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  #1  
Old July 13th, 2006, 10:09 AM
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Thomas F
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Knocking Noise

So I have recently started hearing a knocking noise and by the time I try to pop the hood and look, it stops. I will drive for a while and come to a stop then hear it again. It usually does it 3 or 4 times then stops. No over heating, seems to not be related to anything with the drivetrain/wheels/joints. Sounds like it is coming from the front near the fan/radiator. I looked at some other posts and saw some about fan clutches. Any other things to look for or try to diagnose?

Thanks,
Tom
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  #2  
Old July 13th, 2006, 10:48 AM
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I went through this a little while back with my 95 Disco. Seemed to be related to low oil pressure (only after engine was normal temp, and at idle). Got progressively worse-drove me nuts. Took it to dealership 1st time. They said it was exhaust manifold leak. Fixed that myself. No improvement. Took it back to them 2nd time. Chief mechanic said it was definitely a worn rocker arm. apparently they get worn and loose after about 90k. replaced the whole rocker assembly, lifters, and rods. no fix. took it somewhere else, and they said that one of the piston crankshafts was worn, and was knocking as the piston goes up and down. nothing can be done until the engine is rebuilt or replaced. Gave up and decided to live with it. 2 months later- it went away, permanently. my theory, one of the oil veins running into the lifter gets clogged, so one of the hydraulic lifters isnt' getting enough oil, or is getting stuck and not coming back down on the downstroke, so there's a little gap between the lifter and crankshaft. But the truth is, I'll never know. sold it to my buddy, who dropped a 2.8 diesel in it. Now, we love the knock.
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  #3  
Old July 13th, 2006, 12:57 PM
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The Rover V8s can also have a cam knock...basically the camshaft tapping against the front of the block. The old style engines with the distributor driven external pumps relied on the load from the oil pump and the cut of the cam lobes to keep the cam seated against the block. When they went to the crank driven oil pump they also added a retainer plate to the front of the cam to keep it from walking out. Once the cam has been in service for a while there is a little wear on both the lobes and the retainer (we're talking thousandths of an inch here) and the cam can move back and forth and make an audible tapping sound as it hits the block. There was a bulletin about this where you could replace the cam bolt with a special bolt with a plastic bumper glued to the end that would stop the noise...until it fell off. They also redesigned the cam retainer...originally it was kind of a half circle shape. It was redesigned to a full circle shape. In extreme cases I have had these surface ground to get the tolerance to the tight end of the spec and quiet the noise. If the noise is intermittent and as you describe it is probably cam knock. It can be fixed if it bugs you, but a lot of the cars do it and I have never seen it cause a problem.
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Old July 24th, 2006, 04:59 PM
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Thanks for the replies. I have checked the oil at numerous intervals and it seems to be fine. The only other thing I have done recently is to replace the fuel filter. I doubt that would have anything to do with it, but hell...I am open to any possibility at this point. I don't mind the sound however, my Homer Simpson logic just tells me that loud irregular noise = something bad. It does not click/knock when I apply any amount of gas, just seems to do it when it is idle or in park. As I said before, it goes away after about 15 seconds, then starts up again after I come to a stop.
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Old July 24th, 2006, 05:12 PM
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That sounds like a low oil pressure situation, probably a bad lifter is my guess, how many miles on the engine?
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  #6  
Old July 24th, 2006, 06:13 PM
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Mine's starting tapping in a manner I'm not used to. I've seen the lifter noise on LR's and other cars at startup, that goes away after a few seconds. 'can usually be fixed by changing the oil filter or cleaning the pickup screen.

This time, however, it doesn't do it when cold, but starts once is warms up. On real hot days, like we've had lately, it'll do it right away. Any ideas?
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Old July 25th, 2006, 09:34 AM
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Hans--

77K on the engine. I only put about 6K on a year since I travel all the time.

Barry--

What you mentioned about the heat seems consistent with what I see as well. I got back and picked up the 90 at the airport (it had been there a few days) and it did not make any noise. Hotter the engine, the more it seems to happen...however I think you may be on to something with the oil filter. I was gone for a long time and I had to have a friend take it to get the oil changed and it of course they fuct around with everything even though I explicitly told the place just to change the oil. I am going to change it this weekend and let you know if I see any improvement.
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Old July 25th, 2006, 10:43 AM
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You might try going to a more viscous oil, especially if you see any flickering of the oil light especially at low idle. Sounds to me like it could be a sticking lifter--hard to tell without hearing the sound.
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Old July 26th, 2006, 04:56 PM
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Sorry for the ignorance...can someone elaborate on what the lifter does?
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Old July 26th, 2006, 05:19 PM
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Thinking in another direction..

What about a cracked flex plate?

This makes a tap/ ticking noise that is heat related and also related to a load on the engine in gear.
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Old July 26th, 2006, 05:21 PM
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I'll try; someone correct me where I get it wrong; if by "lifter" they mean hydraulic tappet, they sit between the camshaft and the pushrod. They are used to automatically adjust for valve clearance, and work via oil pressure.

If they are sticking, it sounds like an old-style engine in need of a valve adjustment (bought an old Ford Ranger once that sounded like that, until I had the adjustment done.
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Old July 27th, 2006, 02:49 PM
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Quote:
Originally Posted by ECR
What about a cracked flex plate?
OK, my turn for a stupid question: what's a flex plate?
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  #13  
Old July 27th, 2006, 03:00 PM
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Mates the torque conv. to the engine in a totally non technical way of saying it.
After time the bolt holes can develop cracks and it allows the bolts to shift a little. It sounds exactly like a bad rod or knocking engine, but it goes away as soon as you put it in drive and take up the "slack" in the bolt holes.
Heat related to as when it first starts the cracks can swell and not rattle when teh flex plate gets hotter.
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Old August 1st, 2006, 11:45 AM
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Well I figured out that it is coming from the radiator, however I have no idea what in the radiator it might be. My guess is that maybe the knock is coming from a boiling or something. It does it now even when the car is off (but the engine is still hot). It seems like the engine does not do any of the knocking...just the radiator. I put new oil cooler lines (stock rover parts) in about a year ago, so I am thinking that maybe it is just time for a new radiator. Like I say, the knocking does not bother me and the temperature is always normal...just don't want things to escalate.
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Old August 1st, 2006, 01:15 PM
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If you have "boiler knock" in the rad. and your temp gauge is showing "normal" then you have some pretty big problems. Lets hope that isn't the case.
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Old August 1st, 2006, 01:55 PM
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Meaning you think that either the thermostat is broken or...?
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Old August 1st, 2006, 02:01 PM
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Meaning coolant doesn't boil (aka make noise) in the radiator after a shut down unless you have some quite serious overheating issues.
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Old September 6th, 2006, 12:34 PM
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Sorry to bring this one back to life but I wanted to see if anyone has other ideas. I had an infrared gun on it and it never over heats so the gauges are working, however I keep hearing this knocking/clicking noise. It does not do it when the car is turned off, only when I come to a stop or if I start the car after it has been off for a while, then it goes away. It is for sure coming from the radiator area as well. Have any of you who have had oil cooler line issues heard something similar to this? I replaced mine last year and this only came about a few months ago. I am thinking about just throwing a new radiator in all together, but it seems like a shame if the car is running cool.
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Old October 21st, 2006, 11:08 AM
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I finally figured this out. I put a new radiator in, however this did not stop the knocking sound. It was time for a new one anyway, however the problem was the transmission cooler (kind of). I bought a new one b/c this was the last thing that I could rule out of the equation. I took the brush guard, bumper, and front framing off. Then I loosened the cooler and no more noise! I tightened everything back on and I don't hear anything now. So the short of it was that I think that the heating of the transmission cooler metal was causing something to expand. So if anyone needs a tranmission cooler for a 97 let me know. I still have the old one in the box. I want to give it a few more days before I sell the cooler, however PM me if you want the new one.
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