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Wartsila’s User Group Forums 50 SG Engine Sparkplug spring-connector failures

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    We’re seeing quite a few failures of the sparkplug spring-connector (part# 501 111) on our 50SG units.  Some are found broken and burned, some have burned away completely.  This arcing has resulted in burning and cracking of the lower end of the coil extension in some cases, requiring replacement of the extension.   Since commissioning we’ve not run more than a few hundred hours without coil & valve cover removal to check or change valve clearance, replace pre-chambers, or other activities related to meeting performance test requirements, so we’re nowhere near the expected 1000 hour service life of the sparkplugs in a peaking application.

    We’ve been careful to install the sparkplugs and connectors in a clean and dry state per Wartsila’s recommendations, cleaning the electrical connections with contact cleaner each time the coils are removed.  (sparkplug threads are anti-seized, of course)

    Our findings have us wondering if silicone sparkplug boot grease would improve the service life of the spring connector, as is common practice in automotive applications.

    Has anyone else experienced similar failures and tried using sparkplug boot grease on your units?

    Thanks in advance for any shared experiences,

    Dave Mordecai, City of Tallahassee, Hopkins Station


    Dave –

    UMERC has also experienced quite a few broken ignition coil springs.  UMERC has an open warranty claim with Wartsila for this issue.  Wartsila did provide a failure report with multiple potential causes for breaking springs, and they are currently working to identify the cause.

    As far as boot grease – UMERC received a thumbs up from Wartsila TS to use di-electric grease on the spark plug boot; however recently Wartsila rescinded that recommendation and told us not to use di-electric grease on the boot, because the grease collects dust/debris that can cause arcing.


    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.


    We have been using Dielectric grease on our coil boots for several thousand hours, and it has not caused us any issues whatsoever.


    Update for UMERC: continue to have coil spring failures;  Wartsila has been on site to investigate and provided feedback on site maintenance practices for spark plugs.  UMERC has experienced a lot of contamination build up on the spark plug, boots, extensions, coil springs and the chamber such that Wartsila has requested extensive cleaning of these components.  Dielectric grease had been used on the inside of the boot and on the springs, but Wartsila has requested this practice be stopped until cleanliness is restored.  The root cause of the coil spring failure is still unknown, and until it is determined coil spring failures will most likely continue.  At this time UMERC continues to push Wartsila for root cause of coil spring failure.

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