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Discussion Starter #1
Turns out that knocking sound was not just a loose exhaust system. Last week Telegraph road took it upon itself to tear off my muffler. So I got the new exhaust system. The knocks and rattles it was making are gone, now I hear the knock coming from the engine's lower end clearly. From 2800-3000rpm.

I was going to put new plugs in...so I was thinking if I ran the engine w/out a plug I could pinpoint which cylinder was knocking. I was just concerned that this may be bad for the alternator or some other electronic device.

Also, I read somewhere that dripping transmission fluid into the open plug hole can clear up cylinder noise...anyone familiar w/ that?

So, uh any advice on driving with a rod knock? I figure I should keep a close eye on the oil, and avoid sharp turns. Are there any motor oils, treatments available that can help? Particularly in cold weather.

If I can keep this thing running for 1 year, the summer of 2006 I will be able to afford a sr20det or rb swap. If it dies this year I have to put the 240sx in storage and find another beater to hate driving.

I do have access to a 4-bay heated garage. A good friend of mine's dad retired, moved out to the country and buillt a real nice place. He has everything needed to do anything to a car.

He and his friends are buying up Austin Healey Sprites and restoring them. He has 7 at his property. And a bad ass TR8.

So I don't know how to change bearings,pistons, etc, but he does, and my brother can help too(airplane mechanic). Is it better (cheap)to jump on the rod knock during winter or spring break?(I am a teacher, hence the brokeness). I do not want to commit too much time/$$$ on a knock that will probly come back.

Sorry about all the questions all at once...had to get it all out during my prep time.
 

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Nismophiliac
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sorry....but there is no remedy to cure a rod knock without tearing down the entire engine. If you keep driving the SOHC engine with a rod knocking, it will throw a rod through the block, and then you will have a huge mess on your hands. When i bought my 89 240 it had a hole in the block from a thrown rod. I've just about got the sr swap finished, except for the wiring. If you are saving for the sr swap, go ahead and drive it till it blows for good. (that's if you are not imbarassed by the knocking :) )


And if anyone asks you how it came to be knocking, just say you used a little too much NOS, it will make them go away. hahaha.

Good luck. If you would like, i can try to find you a sr at a decent price. I paid 500.00 for mine with a trans, and ecu, and wiring harness. But its the N/A motor.
 

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You can diagnose what cylinder is knocking by just pulling the plug wires one by one while it is idleing. I did this and realized that it was my #4 cylinder that was knocking. I tried to drive it on only 3 cylinders...it doesn't work, when you pull the plug/plug wire, there is no spark in the cylinder, thus there is more raw gas going through the header, your O2 sensor picks this up and calls for more air, over compensates on the air,runs really lean, and shuts itself down. Sorry, there's no fixing a rod knock.

Now don't forget, your rod might be perfectly fine, there are other things that can go wrong to make a knocking noise. It could be a wrist pin (the pin that connects the rod to the piston head). If the wrist pin is messed up the piston and rod run rather loosley and smack against each other on each revolution. If it is your wrist pin, you might be able to get away with just changing the piston, ring, and wrist pin...the rod might be fine. Just some things that I've been asking around about and the answers I've been getting about my "rod knock"...Good Luck! If you find anything out that might help me PM me...both my 240's are out of commision right now...
 

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Discussion Starter #4
could be a bad injector?

While trying the plug removal test, I stumbled on another possibility.

My injector(s?) are leaking gas. It only is really noticable at 2500 rpm. I had been trying to track down the source of the gas stink , but could not at idle or engine off.

I never got to finish what I was doing (my toddler boys are pukin all over each other+the cats...seriously). So I can not be sure.

If the bad injector can mimic the sound (cylinder slap) of a knock, then the spark plug test would give me a false rod knock diagnosis.

And yeah, if you can track down an sr/rb engine for that kind of $$$...by all means let me know. I have been looking around Ontario and Ohio, preferably Canada with the exchange rate and all. Somewhere I can drive, to save shipping. Plus I like going to Canada anyway.
 
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