Q: My Tri-Pacer has an O-320 with a narrow deck (A) engine. It has SL32000N-A1 Millennium cylinders, which are are installed with no plates and splined nuts. Can this be correct? I have no wide deck cylinders to compare them to.
BLAIR MOHR, via e-mail
A: Let me see if I understand what you’re telling me: You have an old Lycoming O-320 Narrow Deck engine that has Millennium cylinders installed using the spline type cylinder hold-down nuts? Yes, it could be possible that these cylinders would be installed without cylinder base hold-down plates, which was done on the early low compression engines.
The spline type nuts have been long gone but, as you mentioned, apparently still in use. Should you wish at some point to convert to the more recent Cylinder Base Allen Head Nuts, this may be accomplished by complying with Lycoming Service Bulletin 213A, dated way back in 1957, but I’m not certain I’d go through the work. I think what you’ve got should work just fine.
Paul McBride, an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.