Any wisdom on KTM 790/890 Cam wear problems?

[jeff78]

Relying on a squirter is not the most robust design solution. Cars like the Mazda Skyactiv engines have an oil feed rail over top of the cam, that dribbles/sprays oil from on top. Even if pressure was poor, the cams would still get oil.

Yeah, the first time I saw a video of the inside of a KTM 790/890 head and saw those tiny little oil jets that are not an insignificant distance away from the followers, the first thing I thought was

The Japanese Big 4 all have 200hp production bikes that run finger follower valvetrains and they're not experiencing similar failures, at least not at this scale. But none of them lubricate the followers the way KTM does it.

For example, the Yamaha R1 has used finger followers for about a decade now. The followers are fed oil the same way the cam bearings are - from oil in the cam. There are holes drilled in the base circle of every lobe, and these holes are large, the same size as the holes in the cam journals, maybe a good 3-4mm in diameter. Plenty of oil everywhere at all times. These bikes may snap cranks, but their cams always look great.

I think these failures are not the result of just any one thing, but multiple possible contributing factors and when they all line up 'right' (wrong), your cam goes sayonara. The 'Swiss cheese model' as others have alluded to.

Poorly aligned oil passages during manufacture, low oil pressure/flow in certain conditions, debris blocking oil jets, shooting oil at the followers from a mile away instead of from nearby, etc.

 

[ktmDuke890r]

The mechanic who replaced the oil pressure relief spring with a part from the RC8C said that the left CAM was the most worn if there was any wear occurring. Due to the left CAM being at the end of the oil flow path. He didn't like the design either.

Good discussion.