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YOUR RESEARCHBad idle, then CLANG... borescope shows valve hitting piston head?
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Replace plugs (as well as a bunch of other parts)
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Performed · outcome unconfirmed · Original poster
Anyway, long story short - changed the plugs (as well as a bunch of other parts), ran great for a few minutes then stalled.
Bad idle, then CLANG... borescope shows valve hitting piston head?
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Leading evidence: 'Replace plugs (as well as a bunch of other parts)' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Repair reinstall and send it' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion · Original poster
I'm thinking best case scenario is a stuck open valve - lower/drop engine, pull bank 2 head, have it repair, reinstall and send it?
Bad idle, then CLANG... borescope shows valve hitting piston head?
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My poor old 1999 996.1 tiptronic cab has been resting up over our (Aussie) winter, while I slowly was chasing down a weird bad idle problem. Was driving home as normal when there was an obvious misfire and P0306. No persistent code except for P0341 (which I've been ignoring for 3 years!)
Anyway, long story short - changed the plugs (as well as a bunch of other parts), ran great for a few minutes then stalled. Next startup - all I heard was a metal-on-metal sound - not good - stopped the engine immediately.
Removed plugs and had a look with my borescope - all good everywhere, no bore scoring I could detect... until I got to cyl #6 and saw this
Imprint of a valve on the piston and a bit of oil pooling - coming from the head, relating to the valve?
Didn't see any cylinder scoring in #6, couldn't see any metal debris or anything else.
So, have been searching for information far and wide... have come across some people with dropped valve seats, others with bent valves.
Options?
I'm thinking best case scenario is a stuck open valve - lower/drop engine, pull bank 2 head, have it repair, reinstall and send it?
Have also heard of complete engine rebuilds being required due to damage to bores, rods, bearings etc. But realistically this car has 258,000km, 1999 996.1 tiptronic cabriolet which I'm not going to sink a whole lot of cash into rebuilding the engine when it wouldn't make sense financially to do it. Would send it to a salvage auction and move on - have a new Z on order too.
Any ideas, comments, opinions etc welcome!
Just a wild-*** guess, but broken valve springs are not unheard of in these engines, can result in a “dropped valve”. You can guess the rest. Good luck!
Not, that shiny spot was a reflection of the light on the oil. Couldn't see any metal debris at all
1999 3.4L. Reckon I have a chance at just getting bank 2 head repaired and refitted, or is there going to be more hidden damage that can't be determined without a stripdown?
Bit sad about everything right now
u just have to go at it. Drop the motor and pull the head. Its not really that hard to do. Then pull the sump and look for debris. No use in guessing. Many have just done head work to these motors and put them back together with very good success.
This is a source reference. Confirm exact model applicability in the original material.
