Engine Noise Diagnosis ?

[jigmaster flash]

hi everyone, just bought an old 98 LS400, and after conducting a diy service and fixing a few problems i'm left with two issues that I hope someone can help me with.....

1) Intermittent screechy noise when a/c is off, quietens down to almost nothing when aircon is switched on.

I replaced serpentine belt last week as part of a full service, but its definately noisier now!

I've checked the belt is routed correctly, and to my untrained eye (and after a little jiggle/spin) each pulleys/tensioner seems ok ....

The noise is definitely manifesting from near the A/C pulley, and ive noticed the clutch cover on it sort of "jogs/jerks" round intermittently in synch with the noise with the aircon off. When I turn A/C on the clutch cover spins with the pulley and noise is vastly reduced.

My intuition says my problem is with the belt tension (which may or may not be caused by a pulley issue) rather than the A/C clutch/bearing/pulley ... Can anyone point me in the right direction of what to test/try in order to pinpoint cause ?...

2) Ticking from rear of engine - now i read a LOT of info on ticking UFC engines, and to be honest its fried my head! - valve clearences/injectors/egr pipe etc etc etc!

Mine ticks loud enough so you can hear it with hood shut. The ticking seems to eminate from the rear of engine cover, and seems to be constant in tone and volume regardless of whether idling, high revs, cold or hot...

I put some injector cleaner through but made no difference - I mentioned it to my local mechanic, and he told me not to worry about the ticking injectors, reckons they always get loud with age and the cleaner they are the louder they'll be.

Anything for me to check before I try and ignore the ticking?!!

sorry for asking questions that have probably been asked many times before - ive searched the archives and read lots of different opinions/advice etc and being only moderately competent mechanically i'm nervous of trying to fix without being confident of the cause!

all the best,

marty

[mgilly]

Nice to see you here aswell , i jointed club lexus this morning more the merryer

[1990LS400]

Using an automotive stethoscope can help locate a noise source but be very careful while using one around moving parts. I bought mine at an auto parts store 20 to 40 years ago - it looks like this. Don't remember what it cost but I do remember that it was cheap.

The screech might be a pulley bearing going out.

Valve related ticking was common on the gen 1 LS400 but don't remember anyone reporting it on the 98-00 LS400.

[jigmaster flash]

will hunt out a stethoscope, but the ticking is definitely not from the valve covers, more like dead centre right at the rear of block...

thought i'd cracked it after reading lots of EGR pipe stories, but the 98-00 models don't have one so still scratching my head!

[curiousB]

Belt noise is likely either AC bearings or maybe the AC clutch mechanism. Clutch may be repairable on its own but it may be hard to source since that part as it is often sold with the compressor as a complete unit.

Not sure about the ticking but since its a '98 maybe you just live with it.