KA24de rattling noise, RPM and load dependant

[duke]

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.

[hang_510]

being recent, is it possible something not engine related is loose?
i hate trying to track down vibration noise

[duke]

I thought the same thing when it initially started. It really sounded like it was something loose in the dash. However, listening to it with the hood open standing over the engine, it is quite obvious that it is coming from the motor.

[510Martinez]

Detonation (pinging) can sound like a rattle or something loose. I would back the timing down a little and run some premium fuel and see if the noise changes. The fuel mix should not be lean and the engine needs to be proper temp also. The fact that it happens under load makes it a good possibility.

[duke]

Detonation (pinging) can sound like a rattle or something loose. I would back the timing down a little and run some premium fuel and see if the noise changes. The fuel mix should not be lean and the engine needs to be proper temp also. The fact that it happens under load makes it a good possibility.

Well, looks like you hit the nail on the head. I had ruled this out because I was running 89 octane (87 is recommended for the engine) and the timing was set to spec. I also couldn't think of anything that I had changed that would cause this. However, I did know that it was running a little lean. So I just went out and played with retarding the timing (not sure how much, I need to get a timing light on it) and the noise has gone away. Looks like some 91 octane fuel will be in order until I get some fatter jets for the carbs. Thanks for the help, I really appreciate it.

[510Martinez]

You're welcome. I would hate for you to destroy the engine not having ruled that out. The small fly in the ointment is that you can still have a little pinging and not hear it, so be thorough in your evaulation of your setup. You may also want to run a little engine/carbon cleaner through the system (fuel additive) in case you have a hot spot in the combustion chamber.

[bertvorgon]

I just noticed this post. As you found out, you had the classic light load, part throttle pinging/detonation. 87 octane is pretty low, and even though a lot of motors come spec'd for this, the older they get, so does the reqirement for a bit better fuel. My GTS was spec'ed for 87, but, when the summer temps get up there, 87 pings to beat the band as soon as the load goes up a tad. I run 90 octane in it now, no problems. carbon build up, and other rough edges all contribute to starting points of pinging, if the heat builds up.

This is a picture of the piston that was in my original motor, where all that light pinging, that I did not hear, finally took it's toll. Interesting thing though...look at the piston top..perfect. We think it broke a ring, and the products of combustion went down the side of the piston, and slowly melted a hole back through the piston. If your plugs are too hot of a range also, that can contribute to pinging.

[tycot1]

possibly a broken chain guide? mine was.

[duke]

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.

Tycot1, which timing chain guide was broken?

[5TINGUY]

I have had rod bearings go bad and it would still knock with spark disabled. The bottom of the piston was hitting the crankshaft counter weight. You might have to drop the oil pan and take a look. The sound is different from valve train noise or timing chain guide noise, wish I could hear it.

[5TINGUY]

Or if you had a spare head to throw on. Sounds like you are getting good at KA head jobs.

[duke]

**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.

[5TINGUY]

Hard to hear noise in first video, but the second one does kinda sound like chain noise. Good luck hope you figure it out.

[zootowndime]

Sorry to hear about the engine troubles duke. Hope it doesn't impeed too much on you being able to enjoy driving the car. KA's are known for their chain noises. But it is certainly frustrating.

I have a somewhat similar problem w/ my ka as well. It is definitely a chain noise and is only there at the initial startup. After about 10 secs of the engine running and oil pressure building up it goes away so i haven't looked too hard into what may be causing the noise. My engine also burns a bit of oil after i rev higher than 5k and then let off the gas, it blows white smoke if i am decelerating for a couple seconds. It sucks but the motor still pulls hard, and i am not going to worry about it too much as i am building a new motor, an sr20ve.

[defdes]

One of the upgrades we use on the FJ20 is a ratcheting Mazda tensioner. This takes up the chain rattle that FJ's are famous for on start up and when worn in. I don't know if they'd work or if there is an equivalent.