Collapsed lifter, perhaps? For a while I had an `82 Malibu with the V-6
that would make horrible loud death-coming-soon whacking noises every
once in a while, always while hot, always in hot weather -- this a few
months after my `79 CJ had spun a rod bearing on my way to work (the
motor kept turning just long enough to get off a busy interstate and
into to a commuter parking lot). As the Malibu was my only ride at the
time (and I was broke) it scared the bejeasus out of me the first couple
of times it happened. Apparently it was a gummy lifter that would come
and go at will. I got another 30K out of that motor.


Jeff DeWitt wrote:
> The last few months of driving my good old Cherokee with a 4.0 engine
> and about 300,000 miles has been making a bit of a clicking sound when
> the engine is cold. Tonight as I was driving along the clicking sound
> got a lot worse, and the engine was hot.
>
> As this engine has a BUNCH of miles on it I'm really afraid it might be
> a rod bearing letting go, but I'm hoping it might actually be a lifter.
> The noise is now always there, and it seemed to be getting worse as I
> drove, it is somewhere between a click and a clatter. The oil pressure
> is at least good enough the idiot light stays off, and of course the
> crankcase is full. Under moderate to heavy acceleration the noise goes
> away, it's always there under light acceleration and when cruising or
> idling.
>
> Is there a quick and dirty check? I seem to recall if you pull the
> spark plug wires off one by one and the problem really is a bad rod
> bearing it will quiet down when that cylinders wire is pulled, but if
> it's a lifter pulling wires won't make any difference.
>
> If it is the rod bearings what kind of luck have you guys had with used
> engines vs rebuilt. I have neither the money or the inclination to buy
> a new Jeep and plan to keep this one for as long as I can. (Well, a new
> Wrangler Unlimited with a hardtop would be really cool, but that's only
> going to happen if the Prize Patrol shows up!).
>
> Jeff DeWitt