240z l24 rod knock - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 16 (permalink) Old 11-19-2019, 06:24 PM Thread Starter
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240z l24 rod knock

https://youtu.be/4kStjnFagcU

so as shown on video cylinder 2 seems to have a nice rod knock, I drained some oil and noticed copper flakes so I'm 100% it's the rod bearing. Car was sitting since 1988 and we got it running yesterday to find this noise, oil looked new and was at proper level. So now I'm wondering two things, how did this happen and what is the best plan of attack? Replace all 6 of the rod bearings and put it back together? Disassemble and send the crank / block to machine shop then reassemble with new main, rod bearings, and piston rings?
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post #2 of 16 (permalink) Old 11-19-2019, 11:10 PM
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Mr.Z44:

Bad luck, indeed.

If I may offer, the issue of "how did I get here" is, while intellectually stimulating, not nearly the issue that "where am I" is.

In this situation, the standard procedure is to define just where you are.

You have a choice at this point; you can raise the engine a bit and remove the pan to try to access the lame rod bearing with an eye to replace the failed bearing only. This is called the "lick and a promise" approach which could, should you be a very lucky fellow (and the current evidence does not favor this assumption), get you down the road awhile, provided the other bearings are not similarly disposed.

Or. You could begin where you will be eventually anyway, and pull the engine and make a proper job of rebuilding.

Pay me now, or pay me later, with interest.



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post #3 of 16 (permalink) Old 11-19-2019, 11:30 PM
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post #4 of 16 (permalink) Old 11-20-2019, 12:23 AM
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Ensys has it right.

Pull the engine, send it to a machine shop and have the problems corrected. I'll bet you didn't have that in mind or budget.

You can also look for another (used) engine that doesn't have a rod knock.
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post #5 of 16 (permalink) Old 11-21-2019, 03:01 AM
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No, Mr.Z44 has it right.

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Disassemble and send the crank / block to machine shop then reassemble with new main, rod bearings, and piston rings?
Is this poor puppy a recent acquisition? How many miles on it? Original engine?

In any case, this will be a fine opportunity to really make it your own. Z engines are easy to work on and rewarding to rebuild. Plus, you're tuned in to folks that will offer good advice along the way.

Of course, disassembly will tell the tale, but all things being equal, it's unlikely that the block will need a machinist's attention. Save your money for the head and, if you don't have it already, a Factory Shop Manual. With a little luck, the manual will be the more expensive of the two.

The L-series engine is a sturdy rascal and if not badly abused, is fairly resistant to wear. Just check things carefully and trust your instincts and the manual.

Keep us posted. There's no such thing as too many rebuild threads.



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post #6 of 16 (permalink) Old 11-21-2019, 01:50 PM Thread Starter
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hey guys thanks for the replies i do appreciate it. Well my inexperience is showing and i might have jumped to conclusions, after talking with a mechanic of mine he said its just a exhaust manifold leaking, i guess around the cylinder 2 exhaust runner? he said no way thats a rod knocking. I really hope hes right so ive been watching videos of rod knocks and exhaust manifold leaks and to be honest it does not sound anywhere near as bad as any rod knock video ive watched (heavy gross sounding metal to metal knock) sounds almost identical to a ram truck with a leaking exhaust manifold although sound through videos isnt always the most reliable. Now about the particles i saw in the oil, we drained only a little bit of the oil into a very old and dirty oil container so theres no way to be sure if that was from other cars oils or the 240z. Today we plan on draining the rest of the oil into a new oil container so we can properly asses the old oil, if it checks out we will replace with new and start replacing the exhaust manifold gasket. This is a really really nice RUST FREE 240z with numbers matching l24, we just bought it as a project and our plan is to replace the auto trans with a 5 speed manual out of a 280z while trying to keep it stock as possible but doing a few tasteful mods here and there. fingers crossed and will keep this updated as i dig further into it!

Last edited by AlexZ44; 11-21-2019 at 01:54 PM.
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post #7 of 16 (permalink) Old 11-21-2019, 04:14 PM
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Sounds like an exhaust leak to me. Put your hand near the exhaust port on #2 . You’ll feel it. Do it when she’s cold.
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post #8 of 16 (permalink) Old 11-21-2019, 04:19 PM
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This is a perfect time to use an automotive stethoscope. They cost like $10 and are available at mos parts stores.

They have a long rod that you press against things to hear the sound transmitted from various parts of the engine or from accessories like an alternator or water pump.

With that tool, you can press it against the lower block and listen. If there's a rod knock, you will hear it. You can move to other parts of the block as well. An exhaust leak won't pick up much, if at all, on that test. You'd have to press against the exhaust manifold to hear a leak very well.

I agree, an exhaust manifold leak can sound very much like a knock. Given how solid the lower ends on those engines are, I wouldn't be surprised if it's a leak.

These are invaluable for situations like this...and more effective than pressing a long screwdriver against things and pressing your ear to it.


Last edited by pilgrim; 11-21-2019 at 04:23 PM.
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post #9 of 16 (permalink) Old 11-21-2019, 06:08 PM Thread Starter
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Yep, got myself a clean drain pan and drained out 4 quarts of oil to find lots of visible brass color specks and flakes 😞 . next I guess is drop the oil pan and check #2 rod for play.. agghhh I guess I got my hopes up on it being a exhaust leak, I actually pulled the exhaust manifold and. Couldn't see any cracks or soot around the head suggesting a exhaust leak. Just kinda strange how it doesn't sound as bad as any of the rod knocks I watched on YouTube
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post #10 of 16 (permalink) Old 11-22-2019, 08:15 PM Thread Starter
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ok can i get some advice on the condition of these bearings, im not liking the one from number 4 i can catch my nail on it.. number 2 looks decent?

https://ibb.co/xjJwLDZ

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