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Comp Roller Lifters Problem |
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73XBGT
AMC Apprentice Joined: Jan/28/2010 Location: Huntsville, AL Status: Offline Points: 123 |
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Thanks for your input and advice. By visual inspection, it doesn't look like .030" exposure in the oil passage...more like .005" or .010" at max lift. Another thing that could cause variation between blocks is the depth that the spotfaces were cut. My oil passage to lifter spotface measurement ranged from 1.180 to 1.220, but visually, the lifter eyebrow exposure visually appeared to be the same amount in all of them.
Thinking back to one of your previous posts, the eyebrow is only exposed to the oil passage for a brief time during the entire cam cycle, so I suppose that's why most folks don't appear to have an oil pressure problem with the new lifters. If Crower comes through with even more shrouding on the lifter, AMCers can run even bigger lift without oil pressure concerns, and without bushing.
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SKeown
AMC Addicted Joined: Jul/30/2009 Location: Texas Status: Offline Points: 3085 |
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You're right about the spotface thing. Consider this, when the little bit of oil is lost at max lift, there's no oil going through the pushrods, so in all likelyhood that effects the oil pressure less than feeding the rockers for that brief period. Besides that a little extra oil on the rollers and cam might be a blessing?
I'm glad weve examined this so cloosely, I've wondered why the reliefs for the roller wheels weren't straight across rather than raised in the corners, but the engineers may have done that intentially to feed a bit of oil to the rollers during max lift? Unless you are running really big lifts, like over .7" at the valve (which would probably require bushings) the oil flowing from the bottom of the lifter wont exceed the ammount going upstares via a .080 hole in the pushrods when the oil supply groove is alligned with the oil galley.
Okay, I just took a hot bath and pondered this more. I think we can put a difference in the blocks behind us. But to do it scientifically lets use both cam/lifter combos in the same block. Now, I discovered that I said the distance from the bottom of the roller wheel to the first possible leakage was .590 on Crane lifters, that's incorrect it's .580, I somehow added .010 from what I wrote down in the garage and what I posted here. Anyway the Comp's are .610, so I can run .030 more lift, but you're base circle is .010 less, so that reduces it to.025. Now consider that I'm running .026 more lobe lift than you, now your lifters roller reliefs will be exposed .001" less than mine. On that thought, I'm letting this horse go!!
SKeown Edited by SKeown - Jun/17/2010 at 12:56am |
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Red Devil
AMC Addicted Joined: Jul/10/2007 Location: Canada Status: Offline Points: 1743 |
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Doesn't base circle normally get smaller with more lobe lift anyway, so as long as the max lift point is OK, more lobe lift shouldn't be a problem for reasonable lifts? Understanding is a bigger base circle helps get faster rates of lift without getting into an inverse curvature lobe profile - e.g. if you grind a small Chevy profile on an AMC blank, you'll see more duration. 'Guess it depends who grinds the cam
Also, a Crower lifter option would be great ... if it works well without bushing and has pressurized roller oiling.
Thanks! RD. Edited by Red Devil - Jun/17/2010 at 9:39am |
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forest
AMC Addicted Joined: Nov/14/2008 Status: Offline Points: 2114 |
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yesterday, Crower and I discussed this for while and the only way they would offer the lifter would be with the high pressure option, and today we should be coming up with an orderable part number for everyone.
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setting guys out by car lengths....
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73XBGT
AMC Apprentice Joined: Jan/28/2010 Location: Huntsville, AL Status: Offline Points: 123 |
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Allright, the horse isn't dead yet. Here's another one for you engine guys - How small of a base circle diameter can you "safely" run in a solid roller cam with around .650" lift and 500 lbs. (open) valve spring pressure? When I say "safely" I mean without too much camshaft flex or possible breakage. Also, are there any other disadvantages to consider with having a small base circle in an AMC? How small is too small? Anyone ever run less than a 1 inch base circle. It will be good if Crower comes through with a new lifter design with more shrouding for the roller wheel, but I'm still weighing my options. I've been reading some posts on another forum where a guy's engine (with the old Comp rollers)had sufficient pressure on the dyno, but did not have enough pressure when he put it on the street. At some lift point, even these new Comp lifters are gonna have pressure issues. We need a design that will actually seal without having to bush the lifter bores, or worry too much about base circle diameters.
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forest
AMC Addicted Joined: Nov/14/2008 Status: Offline Points: 2114 |
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we are working on the drawings right now, and should have a number by the middle of next week im thinking. they already have the lifter bodies ready to go, just need to decide how far down to bring the shrouding down around the wheel... will keep everyone posted when they are ready.
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setting guys out by car lengths....
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amx39068
Supporter of TheAMCForum Joined: Feb/21/2008 Location: Arizona Status: Offline Points: 11576 |
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I agree. That old post may have been mine from a while ago as what you are describing is exactly what happened with my engine when I used the old Comp solid rollers. They knew about it and only amitted to it after I figured out what the cause was.
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Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development
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73XBGT
AMC Apprentice Joined: Jan/28/2010 Location: Huntsville, AL Status: Offline Points: 123 |
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Forest, have you considered contacting somebody like Barry Allen to get his input? He may be interested in offering up some advice on the lifter features, since he builds a lot of roller AMCs. Example - what's the optimum metering size of the push rod oil feed holes, and their location on the lifter itself. Also, what's the best location and width of the oil band itself. I know with my setup, the centerline of the oil band on the new Comp lifter is still above the centerline of the oil passage when the lifter is sitting on the base circle (my base circle diameter is 1.168"). At max lift (.614"), the oil band is actually above the passage, possibly restricting oil to the rockers (probably not though). I'll be glad to take any measurements you need on these new Comp lifters if it would help you or Crower.
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SKeown
AMC Addicted Joined: Jul/30/2009 Location: Texas Status: Offline Points: 3085 |
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A cam's lift plays nowhere near the importance in producing power in an engine as does it's duration/timing events. For every .010" decrease in the cam's base circle, you'll only alter it's ability to enhance the lift by half that amount.
SKeown
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73hornut
AMC Addicted Joined: Jul/03/2007 Location: Southern Oregon Status: Offline Points: 3132 |
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By now, you could have bushed the lifters.
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71 Javelin
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