New views on hydraulic cams., Dare I bring it up?!?!?!?! Options

[jk76.914]

Well, I have this hydraulic cam in my engine. And last fall I committed to making it work, and so now I have an update.

I'm hoping I won't get called a moron again! But here I go! This will probably be done in 3 parts- lifters, pushrods, and rockers.

So I got convinced that the real issue with hydros is lack of adequate lube to the rocker boxes. I found a website that was discussing major problems with Lycoming (4 cylinder, air-cooled aircraft engines) when they transitioned to hydraulics in the late 70's. That was about the same time VW and Continental (aircraft) transitioned. VW had very similar problems, but Continental was virtually trouble-free. Many (all?) of the Lycoming problems can be explained by their implementation of hydros as opposed to the well known fact in 914 circles that hydos are, in fact, evil. In the article, it is observed that the hydraulic lifter has two roles- 1.) to adjust to changes in engine tolerances due to wear and temperature and keep the valves at zero lash, and 2.) to convey oil up the pushrods so as to lube the rockers. Inadequate oiling means inadequate cooling, stuck valves (due to oil coking on the stems), broken valves, bent pushrods, galled lifters and cams, etc, etc, etc... sound familiar? sound evil? How about valves failing (shattering) in flight?

In the article, the authors go on to "point out a major shortcoming of the Lycoming design that we believe substantially accounts for valve train problems including stuck exhaust valves, prematurely worn valves and guides, and camshaft distress and failure."

The early implementation in Lycoming (and VW?) focused on the first role and missed the second. I'm open to correction, but I think this was the VERY first use of hydraulic valve actuators by VW.

Anyway, here's the article: http://www.prime-mover.org/Engines/Marvel/tbo3.html
Every time I read it I get something more out of it.... It also touches on sodium filled valves...

On my own engine, I noticed that when I adjusted the hydros to +.006" (clearance) and then idled it, there was significant oil flowing out and all over my driveway. (This in spite of the fact that I installed a half valve cover to catch oil.) When I then adjusted to -.006", the flow virtually stopped- the pushrod seated in the rocker like a valve in its seat.

I re-read the article, and then started at the lifter. I bought three brands of T4 lifter- Meyle, Febi, and Isky. I disassembled them and looked at the various schemes of metering oil to the head.


Meyle
Febi (may be the same as Sealed Power)
Isky (may be made by Delphi?)

Both the Febi and the Isky have a metering disk beneath the pushrod seat that meters oil from the plunger to the pushrod. The Meyle relies on oil leakage around the pushrod seat and then into the side hole and then through the pushrod seat to the pushrod. This does not seem to me to be a reliable way to forward oil up the pushrod.

Also, there is a reference to two designs of VW hydraulic lifter at this article- http://www.ratwell.com/technical/HydraulicLifters.html . In the article, Richard Atwell speculates that VW improved the design because it changed from having a paper clip style retainer to having a circlip retainer to hold it all together. Well, Meyle (questionable oiling) has a paper clip style retainer, and Febi (improved oiling) has the circlip. My theory is that VW migrated from Meyle to Febi, because the Meyle was causing failures due to inadequate lube. It's all anecdotal and speculative, but for the life of me I can't imagine how the Meyle can reliably and predictably convey oil to the head..... (beating the same dead horse)

Meyle, Isky, Febi oil metering to pushrod.

In addition to the article on Lycoming and Continental, I looked closely at Corvair (freakin' Chevy to some). 1.7 million Corvairs were built over a 10 year period, and all had hydraulic lifters. And they were never considered a reliability issue. The Corvair is basically a six cylinder Type 4 (though Corvair predates T4 by almost 10 years). So I also purchased 2 Corvair lifters- one used original Chevy and one new Sealed Power. Upon disassembly, I found oiling similar to the Isky and the Febi- both have a method of metering the oil, as opposed to relying on leakage. When GM discontinued the original Corvair part number, there was quite a bit of activity on the internet about substitutes and how effective they are in transferring oil to the rockers, so clearly it's a more openly understood requirement with the Corvair-meisters than with us T4 guys whose starting point is solid lifters...... (one of these days I'll get around to taking photos of the Corvair lifters)

So anyway, after I was satisfied with which lifter I would use (I stuck with my Iskys, thought I wouldn't hesitate to use Febi either), I moved on to the pushrods.... and I'll get into that in my next post, probably in a few days....

[Jake Raby]

Solid lifters do not rely on oil pressure to function, hydros do- huge difference.