Is my engine toast?

[Chero77]

About an hour ago my engine started making a loud clacking or rapping noise. The noise increases with engine speed and sounds like an internal noise. This was a sudden occurrence. One second cruizing along fine, the next . . . strange noise.

So far I have disconnected all of the belts and started the engine. No change in the noise. So its not an accessory. I have pulled the spark plug wires one by one and started the engine to see if the noise changes. No change that my untrained ears can detect. Have listened all over the engine with a pipe, particularly over the valve covers, but cannot locate the noise. I will pull the valve covers tomorrow to see if I can find anything (its too hot right now). A broken valve spring would be obvious, I guess.

But, how would I tell if a lifter had collapsed?

Do pushrods break? How would I know?

The engine still idles smoothly and revs freely, but something is obviously wrong.

Any suggestions? If I can't find anything wrong after pulling the valve covers, I guess I'll take it to a mechanic for diagnosis. This is really lousy timing as I have absolutely no time to deal with major engine work right now. This rig may have to be stored somewhere for a year or more.

Since I may be facing an engine rebuild any opinons on a new Chevy 350 vrs a reman 401?

Thanks for listening.
Dave
:eek:

[Bob Barry]

If the sound is more of a ticking than a rapping, and it's from the top part of the engine, I would imagine you've punched a pushrod through a rocker arm, or a lifter has self-destructed.

If it's lower in the block and a deeper sound, then start looking for another motor.

[Crazy_Jeepman]

How is the oil pressure. Does the noise change when placed in Drive and back to Park may have a broken flexplate. How does it run other than the noise, does it miss. How many miles on it maybe the cam flattened out. good luck hope it ain't serious. ;)

[Chero77]

Having nothing better to do tonight, I pulled the valve covers. The valvetrain looks fine. No broken springs, bent pushrods, or anything else amiss. Put everything back together and started up. Same clacking noise. Good oil pressure. No miss. Engine revs smoothly.

The noise does change (becomes louder and slower) when shifting from nuetral to drive. So, I got under the truck (I hate doing this with a running engine). Anyway, I think Crazy_Jeepman may be right, it may be a broken flex plate. The noise is noticably a bottom end noise and does seem to be coming from around the flex plate or at least from somewhere at the rear of the crank. However, I couldn't tell for sure whether its the flex plate, or a conrod, or a wrist pin, or whatever.

I expect a good, HONEST, mechanic (is that an oxymoron) would know exactly what a broken flex plate, conrod, or wrist pin sounds like and could immediately identify the noise. Unfortuneatly, I don't know any such person.

The TH400 was rebuilt about a year ago, by a local trans shop. Monday, I will drop by there and get an opinion.

I have to admit that I did go out to the Anza-Borrego last weekend with some friends and pounded the Chero up Palo Verde Wash and when we got done with that went up Di Giorgio road. So maybe the Jeep gods are paying me back. They better not hit me up too hard or this rig is going to be retired.

[Brown Bear]

Before you make the foolish mistake of taking your jeep to a mechanic, please do one thing for me. Take the inspection cover off the front of the belhousing. Have someone turn the crank with a socket and ratchet. Take a ratchet and tighten up the flexplate to torque converter bolts (I'm supposing this is an auto). Mine came lose on mine after my brother put it through some rigorous excercises. Tighten em up and it ran great. The sound was just like a bent rod.

[Crazy_Jeepman]

Reason I asked if oil pressure was good is because most of the time if you have a bad rod knock the oil pressure is likely to be very low or 0 at idle. Very unlikely it is a wristpin as AMC never realy had any problems with wristpins, Rods yes, wristpins no. Engine runs smooth with no miss tells me that a valve train problem does not exist in the way of broken parts anyway, you could have bad lifters or burnt valves but unlikely would it cause the noise you describe. This being a sudden occurrence also tells me it is not in the rods as they usualy start slowly knocking prgressively getting worse (not always the case). Flexplate breaking yes, fairly common more so the TH400 flexplate. Well good luck hope it is a cheap and easy fix. If it turns out to be a Flexplate buy a new one to much work involved to put in a used one that may break soon after. smile.gif

[BlueMule]

BrownBear is probably on the right track. Had the same exact symptoms two years ago. Made 360 into about 400 little parts. No luck there. Since I am a terrible (but very fearless and completely enthusiastic) mechanic, I had to tow it to a fleet mechanic who reassembled the engine ($600) and then chuckled and tightened my flex plate ($9 case of beer). <Sigh>

[GLADIADOR64]

are you sure?? maybe something is in the combustion chamber like a nut or a bolt, that can make that sound. is only a sugestion sorry for my grammar because im don't speak english
smile.gif

[Joker's '88 GW]

My truck has the same symtoms with a few differences...

I have loud tapping sound that comes from the rear of the engine. I have not been able to identify a specific side or cylinder. I have had the valve covers off and didn't see anything out of the ordinary. The valve train looked fine.

My noise gets quieter when I rev my motor, and returns just as loud when it idles. The motor starts beautifully and idles good and runs very well. (Other than the pinging issue that I posted)

The "Rod knock" sound hasn't increased or decreased since it started.

Is it possible that I am having a loose flexplate issue also? That would be great to find.

Just curious..