How much slappy slappy is too much slappy slappy from a 4.0

[evanlove]

Just got my first Comanche and got it to run after it had sat outside in Colorado for 15 years. 

 

It sounds like a serious piston slap when it's firing, so I shut it down. 

 

I got no history with it when I bought it, so I have no idea if it was parked in good running order (had brand new looking 15 year old tires and new looking cat-back exhaust, so, maybe) or if this slappy sound was there when they parked it. 

 

Is there anything other than piston slap that could cause such a noise in a truck that sat 15 years?

 

It's a 1988 Comanche Pioneer, 5 speed manual, 4.0, 4x4, short bed

 

Thanks, 

 

Evan

[gogmorgo]

Are you running sat-for-15-years oil or something more recent? Did it seem like you had oil pressure?

[Classy Comanche]

I mean lifters do tick. The truck is 34 years old. Mines a 1988 Pioneer too. The little 4.0's are a tad noisy anyway. I'm not saying you don't have anything going on but majority of 4.0's do slap and tick. And the ticking silences when throttle is applied. As long as it isn't like grinding, whining or knocking it in theory isn't anything catastrophic. I know Cruiser and Pete here can definitely fill you in on that a lot more with a lot more knowledge. There's actually a thread made if you scroll a bit that talks about noises. You can hear mine and the other guys truck in question. It was around August 16th I think? Here's the title of the thread for you. Oil also is a fantastic question. Has your oil been changed or is it still running the old 15 year old oil? If so that very well could be your issue 

 

Is that knocking I hear, or just "Jeep noises"?

[cruiser54]

gogmorgo asks good questions. 

[75sv1]

What I'd do is change the oil and filter. Then remove the coil wire. So IE no spark. Crank the engine over a few minutes. Then attach the coil wire back on and start it. See if it clacks then. I'd also change all fluids, radiator cap if you plan to drive it.

[81Chero]

I traded a crx for a 96 2-door Cherokee from a guy who thought he had a rod knock. I knew it was just the timing chain guides.

So got it home and sure enough, whoever did the timing chain didn't pull the pin in the tensioner!

(4cyl but same concept)

[Minuit]

9 hours ago, 81Chero said:

I traded a crx for a 96 2-door Cherokee from a guy who thought he had a rod knock. I knew it was just the timing chain guides.

So got it home and sure enough, whoever did the timing chain didn't pull the pin in the tensioner!

(4cyl but same concept)

The 4.0 actually doesn't even have a timing chain tensioner. It just lets it slap around with the only form of "tensioner" being a stationary guide that slips into the timing cover. Later engines changed the chain design to quiet it down a bit.

[jpnjake]

On 11/19/2022 at 6:10 AM, evanlove said:

Just got my first Comanche and got it to run after it had sat outside in Colorado for 15 years. 

 

It sounds like a serious piston slap when it's firing, so I shut it down. 

 

I got no history with it when I bought it, so I have no idea if it was parked in good running order (had brand new looking 15 year old tires and new looking cat-back exhaust, so, maybe) or if this slappy sound was there when they parked it. 

 

Is there anything other than piston slap that could cause such a noise in a truck that sat 15 years?

 

It's a 1988 Comanche Pioneer, 5 speed manual, 4.0, 4x4, short bed

 

Thanks, 

 

Evan

I just got finished with a 2001 4.0 swapped into my 2000 XJ. The 2001 motor had been sitting under a bench since 2003, and when we first started it up it had really bad lifter tick with brand new oil, i just poured the recommended amount of seafoam in it and let it run for a bit and after a minute it cleared right up. Things don’t like to sit. 

[gogmorgo]

Not much point in speculating until the OP gets back. ¯\_(ツ)_/¯ 

[evanlove]

Thanks everyone. 

 

I changed the oil and filter. 

 

The oil pressure seemed good when I was just turning it over but not firing, and it all sounded good then...

 

... but as soon as it fired, it made that very loud metal on metal slapping noise...

 

... and the oil pressure went down. 

 

 

At first I thought maybe the slapping noise was external to the engine.  I looked around for something moving and physically hitting it from outside.  My friend listened to it from the passenger side with a mechanics stethoscope against the engine and he quickly thought it was the crank jumping around inside (i don't know his level of expertise with cars) so I shut it down.

 

Accelerating the rpms did not quiet the engine. 

 

If it is fixable I'd love to not rebuild this engine. 

 

The truck sat a long time, but had brand new tires and exhaust installed just before being parked, though it did have a tow bar on the front of it, soooo?

[87MJTIM]

Sounds like dropping the oil pan and looking up at the crankshaft and pistons will answer many of your questions. 

[AZJeff]

1 hour ago, 87MJTIM said:

Sounds like dropping the oil pan and looking up at the crankshaft and pistons will answer many of your questions. 

YUP.   This is going to be the best way to determine if starting/running the engine any further is going to do any serious damage to what is in there.

[cruiser54]

I'm not convinced you or your friend know the difference between a clattering lifter and a rod/crank knock.

 If it's knocking that bad and it isn't lifters, the engine will need an overhaul anyway. 

Why not eliminate the possibility of lifters first? 

How about the flexplate bolts being loose? 

[evanlove]

It's a manual trans, so not a flexplate, but I like the alternative things to consider. 

 

It's a higher pitched slapping noise, very loud, but doesn't sound like a mere lifter tick (i wish it was) unless this particular engine can make that level of noise from just a lifter. 

 

I would think a rod or main bearing would be a lower tone knock (rather than a slap) from audibly deeper within the engine, but i suppose either could cause an actual piston slap.

 

Any thoughts on why it sounded really good before firing and had good oil pressure, but then sounded really bad when firing and oil pressure dropped? 

 

I would think higher rpm would have higher, not lower, oil pressure.

 

So, ya, the sound was loud enough and more slappy than knocky, that I wasn't completely sure it wasn't external to the engine...

 

... though the mind plays tricks when it is in denial and I really didn't want to hear what I was hearing. 

 

Some smoke did rise up from the open circle in the valve cover where the hose to the air box should be for a little while after I shut the engine down (previous owner replaced the air box with one of those cone shaped air filters and left the air hose to the valve cover open).

 

Also, there was a valve cover gasket, unopened, behind the seat...  ... and it looks like newer freeze plugs in the engine...  ... truck has 235k miles...  ... had new tires and exhaust put on just before they parked it...  ... tow bar was on the front as if it was towed into place...  ... I did have to replace the fuel pump to get it to fire, and regap the plugs... ... it was being held as collateral for a personal loan and then the owner that owed the money died and never returned for the truck...  ... so, no previous owners information on the trucks condition other than the odd collection of clues (new tires and exhaust on a truck that was towed into place, valve cover gasket behind the seat, dead fuel pump when I got it, plugs gaped at 55 wouldn't fire until regaped to 35, aftermarket freeze plugs in engine) 

 

I appreciate any feedback, and, I will pull the valve cover and pan and see what can be seen and feel what can be felt from there. 

 

Anything I should try before wasting all the brand new oil and filter? 

 

I guess I could try pulling one spark plug wire at a time and see if that changes anything.

 

Thanks

 

Evan

[cruiser54]

Perhaps pull the valve cover. Maybe a pushrod popped out of place. 

[evanlove]

That's an interesting thought...

 

... I'll look into that

[dasbulliwagen]

I had a pushrod break on a VW I used to have. It sounded horrible, and I thought it was the end for that motor. I got lucky with it. If the truck sat for a while it could have had a stuck valve that bent the push rod. Its easy enough to check before investing too much into it. Id also do a compression and leakdown test. Get a mechanical oil pressure guage to verify pressure. 

[OldManComanche]

Look at the crankshaft pulley on the front of the engine; loose or rubber insulator shot? Is there slop in the timing chain? Unhook the belt and see if the knock stops.

[Tactical Bacon]

Wouldn't hurt to record a video of it running and posting it for everyone's listening pleasure.

[evanlove]

Thanks everyone,

 

I'm not in the same state as the Comanche right now, but as soon as I get back to Colorado I'll look into these things and report back...  

 

...and make a video with the sound too