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As far as I can see, this post is rather old. However, I am a bit surprised that viscosity, vaporization, and heat are the only topics mentioned. I want to pose the question that Harley's have roller bearing engines. When you use full synthetic, it is too slippery and creates a flat spot. Therefore I believe the bearings need something to grip onto. That being said, I would like to know if anyone has a favorite dino oil? Or would a synthetic blend be the best of both worlds?
Really? Oil that is too slick? If it's so slick that the roller skates, it would also be too slick to wear a flat spot. Friction is the enemy in bearings so it's nonsensical to think a lubricant could be too slick.
I want to pose the question that Harley's have roller bearing engines. When you use full synthetic, it is too slippery and creates a flat spot. Therefore I believe the bearings need something to grip onto.
This is an old myth that will never die. I first heard it back in about 1997 and although I didn't believe it I decided to call Torrington (the bearing mfr.) for info. I spoke with one of their engineers and he said he had never heard it before, but that could never happen in an internal combustion engine. In a zero-load device like a centrifuge he said it might happen, but in any environment if the lubrisity of the oil was so high (slick) and friction so low that a ball bearing would fail to turn, it would also not wear. I've also run this idea by some oil engineers involved in the Mobil 1 racing team and they just smile and shake their heads.
FWIW, I ran my Evo RK for 106k miles on synthetic oil and never had the heads off the bike. A friend has 114k on his 2000 WG running Syn3 and no problems except cam-chain tensioners at 70k.
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