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MG MGB Technical - Can you help me diagnose noise at startup?

As the title suggest there is a noise at startup of my 68 mgb roadster. It sounds like a pebble rattling around in an empty Coke can. The noise starts immediately when I crank the car and continues until the engine fires and then it stops shortly after the engine is running. My guess is something to do with the starter since the noise ceases after the engine is running. Have any of you had experience with anything similar? Is there anything I can look for to help diagnose? And is it fixable or do I need to replace the starter? Thanks in advance for your help.
Jack Caulder

Could this be low oil pressure on start up?

Iain
I D Cameron

Fan hitting radiator hose clamp, alternator fan hitting case, water pump going bad, balancer delaminating, fan belt coming apart, exhaust pipe hitting somewhere, insulation on hood dropping onto fan, connecting rod bearing worn out, ring gear on flywheel loose, throughout bearing worn,...

Need more info.

Wayne
Wayne Pearson

What info is needed?

I know the hood insulation isn't dropping onto fan. I just checked the exhaust pipe and it's secure. Fan belt looks fine, there's no interference with the fan or alternator fan.

Maybe I should rephrase the question - what types of problems occur with the starter that would generate such a noise? It seems relatively certain that's the problem as the noise occurs every time a I start the car and at no other time. The noise stops shortly after the engine starts running.

Thanks.
Jack Caulder

Does it only happen when the engine is cold?

Does it happen if you turn the engine off and restart immediately?

Is it at the same frequency as the engine RPM?

Or is it at the starter RPM frequency?

Is the starter secure on its bolts?

Try listening for it using a piece of tube while someone else turns the engine - disconnect the coil to stop the engine starting so you can hear the noise.....
Chris at Octarine Services

what type oil filter do you have? Stock cartridge? spin on? inverted type? If it's the latter, you could have a filter cartridge that doesn't have a check valve to prevent the oil from flowing out. In that case, you're initial cranking is just pumping oil back into the filter and not to your bearings. The sound you're hearing could be your bearings, begging for lubrication.
R. L Carleen

Probably one of those bolts you dropped and couldn't find.
Mike MaGee

Jack,
Looks as if it could be the big end bearings waiting their first rush of oil !!
This is very common and not necessarily a problem. Just make sure that when you start the engine for the first time each day that you don't raise the engine rpm over about 1000 to minimise bearing load.
Watch the oil pressure gauge and if the noise dies as the gauge rises then this is almost certainly the cause. Don't worry about it the engine could well last another 60,000 miles.

My only doubt here is that you say the noise starts before the engine even fires. Can you simulate the noise if you disconnect the coil and remove the plugs to give you a longer time to crank and thereforelocate it?

Alternatively start the engine by running the car down a hill thus eliminating the starter and see if the noise still appears. This method may however may mask big end noise unless you declutch immediately the motor fires.

It's always difficult for someone else to put a finger directly on it unless you hear a noise for yourself.



Iain

Iain MacKintosh

If it stops *immediately* you stop cranking then it could be something to do with cranking, like a flywheel tooth. If only shortly after then probably oil pressure and bearings. Start and run a cold engine until you have full oil pressure then disconnect the coil and immediately start cranking again. Cranking should be enough to maintain full oil pressure when cold, does it do so? And does the noise return or not? If so it is something to do with cranking, if not then oil pressure/bearings.
Paul Hunt

Thanks for the ideas on how to troubleshoot - I'll try them out and report back. The noise does occur every time I crank the car, even after it has been running for a while.
Jack Caulder

I don't think this is anything to do with oil presswure/bearings as it happens every time you start the car and it seems even if you run the car, stop it and then restart. However I'm having difficulty relating to the pebble in the coke can!! Is this rattle speed related i.e does it speed up with engine ?? Take the fan belt off and try again (by any chance is the alternator pulley drive nut slack or the alt fan slack on the keyway?)

The only thing you haven't mentioned is whether or not the noise still exists if you start the car on a hill or push start it.

If all this is negative and you are sure it is not an exhaust mount which I'm inclined to agree with then you are going to have to take the starter off and have a look.

Perhaps you should abandon the soft drinks and go for the hard stuff.

Iain
Iain MacKintosh

Jack,
I had a similar thing happen on a 71 Datsun 510 years ago and, because it was using the infamous AIR injection system, that car had a similar (nearly identical) smog pump on it. If your car still has the smog pump, it could be that the carbon vanes in your pump have worn/disentegrated to where they flop around abit at low cranking rpms, but then shut up as centrifugal force picks up at engine idle and keeps them flung out to where they ride quietly. The same noise can return as the engine is shut down and momentum and low rpms allow the vanes to flop around again. Just another option.
Bob Muenchausen

How about:
1.) A metal fan blade loose/cracked and about to spin off?
2.) On my previous MG the fanbelt pully on the waterpump was cracked between the four bolts and creaked a bit, til it completely broke.
3.) Rocker assembly worn?
4.) My '77 had a very similar sound emanating from the air intake at the end of the air filter housing. There was a flap that slapped around until a certain air temperature was achieved. Yanked that sucker off real quick.
Luigi

I had the same problem with my MG. I turned up the radio real loud during start up and the noise went away.
Jay Leno

This thread was discussed between 20/01/2004 and 21/01/2004

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