Originally Posted By: fuel tanker man
I think the Harley Engine is fine on lighter oil until you consider the cam lobes and the roller lifters. If the oil is too thin, the film may not hold up well enough to prevent excessive cam lobe wear. A lighter oil with plenty of ZDDP might prevent metal to metal on the lobes, but I'd rather have an oil with a thick enough film so as I'm not falling back on the zinc/phos/moly barrier.
On the other hand, if the oil is too thick it may not pump quickly enough to all the places it needs to go in order to prevent wear in those areas. So it's a balancing act, of sorts.
I think the Evolution engines shear oil because of the cam gears. The Twin Cam engines run cam chains, but the older engines (Evolution all the way back to 1903) use gears, not cam chains.
Dan
Roller lifters and rocker arms have little wear. Do the research -- that is why they use them. Only flat tappet lifters are prone to excessive cam wear. I'll give Harley this much, they did their best to make a trouble-free engine. Everything in the TC engines runs on high-quality bearings. You Harley guys are going to have to realize these new TC engines are not your grandad's Harley, these may be an old design, but they are thoroughly modern inside, thus modern oils apply. You don't need those "thick" oils anymore.
If you want to qoute the service manual, why even come to BITOG? This forum is about using oil OTHER than the recommended.