Is there a material difference in the CHT on the Lycoming engines with roller tappet engines vs flat tappets?
Roller tappets were introduced to overcome the spalling and corrosion problems caused by the camshaft position on Lycoming engines. I don’t know if this mod is still being used as I believe there were problems with the rollers at one stage.
The US engine ship which did my engine in 2008 said that roller tappets appear to solve the camshaft issue but do not generate more HP for the same fuel flow.
A notable issue with them is that they make a prop strike cost a few k more because they are mandatory-replacement on a shock load inspection.
I would be amazed if there was a CHT difference. CHT numbers are hugely dependent on the cooling airflow which is critically dependent on how well the baffles fit, on the condition of the baffle seals, etc.
I believe the CHT temp drops a bit due to reduced friction between the cam lob & tappets.
Another issue with roller tappets is that you can’t get them unless you send your engine for overhaul to Lycoming. Other overhaul shops aren’t allowed to install roller tappets in an engine with flat tappets.
There are also new flat tappets (PN 262626) that are supposed to improve the spalling problem.
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.
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?
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.
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.