Our rebuilt 2.1 has about 10,000 mi. on it. = We've been getting alot a valve clatter on one lifter. Figured it made sense = to adjust all valves as a follow-up to the rebuild getting broken in. = As I tightened the adjustors, all but one got snug then I went 1 turn beyond. = That one snugged very slightly then kept on screwing down. It seemed to = bottom out just as the screw became level with the locknut. I backed it out = again to the same adjustment as the others and pushed on the rocker arm. I = was able to collapse the lifter very easily. I'm assuming that I have a bad = lifter. I ordered a lifter and a "collapsable pushrod tube from = The Bus Depot. While I wait for delivery, I'm trying to figure out how = serious this situation is. I did adjust this lifter down to where it = bottoms out, thinking that I might be able to treat it like a solid lifter. For = safety, I then backed it off 1/2 turn. Started the engine and heard...nothing. Well almost nothing, slight ticking presumably = from my backing off 1/2 turn. Nothing like before though. Question is, = am I Ok driving like this? Should I set it back like the other valves and = just let it keep ticking? Hydraulic lifters continue to be a bit of a mystery to me; = I seek the collective wisdom of The List. Thanks.