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Another occurrence
The second occurrence of this mode of failure in 10 months.. Yet again this one was misdiagnosed as an IMS bearing failure.
The IMS bearing is intact and has no symptoms of failure, but upon inspection we found a chunk of the IMS tensioner paddle wear pad in the oil sump. This sparked a boroscope interrogation of the IMS area through the IMS tensioner bore after the tensioner was removed.
The engine is not totally apart, but after I did a thorough inspection with the boroscope I can see that the tensioner paddle is missing it's plastic wear button and the entire wear pad has been ripped off and chewed up by the IMS drive chain. The remnants are laying at the bottom of the crankcase beneth the IMS drive as depicted here in these somewhat blurry photos from my boroscope from deep inside the engine.
The early engines had metal wear buttons for the IMS tensioer to rest against, that was too expensive so around 2001 this was changed to PLASTIC and when it wears thin and fails this sort of failure occurs since a ton of 'slack" exists in the IMS drive chain which causes the chain wear pad to be eaten up, resulting in an engine that has variable valve timing in a very bad way. The billet chain tensioner paddle that we have made with LN Engineering includes a STEEL wear pin that will resist this sort of failure; needless to say I use this in EVERY engine we build.
This engine is more than likely totally nuked. My forecast is that the majority of the pistons have had collisions with the majority of the valves and that most everything internally looks like 3 mile island.
More will be known when I complete the autopsy and fill out the failure report. For now it's clear to see that the IMS and chain are intact but that the wear surfaces and plastic wear button are FUBAR.
More pics later
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