Victim: 2001 M96 engine pulled from a Boxster S. Mileage reported to be 45K
Catastrophic Failure
MOF #14
We have discovered another MOF (Mode Of Failure) related to the M96 engine. This one is our most recent tear down that occurred with a 45K mile engine. It is one of the most radical failures that could occur with an engine and we have gained a good understanding of why it occurred. More importantly we are in work already on another "overkill" part to solve this issue that we can apply during our engine updates for our complete engines and component kits.
This is interesting, because this engine fooled us, it also fooled a Porsche Dealership and another independent Porsche shop that had diagnosed the engine prior to it being sent into us. The engine had all the classic symptoms of a seriously failed IMS that had resulted in valve timing alterations, thus colliding the majority of the valves with the pistons, a true nasty affair. When the intake manifold was pulled we immediately saw carnage (broken valves and chunks of piston in the intake ports!) and since I love to dissect engine failures I stayed late to see what was inside this beast.
As the engine was torn down I was expecting to see the IMS shredded, but every time we turned the engine while removing the valve train the only symptom that the engine had was altered valve timing, this was odd. Typically when an IMS fails this badly the shaft shears in half and "parks" the valve train that operates from the opposite end of the IMS drive, located at the flywheel end of the engine (I am trying to explain this so you guys can understand!) and that results in all the things we had witnessed. When this happens the IMS will not turn, so the oil pump stops functioning and 3 cylinders worth of valves stop actuating, resulting in a big mess.
This is where it gets interesting:
When the IMS fails to the point of allowing piston collisions with the valves the IMS is most always sheared.. But when this engine was rotated fore and aft the IMS was responsive to the change in crank position and the typical damage to the oil pump that results from IMS failure was not present.
How could an engine have such a radical failure, with all the same initial symptoms as the IMS failure and have an IMS that was responsive to crank position changes, intact and still functional??? Read on...
When the first cylinder head was removed the engine still had all the symptoms of an IMS failure, but when the second head was removed that cylinder head was found to be perfectly intact with zero piston/valve interference and no damage. The engine was still spotlessly clean inside and showed no signs of abnormal wear on the "intact" bank of cylinders.
As we went deeper it got interesting as it seemed the valve timing was radically off on both sides of the engine, but all the timing chains were intact, nothing was broken and all was in decent condition. At this point of the autopsy we knew that when the case was split we'd find something we hadn't seen before.
When the case was split the IMS came out in good condition without any oil inside it and without any signs of bearing failure or wear. We immediately removed the crank carrier and then we saw the culprit..... The crank/ IMS drive chain tensioner pad was non existant and the tensioner was broken in half! We then dug through the rubble and found the broken pieces and started putting the pieces together to figure out what happened.
Why the valve timing changed:
Because the main drive chain for the IMS lost all tension when the "tensioner" sheared in half, thus allowing the IMS to stop rotating and "parking" the valves. When this occurred a couple of cylinders had open and partially open valves that then collided with their pistons and that resulted in scattered parts, a loud bang and chunks of piston being emitted from the tail pipe...
What we learned:
Something we had never really paid close attention to was the shape and thickness of this tensioner through the various years and models of the M96 engine. We pulled this piece from several engines and started comparing them in shape, interchange, composition and design. We immediately noted that the the early 2.5 tensioner was thicker across the area where this tensioner had broken and that the early unit also had a hardened steel contact surface for the chain adjuster to ride against. The later 3.2 unit had been made thinner through the area where the breakage occurred and had a PLASTIC surface for the chain adjuster to contact.
The part number from the two parts were the same, but one was a .4 while the other had a .5 suffix.
So, why was this part changed? Why would anyone ever replace a hardened steel wear surface with something comprised of plastic, when even the steel wear surface does typically wear....
This is a MOF that we have never seen before and never heard of occurring. After seeing this failure and it's symptoms I believe that some of the "IMS failures" that are diagnosed without an engine tear down are actually this MOF, or at least something similar to it, that cannot be thoroughly understood without complete dissection of the engine.
That said, we are already in work creating a two new components that will solve this MOF issue. First we are making a billet aluminum tensioner unit made to use the OE tensioner pad, this will replace the lightweight, cast aluminum factory unit. This will incorporate a larger, tool steel wear surface much like the earlier 2.5 unit pictured below. Making the wear surface larger will increase the contact patch that the chain adjuster sees, thus increasing service life.
Secondly we are making the wear surface "button" compliant with the OE tensioner, so those that have the early tensioner can replace their wear surface with a larger, stronger part if they don't choose to utilize the entire billet tensioner that we are creating.
I'll never trust one of these OE tensioners again, we'll be applying the billet units to ALL our engines effective immediately and all builds are currently halted while this component is being made.
The key to avoiding problems like these are to make the parts heavier duty than they "need" to be on paper... I call it "overkill Engineering" and it's what keeps things from failing... Its nothing more than classic hotrodding being applied to these newer, robotically assembled, mass produced engines.
We are now going through cores and doing research trying to specify when Porsche changed this tensioner.... I'll report back when we have concrete evidence.
Now for the pictures... More will be posted today on the "reliability" page at
www.flat6innovations.com
The pictures speak for themselves, its mass carnage of an unreal kind.. The kind of stuff that makes it to our "trophy Shelf" filled with offerings to the Gods of Speed...