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last weekend, i made a long ride after two months not using the jeep. The jeep starts fine. After an hour driving i hear a clacking sound, just like a diesel engine. The engine idles normal, no loss of power but that sound. I let it cool down for a few hours. The noise was away. When the engine is on workingtemperature again, the sound was back. The valves where adjusted last year. The sound starts only when the engine is warm. Someone an idea ?

Erik

It would help us for you to use a stethoscope and determine what location in the engine the noise actually emanates from.

Also noises can generally be grouped:
1-clicking or light metalic tap. (Usually valve train noise)(could also be timing gear noise)
2-Heavier metallic clack. (Fuel pump arm)
3-Medium metallic banging. (Usually a rod knock)
4-Heavy thud. (Usually a crankshaft bearing)

Try to offer as many operating parameters as possible. IE actual coolant temp, oil pressure, speed, gear and so on when the noise occurs.

Next weekend i recheck everything.

3-Medium metallic banging. (Usually a rod knock)
4-Heavy thud. (Usually a crankshaft bearing)

is not the problem, a rod knock will be stronger under power and the oilpressure stays stabil end of scale as usual during driving, about 25 at idle, not fluctuating. The jeep has all normal power

I thought the vallve clearance will be smaller when the engine is on workingtemperature ( valves warmer, thicker and longer ). I will use a stethoscope to locate the sound. What i surprised, when the engine is cold, everything runs smooth. A friend adviced me to put some lubricate together with the fuel to lubricate the valveguides. The jeep is staying in a barn, so fluctuating of the temperature ( winter here ) can cause condensation and corrosion on the valves...).

I let you know further investigation..

Erik, thanks anyway !

sounds like rod bearing to me .if you slowly revv it up does it get louder with no load ? the oil gets thinner when it gets to operating temp,which could be too much clearance making the knocking noise.look at the oil from dip stick under light and see if you have sparkles .it could be a sign of babbit from the bearings .i have seen a cracked piston make the same sound but would make a clacking noise when you accelerate under load .If it makes it on idle when hot you can take the plug wires of one at a time to find which one it is .Good luck and hope it is not bad !!

I doubt it is a rod bearing. Look at the oil pressure level he posted.

problem solved ! I add some upper lufibricant together with the fuel.
Product from marly, a product to lubricate valve guides and inside upper cylinder components. It is graffite mixture. After a few miles the noise disappeared almost. A mechanic here adviced me to use it a few times. The fuel these days has no lead in it, and the leadreplacer mixture does not always do the job as lead does. The fuel is very dry and valves can become rusty inside the guides, special when the jeep is stored in very cold places, and the temperatured goes up and down, this makes condensation and rust ( just a little) , just enough to make the valve stick when she is hot and has becomes 'bigger'.
End of the story, nothing wrong with the engine...

Erik

Erik,
If you have access to aviation piston engine fuel like LL100 you can obtain several liters and mix with you regular gas for the jeep say 25% 100LL to 75% regular no lead gas. This will add the necessary lead and improve the storage capability of your jeeps fuel.

Is there an over the counter additive I should be running in my fuel for my M38?

Thanks Bruce

The lead substitutes aren't really needed in these slow turning low compression classic engines. Stabil does help with making the fuel hold up to long term storage better.