Autopsy

[alniki]

Autopsy of my broken engine due to oil starvation and subsequent failed rod of cylinder #5. Picture shows cylinder, piston, broken/bent rod cap, bent rod bolt, broken pieces of the engine case and oil sump plug.

[Grady Clay]

alniki,

Sorry to see the carnage in your engine.

Much has been written about your best course to recovery and building the best engine you want. There is lots of good advice (and some other). Run your plans on this forum and listen to the feedback..

What is the long-term history of the engine and car? What is the general condition of the car? What is the wear situation of the non-broken parts? Did the “oil starvation” damage other (non-broken) parts – like cams, rockers, other cylinders, etc?

How do you know there was oil starvation? Was the engine run out of oil? Was there a sudden leak or failure? Did someone just not pay attention? Was it not refilled after draining? There can be many causes but you need to identify which. This is important to identify so it can’t happen again AND to identify areas in the engine that will need attention during the rebuild.

There are other possibilities for this failure. Over-rev is first on the list. If so, other components are now suspect.

Serious attention needs to be paid to the oil system in the chassis. It is surely contaminated with debris from the failure. I would remove from the chassis, disassemble, clean (or replace), assess and service the entire oil system. That is everything from the oil tank to the front cooler and everything in between. Simple flushing in situ will not suffice.


Your posting questions and your proposed solutions will lead to a good outcome.

Best,
Grady

[alniki]

Grady,

The car had been sitting for years before a car dealer resurrected it and sold to me. It consumed a lot of oil and idled rough. Plugs of Cyl #3 and #6 got fouled quickly but I changed the plugs frquently and lived with it for almost two years because I only drove it for a couple hours on weekend and it ran well enough at high rpm/speed to entertain me. In the meantime, I was reading and websurfing to prepare myself for an engine rebuild.

This spring, after a good set of replacement fuel injectors, the engine finally seemed to work perfectly. It idled smooth and nice and was more powerful in the entire rpm range up to 6000. I was busy enjoying it and became complacent even when the oil pressure light continued to blink at idle because I read in the owner's manual that it is normal at idle. Before that I'd add two quarts of oil at the first sight of the oil light, usually at cornering or braking. If I had not read the owner's manual the engine would not break, I think

The break came during a slow down from 5000 rpm when a buzzing sound emerged and quickly turned into loud clank. I stopped at curb, shut down the engine, checked the engine bay, nothing, restarted the engine, and drove home. Retrospectively, I think the case was already broken when the clank emerged and the buzzing sound before that was about conrod grinding its bearing againt the crank journal. And I drove it uphill for about 0.3 mile after that disaster. Talk about robustness and spartanism.

At the garage, the mechanic took off the sump plug and could hardly drain any oil. As for the oli tank, he said there was about 3 qts left in it. So he concluded it's oil starvation. Me thought it's a failed rod bolt, so as to forgive myself for the ignorance and stupidity, because the oil pressure was fine at 5000 rpm before the engine broke.

After dissambling the engine, I found a small oil pool between the #6 piston and cylinder wall that may explain the high oil consumption, probably due to worn piston ring. The case rib at Cyl #5 was also damaged by the broken rod. The crank was not shown here but I mearsured it and all are within spec except for the #5 rod journal. Some minor scuffing was noticed on the wall of a few pistons. The #3 rod bearings was sticking to the crank journal after the cap was removed and curled inwards when I took them off the journal. These might be the next to go if I ran it longer.

Now for the debate on the need of thoroughly cleaning the oil system after a catastrophic failure. I got an engine that had been sitting in a dismantle yard for a couple years and installed it in my car. It ran like crap and smoked a lot. This engine was recently disassembled, too. My mechanic said it's been rebuilt and the cam sprocket was reversed and timing incorrectly set. I checked the crank, all within spec. The bearings, used, but not scratched except for the #3 rod bearing. The inner IMS bearing showed copper on one side, similar to that of my original engine. I didn't see strong evidence of scratches due to shavings/debris from the failure. But I'm gonna to clean the entire oil system anyway.

Thanks for your attention.

[lucittm]

alniki,
Sorry to hear of your broken engine. This has happened to me before with motorcycles, but not in a car. I think the effect of momentary oil starvation is the same:
Either the piston seizes in the upper (hot) part of the cylinder because the rings/piston become momentarily welded to the cylinder, or a main bearing/rod bearing will freeze to the crackshaft. It is often the bearing with the largest surface area because without oil it will generate the most friction and heat. Other times it is the most remote bearing from the oil pump because the flow at the end of the line is just too low.

The usual result is that the connecting rod interface to the crankshaft or the piston pin transition will fail and the heat has something to do with this. Much of the resulting damage comes from the broken pieces of the rod impacting the spinng crackshaft or the stationary engine casing.

Some questions. Do you normally operate the engine at 5000 RPM? Was your piston stuck in the bore? If so, at the top of the bore? What was the condition of the #5 bearing? With the 3 quarts left in the oil tank, was any showing on the dipstick?

Some good lessons here.

Thanks,
Mark

[alniki]

Originally Posted by lucittm

Other times it is the most remote bearing from the oil pump because the flow at the end of the line is just too low.

Some questions. Do you normally operate the engine at 5000 RPM? Was your piston stuck in the bore? If so, at the top of the bore? What was the condition of the #5 bearing? With the 3 quarts left in the oil tank, was any showing on the dipstick?

Recall reading a post here arguing the crank journal most vulnerable to oil starvation is actually not #2 or #5 but the others that are nearer to the oil supply to the crank by fluid dynamics. But my case suggests #5 fails first, compatible with what Wayne suggested in his engine book, though as I have mentioned, the #3 bearing seemed half toasted, too.

I did frequently operate my engine at high rpm, mostly above 4000 and up to 6200 rpm, as I think that's when the Porsche flat-6 sounds most sweet and the car most enjoyable.

The piston was not stuck but has a shallow valve impression on the top, though the valve was not bent. The #5 journal may need a 0.5mm undersized bearing if to be ground and reused, the original #5 bearing has become shavings and debris in the case. Fortunately, the debris/shavings seemed to concentrate within the #5 compartment, which happens to be near the magnetic oil drain plug.

Due to heavy oil consumption, I was never able to keep the oil level up to the dipstick for long. I just added oil when the oil light glowed but I watched the oil pressure gauge closely.

[T77911S]

i have heard that the 3.2's had rod bolt problems anyway. someone may confirm or correct me on that.

if i read it correctly, you were adding oil based on the oil light coming on? if so, you were asking for trouble, especilly at 5k rpm. your car should have at least 10qts in it. i dont run mine at the full line, more around the min line, but i i know i have plenty of oil. i keep mine low because it seems to use less that way. otherwise i get more oil blow by and leakage throught he valve seals, but my oil light NEVER comes on and my oil temp is always good.

[Flat6pac]

Thant was not a rod bolt problem..
Bruce

[T77911S]

Originally Posted by Flat6pac

Thant was not a rod bolt problem..
Bruce

no, not with the oil light coming on