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what makes the knocking when the timing chain or gears make noise?

16052 Views 11 Replies 4 Participants Last post by  cyberpigue
can someone explain what is actual making the noise when the timing chain or gears make a knocking noise and sound like a bad rod bearing? The chain slapping and hitting the cover?
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Sounds like a loose chain. I just helped a friend repair his Toyota that had done that. The chain being loose had eventually worn down the head of an adjustment bolt head it had been hitting against.
Visualize a bicycle chain. When you put pressure on the pedals the chain sags between the front (drive) and rear (driven) sprockets at the bottom since the top is being pulled tight by the pressure on the pedals - gravity pulls the slack in the chain down and keeps it from bunching up at the rear.

A timing chain does the same thing except the drive sprocket is below the driven sprocket where gravity doesn't help with the slack as much. To deal with the slack there is a tensioner on the "loose" side to keep the chain tight and not bunching up. As the chain stretches over time and the spring on the tensioner weakens over time, the slack in the chain begins to become greater and the chain begins to fluxuate like a wave. The high points on the wave can hit the timing case cover, or move the tensioner in and out causing the noise.

Just as in the bike, if the chain gets too loose, it can fall off or jump a tooth on the sprocket. That's big trouble in an engine because now your valve timing is not aligned with your crank timing. Besides running poorly, if the valves don't have sufficient recess in the head, an open valve may make contact with the piston at top dead center - blown engine.

By simply replacing the chain set (chain and gears) and tensioner, engine no breakie...
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Is this common on the 2.0 4 cylinder? Mine is making some noise, but I was thinking it was coming from a bad bearing or something in the bottom end of the engine. Could it possibly be this? Mine has 120k and uses a little less than a quart of oil in an oil change cycle.
It's impossible to tell you whether this is the noise problem with your engine. Even if it was or wasn't common, yours might be something else. Have someone you trust listen to it.

Generally, lower end noises that are rod or main bearing related are accompanied by lower oil pressure since the space required between bearing surfaces to result in a knock are also great enough to allow oil to quickly evaxuate from the journals (tubes inside the crank and block that the oil flows through) causing lower oil pressure.

If you are burning oil, that is generally caused by oil entering the combustion chamber at either the piston rings or at the valve seals. Possible at a head gasket, but much less typical and almost always accompanied by water which causes a lot of steam to pump out of the exhaust.

Oil smoke is a bluish white and doesn't dissipate quickly. Steam is a clearer white and goes away quickly once in the air (plus it smells like antifreeze). Black smoke is a indication of the fuel mixture being too rich - maybe a stuck choke, misadjusted carb float, or bad emission sensor on computer controlled engines.

There are two "most important" factors in your engine lasting... clean oil and good air filtration. Buy the best oil you can afford and keep it changed. Buy the best (not neatest/coolest) air filter you can afford and keep it changed.

Additionally, look for problems where grit can enter your engine. The best air filter in the world is of little use if there is an air leak between the filter and the engine. Great oil with a leaking valve cover sucking in who knows what gets dirt fast. The dirt is like comet scrubbing away your engine metal.

My old Wagoneer has a couple of hundred thousand miles on it. When I got it with 127K miles on it the engine had been rebuilt at 90,000 miles. It already smoked and leaked and wasn't very healthy. I slowly replaced gaskets and seals and changed the oil several times in a short period and it has lasted me six years without a rebuild. Even a worn out engine can be made to last if it gets good loving... and stays away from grit.
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I just got it back from Chrysler after theiy put in $715. to replace belt, water pump and timing gears and chain and still knocks! They say it has valve noise but I had a motor with a bad main bearing and this sound the same. sounds like a Allis Chalmer tractor at idle and when you rev it, it speeds up and sounds more like a rattel then becomes harder to hear as the rps increase. then when you let of the gas it you can hear it again. it never goes away it just gets faster so you can't hear it over the engine reving. I shouldn't say it never goes away at one point at idle after running for awhile it sounded good then I drove it and stoped and it was there again.
I just got it back from Chrysler
Did you ask them to replace the timing chain or did you ask them to fix the knock? If they misdiagnosed the work, you need to speak with the service manager. Be nice but firm. If that doesn't get you anywhere, speak with the general manager, then owner. At the very least the work should be discounted. You did get something of value, but the wrong something of value.
I brought it back to the dealer I bought it from on Thursday. and they thought it was the timing gears and or chain. They then brought it to Chrysler to get a second opinion. They said the same thing that the sound was coming from there. So they replaced them. i really don't know what was said from one dealer to the other.
Did the dealer you bought it from pay for the repair?
they paid all but $225. I wouldn't call it a repair I just went out and listed to it again and it's just as bad. Now I'm thinking or maybe I'm just hoping its the rocker/lifters. is there any adjustment on the rockers? Or how do you fix them if there noisy?
they paid all but $225. I wouldn't call it a repair I just went out and listed to it again and it's just as bad. Now I'm thinking or maybe I'm just hoping its the rocker/lifters. is there any adjustment on the rockers? Or how do you fix them if there noisy?
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