Lotus Elan

knocking noise engine / gearbox

PostPost by: gibbon » Sat Jan 13, 2018 3:33 pm

My elan plus 2 just starting making a strange intermittent knocking noise. Its hard to tell exactly where from, but almost more the middle of the car from the front, but im not convinced its the gearbox. Like a dull knocking.

Doesnt fluctuate with revs, though happens more often at lower revs, seems to clear itself at different rev points maybe, but its not really consistent. Happens irrelevant of if in gear, in neutral, which gear its in etc.

Im hoping its as simple as something knocking against the exhaust at certain frequencies, some heat shield or something maybe, but its very hard to tell and Im a little worried its something more series. I dont have access to ramps so inspection is not the easiest. Any tips where to start?

Worth dropping the oil and inspecting the filter? I could probably do with an oil change anyway.

On that note, any good online guides to DIY filter and oil change?

Im east london based and dont really have a favoured specialist as fell out with the last I used.

Thanks in advance
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PostPost by: rgh0 » Sat Jan 13, 2018 10:36 pm

Most likely the exhaust hitting the chassis could be caused by the engine shifting if an engine mount has failed.

other possibilities are the carbs hitting the footwell or the propeller shaft U/Js or the diff moving and hitting the chassis.

In reality being a Lotus there is a never ending series of possibilities and you need to get it on a hoist. Useful to drive with a passenger and get the to move around and try to figure out where its coming from.

cheers
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PostPost by: toggle45 » Sun Jan 14, 2018 7:00 am

on my LHD Elan S3, when the right side engine mount fails, or a wrong mount is installed, the carb air box will contact the top of the passenger footwell, causing intermittent knock.
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PostPost by: gibbon » Sun Jan 14, 2018 1:42 pm

Thank you guys. Engine mounts sound a probable cause hopefully.

I think to me it sounds like its coming from the LHS of the car.

Not the best video, but does this help diagnose the problem?

https://youtu.be/OwHgakxi3UY
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PostPost by: alan.barker » Sun Jan 14, 2018 5:20 pm

It seems to me that the tickover is a bit too slow.
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PostPost by: JonB » Sun Jan 14, 2018 5:39 pm

Sounds like a diesel engine on tickover. I'd be worried if it carried on when you rev the engine.

My suggestion: look for witness marks. These are little scuffs and scratches that are left when bits rub together that shouldn't. For example, the airbox - take it off and see if there's any scoffs underneath, especially in the corners. Easy as yours is painted. Look round the engine bay for things that are really close to the engine itself. The things that might touch when the engine revs.

Good hunting.
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PostPost by: Hawksfield » Sun Jan 14, 2018 6:46 pm

HI

sounds like something around the cam followers or timing chain slackness
Make sure the chain is adjusted correctly, try adjusting it up a bit at a time and blip the throttle. see if it changes the knock
I adjust the timing chain by sound too tight it screeches too slack it rattles

Good luck
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PostPost by: rgh0 » Sun Jan 14, 2018 7:56 pm

Have a look for exhaust leaks
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PostPost by: gibbon » Sun Jan 14, 2018 10:07 pm

Thanks all.

The idle is a touch low as the engine was stone cold and had literally just been started.

The sounds doesn't continue consistently with revs, its certainly not rev proportional, is very intermittent, like its almost frequency related, and is worst at or near idle.

I'll try to find a local garage that will get it up on ramps to have a real poke around and try to identify where the sound is coming from.

Should it be fairly obvious if the mounts have failed? The engine does seem to rock and move around a fair bit, though im finding it hard to tell if thats increased or not. The car certainly jiggles around a little bit when stationary with the car idling, even at a normal engine idle speed.
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PostPost by: billwill » Mon Jan 15, 2018 12:19 pm

My guess would be a problem I have... the exhaust system hitting the gearbox, (not the chassis).
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PostPost by: gibbon » Sat Mar 17, 2018 9:35 am

Just to complete this, if anyone has similar, it was the engine mounts, all replaced (including the gearbox mount to be safe) and sorted now.
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