engine diagnosis advice

[tttz]

Hi all,

Since this site is full of knowledgeable (and nice) people i would love to get some advice. Here is my situation:

The engine of my 71 240 is broken and/or breaking. it was making an extremely loud metal-on-metal tapping/knocking sound. I am a newbie to car engines, so this is my first experience in trying to diagnose a problem. Anyway, i managed to pull the valve cover off and everything appeared normal. i discussed the situation with some friends and they suggested removing the oil pan and looking up into the block for the problem.

So, my question(s) is/are:

1. Will looking up into the block provide enough info to diagnose the problem? I suspect that it could, but not necessarily.

2. So, would it be wiser to just pull the engine first, since there is a high probability that the engine will need to be repaired/replaced anyway?

If it is recommended to just pull the oil pan, i've searched this site and seen that you'd have to raise the engine off the mounts. i spent some time last night trying to figure out how to do just that, and it seemed like it would take nearly as much work as pulling the whole engine.

3. What would be the recommended procedure for lifting the engine off its mounts? do all the hoses and wires need to be disconnected? where is the best place to put the jack to lift the engine?

Thanks for any advice. Again, i am a novice so i may have missed something obvious or made poor assumptions.

Thanks,
Ty

[kmack]

Originally posted by tttz
The engine of my 71 240 is broken and/or breaking. it was making an extremely loud metal-on-metal tapping/knocking sound.

Unfortunately, this description is only somewhat useful, but mostly vague for an accurate diagnosis. Is the noise up high in the engine or is it coming from down low? Does it vary with engine speed? How is it under load or while driving? Is it a tap, or a knock? (there is a difference)

First off, there is not much diagnosis that can be done by just pulling the oil pan off the engine while in the car. This procedure is used mainly for when you want to replace the oil pan gasket only! You might be able to visually see if your main bearings have spun, but if you have that kind of noise coming from the engine, you WILL be pulling it!

As for the sound, easy/quick diagnosis says that the valves need to be tightened. When the gap between the cam lobes and rocker arms becomes too much, you can get a very noticable tapping sound and it comes directly from underneath the valve cover. Get your service manual, Haynes manual, or what-have-you and get the gap set to the right dimension. That may cure it.

In one instance, I have had the fuel pump arm off the mechanical fuel pump make a bit of a tapping sound. It was an aftermarket fuel pump on my old '73 motor and the arm would not make complete contact with the drive lobe off the cam. Another fuel pump cured the problem.

If the sound is a deep sounding knock coming from low in the engine, then we're talking about a bit more serious problem. That usually means that the lower bearings are "loose" and the piston rod is knocking around during power cycles. Time for a major overhaul then. But this usually doesn't happen to the L series motors until close to 300K miles unless they have been seriously abused.

Try the valve adjustment first and see if that helps/cures the problem. If not, then see if you can locate from where the noise is coming from. If you can't pinpoint it, get a long piece of small diamter tubing to use a stethescope or you can use the old-timer screwdriver-in-the-ear trick, but that one never worked for me.

[tttz]

thanks Kmack.

i guess i should elaborate on the background. the last time i drove the car, i was doing a bit of spirited driving getting onto the freeway, probably took the rpms upto 6k, maybe higher because the tach doesnt work very well over 4k, but anyway, about a mile down the road i notice a tapping sound under acceleration. the noise wasn't audible without giving it gas. I decided to pull off the freeway. as i slowed down, i gave it some more gas to hear the sound without so much background road noise, and the sound became louder and i could begin to feel vibrations in the shifter. so when i tried to gently accelerate from the off ramp to the nearest safe place, the sound was extremely loud, with extreme vibration coming through the shifter (then into my arm and then heart ) and i could guess that it was pretty serious. Some guy who had heard the noise said that it sounded like a broken rod. That was about a month ago.

Since then i've turned the engine over (after disconnecting the coil) and i could only hear a slight tapping. of course the engine was only doing a few rpm, instead of a few thousand...

So, i think i might as well pull the engine now that i know that oil pan removal is just for replacing the gasket. Thanks kmack!

[kmack]

Hmmmm.....

Vibration coming through the shifter throws a whole new ball into the pit. Was the noise/virbation the same with clutch in or out? I'm wondering if maybe there is something else along the driveline that may have "snapped?"

Will the engine start as it sits now? If so, is the noise/vibration still there and as loud?

FWIW, while racing my old '73 motor, I used to routinely wait to shift until between 6500-7000 rpm. Kind of trying to see how much that old oil-burning hunk of cast iron would take. It actually held up. Never heard any knocking or otherwise bad things coming from it. It even made decent hp figures on the dyno last year.

How many miles do you have on this engine, estimate if you have to? Do you know the history? What condition was it in before this happened? Anything ever happen before that may give doubt to it's internal integrity?

Either way, pulling the engine out is not too involved and rebuilding it is fairly easy also. Make sure you have at least one manual on hand while rebuilding. I'd also try to find a few fellow Zer's locally that might help diagnose and/or help with the rebuild.

Good luck and let us know the outcome.

[tttz]

Thanks again. My basic question has been answered, which is that i'll just pull the engine rather than try to examine it by removing the oil pan.

i don't recall what difference teh clutch made. that would have been good to find out though. if i started it up now, could i determine if there was any other driveline damage? Or would it have to be driven to figure that out?

-Ty

[kmack]

Originally posted by tttz
if i started it up now, could i determine if there was any other driveline damage? Or would it have to be driven to figure that out?

If the amount of the noise/virbation is less now, than it was before with the car in motion, then you effectively eliminate anything beyond the driveshaft.

If the noise/vibration increases with the clutch engaged/disengaged will be a determinating factor if something is wrong inside the transmission.

If the noise is uneffected by the clutch engagement and is the same as before even though the car is not moving, then you're left with it being soley in the engine.

Does that make sense? I only ask because a lot of times, my head speaks clearly to itself, but not necessarily to other people!

[1971rb26dett]

From what you describe it sounds like you spun a rod bearing. If its not coming from the valve train or the drivetrain that is the most likely suspect. Very few people have ever spun main bearings on these motors so hopefully you are not one of those few. Anyway, if you are gonna pull the motor you will find the problem very soon after you pull the pan off and start digging in.