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MG Midget and Sprite Technical - Name the tapping

Hello all...

I recorded my 1977 (US) MG midget with the 1493 engine, so you could hear, and may be able to help me pin point the tapping noise.

The video shows the car at 2500 rpms down to about 1000 rpms, where the tapping is heard the most.

The car is warmed up and has a temp of 180.

There is no tapping when the car is first started

http://www.youtube.com/watch?v=rS2NXjAVT58


Any ideas....


Thanks
K Samen

That sounds like an exhaust leak to me. also I seem to see number two spark plug dancing around. It may be just an illusion but???
Sandy
SANDY SANDERS

It wouldn't be anything as simple as a loose rocker adjuster, would it?

-:G:-
Gryf Ketcherside

Irrespective of the tapping noise, I agree with Sandy's reply: #2 spark plug lead shouldn't dance about.

Re. the noise - have you eliminated the rad fan-blade and/or alternator fan and/or alternator belt? I have experienced my 1500's alternator fan/pulley fouling the air intake trunking. And the rad-fan blade does travel close to the top rad cowl. Worth double checking just to make sure that there's good clearance.





Andy Hock

It looks like the fan is hitting the shroud...especially at the 0:30, 0:42, 0:57 & 1:15 times.

Check shroud clearance, fan clutch & fan clutch bearing.

Dave
Dave Rhine

And by the way...nice, clean looking engine!
Dave Rhine

Try tightening your spark plugs....

Mark.
Anita

The sound seems to be louder on the dissy side and that plug does look to be moving. And yeah, very nice under bonnet appearance!

Bernie.
b higginson

Thanks everyone...

I just checked the plugs, they are all tight, plus I checked to make sure all the wires are firm too.

I checked the rad-fan blade and the top rad cowl... There are no marks on the paint of the bottom of the cowl or the blades themselves.

I think that Sandy's idea of the exhaust leak may be it... I bought a Mechanic Stethoscope today and used it to listen to the engine. The sound is the loudest around the exhaust manifold. Now what?? Gasket?? Crack??

As per Gryf's suggestion.... "loose rocker adjuster"
Is there a touque setting one these screws? Did not see in "Haynes"

Thanks



K Samen

"Rocker pedestal to cylinder head: 32 ft-lbs" per "The complete official MG Midget 1500 1975-1979"

R
R. J. Reeves

"Rocker pedestal to cyl. head: 32 ft-lbs" per "The complete official MG Midget 1500 1975-1979"

R
R. J. Reeves

K. A mechanic's stethoscope is your friend and will allow you to narrow your focus as to where the noise might be coming from. No, there is no torque specification for the adjuster screw when setting the valve clearance. You get to know what is needed over a period of time. Tighten firmly, but not excessively, is the best advise I can give on this. Check it after a few hundred miles and see if any have loosened. (To do this, put a box end wrench--a ring spanner, on the nut and try to tighten it. If you can tighten it easily, its adjustment has slipped and you need to readjust that valve clearance and tighten the lock nut a little more this time.) This is not a complex issue and one seldom sees problems with insufficient tightness of the rocker arm adjusters.

RJ. You are giving the torque specification for the nuts which hold the rocker arm assembly to the cylinder head--the ones other than those which are part of the cylinder head hold down mechanism. K is asking about the torque specification for the rocker arm to valve stem adjustment mechanism. Hard to apply an exact torque value to these because you have to hold the adjustment steady, using your screwdriver, while tightening the locking nut. Hence, very difficult to apply a torque value, using a torque wrench, without a "crow foot" wrench adapter and knowing how much that extension effects the reading on the torque wrench. Hence, part of the "general knowledge" taught to professional mechanics in their training. Often misunderstood by those of us whom have not trained as professional mechanics.

Les
Les Bengtson

Could it be a leak around/in the remaining emissions stuff?
Trevor Jessie

Just another two cents, based on my own experience with the 1500 - A few years ago, my manifold gasket burned through, just at the bottom of the exhaust manifold center branch. So I ordered a new gasket, but prior to fitting it I used a straightedge to check the alignment of the manifold mounting faces. Lo and behold, the center branch wasn't aligned with the front and rear faces; there was a noticeable gap between the center face and the straightedge. Obviously, even with all of the fasteners torqued properly, the center branch wasn't clamped firmly against the gasket - hence the leak.

So since you're hearing the noise around your manifolds, this may be worth checking. I ended up taking both manifolds to a local engine shop, where they skimmed all the mounting faces dead flat, and I haven't had any problems since.

Cheers,

-:G:-
Gryf Ketcherside

This is a little out there but I have had the porcelan come loose from the body on a spark plug and not pop out right away. Could be your dancing???
Hank Wilson

I notice that your protective rad cowl (bolted on top of the rad) is flexing. Is it not fabricated from mild steel?
Andy Hock

This thread was discussed between 05/12/2009 and 07/12/2009

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