500 tool Wartsila is clearly so proud of.