Serious lubrication problem in my top end..., possibly the cause of hydraulic cam failure? Options

[jk76.914]

I was lashing my valves on my '76 2.0, after 1000 miles since the rebuild. When I took the valve cover off, I was mildly surprised at the lack of oil in it. Everything was coated with a film, but there was virtually NO liquid oil in the top end.

I didn't think TOO much of it until I started my adjustment process. I had installed an hydraulic cam when I did the rebuild. This was based on 100% reliability experience in 3 Corvairs over about 450,000 miles. Anyway, I really wanted to lash them like a Corvair- with the engine running, back off to clatter, allow to stabilize, turn in 1/4 turn, allow to stabilize, turn in 1/4 turn, etc until I reach the desired lash of 1 turn. I can't do that on the Type IV of course, because the adjuster screw is moving when the engine is running. So I decided to approximate the process. I'd set the valves to .006" clearance on all 4 valves (I did one side at a time), and let it run for about 10 minutes. Then I'd shut it off, turn each adjuster in 1/4 turn, start it up, run for 5 minutes, shut it down, etc until I turned each adjuster in 1 turn from .006" clearance.

To facilitate the process, I cut an extra cover in half lengthwise, put a half gasket in, and held it on with the bail. That way, I reasoned, I could shut it down and do the 1/4 turn and restart without having to remove and replace the cover everytime.

So. After adjusting the valves to .006", I started 'er up. And what do you know? COPIOUS amounts of oil were splashing around in there. A puddle formed on the heat exchanger, causing white smoke, not to mention what it did to my driveway. And this was with the half cover collecting oil from below.

So, after 10 minutes, I shut it down and turned them in 1/4 turn, put some plastic down on the driveway, and started 'er up again. And guess what? The oil stopped! What was happening? The push rods have a hole in the end to deliver oil up from the lifter to the rocker box. At .006" or .008" clearance, there is plenty of space for the oil to come splashing out. At 5000 RPM, I suspect it GUSHES out because of the higher oil pressure. At zero lash, the domed top of that pushrod mates into the hardened cup of the rocker and is held there by the oil pressure acting through the lifter- and it gets turned off like a faucet.

Then I thought about my Corvairs again. In that design, there were two holes at one end of the pushrod. One in the tip, and one on the side of the pushrod. The manual states that this goes at the rocker end, and the side hole delivers oil to the rocker mechanisms and valve stems and springs, and the end hole just lubes the tip at the rocker. Eureka! I was starving my top end of oil!

To confirm whether you need a LOT of oil up there anyway, I started searching on the internet. I discovered that Lycoming and Continental aircraft engines both migrated to hydraulic lifters in the late 70's. Both are horizontally opposed, air cooled, pushrod, overhead valve engines. Continental was very successful, with minimal problems, while Lycoming had problems with lifter spalling, cam lobes going flat, valve guides failing, pushrods bending, and (picture this) valves disintegrating in flight! Sounds like the 914 experience a lot of people have had. Anyway, the Lycoming problem (never directly admitted to by Lycoming, by the way) was due to inadequate oiling of the top end! In their case, it was due to using a lifter design that was originally intended for a flat head engine, not OHV. It was never intended to deliver oil up a pushrod. The Continental engine used a barrel lifter, almost exactly like the automotive lifters used today with OHV engines.

The failure mechanism was inadequate lubrication of valve guides, causing coking and valve sticking, initially. The sticking required inordinate forces to open the valve, which overstressed the lifters, and caused galling and damaged lobes.... Eventually the valve could stick fast, and break something....

Here's one article I found on the topic. There are many more, lots of pictures, other descriptions, etc., but this one covered most bases the best I think....

http://www.prime-mover.org/Engines/Marvel/tbo3.html

It's a long article, but very interesting reading. To quote their summary paragragh-
"What you need to remember is simply that we have found an inverse correlation between oil flow to the rocker boxes and valve and guide distress. Valve/guide distress in turn places huge loads on the lobes of the camshaft during the valve opening sequence and we believe this is most likely the cause of Lycoming's camshaft problems, which also have never been formally solved. You also need to know that even if you do everything involving engine operation and maintenance perfectly, you may still encounter upper end problems if the mission of your aircraft involves extended flights with cruise power and cruise mixture set, regardless of CHT levels . This is the fault of the design, not of the pilot or of the mechanic who maintains the aircraft. In short, if you have this problem, there is nothing you can now do to prevent its continuation other than to fly at greatly reduced power levels and/or enriched mixture settings."

Other points. Maybe these aren't relevant to us, but they're certainly food for thought-

1. better oiling of the top end will increase oil temperatures, as the oil now is carrying away more engine heat. Later versions of Lycoming engine were the same in HP and displacement, but needed bigger oil coolers.
2. sodium-cooled exhaust valves will make the problem worse because the stem will run hotter. If there is good oiling to the rocker box, however, sodium-cooled exhaust valves will help.


Things I still need to find out-
- Was it just my kit, or do other manufacturers hydraulic 914 kits address top end lubrication? I suspect not, because I really am thinking this is the root cause of the "hydraulic cams are evil" movement...
- what did VW do to make up for lack of lubrication at zero lash when they went to hydraulics in '78? Different pushrods a-la Corvair? Or special rockers with oil passages instead of a blind cup?
- what do I do now? I've "grounded" my 914 until this is resolved. I'll probably order a set of custom length Corvair pushrods to use, but I'm still investigating.

Sorry this was so long. I hope somebody actually reads it!!!