The disadvantage: #1 - adjusting valve lash in the back of a Pantera. Unless of course you've got a hot young girl who volunteered to adjust it for you. We're not gettin' any younger Bill.
The cam grinders do offer street solid roller cams, but in order to make a solid roller survive in street applications, the cam grinders use the same lobes as their hydraulic rollers, this allows them to use hydraulic cam type spring pressure. Anything more aggressive than that runs into problems.
The primary problem with solid rollers is the lash clearance. As the valves close and come to rest on their seats the lifter bounces (chatters) on the cam base circle in the approximately 0.020" lash clearance. This action slowly damages the rollers. The solution to this problem is a rev-kit, springs that hold the lifters in contact with the cam lobe. To my knowledge the only rev-kit manufactured for the 351C is manufactured by Porting Dynamics of Maple Grove Minnesota, but the springs operate with a big bend in them, it doesn’t appear they would last very long that way, so the issue of longevity isn't resolved, it shifts from the roller bearings to the rev-kit springs.
The second problem is spring pressure. Most solid roller cam profiles have very steep opening and closing flanks, and they require extreme "open" valve spring pressure to keep the lifter in contact with the cam lobe over-the-nose. The valves are also closed quickly which requires high seated valve spring pressure to prevent valve bounce. All of this spring pressure wears the roller lifter, rocker arm, valve tips and valve seats prematurely. Most solid roller cams aren't ground with longevity in mind.
The third problem is roller lubrication. All hydraulic roller lifters and most solid roller lifters rely upon splash lubrication of the roller bearings. Below 2000 rpm there isn't enough splash lubrication to meet the needs of a solid roller lifter because it is loaded much more heavily by the valve springs. A solid roller lifter that relies upon splash lubrication will quickly fail when used for stop and go driving situations, or even when a motor idles at less than 2000 rpm. Solid roller lifters featuring pressurized oil supplied to the roller bearings are available, but the real purpose for pressurized lubrication of the roller bearings is to increase the load bearing capabilities of the lifter, not low rpm use.
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Some enthusiasts are attracted to roller cams because there is angst these days about flat tappet cams failing prematurely. But for decades we used flat tappet cams without a worry. AND it is important to realize that during this last decade most enthusiasts installed new flat tappet cams without a single problem, the problems occurred to a small percentage of enthusiasts. The problems occurred for one or two reasons, (1) the reduction of ZDDP in motor oil and (2) quality control issues in the heat treatment or surface finish of "off the shelf" cams and lifters. So the solution to these problems is easy enough, when purchasing a camshaft and lifters don't purchase them off the shelf, purchase directly from the cam grinder and request the cam grinder's best heat treatment and best surface finishing. Then use motor oil designed for racing (off-highway usage) which contains generous amounts of ZDDP. Remember the distributor drive gear also needs ZDDP, so use of a roller cam does not equate to freedom to use whatever motor oil you want without consequence. If we approach building the valve train this way, with a bit of engineering precaution, there is no need to fear the use of flat tappet cams, the cam & lifters should be damn near bullet-proof.
Factory flat-tappet cams were phosphate coated for break-in. It would be nice to have a cam phosphate coated it that were available from a cam grinder.
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With a 351C we can achieve any streetable power goal with cams having valve lift in the range of 0.600" +/- 0.030". That sort of valve train performance doesn't justify the use of a solid roller cam. Solid roller cams are for big lifts and motors that aren't expected to go very many miles before rebuilding the valve train is required.
You know I'll help ya with whatever you decide to do, but if it were me I would select a hydraulic flat tappet cam or hydraulic roller cam for most builds, and a solid flat tappet cam for big power builds. I consider solid roller cams as drag race only stuff, never sports cars, endurance racing, road racing or performance street.
Keep in mind, although you have one hydraulic lifter acting up, you have 15 that are still performing OK! The motor is 40 years old, its not uncommon for hydraulic lifters to develop problems in old motors.
-G
