roller cam follower lubrication?
roller cam follower lubrication?
(OP)
Hi,
Just wondering why OHC with roller followers need lubrication, if it's rolling contact everywhere? In theory, if we remove the valve guides from the equation, does an engine with OHC roller followers even need to have the top lubricated?
Just wondering why OHC with roller followers need lubrication, if it's rolling contact everywhere? In theory, if we remove the valve guides from the equation, does an engine with OHC roller followers even need to have the top lubricated?





RE: roller cam follower lubrication?
E.g., my Ford based Esslinger 2.0 that is in my 23 T revs to 9000 rpm and the little roller rockers really like that shot of lubricant! ;o)
Seriously, the cam gear, springs, valves, lifters, rockers, etc. generate an enormous amt of heat and require a steady flow of oil for cooling and lubrication.
Rod
RE: roller cam follower lubrication?
Even if the followers survived with no oil (which they won't as Rod points out, everything Rod says, plus cam bearings will fail.
Regards
Pat
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RE: roller cam follower lubrication?
RE: roller cam follower lubrication?
Regards
Pat
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RE: roller cam follower lubrication?
RE: roller cam follower lubrication?
Take a look at Henry Fords original racer with Barney Oldfield. That massive engine had exposed rocker arms and top end. Of course, there was no warranty and engine life was in hours, not years.
Franz
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RE: roller cam follower lubrication?
Reduced sliding contact in roller follower valvetrains is enough to change the anti-wear performance requirement for the lubricant that is used.
The implication that valve springs generate enough heat to require liquid cooling is surprising.
RE: roller cam follower lubrication?
Rod
RE: roller cam follower lubrication?
Regards
Pat
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RE: roller cam follower lubrication?
RE: roller cam follower lubrication?
There should then be no reason to pack wheel bearings with grease etc.
As a youngster I ran a 2 cycle gasoline engine without lubricating the bottem end, ie the crankcase, the piston had enough oil the way I was introducing the fuel, the big end with the needle bearings gave way.
The end answer is there is always friction, if not you could spin a perfectly balanced shaft with rollers and it should perform like its in orbit around the earth, with zero friction losses. Well I guess we need to get away from gravity too. In the end all friction less metal bearings need lubrication. I suppose ceramic do as well.
RE: roller cam follower lubrication?
I think lubrication in ball bearings are for the cage to ball contact, no? Otherwise I'm still having difficulty grasping why you need lubrication for rolling motion - except for maybe shock absorption?
RE: roller cam follower lubrication?
What else do I have to go on? Sixteen years of school and fifty two years of experience is all I have.
Theoretical? Missing the point? I don't think so. Even the most basic concept of "ball bearings" accept the actual non rolling friction part. No non lubricated bearing will actually "roll" 100% of the time. Especially with heavy and variable loading. Your missing some basics in trying to create a hypothetical situation that in the real world just cannot exist. HEAT REQUIRES COOLING if you want your bearing to live. In most cases that means LUBRICANT.
Sorry for the rant. The question is silly.
Rod
Rod
RE: roller cam follower lubrication?
The roller follower uses uncaged needle rollers and they are all side-by-side with little gap in between. Bearing people call this a "full complment" and it gives the follower a higher load-bearing capacity than the lesser amount of needles in a caged type. It also means that the sides of the needles touch each other and they are moving in opposite directions - very much a case of sliding and not rolling contact - so they need lubrication.
Engines have very elaborate lubrication systems - it may be possible to not lubricate the cam and follower system but there is no advantage in doing so.
RE: roller cam follower lubrication?
Don't worry, it won't happen again.
Regards
Pat
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RE: roller cam follower lubrication?
And what about, the cause of bearing failure related to surface wear created by microscopic "cold welding" (look up the definition of cold welding) of ball material to the race. The cold welds break as the bearing rotates, creating surface roughness that leads to heat generation and bearing failure.
Lubricant provides a microscopic film between the rolling elements to prevent abrasion and skidding. In addition, it protects surfaces from corrosion, and protects the contact area from particle contamination.
So in the end especially metalic type frictionless bearings need some form of lubrication, period. No ifs ands or buts.
RE: roller cam follower lubrication?
Even though roller cam follower systems are rolling contact, there is still a fair bit of sliding contact which requires lubrication. These come from:
1. needle rollers have friction on the sides
2. the motion between the cam and follower has non-negligible sliding when subjected to high accelerations
3. Cold welding of balls to races due to extreme point and line contact pressures create roughness that causes premature wear
Furthermore, the friction caused by the above mechanisms generates heat, which can be dissipated by the flow of oil which acts as a coolant.
These answers were very helpful and exactly what I was looking for. Thank you.
The answers that I said were not as helpful were along the lines of:
"I drove an old tractor once that had unlubricated cam followers and it didn't last for more than 100 hours, so you shouldn't run your cams unlubricated and it'll never be possible!"
Thank you for all your help. I hope I didn't offend anyone.
RE: roller cam follower lubrication?