Top-End rattle, STR
 

Hey y'all:
I took my STR for a spin last week. It was the first time we'd really seen the sun here in weeks. I warmed-'er up for about 20 minutes, while I cleared the snow from the hill leading to my drive.....:icon_evil: and then took 'er out.

A couple agressive on-ramps later, I noticed a "rattle" in the top end, when under load, above 3500rpm. I would normally call that a detonation (ping), but it sounds much more substantial, and I would've expected codes to be thrown if it were detonating.

Doing some searches, it seems that there are some anecdotes of the superchargers developing a rattle, but many suggestions that it would more likely be an idler/tensioner bearing. But it seem slike most of these threads END before anyone reports back what their actual diagnosis and repair is / was. :icon_gunhead:

I guess my questions would go something like this:
- Has anyone else experienced this, and what was the eventual diagnosis?
- Can I remove the S/C belt and get the thing under load to see if it has quit.... and will that really tell me what I need to know? (I mean, if it's a detonation problem, it should stop when there's no boost... so how will I know if it's detonation or mechanical in the S/C?)
- what am I missing, and does anyone have anything they can add to this? I'd obviously like to limit the troubleshooting in the cold by starting with the most likely culprits.

this would be a good time for some pathomenogeny. :icon_atari:

As you can see from the codes PDFs, a lot of the codes require 2 drive cycles. You might have pending codes so check for those.

Mcjaguar, you can remove the supercharger belt and drive her under load.

Ya just don't expect it to be fast.... I had to do it once when I needed a part from the store and I didn't have my belt back on. Made it feel rather slow.

thanks all.
JagV8: good call... I thought of it too. And no codes, pending or otherwise.

I'll pull the belt and take 'er for a spin.

if it's the SuperCharger causing the rattle.... what does that? Is it a bearing? A gear-drive? A bent screw? ?? I've never had a S/C apart on my bench to look at what would make a noise like this.

I would lean towards a bearing failing. Good reason to upgrade to a twinscrew

My guess (!) is that it isn't the SC but let us know...

My 03 STR does the same thing especially when it is colder outside and usually only for the first few off the line starts. Once the engine is good and warm I dont seem to notice it.

I was planning on digging into it when the warmer weather gets here, but for now I just baby the throttle until she is good and warmed up...

Mine has been doing this for the past 12-18 months and hasnt changed or worsened at all. Its really been more of an annoyance than anything...

Let me know what you find and I will do the same!

If it's from cold and especially at low revs then it's covered by a TSB that replaces a bunch of stuff including going to a double-sided belt. The OP's doesn't sound like that issue.

Thanks JagV8!

Anyone know the TSB for this so I can research it and see what that "bunch of stuff" is that I will need to replace...

That's not what the TSB is for. The TSB is for a noise when cold and first started.

I think you are hearing the SC coupler rattling. You can replace it yourself but you might consider having the blower gone thru with new bearings and checking the rotor clearance.

The Eaton is very durable and you can most likely keep driving it. The factory coupler has springs to help with the noise. The aftermarket usually will replace the coupler with a solid piece for better durability.

See the difference;

https://www.jaguarforums.com/forum/a...1&d=1360695908
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tbird6 posted a list of what he had done under warranty. Mine and yours are well out of warranty and the list looked not worth the price to me.

I think it's here engine sqeaks - Jaguar Forums - Jaguar Enthusiasts Forum

Thanks guys, but thats not indicative of my issue...

Mine is a rattling sound almost like chattering teeth under low throtttle position from a standing start. Almost like the valves chattering. It does seem to go away once it reached operating temps and I wonder if its not an issue of the valves making noise before the oil gets pumped through the engine and warmed up...

I dont know maybe its just an old car and in need of a valve job...

Maybe something such as the tensioner? Could be worth removing the belt (*) to see if it still does it.

(Depends on the sound and I'm not very good at recognising which is what so if posting a sound track sorry but I won't know!)

(*) er, probably each belt in turn and fairly briefly

From your description I would follow the advice above and remove the blower belt for a bit of testing. The car will drive fine but will be a dog with the low compression of the motor. Should tell you real quick if the SC is involved with the noise.

But I vote for the coupler from what has been posted.
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To do a quick check for detonation pour one gallon of toluene or xylene in with half a tank of gas. This will boost your octane well above the level of 91 pump gas. If the noise goes away then you know it was detonation. These are both unleaded, so no harm to the o2 sensors from leaded race gas.

I don't believe it was detonation because the PCM will avoid it or flag codes. Reduced performance if it really can't avoid it. It can sense it long before you can hear it.

Thanks to everyone who has helped with this so far.
I spent some time in the car this weekend, and tried to narrow-down the noise a little more.
It seems it's not necessarily only under load: it seems to be MOST prevalent when transitioning from throttle to part-throttle, and especially in the 3krpm range. And it comes and goes, seemingly independent of temp (engine or ambient).

Does this fit the S/C coupler idea as described by Tbird6 above? I am not even sure what the coupler does (I imagine it couples :icon_wub:) or where it is located. Based on the photo, I'd imagine it must be exterior to the S/C, maybe crank-mounted and turning the drive-pulley?

I haven't had time to pull the belt yet, to see what I get.

The more I read your description the less it sounds like the coupler??
Sorry about that!

If you are interested this set of pictures shows where the coupler is:

How to replace an Eaton Supercharger Coupler : SuperchargersOnline, Worlds largest Supercharger Resource. Get Serious About Power
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I'm going to guess that JagV8 is right, based on what once happened to me with a previously-owned Saab 9000 turbo. Tensioner was the problem.