1989 FLH. Service manual says 20w-50 (but I could not find any information on ZDDP). Did a forum search.

Do I need to add ZDDP additive ?

Does Evo engine have a flat tappet cam ?

I have an old classic car, 63 Thunderbird, has flat tappet cam, and I am supposed to add ZDDP with every oil change (as new oils do not have and old oils did).

Appreciate any thoughts.

 

Your engine has roller hydraulic lifters. I like using Valvoline Racing 20w-50 conventional. It has higher concentrations of zddp than most regular oils. It is only recommended for engines that don't have a cat converter because the zddp fouls the converter over long term use. Thus gthe term "racing".

Our evos seem to like conventional and they are pretty easy on the oil. They run cooler than the twin cams and the conventional seems to make our engines run quieter.

Also our engines have a known issue with the cylinder base gaskets having a tendency to leak. Conventional oil seems to minimize this and keep the base gasket swollen. That, along with letting your cylinders "grow" in length from the heat. The cylinders grow in length with heat and tighten things up when they warm up, so wait a few minutes after starting the bike to let it warm up before loading the engine. When the head gets to point where it is uncomfortable to touch with the back of your hand, then ride on.

Head over to the 1340 evo classics section. Lots of good info. Good luck with your bike. YD

 

Great post, very helpful, thanks !!

 

1990 FLHS here, owned from new. Do you need additives? Not in my opinion - I've never used any. For future reference we have an Evo section, where you can meet fellow owners.

 

ZDDP or Zinc dialkyldithiophosphate is an aggressive compound. Used in too high of a concentration will restrict other necessary chemicals and compounds from doing their job.

Oils that are marketed as having a very level of zinc are typically racing oils and those are normally used for relatively short durations. High zinc levels might be an effective strategy in racing but not normal street use.