Sir. can you expand on the complete details of the "stack up" scenerio.
"Stack up" refers to all the flanges, washers, spacers and other components fitted between the threaded fastener's first bearing surface and the nut that retains them.
ie, How many layers were sandwiched ?
As I recall, the only component in the cylinder hold-down stud's stack-up is the cylinder base flange. There are more components involved in the through-bolt stack up (the crankcase halves and the silk thread between them come to mind), but that stack up is less critical.
When the cylinder base nuts are torqued, the stud stretches a tiny amount. Once stretched even that tiny amount, the stud acts as a powerful spring that holds the cylinder on the crankcase despite the tremendous side-to-side movement the cylinder experiences during normal engine operation.
Let's say that when the hold-down nut is properly torqued, it results in the stud being stretched by 1/1000 of an inch (just for illustration). It is that stretch that squeezes the parts together with thousands of pounds of force. (The squeezing force is called pre-load.) Furthermore, the nut can't rotate off the fastener because of the tremendous torque that would be required to move the nut.
Now let's say that in the stack up is a washer that is 1/1000 of an inch thick. Let's imagine that during engine operation the washer splits and somehow is lost from the stack up. The stud will instantly lose all its stretch. The assembly's pre-load will instantly disappear. The nut, though it hasn't yet moved on the fastener, will now only be finger-tight. The nut will vibrate off in seconds and the engine will fail.
TCM warns that there should be no paint on the top of the cylinder base flange on the hold-down nut's bearing surface. The reason is that the paint will act as a very fine washer in the stack up. It will resist the pre-load forces as the nut is torqued down. Over time, however, the tremendous forces imparted by the stud stretch and the engine operation will cause the paint to degrade and disintegrate. The stud will lose its stretch. Once that happens, the nut will lose its torque and vibrate off. Engine failure will result.
TCM also expressly warns that there should be nothing on the mating surfaces of the cylinder base and the crank case. The reason? Whatever you put there may hold up through the torquing process. However, during engine operation, it will disintegrate or degrade. Just like when a washer is lost from the stack up, once the "foreign" material on the mating surfaces degrades, it will cause the studs to lose their stretch.
GasketMaker is an interesting substance. It can withstand tremendous loads and thus will bear up against the studs being stretched. But when exposed to engine operating temperatures, the GasketMaker degrades after about 200 hours. Thus, GasketMaker must not to be applied to the cylinder-to-crankcase mating surfaces.
Teledyne's manuals warn that the mechanic should apply nothing to the cylinder-to-crankcase mating surfaces.
The manuals do, however, allow GasketMaker to be applied to the cylinder base oil seals. Problem: no matter how careful you are, when you torque up the engine, some GasketMaker is going to get squeezed off the seals and onto the mating surfaces.
A layer of GasketMaker less than 1/4 the thickness of a piece of paper someplace on the mating surface is enough to cause the engine to come apart.
The total volume of goop necessary to cause havoc is less than the size of a pea. Experts testified it was less than 1/4 of the volume of a penny.
Did Teledyne strictly forbid this practice ?
No. That was the problem. Instead of forbidding the practice, its manuals authorized applying GasketMaker to "all uncoated oil seals." The cylinder base O-Ring is an uncoated oil seal.
Was it written anywhere in the service manual not to do that ?
No. It was written that nothing should be on the mating surfaces. But you can't tell that sealant has migrated from the oil seal to the mating surfaces since the surfaces, once torqued up, are not visible.
I agree someone can stack up numerous gaskets layered with a sealing compound and that can cause incomplete compression of that joint so I would really like to read the report that clearly spells out what happened in this particular case... Can you provide me with a link to those documents.
There is no "report." There is recorded testimony of various engineers but it isn't on line. If you are interested I can perhaps send you hard copies of the transcripts. But you seem to get that stacking up numerous gaskets can cause imcomplete compression. That's because the gaskets "give" over time. Some joints are engineered to allow for that. The cylinder-to-crankcase joint is not. That's because the cylinder hold-down studs are very short and stretch only the tiniest amount. Unlike the through bolts, which are longer and can be stretched further, the studs cannot accomodate any change in the thickness of the components in the stackup without losing pre-load.
Hope this is helpful. But my real point is that
there is often more to a jury verdict than meets the eye. When we first hear about the verdict, we think it's BS. "Clever plaintiff's lawyer fooled a stupid jury." But if we were on the jury for the six weeks and saw all the evidence, we might have reached the same conclusion that the jury did. Even though the conclusion was totally different from the NTSB's.
Possibly.
Mike Danko
www.aviationlawmonitor.com
. No, it wasn't 'joe shade-tree' who got shaken down, it is the 'deep pocket', in this case the overhaul shop that did the work many years earlier and Conti who didn't say that 'gasket maker' can't be used on cylinders.
