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KA24de rattling noise, RPM and load dependant


Duke

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My KA has recently developed what I can best describe as a rattling noise between about 2000 and 3000 RPM. The noise is most apparent with the engine under load (climbing hills, hard acceleration), but it is still there if the engine is revved in neutral, just not quite as loud. If the engine is held at around 2500, the noise remains.

 

All of these signs point to rod knock, but I don't really think that is what it is. First of all, the rattle really sounds like it is coming from the valve cover, near cylinder #4. Pulling the plug wires one at a time (taking the load off of the bearings) doesn't make to noise go away. The bottom end is also a rebuilt short block with a little more than 1000 miles on it.

 

I have checked the valve lash on all valves and it is in spec. Also, the "upper timing chain guide" which can be a source of noise on a KA, has been removed. I'm trying to find some idea's on what this could be before I pull the motor to check the rod bearings:o.

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check the lifters and the feed passage from the filter through the head and rockers plug up and in some cases the head has to come off. Or the check valve or pressure relief valve takes dump at the filter in the block.

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Figured it out. Ended up being a little detonation. Kinda threw me off that it was only at a specific RPM range. Retarded the timing a bit and its gone. I now need to get some fatter jets for the carbs. Thanks for the help though.

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check the lifters and the feed passage from the filter through the head and rockers plug up and in some cases the head has to come off. Or the check valve or pressure relief valve takes dump at the filter in the block.

 

The pressure relief valve at the filter is always closed. It would only open in the rare event the filter plugged up. If it did unfiltered oil would be circulated through the motor.... better than no oil.

 

Unless the KA has hydraulic lifters, a loose one would make noise at all RPMs and the noise would be the same volume.

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  • 1 month later...

Well, the problem persists. I removed the head to check to see if anything was out of order. One thing that surprised me was some rather significant carbon buildup on the intake valves. I thought that this could be the source of the detonation. I also rechecked all of the valve clearances, and they are all within spec. I reinstalled the head, and found no change in the noise.

 

The times that it is most prominent are right after start up, before oil pressure has fully built, and when driving slowly down my driveway (1/4 mile long gravel driveway) at low engine speeds. I usually idle in at around 1500 rpm and can clearly hear it when I do this. There is very little load on the engine. It is also very audible under acceleration.

 

This has me really stumped. Many of the symptoms that I have point to rod knock, but the noise does not change at all when I kill spark to individual cylinders. Changing timing also has no affect on it as I had previously believed.

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I'll try and get some video within the next day or two.

 

As for piston slap, I have considered this, but it really sounds like it is coming from the top end. I could of coarse be completely wrong, and it could be a bottom end problem.

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**Update** with video

 

I think I have narrowed it down to the lower timing chain. I purchased an engine stethoscope and started poking around. It sounded like it was coming from the upper timing chain. So a new timing chain and tensioner later, it is still making the noise. I pulled the upper timing cover again to poke around and discovered that the tight side of the lower timing chain seemed a little loose. I tried to cycle the tensioner and with a good deal of force I was able to push it in, but couldn't get it to return without moving the guide. I'm thinking that it may be a combination of a sticky tensioner and the pivot of the guide being a little tight. This would make sense because the noise seems to have a resonance where it is most loud, and it is also louder on start-up before the oil pressure has gotten a chance to build.

 

 

I need to pull the transmission again so I think I will just pull them as a pair and go through the engine to see if I can find anything.

 

Here are a couple of video's...the first is start-up and the second is revving the engine. Tell me what you guys think.

 

th_IMGP2168.jpg

 

th_IMGP2161.jpg

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The lower timing chain is a single row. The common timing chain rattle on KA's comes from the upper chain hitting the guides. Nissan has deemed that the guides for the upper chain are useless, so I have removed both of them. As for the lower guides, they are both new and in good condition.

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Seems to be louder when throttle opens placing a load on internal parts. Everything from the valves back... springs, cam, cam drive, tensioner, guides and chain/sprockets are not load sensitive. They turn or open and are not under more pressure just because the throttle is more open. If one of these items is making a noise it will not get louder with load, just speed up or slow down with engine speed.

 

Rod knock is usually that, a loud dull knock and not a higher pitch tap like yours. It cannot be cured and gets progressively worse until the bearing fails. Lots of fresh oil and easy driving can extend this time but best to head home.

 

Piston slap usually occurs when engine is cold and goes away quickly as it warms. It's a cold clearance or wear thing. Cannot improve with time. Changing oil brand or to a thicker viscosity can sometimes help. Do not use additives.

 

Pre ignition has your sound. Like a rattle spray can. (dentists sell kid's teeth to paint can manufacturers) Heavy carbon deposits can collect heat and become glowing hot. Add full throttle and the added heat from compression can cause ignition just like a diesel. A spark plug that is too high a heat range can do the same thing. In both cases the cylinder fires too soon pounding downward on the up-rising piston and rod.

 

Spark knock occurs just after ignition. Cylinder pressures rise sharply and cause fuel in another area to self ignite. When the two flame fronts collide there is a pinging sound. Both pre-ignition and spark knock are very damaging to your engine. Both usually occur in a hot engine.

 

Causes of pre ignition/spark knock are engine too hot, rich mixture: carbon build up, cheap low octane gas, compression above stock from modifying, over advanced ignition timing or a faulty knock sensor.

 

 

Try super premium octane gas to try and eliminate pre ignition/spark knock. If this reduces or fixes the problem you are on the right track.

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Do you have access to a wideband O2 sensor to see where your air-fuel ratio is?

 

Yes, it is running at high 13's to low 14's throughout the rev range.

 

 

Mike, I initially thought that detonation was the problem. When I removed the head I found a good deal of carbon buildup on the intake valves. To be honest is was caked on pretty well. I thought I had found the problem. I gave the combustion chamber a very thorough cleaning and reinstalled the head. The noise came back right away. I am running colder plugs than stock and I have been running higher octane gas than what is factory recommended. Retarding the timing also doesn't have an affect on the sound as I had previously thought. Also the engine temperature has no affect on it.

 

Another factor that leads me to believe that it is the timing chain is that it seems to have a sort of "rattle down" as the rpm's drop.

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have you checked the hydraulic lifters? Mine makes a similar sound to that at start up and then goes away after a few seconds when the oil pressure builds up. i have a ka24de also. I've been told with hydraulic lifters, I would have to soak the lifters in oil when taking them out so the oil doesn't drain out from them. I had a same issue on a previous car. The remedy was to rev the car slowly to about 3500 rpms and keep it there for a little bit and then let off the throttle. I did this about 3 or 4 times and the noises went away. I guess the point of that was to build up enough oil pressure to fill the lifter with oil again.

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Guest DatsuNoob
Sounds good. And yes, most people remove the upper guide. Prone to fail and well if it breaks you're pretty much screwed.

 

BTW read over your build thread. Looks really good.

 

The kid who came over to buy my S13 tranny said he took all of his off after calling Nissan. He claims they told him they were basically useless, but I'm not so sure. You must need atleast one, right?

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  • 3 months later...

I'm not sure if Duke's problem is this, but it is worth checking. I overhauled a 1993 KA24 engine for a D21 truck about 2 years ago. It has had a rattle noise at crank up ever since. I just figured it was the lifters. Noise goes away after oil pressure builds. Lately I noticed a louder rattling noise when revved. The noise gets louder with rpm. Come to find out the lower alternator mount bolt was not tight and had beat the alternator mount hole into a keyhole shape. I discovered this with a stethoscope while under the vehicle. I changed the alternator and noise is gone. The engine still has a rattle at crank and slight ticking at idle which goes away when revved slightly. Possibly lifter bleed down.

 

BTW Oil pressure is:

70psi cold idle and tapers down to about 10 psi after hot

50psi when revved 2000

 

This problem bothered me for a year or so. I was thinking piston slap, detonation , wrist pin, low oil pressure and everything. Guess you have to check the simple stuff first.

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I have a bit of an update on this problem. I seem to have narrowed it down to pre-ignition due to over advanced timing. What I have done to "cure" it is to totally lock down the distributor. NO advance. Yeah, I know, not ideal at all. I am currently running straight 20*advance. I still get a little of that rattling sound around 2000 rpm's, and sometimes under hard acceleration, but it seems to have gotten rid of it for now. My plan is to switch to crank fire igniton with megajolt so that I can fully program the ignition curve. This should happen around the new year.

 

Until then though, it acutally drives fairly nicely, just really runs out of steam after 5000 rpm.

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  • 3 weeks later...

Check your upper timing chain tensioner, I know when they go bad, the don't keep tension on the chain. You should be able to push it in with your hand when it's on the engine. If not, it's bad. pull it off, shoot some oil on the cylinder and push it in. if it still doesn't move, then replace it. if it moves and oil squirts out towards you, then it's good. Reinstall and listen.

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