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YOUR RESEARCHIt isn't always the IMS...
Reported or suspected cause
cam chain tensioner failure
Reported cause
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Reported cause · Original poster
The damage was confined to one head (the 1-2-3 cylinder side) and as best we can determine was caused by a cam chain tensioner failure.
Leading evidence: 'cam chain tensioner failure' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'cam chain tensioner failure' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Clean side of the engine oiling system and so' (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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Depends upon of course when one knows what really happened and if there is any metal bits on the clean side of the engine oiling system and so on.
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20 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
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The local PCA region hosted a tech session this past weekend on the Boxster and M96 engines. We had an '03 Boxster S with a failed motor to play with. The suspicion was, of course, an IMS-related failure. However, we did not know exactly what was up until the engine dropped.
We still have to take the engine apart to fully understand this failure... but let's just say that the overwhelmingly Boxster-owning crowd left kinda shook up.
Hard to say quite yet. The motor turns over manually, sort of. The IMS bearing seems intact on visual inspection prior to removal.
Something broke internally, possibly bending the valves and this cover was the weakest link as it all came apart. We'll know more when we get it apart in a week or two.
Looks like a timing chain guide/rail failed and was caught between the camshaft sprocket/chain and the camshaft cover. That breaks the cover.
The camshaft timing at least on one camshaft might have jumped but if you can still turn over the engine it might have jumped the best way. That is in the direction in which valves do not make contact with the pistons.
Had this occurred it is unlikely the engine would turn over at all.
All and all a sick looking wound but the engine may be repairable. Depends upon of course when one knows what really happened and if there is any metal bits on the clean side of the engine oiling system and so on.
Sincerely,
Macster.
IOWs a camchain guide/rail failed and a portion of this got caught between the sprocket and chain which of course caused the chain to be pushed against the cover and broke the cover.
Even with the debris between the sprocket and chain the chain and sprocket managed to (hopefully) maintain the proper timing.
The above may be the better explanation (or in my case WAG) than my earlier one.
It will be interesting to learn what a teardown of the engine turns up.
Sincerely,
Macster.
UPDATE
We got together on Saturday and pulled the engine apart with the assistance of a master Porsche engine builder. The damage was confined to one head (the 1-2-3 cylinder side) and as best we can determine was caused by a cam chain tensioner failure. The IMS and bearing was intact.
It seems like the tensioner lost tension for some reason, causing the chain to slip and tear up some of the cam teeth. Bits of broken teeth found their way into the oil scavenger pump and caused it to seize. That stopped the motor immediately. The valves in that head bent, but the pistons and bores were intact.
The engine can be rebuilt with a new head. Good news for the owner who now has some additional funding for his V8 swap plan!
As a side note... tearing the engine apart, the overwhelming complexity of the M96 engine really hits you. I'm not sure this design was Porsche's finest hour.
Tearing it down is the "easy part", although I'm learning during assembly that if were to have spent more time cleaning and preparing during dis-assembly, re-assembly would probably go much quicker. Wait until the real fun begins when you reinstall the wrist pin clips in the 4-6 pistons.
Classic example of another failure that could be confused as IMS Failure.
Once one becomes proficient with the M96 it couldn't be simpler.. To be honest we now turn away all internal air-cooled 911 work and only focus on the M96/ M97 engine. We can assembled an M96 two complete days faster than an air-cooled 911 engine, or even a 356 engine! The key is proficiency and understanding.
Glad to see you found the issue.. have any revealing pics for us? I always love those!
Get me some pics..
Debris of ANY sort that finds its way into the scavenge pump will lock it up. This causes the cam drive to continue to operate the scavenge pump, so the pump drive breaks.. When that happens the cam timing on that camshaft becomes retarded and the pistons hit the valves.
This is MODE OF FAILURE #1.. This was the very first documented mode of failure that we experienced on the very first M96 engine that we reconstructed. This is not new, not at all.
This is a source reference. Confirm exact model applicability in the original material.
