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Low RPM knocking

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Haven't been here in a while due to a busy work schedule, but I've been driving my Esprit regularly.

About two months ago I noticed a knocking that I'm hoping is just a motor mount rather than a rod bearing.

Typically, for the cool Spring weather we have here, I start the car with the choke pulled out and it starts easily and idles at about 1100 rpm. It sounds fine. A few minutes later, I push the choke in and the tach drops to about 700 rpm rather than 900, which is unusual. At that point there is a rhythmic knocking which is quite loud and the car actually shakes. I don't let this go on, so I rev it up to 1100 until the car gets warm (about five minutes -- I don't drive off after starting, as the car runs like crap when it's cold). But, even at 900 rpm I think I can hear it knocking a bit - right now I'm not sure what I remember.

Out on the road, at highway speeds, the car seems fine. Oil pressure is fine. In these last few months I've driven about 200 miles in the car. Would this be possible if the rod bearing was failing - wouldn't it be getting a lot worse?

This knocking symptom was overshadowed because I thought it, and the rough running I've been having lately, is due to the E10 (10% ethanol) fuel that's now mandatory, or a partially clogged fuel filter, or possibly due to fouled plugs. But, having read of similar knocking symptoms on an MG, I'm now concerned about it being a rod bearing.

I've heard that a good way to test for a bad rod bearing is to temporarily disconnect spark plug wires one at a time while the engine is running and if the knocking goes away, you've found the bad rod.

I don't have anyone to assist me in an experiment like that, so is there another way just one person can determine the nature of the knock without risking the engine? Obviously one thing I'll do tonight is try to get a good look at the motor mounts, but I wonder if I could tell anything just by looking. In my situation, I already know I wouldn't be able to take the oil pan off.

It seems to me that perhaps I should avoid starting the car at all if there's a risk of putting a rod through the block (is that what would happen?). Maybe I should just have it towed to my mechanic.

All advice greatly appreciated.

-Dave


All Cows Eat Grass

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Disconnecting spark plugs is a good idea..the engine doesn't have to be running, you can start on 4 and warm it up a bit ,then stop it, disconnect no.1 plug, start it up again and see if it knocks..then stop the engine and repeat the procedure for the other plugs. A bit of hopping in and out and walking around the car, but it can be done single handed. It is extremely unlikely that you'll put a rod through the block..if your oil pressure is OK, then the main and big end bearings are still serviceable; it could be a little end, but that's not likely either. Most likely is due to engine mounts, engine/gearbox assembly wobbling about and hitting some chassis member, or some other mechanical knocking caused by the engine vibrating about. A good look round whilst the symptoms are present would be an idea, also try grabbing hold of the cam covers and physically restraining the motor; move it about (if you can) and see what happens to the noise!!

You could, of course, tweak the slow running up a bit so the engine sounds happier.....

Edited by molemot

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Disagree about the dangers of putting a rod trough the block. If a big-end bearing is worn the clearance to the crankpin has increased. Thus the rod will hammer the crank which puts a lot of tension on the big-end bolts. This could lead to one of them breaking with disasterous results.

If the oil pump is good, it may be able to maintain oil pressure with the increased oil flow that a worn bearing would give. Do the checks as mentioned and have a good listen around to try to work out where the noise is coming from.


S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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If you have a knock at low RPMs when you first start the car, chance are something external is loose/banging.

I agree with molemot.

A few more suggestions:

- Check the emissions equipment. Does your car have a smog pump? If so, check the pump and its pulley, as well as the pulley on the end of the camshaft -- they can come loose and bang around (or the thrust washer bangs around).

- Check that somet part of the exhaust isn't banging something. When I first got my white S1, it had a knock. It had a few, actually. One of its various knocks was something in the exhaust system -- I "silenced" it by pressing my shoe against the tailpipe! Removal and reinstallation of the system cured it.

- Could also be loose element (honeycomb) inside the catalyst

Just a few things to check! :devil:

I'm not worried it's a bearing yet.


Tony K. :)

 

Esprit S1s #355H & 454H

Esprit S2.2  #324J

1991 Esprit SE

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Is the knocking just when the car is cold? Does it sound like it is coming from the air filter? Could it be induction knock? If so check valve clearances, valve timing/ignition timing, carb mixture etc. Sounds fuel related if the knock only comes when cold and especially if using the choke cures it! Have you noticed any pinking when the car is hot?

Hope this helps

Simonf


REHABS FOR QUITTERS!!

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It could be that the knocking is external - the plastic air intake/duct is very close to the cam towers and is loose; I am hoping that was it.

As for the rough running and low RPM behaviour at startup - my mechanic tells me both of my carburettor floats were sunk and was surprised that car was as drivable as it was! He has been trying to get floats for my Dellortos for a few weeks now and, after much searching, it sounds like there are none to be found in the country. So, he's getting them from the UK and we are just waiting on delivery.

regards,

-Dave


All Cows Eat Grass

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Relax.

It's sounds very much like you have piston slap. This is very common on these engines, and goes away when the engine reaches normal operating temperature and all the clearances normalise. It's nothing to worry about.

If you had a bearing failing, it would be much worse when the engine is under load.

My 25k miles S3 did it, and so does my Excel SE.

I have even seen road tests where they complained about 'piston slap like an old Cortina'.

Paul.

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My 1987 S3 (NA) developed a nasty knocking a few days ago. Sounds a bit like a diesel engine when it idles. The knocking dissapears over 1500 rpm.

The knocking also varies a little bit on idle. I suspect one of the valves are stuck (Sticky valve syndromoe).

The cam-covers are coming off this week-end and I'll measure the clearances.

I'll post a separate post of what I find.

Bjorn


Dream as if you'll live forever. Live as if you'll die today - James Dean

"If it isn't leaking, it's empty" - Comment from a British sportscar enthusiast after being made aware of an oil slick under his car

Lotus Car Club Norway (LCCN) - lccn.no

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Reading this threat there seems to be a fundamental missing, what oil are you using, what cold pressure are you seeing, how long does the engine need to run before the gauge reaches maximum, what does it go down to at idle when it's hot.

If you eliminate exterior knocks, then I'd be doing an oil change to a Lotus recommended product, I use Castrol and see what that does.

Roger


Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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