Intermittent rattle search

[Rolf]

Try to find the culprit for a rattle.
Started at roughly 18000 miles only once in a while, now clearly prominent with 19000 miles when engine cold, disappears during heating up, comes back intermittent when fully warmed up.

We checked the pulleys by hand, only one showed very slight play, original Toyota part item 8 in 41.03 parts diagram, exchanged, no difference.
Exchanged pulleys 18 and 19 after talking to Lotus mechanic for possible problem pulleys, no difference.

 

Drive Belt tensioner is working without problems. When rattle is ongoing, tensioner is moving a bit, but normal according experienced mechanic.
AC on and off has no difference.
No failure codes, car runs fine otherwise

Anybody got something similar?



 

 

[Kristof Thys]

Would suggest to use an automotive stethoscope to try to pinpoint the culprit?

[Rolf]

Thanks for the hint Kristof. The experienced mechanic checked it a while ago with a big screw driver and said he cannot locate it. I have a stethoscope around from my Esprit times, will give it a try myself. Main problem is awful accesability, and it is quite scary / dangerous near to the running belt.

[Kristof Thys]

I have been thinking about this one.  Could be worth checking out the supercharger pressure relief valve/actuator thingy too; just as a thought.  It's near the throttle body.  Suggest holding the rod to see if it makes any difference in noise (I was thinking in the direction of pressure builts up, gets relieved (too soon) and noise changes, repeat)

Edited November 5, 2020 by Kristof Thys

[Mark030358]

That sounds like the supercharger, definitely a metal to metal rumble I think.

good luck sorting it, I hate stuff like this.

cheers

 

[Rolf]

Started the car and had around 5 loud mettalic "Klacks" in the first 10 seconds. Then rattle as usual.
Would say Klacks came from the downwards belt area.
Maybe drive belt tensioner had a hard time from something blocking / loosening / blocking etc. and knocked.
Definetly something on the way out soon.

@Kristof: Actuator rod from the supercharger pressure relief valve is not moving on idle, no influence.
Results from stethoscope check:
The compressor on multiple places is without any intermittent rattle, constant bearing noise. 
Screws #21 from pulleys 18 and 19 pinpointed from the backside: Normal bearing sound.
Number #16 bracket assembly transfers the intermittent rattle clearly.

Had the car driven over an hour. The intermittent rattle has now a new friend, a metalic grinding sound. 

Next step could be ordering pulleys #17 and #23 and try to change them during the drive belt exchange.
Not clear to me is if they can be changed with the bracket assembly only loosened.
There is only a small gap to remove the belt after removing a lot of brackets and disconnectiong the right engine mount.
The bracket assembly #16 can not be removed out of the engine bay according to service notes, only with rear clam removal.

Still not sure if that is the rattle culprit...
What a PITA.

[Rolf]

Finally found the rattle culprit, it was idler pulley 17.
The outer bearing race was spinning inside the idler.
Bearing itself is still fine and spinning freely by hand motion.
Looks like somebody made a to big hole inside the pulley.