Camshaft Design

bmetcalf

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I went to the Washington DC Auto Show and viewed a cutaway Ford 4 cyl engine. The base circle of the cam lobes was manufactured to be narrower than the lobe, since the loading is lighter there. I thought it would be of interest.

Camshaft.jpg
 

passenger0_0

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Thank you for pointing this out Bruce. I wonder if it's there to reduce friction and would be interested to know what affect having a discontinuous oil film has on the cam follower? So many questions . ....?
 

ClassicBiker

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I would think it has little affect. Looking at the photo Bruce posted it is an over head cam engine. If you look to the left of the cam profile where the cover begins you can just make out the valve bucket/valve lifter. I suspect the bucket is continuously covered in oil given it's position. If the lifter isn't a hydraulic type, which it doesn't appear to be, then there is most likely a running clearance there. I know that on the Honda 900 custom a friend of mine had, my father's TR7, the Yamaha XS750 I had, and my Triumph Sprint, which are all overhead cam there is a running clearance between the base circle of the cam and the lifter, so contact is intermittent, not continuous. Plus given the gov't inducement to increase fleet mileage and reduce emissions or face stiff penalties vs. the potential cost of warranty claims for premature/excessive wear.....finding ways to reduce friction wins out every time.
Steven
 

bmetcalf

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Good pint on the bucket getting a lot of oil. I would be surprised, though, at a 2017 engine not having hydraulic lifters in the mechanism somewhere.
 

ClassicBiker

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Hi Bruce,
I'll admit I could be (was) wrong about it not being a hydraulic lifter. It just didn't, to me, appear to be one. After reading your comment I did a quick "google image" search. I had thought that if the cam was bearing directly on the bucket it was most likely a solid lifter. I had thought that OHC designs that have hydraulic lifters, the cam bore on some rocker of sorts and the lifter was off to the side in some fashion. But my non-scientific search revealed that appearances may be deceiving. I found some Ford images where what we are referring to as the bucket is indeed a hydraulic lifter.
But even if it was a solid bucket and contact between the cam lobe and bucket was intermittent due to running clearance I don't think it would matter. Plenty of OHC engines are/were designed with clearance between the cam lobe and bucket.
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Steven
 

bmetcalf

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For us manly motorcycle riders, adjusting valves is recreation, but those pampered car drivers want their hydraulics. (And we air-cooled Buell riders.)
 

kettlrj

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Engine manufacturers are always looking for ways of cutting down friction, oil drag and weight (which leads to reduced inertia) in all of the rotating components. This slimming of the lobes in the un-loaded area of the cam satisfies all these requirements as well as having to remove less material during manufacture.
 

macvette

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Engine manufacturers are always looking for ways of cutting down friction, oil drag and weight (which leads to reduced inertia) in all of the rotating components. This slimming of the lobes in the un-loaded area of the cam satisfies all these requirements as well as having to remove less material during manufacture.
I thought these were used to vary valve opening or to take cylinders out of operation at different engine loads
 

kettlrj

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Macvette has totally missed the point of the original question, which was why is the cam slimmed down on the base circle. It has NOTHING to do with variable valve timing or of taking cylinders out of operation.
 
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