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MG MGB Technical - Rattling noise from engine
|I have just put a reconditioned GB engine in my 1963 MGB. Everything seems to work well, but there is a strange rattling noise that I believe comes from the front of the engine.|
What really confuses me is that this noise is particularly noticeable in situations where I would expect pinking with a badly adjusted engine or low octane fuel. For instance when accelerating out of a roundabout in relatively low gear. The noise itself sounds a little like pinking when driving, but the rattling is also present when the engine is idling.
I have been through some possible causes. The water pump is supposed to be new, and the bearings feel very precise. The rubber grommets on the fan are relatively new, and not loose. The ignition is set at 10 degrees static, and the engine pulls very cleanly even from low revs.
I suppose that leaves the timing chain. Can it be that the chain tensioner is not working? And is there any logical reason why this rattling sound should be particularly noticeable in typical “pinking situations”?
I also wonder wether the breather valve on the GB engine makes any noise that can be heard from inside the car when driving. I would expect not.
Since it will do it at an idle, it would be simple to remove the fan belt and start it for a short period of time to see if the noise is still there. That would at least narrow your list of candidates.
|C R Huff|
My first thought when I saw your thread was the timing chain as well, but the tensioner is self adjusting. Could the chain be worn?
Have you re-torqued the cylinder head, and re-set valve clearance. Could one, or more valves be too loose?
Finally, dynamo bearings (if equipped) come to mind. I've had a chirping sound from the dynamo on my midget when it needs to be oiled?
Larry C. '69 Midget & '74 B/GT
|Larry C '69 Midget|
|I'd try what Charley's put plus especially with the amount of p*ss poor rubber about I'd suspect and thoroughly check any new rubber fan grommets or any new rubber parts or rubber components|
|This weekend I will re-torque the head and adjust the valves. If the sound is still there, and I believe it will be, then I will try to remove the fan belt.|
I know the chain tensioner is self adjusting, but does it have to be activated? I believe I have read somewhere that a bolt should be turned to release the mechanism after the tensioner is in place?
Your quite right the tensioner spring has to be released after installation.
This provides the initial chain tension, aided by oil pressure. I presume you have good oil pressure?
But before getting down to that, which isn't that arduous, check the dynamo pulley and bearings and the crank bolt (70 ft/lbs).
As Nigel and Allan say, but should it come to removing the timing gear cover add to your list checking gear alignment with a straight edge. Their are washers (shims) behind the gears to provide proper alignment.
Good luck mate.
|Larry C '69 Midget|
|Thanks for your input. Yes, oil pressure is excellent, close to 80 psi even after a long run, and almost 70 even when idling.|
|You're using the wrong oil ...|
As well as the other things you can check the timing gear to some extent by seeing how much backlash there is between crank and cam i.e. by turning the crank back and fore and seeing how much you can move it before the cam follows suit. Watching valves that are half open or shut, might be enough, or removing the distributor and drive gear to see the cam itself. However I don't know if tension from the valves will cause the cam to 'jump' at various points in the cycle, they do in the KV6 engine for example.
|The oil pressure in this engine surprised me. On the "old" GA engine ( I had to change because it was leaking so much oil through the scroll seal at the rear main bearing it didn´t pass the MOT ) the pressure was around 60 psi, and 25 when idling.|
That is with the same 20w50 oil to SJ spec. But as the factory spec is 50 to 80 psi I guess it is OK.
|you're still running the engine in presumably so perhaps the oil pressure may drop to more usual readings (whatever they are and vary from individual engines)|
are you putting on plenty of miles on your recon engine and planing an oil and filter change
|Tore Another angle. Being an early model you probably have a bendex type starter motor. A problem I have struck several times over the years with these starters on the early B is a broken return spring on the starter pinion and this allows the pinion to lightly bush on the ring gear. It sounds exactly as you describe and can come and go with acceleration or even braking. Its the very fine spring that is meant to keep the pinion in place after starting. A real tinkle noise. Denis|
I had an MGA in with an 1800 engine fitted with a rattle down the front at idle and at weird times on the road It ended up being the front pulley on the crank
It had an MGA pulley on the MGB crank which is ok in itself but the MGA pulley is held together with rivets which in this case they had become loose and let the outer part of the pulley work on the rivets and rattle
Might pay to check the security of your pulley while you have the belt off it might have the older pulley
Also - in the past I have found a timing chain with a joining link fitted with the clip on the inside instead of out causing the ends of the joining ling to foul on the tensioner every time they went past making a clunking noise at idle and above
hope this helps willy
This thread was discussed between 27/08/2014 and 28/08/2014
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