Knocking Sound under Acceleration

Post by **stephenpolhill** » Sun Nov 29, 2009 6:58 pm

Hello again. After a short drive with Dad and a closer listen we have come up with these symptoms. I have also read about Stuart's broken head gasket and big end symptoms and it doesn't fit either.
My knocking is at a certain amount of revs (midrange ish). I can drive without the noise but have to change gear fairly early. Also the sound isn't noticable at idling.
I took the car a couple for a compression check a couple of months ago due to white smoke and on inspection the 4th (rear) cylinder had a bit of deposit on it and was slightly lower on compression than the others but not dramatically.
Is it possibly a head gasket on the way out or maybe a piston ring going? Like I said no loud bangs, knocking or loss of power. Only a tapping, Dad described it as rattling a stick in a drainpipe though not as echoey.

Hope this helps.
Steve

Post by **eastona** » Sun Nov 29, 2009 10:00 pm

It's one of those noises that is 'once heard, pretty much unmistakable'.

definitely

the way you describe it, it does sound like it could be big end. does it go away at light throttle openings or is it at that rev range whatever the throttle opening?

could be head gasket as you say, mine made a bit of a noise just before it went, but not as "brutal" as big ends.

how about an mp3?

Andrew.

Post by **stephenpolhill** » Sun Nov 29, 2009 10:05 pm

I will record it when I can for you to hear. If I accelerate to a certain speed/rev range and take my foot almost off the accelerator (enough to keep it going) then the noise is still there.So it seems to be associated with the revs, not load.

Post by **MColes** » Sun Nov 29, 2009 10:06 pm

how about an mp3?

Doubt that would work. When the big ends went on my car my friend in his car behind me (I HAD to get the car home) could hear the engine banging

Post by **stephenpolhill** » Sun Nov 29, 2009 10:07 pm

Well we went for a short 5 minute drive yesterday with no problem. Yes the noise was there but it was still the same after a total of 20 miles driving last Tuesday. I won't be driving it around, but it is drivable

Post by **MColes** » Sun Nov 29, 2009 10:07 pm

I will record it when I can for you to hear. If I accelerate to a certain speed/rev range and take my foot almost off the accelerator (enough to keep it going) then the noise is still there.So it seems to be associated with the revs, not load.

That's exactly how mine was when the big ends went

- Only banged at certain revs when idling it was fine.

Post by **stephenpolhill** » Sun Nov 29, 2009 10:08 pm

Hmmm. So what is it more likely to be, big ends, head gasket or piston related.?

linearaudio · Post by **linearaudio** » Sun Nov 29, 2009 10:47 pm

Take the head off! Simple enough to do, a photo guide has just been created by stuart k, as if in anticipation of your problem!!
You will then easily see if it is a blown head gasket. Also by turning the crank so each piston has just gone past TDC, you can tell if it is a big end as pressing down on the piston top will make the piston drop as it takes up the slack if it is an end gone.

Post by **MColes** » Sun Nov 29, 2009 10:50 pm

Stuart K's guide is HERE

linearaudio · Post by **linearaudio** » Sun Nov 29, 2009 11:03 pm

MColes wrote:Stuart K's guide is HERE

Thanks for the technical bit- one day I'll work out how to insert things like that, have to get my 11 year old daughter to show me!

Post by **mike.perry** » Mon Nov 30, 2009 10:55 am

Big ends can go in different stages, gradual wear will give you a tapping sound and sudden bearing disintegration will give a loud knocking. Is your oil pressure light flickering on tickover when the engine is warm? It could also be a badly adjusted tappet so check the valve clearances before you lift the head

Post by **bmcecosse** » Wed Dec 02, 2009 7:59 pm

Yes -sump drops off easily - and so big-ends can be checked more easily than head removed! Why can it not be done in Spridget ?

Post by **stuart_k** » Thu Dec 03, 2009 9:16 am

I'll rephrase that, it can be done but is a devil of a job to access due to the crossmember. I've never tried it myself but I'm told it is almost impossible to get at the front main bearing especially. It's also a lot harder to get under a Midget without decent ramps or a pit as it has a much lower ground clearance. I can't focus easily when things are right on the end of my nose

Post by **stephenpolhill** » Sat Dec 05, 2009 12:38 pm

Hello again. We have finally got round to working on my car. So far we have
-Removed the sump and had a look in
* it was clear of any metallic products, only quite a bit of gunk*
* the crankshaft and there are no signs of over-heating or metal coming out of the big end area.*
-Removed the rocker cover and we will check the tappet gaps to see if they are OK.

We had a listen once the engine had warmed up and the knocking occured at the same amount of revs. It seems to be the same amount of revs whether stopped and holding revs, driving along at a constant speed at those revs or the one most people can relate to is it is at the same revs as when in 4th doing around 50-60mph.
I hope this helps and will keep you posted.
Steve

Post by **bmcecosse** » Sat Dec 05, 2009 2:37 pm

You can't get the front main bearing off on any A series engine - without removing the timing gears etc first - so in that respect the Spridget is no different to a Minor.
When the sump was off Stephen - did you take the big-end caps off ? That was the point of the exercise! To see what the shells looked like. It would be very unusual to see any 'metal coming out of big-end area' - although I agree if you DID see that it would indicate quite a disaster!

Post by **stephenpolhill** » Sat Dec 05, 2009 6:14 pm

HI there. No we are aware of that and now have a decision. We had a look at one of the main bearings and the copper was beginning to show through. I didn't do this, Dad did and he does have a fair idea what to do, but having never owned a moggy, he isn't aware of what to do now.
We did take the caps off and the big ends looked OK as well as the camshaft.
Any ideas?

linearaudio · Post by **linearaudio** » Sat Dec 05, 2009 7:54 pm

Possibly head gasket, as suggested a couple of pages ago? May also explain your lower compression and deposit in 4th cylinder!

Post by **stephenpolhill** » Sat Dec 05, 2009 8:01 pm

Hmm ok. I will recommend looking at the head gasket. But is it worth changing the main bearings soon while I have another car?

Post by **bmcecosse** » Sat Dec 05, 2009 8:10 pm

You should have taken some pics of the big-ends when they were open! You can only get to the centre main bearing - so no point in that. If a big-end had been 'away' then it would have been obvious when you're Dad took the cap off. So - looks like off with it's head for further investigations!

Post by **stephenpolhill** » Sat Dec 05, 2009 8:17 pm

I did take some pictures but I'll have to wait for Dad to see which they are

. I am learning slowly.
We will take the head off when we get the next chance, but if one bearing is beginning to go, is it worth changing them all while we have the chance?