datzenmike diagnosis haha

[The datsun kid]

i have a 71 521 with a l16. so my truck doesnt want to idle till i run it for a min its weird but then i finally warm it up and it doesnt seem to idle very well almost like a pumped v8 idle and it sonds like rattling when im on the gas up to a certain point and it goes away almost sounds like pinging but its a stock l16 with a blown oil ring in cylinder 4 i think unless its a valve seal just thought id see what you guys thought DATZENMIKE your input would be gggrrreeeaattt! haha

[Bullet_theory]

i have a 71 521 with a l16. so my truck doesnt want to idle till i run it for a min its weird but then i finally warm it up and it doesnt seem to idle very well almost like a pumped v8 idle and it sonds like rattling when im on the gas up to a certain point and it goes away almost sounds like pinging but its a stock l16 with a blown oil ring in cylinder 4 i think unless its a valve seal just thought id see what you guys thought DATZENMIKE your input would be gggrrreeeaattt! haha

 

 

sounds like a bolt ina blender?

 

lol love the title btw :rofl:

[datzenmike]

No motor with a carb likes to idle when it's cold. This is why there is a choke and a fast idle circuit to warm it up quickly and keep it running until is it.

 

Once warm there are many things that can cause poor idle.

 

Incorrect valve lash

Idle mixture/idle speed set wrong.

Vacuum leak. EGR valve leaking/not sealing. Should be closed at idle.

Ignition timing, bad wires/cap/rotor/plugs.

Low compression in one or more cylinders blown head gasket. Compression test may show which one.

 

Check the above. This may correct the problem.

 

 

How do you know the oil ring is 'blown'?

[nismo dr]

 

How do you know the oil ring is 'blown'?

 

uhhhh.... Its smiling?

 

 

 

 

 

 

 

[The datsun kid]

see its like the bat signal only in the shape of a datsun logo!!! hahahaha but no i did a compresion test and the cylinder was at 125 and the spark plug had oil on it and i will try to check all those things. kinda sounds like marbles bouncin around so yea a nut in a blender same thing

[Bullet_theory]

ROD BEARING FAILURE!

 

how many miles are on the motor?

 

that explains the oil in the cyl, and still haz good comp, and im guessing when you mash the thin pedal, the sound speeds up aswell?

[datzenmike]

...and it sonds like rattling when im on the gas up to a certain point and it goes away almost sounds like pinging .

 

If the rattle/pinging is load dependent, by that I mean it comes and goes depending on how hard you are driving, then it isn't something loose like timing chain or valve lash. It must be inside the cylinder or perhaps an exhaust leak.

 

If it is loudest when the motor is cold and quieter when warm you may have piston slap. If you are familiar with the sound on start up, and assume it's the #4 cylinder.... squirt some oil in that cylinder when it is cold the next day and start it up. If the sound is gone or greatly diminished... you have piston slap.

[The datsun kid]

alright i'll try that and im lookin for a l20 or l18 or somethin to put in i kinda wanna tear it down and find out whats up haha thanks for the help guys

[The datsun kid]

oh and yea sorry bullet it speeds up or at leat it sounds like it to me

[Bullet_theory]

If it is loudest when the motor is cold and quieter when warm you may have piston slap. If you are familiar with the sound on start up, and assume it's the #4 cylinder.... squirt some oil in that cylinder when it is cold the next day and start it up. If the sound is gone or greatly diminished... you have piston slap.

 

yeah ive thought of that aswell

 

hey datsun kid, just like mike said, try this... its a pretty easy thing to try...

 

First thing in the morning, start the engine up and run it for 15 seconds while you listen carefully and memorize the sound and it's intensity. Shut it down quickly, pull the spark plugs and put two squirts of motor oil into each cylinder, unless you know its #4. Reinstall the plugs, fire the engine up again and listen. If you have piston slap the noise will have been greatly reduced or even eliminated…..for 15 or 20 seconds that is, and then your nightmare noise will come back.

 

if not, im sure a few other people might have some ideas... but my mits 3000gt just had the same issue and it wasnt hard to crack open the bottom end and see i had spun the #6 bearing... it was $9 fix (i spent $54 total just to make sure all the bearings were new), since we had all the tools in our units motor pool to turn the crank and rework the rods/caps