Knocking Sound under Acceleration

Post by **stephenpolhill** » Wed Nov 25, 2009 11:10 am

Hi there. Last night i was on a 15mile drive and doing about 60 when a knocking noise started. I lifted my foot off and it stopped and when I put my foot back on the accelerator to keep at a constant 50 it started again. I pulled over in a layby and the orange light started to flicker so I topped up the oil and turned the engine off. I then checked the oil and it was full and she idled fine with no odd noises. I then started off again to my destination with the sound still apparent and on the way home it still did it. It seems to be when under acceleration and at a certain amount of revs and gets louder when I accelerate more.
Can anyone help with any idea's, experiences or anywhere to try and diagnose this? My car is totally standard with no Mods and is a 1965 1098.
Thanks alot

Steve

Post by **mike.perry** » Wed Nov 25, 2009 2:17 pm

If it knocks under load, stops when you lift off and the oil pressure light flickers then you have a big end gone. Engine rebuild or replacement time. To confirm lift the bonnet on the first start of the day and start the engine with the starter button. If the engine knocks for a few seconds until the oil pressure builds up then its the ends.

Post by **stephenpolhill** » Wed Nov 25, 2009 3:11 pm

I have just tried that and there no knocking only a tap when I lift my finger off the button. I left it to warm up and revved it slightly and there was no knocking

. Is it worth taking it for a short drive to see if the problem returns or not?
Steve

Post by **dalebrignall** » Wed Nov 25, 2009 3:49 pm

sounds like big ends if you get the oil warm drive the car accelerate in 2nd gear if it knocks under load its a big end .

Post by **MarkyB** » Wed Nov 25, 2009 6:26 pm

How low was the oil before you topped it up?

Post by **ssnjimb** » Wed Nov 25, 2009 6:45 pm

Hi

I know knocking is like someone knocking on your front door but has someone altered the ignition timing at all. Mine growls a little when its too far advanced.

How is your oil pressure.

Jamie

Post by **stephenpolhill** » Wed Nov 25, 2009 6:55 pm

The oil wasn't low as I checked it on Monday and it was 3/4. I then emtpied the spare 1litre bottle of oil I had spare, by the side of the road last night. So it is not full. I am not sure about the pressure. How do I check that? And ignition timing hasn't been changed at all. Not since possibly before summer but even then I am not aware of it.

Post by **PSL184** » Wed Nov 25, 2009 7:16 pm

At what frequency would you say the knocking sound was, ie, is it a fast knock (maybe more like a tap) or a deep slow knock, knock, knock.....?

Post by **ssnjimb** » Wed Nov 25, 2009 7:20 pm

a tap could be a tappet that is out of adjustment and a knock the big ends

Post by **stephenpolhill** » Wed Nov 25, 2009 7:35 pm

It isn't slow but isn't fast. I say everytime one cylinder fires but I can't be sure as it doesn't increase in frequency with the Revs.

Post by **simmitc** » Wed Nov 25, 2009 7:55 pm

Check compression - you need a compression tester. The problem with describing noises is that everyone interprets them differently, but this could be a head gasket failure. It might also be an exhaust leak, but I think that highly unlikely as the noise would be different; but a sort of banging sound on one cylinder could easily be head gasket.

To check oil pressure, you need to fit an oil pressure gauge.

Post by **stephenpolhill** » Wed Nov 25, 2009 8:05 pm

With the exhaust, there was a small leak between the manifold and the actually pipe. I knew this because about a month ago I had white exhaust smoke and some came out of that 'hole' when revved. The smoke has gone but I haven't sorted the hole. So what I need to check is :
-Any exhaust leaks/holes
-Head Gasket (was leaking a tiny bit before)
-If all else fails, big end.

After talking to my Uncle he said it's highly likely it's a big end. I just want to find any easier problems it could be before dismantling the engine:)

Post by **alzax3** » Wed Nov 25, 2009 8:37 pm

It's one of those noises that is 'once heard, pretty much unmistakable'. The only time I've had it and it's not been (if you get my drift) was when some of the spot welds on a pressed-steel sump baffle had failed allowing one end of it to contact the bottom of the conrod ..... exactly the right noise in exactly the right place, but a really simple and quick solution. Sadly that was a different breed of car and the Moggy doesn't have baffles.

Post by **stuart_k** » Wed Nov 25, 2009 8:48 pm

Most likely a big end but as mentioned above could easily be headgasket too. It won't hurt to whip the head off and check before you resign yourself to pulling the engine.

aside: Is it possible to drop the sump on a Minor without pulling the engine? Can't do it on the Midget.

Post by **MColes** » Wed Nov 25, 2009 8:55 pm

aside: Is it possible to drop the sump on a Minor without pulling the engine? Can't do it on the Midget.

Yep. Did this on the engine in my old car to confirm big ends but turned out to be a cracked crankshaft.

Post by **mike.perry** » Wed Nov 25, 2009 9:01 pm

I had a very load knocking noise on my Series MM on the M4 one morning. It wasn't the ends knocking it was a broken crankshaft!
I still have it in the garage as a souvenier.

Post by **PSL184** » Wed Nov 25, 2009 10:52 pm

Yep, cranks do seem to crack all too easily - another possibility is a broken piston ring but this would be more of a tick than a clunk.... Engine out to fix either way I'm afraid....

Post by **stephenpolhill** » Thu Nov 26, 2009 8:21 am

Hi again. Thank you for all of your help once again.
I am now covered on Mum's Focus which is at least a car so I have time to work on 'Fiona'.
Is there a specific order we should check things in? Meaning we will find a possible problem before taking the whole engine apart?
Thanks again
Steve

Post by **PSL184** » Thu Nov 26, 2009 8:41 am

You need to listen to different parts of the engine using a long screwdriver, pressed against your ear, and placed at different points around the engine, it head, block, sump etc. The louder the noise will be the general area the fault is. The sump can come off whilst the engine is still in the car. Then you can inspect the crank for cracks. By removing the middle main bearing you can inspect that for wear (the centre always wears first) and all the big ends can be replaced with engine still fitted. If it is piston rings you will have to remove the head also to change but bore damage may have occured also so it would be easier to pull the engine out at this stage....

Post by **stuart_k** » Thu Nov 26, 2009 1:33 pm

If you want to know which things to check first in order of difficulty then I would say

1. Check for exhaust leaks - unlikely
2. Take off cylinder head and check the gasket. It will be obvious if it has blown see pic below of the blown gasket from my Midget
3. Get on your back and take the sump off and check bearings and big ends.
4. If still no joy, engine out.

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