Hello, a bit of a long post, but I'd rather include too many details than not enough...
I'm the original owner of a '78 E150 base van, 300 CID engine, currently approx 150,000 miles.
Except for a few normal wear&tear and mainenance items, it has been extremely reliable over the years, and I intend to drive it as long as it holds out. The engine runs fine, and still starts up as easy as the day I bought it.

The past few months I've noticed a bit of a loud rattling sound from the engine at high rpm under load (when shifting gears, uphill, highway speed, etc).
A few days ago I decided to try my hand at checking the valve adjustment with the engine idling, and noticed a regular tapping sound coming from one valve. Turns out the lifter in that valve had give to it with the engine off and that cylinder at TDC, so I replaced the lifter.
Even though all of the other lifters seem fine, I'm tempted to replace all of them while I have everything disassembled. Push rods and rocker arms are all fine, so all I would do is replace just the lifters.
Also, I pulled a few of the good lifters to check for any dishing on the bottom, and all are perfectly flat, so I'm guessing the camshaft is fine.
Factory specs say to turn the rocker arm nut one full turn after zero lash, but the most I can turn any of mine before bottoming is between 1/2 to 3/4 turn, which I'm guessing is not a problem. I turned them all to just beyond 1/2 turn so none of them bottom.

The only lifters available for that engine these days are aftermarket ones. Locally about the only ones I'm able to get are the 'Sealed Power' HT900 (hopefully not a problem to specify the brand here), which I used to replace the failed original lifter.

Should I leave well enough alone and leave the rest of the lifters in place, or should I replace all of them while I have everything apart?

If I replace them all, are the aftermarket ones reliable enough that I shouldn't worry about one of them being defective right out of the box?

Since the valve clearance check requires completely bleeding the lifters, I'm guessing new lifters don't need to be primed before installation?

TIA for help with this!

 

ok. so here's an update to what I did since I originally posted this in the 'van' section on Sunday...

.. decided to go ahead and replace all of the rest of the lifters while everything was apart with the aftermarket ones, without priming them first ... everything went together fine, engine started up right away, brief rapid rattling, then all seemed smooth, except for a light tapping and sewing machine-like sound coming from the engine. I'm guessing this means a lifter isn't working right...

Naturally, it was a big disappointment, but I've got everything back apart again and would now like to check all of the lifters to see if there's one in the bunch that isn't pumping up.
Is there a simple procedure to check lifter function that a non-mechanic like me can do at home with limited tools?

Hoping the next reassembly will be the last...

 

If you know the Ford part numbers you can find lifters on ebay with a little patience. I even found a pristine factory blue dash cover!!

 

Hi there..I'll try to jump in with a little info that may help. a 300-6 came with at least three types of of rockers and subsequently three different adjustment procedures. I drive two of these motors in an 83, and 86. you may have had a pressed-in stud for a rocker come loose slightly. This would in fact change your rocker final adjustment.
Can you tell if these is one stud slightly taller that the rest? does the sound go away in fact if you hit that stud with a hammer? This may sound goofy, but I understand that the pressed -in stud problem may be relevant to your your year . In later years Ford used a pedestal type rocker that was "non-adjustable"..eliminating that problem. I thought an introduction to this possibility would help you in trouble-shooting your problem. Keep looking into what years your rocker style may be. You'll figure it out...Good luck

 

As another member stated, I found a guy an eBay selling OEM Ford flat tappet lifters, still in original box, sealed! Way cheaper than the aftermarket replacements floating around.

 

After pulling all of the new lifters, I discovered that the plungers in ten of the twelve could still be somewhat easily depressed a tad by simply pushing down on them with one finger ... as opposed to the plungers in the original lifters, which cannot be budged, even with the end of a pushrod.
Am I right in guessing that the new batch of lifters did not pump full after running the engine for about 10 minutes?
Should they have pumped full in that short run time, or should I have primed them before installation? ... If so, how does one properly prime a new empty lifter?

fwiw, the aftermarket ones I bought look virtually identical to the OEM ones, and fit snug and perfectly into the holes .. I didn't take one apart, but from the outside, they can't be distinguished in appearance from the original lifters. Just for comparison sake, they cost $4 each locally.
I couldn't find the OEM ones online, so will have to do a more thorough search to find them. Good to know they're still out there!

Also, thanks for the recommendation to check if the rocker arm studs might have backed out a bit ... I'll try to find a way to carefully tap them down to see if they move .. lol, my father has a nice heavy copper hammer that might be perfect for the job, but he lives far from here .. I don't want to bugger up the tops of the threads .. there's not a lot of swinging room for any hammer .. would a heavy rubber mallet be enough to get the stud to move?
If they've backed out a little might explain why all of the rocker arm nuts bottom on the threads just before or after 3/4 turns after zero lash. I thought that to be a bit unusual for an engine that has no abnormal valve train wear!
I'd be happy with 3/4 turns beyond zero lash ... if the studs are still solidly in place, would it be ok to just bottom the nuts at their approx 3/4 turns, and be done with it?

Another idea would be to shim up the nut with a hardened flat washer between nut and rocker arm pivot ball in order to make more room on the threads for adjustment. Factory specs say to turn the nut one full turn beyond zero lash to set the pushrod halfway down into the lifter plunger travel, but I'd be happy with between 3/4 and 1 turn.
Are there any hardened flat washer types made that would be suitable to do this?

Thanks again for the help!

 

Id that little tap-tap goes away..I'd say ur golden..

 

Don't feel bad about finding out those lifters didn't perform as well. I bought an "old" set of Ford Racing lifters that are the same as your new set. Luckily I did some research and found an eBay member that has sealed in the original box, 302-460 lifters and he will even break the set to sell for your situation. Either way, im working on getting my garage cleaned up so I can replace the set I have in the truck now. The set before that was Comp Cams and I had 2 fail in that batch.