Figured I would pass along a problem discovered during the rebuild of my Daytona's 440 engine. Vance Cummins is doing the rebuild along with the rest of the car's restoration, and he's a pretty good wrench all things considered. He selected a Comp Cams hydraulic roller camshaft with not-too-radical lift, duration and overlap properties in an attempt to get the best performance possible with all stock external components and with a 100% stock sounding idle. They used the "recommended" Comp Cams Pro Magnum 8921 roller lifters as part of the package.
Vance did the dyno pulls a few weeks ago (I'll post those dyno results after Round II is performed), and noticed that there was a pop or two every now and again - sometimes when the engine was idling, sometimes at the beginning of a pull, and even once right after it shut down. They were never in the dyno room when it made the noise, and it wasn't loud enough to scare anyone into thinking there was a major parts failure... it was just something he noticed hearing, like a misfire or something.
Anyway, after getting the engine back to his shop, he noticed the valve covers were seeping oil around the gasket just a bit. Since the engine wasn't yet painted, he wanted to work the seals over or replace them so that there wouldn't be any seepage once the engine was painted & installed. When he pulled the valve cover off, one of the pushrods was totally out of its lifter seat and the rocker arm loose. Upon further examination, he found that several (meaning about 6) of the lifter plungers had "hung up" and were about 3/16" down inside the bore of the lifter casting. See the pictures below, which show a hung lifter plunger in comparison to an unstuck piece.
Of course, that about freaked Vance and everyone else out, since you wouldn't expect to see that type of a problem with brand new lifters from a reputable source. He did a little more checking around, and found out that apparently some guys on Moparts.com had experienced the same phenomenon. Here's a link to that thread:http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Board=Racer&Number=5379327
Vance has ordered up a new set of the Scorpion hydraulic roller lifters to use in the engine, and they should work based on the experience the guys on Moparts have had so far. A followup phonecall Vance made to one of the Moparts posters said that over 500 miles had been put on an engine with the new lifters without incident or problem. That's not exactly a long-term durability test, but we put zero miles and probably less than 1 hour total runtime on the Comp lifters before they developed whatever hitch they had. From what everyone thinks, the pop sound that they heard very well could have been the lifters becoming unstuck and slamming against the retainer ring - which could fail completely if that happened very much.
I asked Vance to go ahead and take the engine back to the dyno shop, since we don't know for sure what the valve lash was doing during the dyno pulls, or exactly when that pushrod came off. When the results of that second dyno trip are given to me, I'll put 'em up here for posterity's sake.