[tinman]

Not being altogether familiar with the inner workings of a Lycoming brings me to this question:
Why do they not have camshaft bearings? One would think that there would be a lot of wear from the valve train loading without the bearings.

 

[Mel]

On a horizontally opposed engine the lifters push in equally from both sides. So there are essentially no loads on the camshaft.

 

[deene]

Yep, cam bearing wear is not the problem, cam wear is...

Unless you have the new rollers, the older style mushroom cam followers really chew up the cam lobes on Lyc's. The mushroom followers are cast iron and rust very quickly. Thus each startup wears the cam lobe and inactivity generates more rust and wear.

This is the reason for the recommended Lyc lube which is added at oil change time or included in the oil (Aeroshell Plus).

My two past 360's had excessively worn cams at overhaul time which did not pass inspection (by a wide margin).
Thats one of the reasons a new IO-390X sits in my shop awaiting installation on my RV8QB...IF I can get off this computer and back to work on it.

Deene Ogden
RV8QB, IO-390X, BA Hartzell, Clark Fastback, James cowl
EAA Tech Counselor, EAA Flight Advisor
CFII, MEI, CFIG

 

[tinman]

Snip
On a horizontally opposed engine the lifters push in equally from both sides. So there are essentially no loads on the camshaft.
End Snip

This being the case, why did VW and Subaru use camshaft bearings in their H4 engines? (My old Subaru had pushrods, not OHC configuration.) I'm trying to get a better understanding of the logic here. Sometimes, what you leave out of a design is as important as what you build in...
Did Lycoming omit the bearings due to oiling complexity, costs or simply because they were not needed?

 

[mahlon_r]

Don, I don't know the engineering reason behind not having the bearings for the cam but I can tell you from seeing thousands of engines, for overhaul, that they are not necessary, as the aluminum cam journal in the crankcases rarely have any wear at all. My assumption would be that the oil film at each journal is sufficient to keep the cam off the bearing surface of the crankcase under most if not all operating conditions, thus preventing any wear to the surfaces. BTW the cam rides in the crankcase, without bearings, on TCM engines as well, and they equally routinely show little or no wear in that area.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."