My 14 yr old 25th Anniv Trans Am is having trouble turning over 100,000 miles gracefully. After trailering it from CA to NJ myself, it developed a clacking all of a sudden that would go away within 30 sec to a couple minutes when started. It would repeat it if allowed to sit a couple hours. Thinking lifters, I added a can of Sea Foam oil treatment to clean 'er out. One day after an unrelated overheat (when it rains it pours!) I was test driving after fixing my fan relays and the clacking came back while it was warm and then a POP followed by a dropped cylinder and much louder clacking from all cylinders. Taking off the oil filler cap revealed the rocker directly beneath was 90 degrees turned and off the push rod. When the valve covers came off, I was impressed that my 14 years of Castrol 5W30 had kept it so clean inside. I saw nothing out of the ordinary, so adjusted the valves and put it together. Good to go for a couple of hours, then clacking returned, POP, and louder clacking…same rocker. Suspecting lifters, and noting that there wasn’t as much of an oil mess being splattered about as I had expected, I took off the intake and replaced all of the roller lifters with Seal Power replacements (Napa p/n 213-1738) and new push rods. The initial startup was quiet and they adjusted well. Problem solved, right? Nope. A few hours later and it clacked about 10 sec. 24 hours later, and full on clacking, POP, and a dropped cylinder. Out of time, patience, and ideas, I took it to Pontiac, where they wanted to 1) adjust the valves–big surprise, it didn’t fix it, 2) change the lifters–I’m not ready to pay someone else to repeat my work, so noting that the mechanic also mentioned a general lack of oil splattering about, I requested that they change the oil pump. They had hooked up a direct-reading gauge to the old one that read a steady 35 psi at speed, and no less than 10 at idle, but put a new one in none-the-less. I picked it up the other day. After paying them $1000, and driving 100 feet out of their parking lot…POP, clack, clack, clack, and a dropped cylinder (not the one under the filler cap) .
My suspicion is that there is blockage somewhere between the oil pump and the lifters that, even though pressure is good, doesn’t let the proper volume of oil get to the lifters to pump them up. Before they pressurize, they have a lot of play in the valve train and a rocker is getting thrown off. However, all they want to do is repeat my lifter replacement.
Is there something that could have shaken loose during 3000 miles bouncing around in a trailer that could block oil flow between the pump and the lifters? A check valve or seal or something? The lifters I removed weren’t worn, and when pumped up, they allow my girl to run like a swiss watch, so no apparent valve spring or cam problems. What about the oil pump shaft? I’ve consulted a lot of lifers in the business and everyone ends up shrugging their shoulders. Any ideas out here?
I’ll take a guess that the lack of head lubrication is causing the valves stems to stick in their guides in either an open or semi open position allowing the untensioned rocker to swivel off the valve end.
First (messy) job is confirm your suspicions and run the engine with the valve covers off, you should be able to confirm both oil flow (since it will be dripping all over the floor) and the sticking valve scenario.
Head lubrication is via the rocker shafts and the oilways are quite small, a strip and clean might be a first eliminator. This may be needed on only 1 head.
Are the rocker studs pressed into the heads? Or are they threaded into the heads? If pressed in, the studs may be being pulled out of the heads as the engine operates causing the rocker to losen up.
Tester
Tester you always beat me to the punch,and I get up early. Good call
Don’t know if this applies to yours or not but… my 92 explorer 135k 4.0 - at start up tiktiktiktiktiktik fades and comes back. Assuming lifter/pushrod wear put in oil additive…tiktiktiktiktik. For a good year at least, then asked engine tech to just take it appart and fix what it needs. He says “lemme try sumthin before I even take off a valve cover.” He gets the garden hose and runs the rpms up ingesting water through the intake for many times each time the rpms would allow. NO TICK NO MAS ! The theory ; carbon build up on the valve stem not allowing it’s quick return with each cycle and the rocker arm would be coming down befare the valve had come up resulting in the tick each time. They make a cleaning chemical for the same reason but the water job ended the tiktiktiktik for me.
Having had both valve covers off with the engine running for valve adjustment, I can confirm that there is not a big mess (not like I’m used to when doing valve adjustments). That’s why I had the oil pump replaced–in an attempt to increase volume even though pressure seemed fine. Also, I’ve heard engines run that had sticking valves, and they seem to have more of a slapping sound as the valve snaps shut on each stroke once the spring overcomes the restriction. Mine sounds more like solid lifters needing adjustment. I did check the studs and determined that they don’t seem to be moving. I replaced all of the compression nuts just in case they were backing off.
As for the water treatment, I’ve seen that before and did the same thing, only with a can of Sea Foam fuel treatment right down the intake after I replaced the lifters and it was running good. Ran even better after I did that “steam cleaning”. (until 24 hours later at least!) Thanks for the ideas, and keep 'em coming!
camshaft is going flat? Lifter harder than the shaft?
Some pushrods have guides that prevent them from moving side to side. The older Pontiac engines had them and they would break sometimes. Check the other pushrods and see what holds them in place. Sometimes the rocker arm is broken. Never saw your engine.
New rocker adjusting nuts.
The locknuts that you adjust the valves with have slightly oval shaped heads that are supposed to keep them from backing off. Yours don’t work any more. Replace the nuts, adjust the valves one last time and be finished with it. This is especially common after overheating, since the nuts totally crap out from the increased heat.
You can get specialty, aftermarket double locking nuts for this, but that usually requires machining the top of the rocker studs flat to make them work. Just get new OEM style locknuts.
already replaced all the nuts when I did the lifters.
push rods don’t have guides on mine, only an opening that they pass through in the head.
doesn’t seem to be the cam since all valves indicate proper movement when you adjust them–not to mention that it runs great when they’re not clacking.
Update: Pontiac is looking for something between the oil pump and the lifters that may be restricting flow. They removed the oil pan and pump again today to verify a particular oil pump shaft type that may have been suspect, but came up with nothing. They put it back together. Tomorrow they’re going to go after a check valve in the base of the oil filter plate (my type has the oil cooler lines that go thru it). I’m hoping that is their culprit.
Does anyone else have access to any LT1 oil schematics that may offer further ideas?
Have you thought about a Studebaker Hawk? It has solid lifters, so the klick and klack is normal.