Knocking sound in 948 Minor

[BobinAustria]

I have a 1958 Minor which I imported to Austria 3 years ago. I had to do some work to fix a oil leak from the rear of the engine to pass the MOT equivalent. This involved new main bearings and big ends (crankshaft was perfectly OK), and (probably the main cause) re-brazing the cover for the oil pump. The oil pump I renewed together with a standard timing chain and sprockets. Since then the car has only done 400 miles. I'm now concerned by a knocking sound, similar to a loose valve clearance but only audible when accelerating- even only gently - not on tickover or on overrun. It's most distinct between 30 and 40 mph in 4th gear, or similar revs in lower gears, at higher revs it's drowned by other noises (gearbox, exhaust, wind noise. I know this is classic for big end failure, (in theory, I've never had a car where the big ends failed) but unless I made a big mistake 3 years ago, they should be OK. Oil pressure is fine - 40 psi on tickover and 60 when cruising when warm.

I have of course checked and adjusted the valve clearances to no avail. I would also expect anything in the valve train to be independent of load and audible on tickover. And in case it was "pinking" I retarded the timing to TDC - didn't help either and ran poorly.

Has anyone had a similar problem and managed to cure it? Or is it just a typical noise? I've searched this forum and found many references to knocking noises but nothing that fitted perfectly to my moggies symptoms.

[win]

Morning, we it is here.

If possible i would do a compression test first, a failed head gasket gives strange noises, especially when oil pressure appears OK.

See the various advice regarding tightening head down after replacing head gasket.

Regards Win

[Murrayminor]

Hi Bob

Firstly pinking is more of a tinkling sound rather than a knocking and usually occurs under load.

Given you have recently had work on the Crankshaft then I would be inclined to start my investigation there, why did you replace the main bearings?
Was the work carried out correctly?, were the thrust washers installed correctly?

You could try and measure the end float on the crank, any excess movement here will be an issue.

[kennatt]

big ends tend to knock on the overrun,as you ease the throttle after acceleration,they will knock under acceleration but need to be well gone by that stage. Mains just rumble all the time .With those oil pressures I would think that its more likely to be the head gasket as suggested. comp. test will show, .do one before looking any further.

[Edward1949]

Also, could be something else completely random. You say it's only under acceleration. This changes the engine position in its mountings, sometimes enough to allow contact by, say, the exhaust against bodywork.
Do the easier checks before taking things apart !

[Nickol]

I will be interested to know any solution to this problem because I have exactly the same symptoms in my other Classic ( OldTimer) english car. There are a few threads on here about this very phenomena and the initial suspects are low oil pressure ( which you do not have and me neither) worn bigends or main bearings ( which you have renewed and so have I ) as well as the timing chain tensioner weakend. ( you have renewed yours and so have I.

I have had the head off mine, installed new valves and springs as well as a new head gasket. No difference to the noise but the engine does run much better. The head has also been retightened.

In an old thread from about 2010, the late Roy suggested looking at the cam followers (Stößelbecher) which on a Minor is quite easy to do. . Also suggested were small end failures which is not quite so easy. The other moving part to consider is the camshaft itself but I would think that if the engine is running smoothly this cannot be at fault?

One question - do you have a any rumbling or heavy knocking on a cold start as well which stops as soon as the oil pressure builds up? I have this.

You may like to try and listen to the engine using a stethescope or long shaft screwdriver in an attempt to localise the noise.

[BobinAustria]

Firstly, thanks for the many, very prompt replies!

@Murryminor: I replaced the main bearings as the rear main showed signs of erosion, the others looked OK .
I did the job slowly and carefully following the original BMC manual, hopefully also correctly. I had the crankshaft checked professionally. I've little experience of this type of job, though I have done done it once before: back in 1974!

@Nickol: I hear no unusual noises starting from cold, the first time I hear the rattle is when accelerating in second gear, it's most noticeable in 3rd and 4th. I do hear a knocking with a screwdriver as stethoscope, louder at the back of the engine than the front

I hadn't thought of the head gasket as a cause, so I'll get a compression tester and check. Apart from the knocking, the engine runs fine but past experience has shown that it's not wise to ignore strage noises.

Will report on my progress.

[kennatt]

gear box mountings,engine steady bar bushes,starter motor bolts,clutch linkage bushes,possible clutch plates .

[Murrayminor]

viewtopic.php?f=4&t=72888

I have added the update to this thread to keep everything easy for people to find as there has been an update.