how would you press the bearings on the cam with the cam lobes in the way? I would have thought the number of rotations life span of a needle roller bearing would not be long enough to warrant a practical use. I'd have to check up NTN's website to see the life span of the bearings. My gut feeling is that the resistance of a roller bearing would be greater than the oil film acting as a bearing so you'd lose a bit of power through the valve train (not very much though). Interestingly enough jetskis use roller bearings on the crank journals but that's possible since the crank can be separated between each journal.
fair enough, the thing i have noticed when looking at the cam followers, is the bluing due to friction, it is merely conjecture on my behalf, i just have a gut fealing that roller bearings replacing the lobe would transfer the load with less load than a wedge arrangement.i like to think outside the square sometimes, regardless of how wrong it may be.
True roller camshafts......>> Use solid lifters with rollers on the ends. They are not attached to the cam lobe or imbedded in them. Doing that would open up a whole heap of balance problems not to mention the problems of retaining one so it didn't fly out at 7000 rpm. The reason why some engine builders ellect to use a roller cam is so they can run far more agressive profiles without the risk of high rpm float.
whoops I misread your post >> I thought you were thinking of putting bearings in the cam journals. But you meant roller rocker arms and cam follwers right? Problem is the cams need to be off to one side with roller rocker arms and there's no room to modify the heads. Roller bearing cam followers would be neat if you could machine the cam lobes down to fit the follower which I imagine wouldn't be too hard. It's got to be much better than relying on the oil film to protect the lobe and lifter and this would free up the valve train to give a bit more hp I reckon.
You can't post a picture.....>> From your PC. It needs to be hosted on the web somewhere. One good free place is http://www.mustangmods.com
Try this...> To me, it would seem that most of the friction would be experienced on the flatter part of the cam lobe because it is at this point where the lobe is trying it's hardest to push the lifter/follower down. The difference that having a bearing on the lobe tip would make would seem minimal. For it to work properly you would have to place pin rollers all around the lobe, making it very complex and likely very fragile. A better way would be to do as wykked suggested and have the bearing on the lifter/follower. It's good to see some inventive thinking though. AB
it is good to have some constructive criticism. the amount of modification require to incorporate roller followers is big. the proto drawing i have created is for concept purpose only.working on lift height of 26mm a spring stiffness of 55kg and a saving of say 5% x 24 springs at 3000rpm is roughly 3.3kw, is still a significant value. the force the spring will exert on turning the lobe is another thing to consider, ie when the cam goes past tdc.
the balancing can be solved by insuring your tool jigging is set accurate the same amount is removed from eash lobe, the mass of the hardened pins 'unbrako' and the mass of the magneto roller bearings would be equal, what is taken out is balanced and what is being replaced is balanced.bearings with the same bore can have different outside diameters.you could make the lobes in a manner were they could be clamped to bright steel allowing not only lift height variation but leading and lagging timing as well.
Needle Roller Bearings Had a old red motor in line six race engine many years ago. It had needle roller bearings fitted in the engine for the camshaft AND crankshaft. They came in a half shell cage configeration. The engine was dry sumped and the crank bearingings also got lubricated a small cup arangement oh the bottom of each conrod that dipped picked up oil. The camshaft had roller followers as well. As a result with the belts off you could grab the the crank and give it a spin by hand and the engine would spin about two and a half times. It was the hardest reving six I have ever seen, coming off the strip with the tell tale on the tacho reading 10300rpm! So I say to you guys any thing can be done !
this looks weird http://www.mustangmods.com/data/14310/rollcam2.jpgit looks silly i know,anyway its possible, balance is a real problem here.
