Knocking Engine? Eek!

[90LS400Lexus]

UPDATE - the knocking was the first stages of the fan bracket bearing failure..... new bearing - no more knocking! Thanks for the replies!

Well, my 91' LS (which is, or was soon to be my moms LS) has what sounds like a knock from the engine! :o

Normally I always have the radio on, or the HVAC blower, so I normally do not hear the engine at idle. Last week, I drove it to work, came home, backed in and happened to have the radio off and blower off. It sounded like a faint knock from the engine when in gear. When placed in "N" or "P", the sound went away, or if I gave it a little gas it would stop. I do not hear it when driving. Its totally quiet and smooth.

Today, I drove it again and when I started it after it had set all day, the rpms went up like normal when first started to about 2000 RPMs and I thought I heard it again until the RPMs went back down. If I recall, I think my other LS400 did this as well and hoping I am either hearing something else, or if the sound is normal for these cars, since both of mine have seemed to do it.

I have NEVER abused my car. In fact, I personally have never even had it over 3000 rpms, so its not like its been over-revved or anything. It does not burn or leak not one drop of oil and the oil still looks like new, even at the 3000 mile change intervals.

Does anyone have any suggestions as to what I may be hearing? If its a rod-knocking, I definitely do not want to pass it onto my mother. Lord knows she has had enough bad luck with cars. Whats worse is that I still owe $3400 on this tank. :(

[SRK]

Your description doesn't sound like a rod knock, and I've diagnosed a few in my time. Sounds more like a loose valve lash, or a bearing in the water pump or idler or alternator. I'm sure it's no big deal.

I wind both my cars to redline at least once a week, and neither makes any knocks, just the normal injector ticking and some valve noise. It's actually good for the engine to work hard every now and then - the converters get cleaned at wide open throttle due to the over rich mixture, and the valves and sparkplugs get a good "Italian tune-up" and the injector tips clean themselves passing fuel at max rate.

[landar]

Because you can put her in Neutral or Park and have the sound go away, I was going to focus on a loose/worn mount of

some kind.

[nc211]

Because you can put her in Neutral or Park and have the sound go away, I was going to focus on a loose/worn mount of

some kind.

Ditto, I agree with that. I'd have your driver's side engine mount looked at.

[90LS400Lexus]

Thanks for the replies guys... well, I know that the motor mounts are bad. I have vibrations at certain rpms when the car is stopped and when the car is moving. 212K, original mounts, so I know they are shot. My dad is aware of this and I told hime that if they took the car that these mounts needed changed.

SRK, I hope it is safe to rule out a water pump. It was replaced with a brand new OEM pump about 30K ago, when the timing belt was replaced, unless its went on the fritz.

I did not hear the noise today. I guess I am paranoid.

Its official that I am giving it to my mom... I have almost closed a deal on a 1991 Mercedes 420SEL, with 65K actual miles. Not a done deal yet, because the car is out of town, but in a town where my uncle lives and he is going to check it out for me, but gone until Sunday on a business meeting. I know, someone kick me for going back to MB. :P

I had good luck with my last Benz though.... it was 1985 and had 275K and still running strong. To my amazement, I had NO electrical issues. Thats a shock for a old MB.

[eatingupblacktop]

I think Mom's got you worried that she's going to give you the "gears" B) for giving her a noisy car! :D

With the number of LS's and Mercs you've had over the years, should be no problem for you to decide what's next (taking for granted that the Landcruiser is definitely out). :whistles: Not!!

Me thinks you've entered a vortex of "car hopping" from whence there is no return. Be forwarned, this kind of expedition inevitably leads you back to where you started. At which point ye shall embark once again on this endless quest for leather, rubber, gas, and steel!

[90LS400Lexus]

Just updating some posts of mine... SRK - you were right... that knocking sound that was so faint was not my engine. As you know, my fan bracket bearing went out a couple of weeks ago and that was what was making the noise. Obviously that faint knocking I could only hear at idle was its first signs of failure. New bracket bearing, quiet as a mouse... also my "bucking" at startup is gone as well. :)

Your description doesn't sound like a rod knock, and I've diagnosed a few in my time. Sounds more like a loose valve lash, or a bearing in the water pump or idler or alternator. I'm sure it's no big deal.

I wind both my cars to redline at least once a week, and neither makes any knocks, just the normal injector ticking and some valve noise. It's actually good for the engine to work hard every now and then - the converters get cleaned at wide open throttle due to the over rich mixture, and the valves and sparkplugs get a good "Italian tune-up" and the injector tips clean themselves passing fuel at max rate.

[SRK]

Thanks for the update - and like I said in the other thread, I'm glad you got it fixed for a reasonable price.

[TexasLexus94]

Wow, I missed this post, but I have the exact same problem-minor tat-tat at very low speeds. 120,000 miles.

Any description of the "fan bracket bearing"? Easy to replace? Cost?

Thanks in advance....

[90LS400Lexus]

Thanks for the update - and like I said in the other thread, I'm glad you got it fixed for a reasonable price.

Wow, I missed this post, but I have the exact same problem-minor tat-tat at very low speeds. 120,000 miles.

Any description of the "fan bracket bearing"? Easy to replace? Cost?

Thanks in advance....

Well, dont be too concerned about the noise being the fan bracket bearing... I was in a drive-thru this evening with the radio off, and the HVAC off and I can still hear that faint knock at idle when in drive. I am guessing it has to be the lifter making the noise... I can hear the lifter "ticking", but there is also a repetitious knock as well thats been there ever since I have had the car and I have put 12K miles on it and its never got any worse. I just assumed that sound was the fan bearing... UNLESS the brand new fan brackeyt bearing is also doing it.

To answer your question Tex - no its not that easy... its about a 3 hour job and almost takes it all the way down to the timing belt / water pump. My local Lexus dealer wanted $268 for a new part, but I found it online for $155. Also, I had to pay a Toyota tech I know $125 labor to change it at his house, then another $50 to have it towed... it ended up costing me about $350, which is sad, because I am in dire need of new engine mounts, but had to use that money I was saving for that for the fan bearing. :( . Some people have changed it (bearing) themselves, but I am not good at mechanicing.