Lotus Elan

Metallic rattle

PostPost by: Mick6186 » Tue Jan 08, 2019 8:48 am

I once had a metallic rattle on a vehicle that only happened in a small rev range. I finally traced it down to a heat shield that was vibrating in harmonic sympathy with the engine at certain revs,
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PostPost by: andyhay » Tue Jan 08, 2019 8:55 am

Thanks all for the suggestions. I’ll undertake some investigations on the weekend.

When I drove the car yesterday it took a full 20 minutes of driving before I heard the noise - so it must need to get quite warm.

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PostPost by: clivetonge » Tue Jan 08, 2019 9:46 am

I had exactly that, but at high revs. Was on the point of ordering timing chain and gears having tried adjustment but put it on the lift for one last look. The back alternator bolt was loose. two minutes later the rattle had gone. If only I'd noticed that the movement had caused the feed wire to break...………...

I suppose the moral is to look for simple solutions first and spanner check!
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PostPost by: RichC » Tue Jan 08, 2019 5:22 pm

denicholls2 wrote:a mixture that goes rich for a moment when the throttle plates snap shut. On Italian cars and motorcycles, this often causes either burbling or backfiring as some of the unburned mixture sneaks out into the header pipe and ignites there

so THAT's whats causing my +2 burble on the overrun 8) i thought it was an air leak at the junction of my headers and middle section ....
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PostPost by: andyhay » Wed Jan 09, 2019 11:55 am

Thanks for all of the suggestions

Haven’t had the chance to inspect the car but did go for a quick drive. The rattle is still there but happened under different circumstances....strange

I did get it to happen when stationary and in neutral although not every time I reved the engine - only occasionally

It happened in every gear under acceleration this time and only very briefly.

Where it happened in the rev range varied a bit.

It also happened a couple of times while the car was idling stationary warming up

I thought I might tighten the timing chain a little- is it ok to do this without taking the cam cover off?

I presume you screw the thread in (clockwise to tighten).


Thanks again

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PostPost by: miked » Wed Jan 09, 2019 12:53 pm

Andy,
Since it has occurred in neutral i would buy a cam cover gasket and lift the cam cover. Not a fan of blind adjustment unless you are doing it regular and aware of noise and feel.
Then check the chain tension in various positions to ascertain the tension. I would also look down at the tension sprocket with a torch and see if there is any unusual side wear on the teeth. Also look at the way the sprocket sits with the chain alignment. I had this going on and it turned out to be a slightly twisted quadrant that was causing the sprocket to run out of alignment with the chain. This was self inflicted. I had twisted the quadrant slightly when it was out when i fitted a new sorocket. The large socket that tightens the axle/bolt can apply a lot of force. I found this early and the wear marks at opposite sides of the sprocket gave witness. Also some very light metalic debris on sprocket.
If not this you can check the chain tension properly. If it is I wrote a script for checking on both planes. Mine only appeared as the engine warmed and the oil got thinner. Also only at certain revs.
Cheers Mike
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PostPost by: 69S4 » Wed Jan 09, 2019 2:09 pm

Starting to sound like an irregular metallic rattle from somewhere forward of the driving seat that I had back in the summer while driving through France. Started as just now and again, then at certain revs and finally quite a lot of the time under about 3k rpm.

I tracked it down in the hotel car park to the bottom right dash fixing screw had come undone and the nut was rattling against the metal bracket.
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PostPost by: miked » Wed Jan 09, 2019 3:42 pm

Just another point. I listened with a long screw driver around the engine and picked up the rattle at the front timing sprocket area whilst playing with the throttle.
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Last edited by miked on Wed Jan 09, 2019 8:02 pm, edited 1 time in total.
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PostPost by: StressCraxx » Wed Jan 09, 2019 7:17 pm

miked wrote:Just another point. I listed with a long screw driver around the engine and picked up the rattle at the front timing sprocket area whilst playing with the throttle.
Mike


I was just about to suggest the screwdriver listening method. Another item to check is the dynamo/alternator bolts top and bottom and the water pump pulley bolts.

Regards,
Dan
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PostPost by: andyhay » Sun Jan 13, 2019 1:44 am

I took the car out again with a mate to help narrow down the source of the noise with some success.

Used the screw driver method to listen for noise at timing chain - definitely not there. It’s lower and back further in the car.

We found a way to make the noise happen consistently while stationary. Depress clutch - put in gear briefly then lift clutch. The noise happens about 2 seconds after lifting the clutch. Happens using any gear and almost every time.
Sounds like some thing metal spinning down and becoming wobbly and brushing against another metal surface.

Any ideas?

Could it be this :

lotus-gearbox-f37/clutch-noise-t22527.html
Thanks

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PostPost by: StressCraxx » Sun Jan 13, 2019 3:57 am

That's your clutch release bearing making the noise. The clutch lever should have about 3mm (1/8") free play from the slave cylinder rod. There should be a retaining spring between the lever arm and the slave body to keep the bearing from contacting the clutch fingers when the clutch pedal is not depressed. If it's missing find a replacement from one of the usual suppliers.

The bearing is worn and has some looseness. Mine has been that way for years.
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