Better To Do Today…
DON’T PUT OFF the maintenance that is needed today before you go flying, or you may not be flying tomorrow.
That’s the moral of this installment. Have you ever had that sinking feeling, knowing that what you are about to do is wrong, but you do it anyway and then you later suffer the consequences?
We can all most likely say, been there, done that!
On a cold fall day, the owner of a Sonerai II LTS wanted to go flying one last time before he pulled his cylinder heads off for a valve job over the winter months.
For the last 20 flying hours, he knew that one of the exhaust valves needed to be serviced, as he stated that he had no valve adjustment left with the rockerarm/valve-adjusting screws. When he pulled the prop through, he could clearly hear the exhaust valve wheezing.
Unfortunately the desire to go flying was a stronger emotion than completing the needed maintenance. So our pilot departed Dupage airport in Illinois and headed to Janesville, Wisconsin, for a late fall breakfast. He arrived there safely, ate breakfast and then headed back to the Dupage airport, when it happened. Bam! All hell broke loose.
In an instant, the aircraft was vibrating so violently that the pilot thought the wings were going to shake off. His forward visibility went to zero as hot oil seeped through the cowling, covering the canopy and jelled, blocking his forward visibility. He could only see through a small area out the side of the canopy. Smoke was also filling the cockpit.
In an instant, he switched the fuel off, turned the engine off and was greeted with the sound of silence, complete with fear and panic. As he searched out the side of his canopy for a place to land, smoke continued to trail from the aircraft.
Losing altitude, he spotted a vacant road for the inevitable emergency landing. Lining up on the road, the wheels touched after what seemed like an eternal flare. Unable to see forward, he did not see the curve in the road that was rapidly approaching.
The aircraft, still traveling at 40 to 50 miles per hour, ran off the road and came to rest in a ditch, crinkled and crunched—a total loss. Thankfully, the pilot escaped with only a few minor scrapes. The engine installed in the aircraft was a 2180cc VW conversion that the pilot had built up with parts from a variety of vendors.
It had a total of 212 hours on it at the time the exhaust valve failed. The compression ratio was 11.5:1, as measured after the accident. 100LL avgas was used exclusively. The high compression ratio was certainly a contributory factor, leading to the valve failing and the subsequent accident.
The high lead content of avgas is what caused the valve to leak in the first place, i.e., lead buildup between the valve face and the valve seat. Photo A shows the line up of valves that were removed from the cylinder head. You may notice that the exhaust valve on the left is missing the valve head. It was never found!
You can clearly see which valves are the exhaust valves in the photo. They suffer a tremendous punishment in any engine. The exhaust valves were a one-piece stainless steel Manley exhaust valve—the best money could buy at the time. Shown in Photo B is a close-up of one of the surviving exhaust valves.
It’s hard to tell in the photo, but the valve had eroded about .040″ in the neck area, just above the area where the white coating ends. Additionally, the sudden engine stoppage caused the valve to bend slightly. This is only a presumption, however, as I have seen valves bend in other engines when they stop suddenly.
The damage done to the cylinder head is shown in Photo C. The spark plug had been sheared off by all the debris flying around in the combustion chamber. Hell has no fury like a broken exhaust valve head on an unscheduled suicide mission.
Photo D shows the external damage done to the engine case and cylinder before the engine was pulled down for examination. If a picture is worth a thousand words, you know the rest. The pilot was very, very lucky that he did not have an engine fire to contend with along with everything else.
Just imagine for a moment, you have a steel connecting rod thrashing around unchecked, beating against the magnesium engine case and cylinder, 3000 times per minute, destroying everything in its path. Magnesium is a very flammable material! The extent of damage done to the connecting rod and engine case is shown in Photo E.
You may make a mental note that the oil cooler location on top of the engine is capped with a block-off plate, meaning there was no oil cooler installed on the engine. Imagine the force it takes to bend a connecting rod like this!
The force was so strong that it even wiped out the top left cylinder head stud. What was left of the pistons is shown in Photo F. The valve head that broke pounded a hole through the #1 piston on the left.
The piston then separated from the connecting rod, welding itself in the cylinder. With all the debris flying around inside the engine, some of it finally found the opposing #3 piston and rod. You can see that the #3 piston had failed also.
Pistons #2 and had to have the wrist pins pushed out, as the lack of oil for just a few seconds seized the wrist pin to the piston. VW’s are supposed to have a floating wrist pin in the piston. Photo G shows some of the damage to the internal engine.
The camshaft gear had teeth broken away. This happened from having metal trapped between the aluminum drive gear on the camshaft and the steel drive gear on the crankshaft. Look at the first two connecting rod journals on the crankshaft.
The rod bearings are welded to it. The #4 main bearing, just behind the prop hub was also seized on the crankshaft. At the bottom of the photo, just below the camshaft, you can see some of the metal debris that was in the engine.
The #1 connecting rod is shown in Photo H. The rod is standing up by itself as if the rod bearing were welded to the crankshaft. The #2 connecting rod is also stationary. You can see the discoloration to the crankshaft, giving a clear indication of how hot the crankshaft got in the few seconds it took the engine to rip itself apart.
The stud side of the engine case is shown in Photo I. This side of the case held cylinders #1 and #2. The #1 connecting rod welded in an instant to the crankshaft and relentlessly pounded the engine case on both the top and bottom of the case, creating additional clearance holes.
The top of the case also had a small hole worn through from the rod as it flailed around freely for a second or two before being welded to the crankshaft. Photo J shows the studless side of the engine case.
Although the damage was not as severe as it was to the stud side of the case, the rod still ripped away the top of the engine case after it was separated from the piston and allowed to rotate unrestricted for a few brief moments in the engine case. Also notice the debris in the oil sump area of the engine case.
Our pilot escaped from this accident with a new respect for not putting off known and needed maintenance that should be done today, and not waiting to do it until tomorrow. Not all deferred maintenance decisions have the dire consequences as depicted here.
VW valves have been described as a weak link in the engine. This is because in the Beetle, the #3 cylinder sits behind the oil cooler in the shroud and runs hotter than the other three cylinders do. VW addressed this by slightly retarding the timing to this cylinder to have it run cooler.
In an aircraft conversion you don’t have this problem, as nothing is obstructing air to the cylinder. The valves used in conversion engines are stainless steel or a standard two-piece welded valve and will give hundreds of hours of service provided the engine is maintained and service is performed when needed.
At a minimum, you should check your valve clearance every time you change your oil. This is recommended at intervals of 25 hours. If you are running 100LL avgas, it has 2 grams of lead per gallon compared to 0 grams per gallon for unleaded premium fuel. The VW engine does not need lead to operate.
Older VW engines had cast iron valve guides that required lead for lubrication. Modern silicon bronze valve guides do not need the lead for lubrication. Avgas has almost four times the lead content of the older, leaded auto fuel we used to purchase.
The main drawback to using 100LL avgas in the VW is lead buildup on the valve face and valve seat. We have seen exhaust valves leak in as little as 10 hours of operation and the cause is almost always lead buildup, caused by the use of 100LL avgas.
If you notice a valve leaking and it’s not out of adjustment, it must be taken care of immediately. One of the best ways to tell if a valve is leaking is to do a differential pressure test, or leak-down check.
When you do a leak-down check, don’t do it with a cold engine. Your engine doesn’t care what it’s doing when it’s not running. It should be close to operational temperature when a leak-down check is performed.
Having an exhaust valve break is not a common occurrence. This is the only example I have seen of a valve breaking in an aircraft application in over 30 years. And, it was 100% preventable!