Only a sample size of two.
Two engines that I know have had the new diamond coated tappets and at overhaul there was zero wear on the tappets or the camshaft. One of the engines was an O-235 on which such findings are as good as unheard of.
Lycoming might just be onto something here.
You need to change to new crackcases to use roller tappets. Generally, the change is financially not worth doing at overhaul, due to this. But it is perfectly possible. And you may need new crankcases anyway if there has been fretting (crankcase bolts not torqued properly) or the engine has had too many overhauls so the crankcases have been machined too many times.
There is a mandatory replacement of the tappets in a shock load inspection, which adds quite a bit of money to the cost of the inspection.
There is no power increase measured on a dyno run. It just makes the camshaft last longer.
No other effect on the engine.
Jujupilote wrote:
Any recent opinion ?
Do you need to buy a new engine from Lycoming to get them ?
I think our factory new 540 has them, no noticeable performance difference (though the new engine is noticeably smoother and roughly 4 kts quicker). Harder to start when hot. (an absolute bitch if I’m honest)
Any recent opinion ?
Do you need to buy a new engine from Lycoming to get them ?
My engine (O-320) has them and no problems so far (400 Hr). I was pleased to see them because the old engine died of camshaft corrosion (2400 Hrs). It is a Lycoming factory rebuild because, at the time, they had a no quibble policy on the core and I knew (and told them) that the crankshaft had the dreaded internal corrosion. And they delivered it in less than 2 wks.
Absolutely no detectable difference in performance but harder to start than the old engine.
They can’t give you a 10,000hr part in a zero time engine in this area as they don’t yet exist.
They can’t give you a 10000hr crankcase in a zero timed roller tapped engine; that’s for sure 
But they can give you a 10000hr crankshaft in a zero timed roller tappet engine.
Yes, I believe it is also the reason that rebuilt engines at Lycoming use parts of a maximum age (no idea but say 2005) when roller tappers came out. They can’t give you a 10,000hr part in a zero time engine in this area as they don’t yet exist.
What was the issue with the roller tappets after they came out?
I was told you cannot fit roller tappets unless you change the crankcases, which makes it uneconomical unless you are buying a new or fairly new engine.
Other overhaul shops aren’t allowed to install roller tappets in an engine with flat tappets.
I can’t see how they could, anyway. The crankcase casting is different.
