any mechanics in here?

[CaneyRiverDog]

My sister inherited a 1998 chevy 3500 with the 7.4L 454 Vortec from a family member fall of 2022. It'd been sitting for 3 plus years. BIL had done the usual stuff to get it drivable tires, new plugs, fuel filter, oil change, 3 cans of seafoam, and a new battery.

They have drove it maybe 300 miles in the last year without trouble. About 2 weeks ago they bought 2 medium sized cans of the R134 with the sealer and dye to try and seal the ac or to find the leak to get it working. It ran fine.

Yesterday they were going to drive it to eat, they dont drive it daily, but when they started it up it had the loudest ticking noise. They sent me a video and it was clacking pretty loud in video. They had a "mechanic" friend come listen to it and he said it sounded like a lifter.

They called the local shop cause they are scared to leave the house with it and they said the 454 was notorious for sticking lifters to put a bottle of ATF fluid in it and run it down the freeway for a 100 mile trip and that would help clear the gook sticking the lifter. Then change the oil again.

I AM NOT A MECHANIC so Ive come to ask if anyone here is a mechanic with advice?

Anyone with any experience with these engines?

It's clacking so loudly my sister is afraid to drive it period ( she thinks the engine will blow)

As always I come here for the collective wisdom and thank you for any insight

[peejman]

ATF is highly detergent and it's possible it will un-stick a stuck lifter. But it's a temporary fix. If the lifter is stuck, it's likely worn or the bore is worn and it'll stick again at some point.  It's also likely damaging the cam, so that lobe will get worn down. 

Assuming it's still got good oil pressure, at least 40psi? 

[Alleycat72]

I got an 454 like this and it ended up as a 700 hp 496. Be careful. 

[LangdoniousRex]

The ATF trick is a hail mary. If the valvetrain is smoked, no snake oil is going to fix the problem. If you go forward with throwing ATF in, you only need to warm it up and drive a couple miles to see if anything changes. Also be prepared to change the oil immediately, if by some miracle it clears it up. The drop in viscosity from the ATF isn't good for the motor long term.

[gary_boom]

8 hours ago, Alleycat72 said:

I got an 454 like this and it ended up as a 700 hp 496. Be careful. 

For only a little bit of money!

[10-Ring]

8 hours ago, LangdoniousRex said:

The ATF trick is a hail mary. If the valvetrain is smoked, no snake oil is going to fix the problem. If you go forward with throwing ATF in, you only need to warm it up and drive a couple miles to see if anything changes. Also be prepared to change the oil immediately, if by some miracle it clears it up. The drop in viscosity from the ATF isn't good for the motor long term.

That one time when ATF MIGHT have been the answer. 

[Alleycat72]

1 hour ago, gary_boom said:

For only a little bit of money!

(But for only $250 I could upgrade to this) × 20

[gary_boom]

I’m surprised no one has wanted to buy the truck. I don’t need it, I don’t need it I keep telling myself.

[Grayfox54]

IIRC those old big block Chevys were known for wearing down cam lobes. Considering the cost of gas these days, I'd sell it as is for whatever you can get. You said it was inherited, so you won't be losing much. I'd consider that a much better option than throwing a bunch of money into a gas guzzler. 

[Frog4aday]

Try the ATF fix. Nothing to lose really. Someone will want to buy it regardless. Anything pre-2000 in trucks is getting more desirable for their simplicity and longevity. Cost to rebuild & fix is still way cheaper than buying new.

[papa61]

My instructor said always start with the last thing that was touched. Take the ac belt off and see if it stops. A/C compressors get really loud when they are about to disembowel themselves. Not sure about big block Chevy but I had a 400cid Ford that would throw the pushrods out of the rocker cups if it sat too long. They only knock for a short time until the pushrods get bent, then you have a dead miss. A collapsed lifter would show as a dead miss. If it's a stuck valve it could be a large ole in a piston. Start with the A/C. Then check for a miss. After that it's removing the rocker covers. Keep in mind, if it is just a lifter, you still need to replace all 16 plus the cam. Now you're into money pit time.