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MG Midget and Sprite Technical - Rattling noise

Chaps

Some spiffing days up here in the Tundra - a heady 20 degrees no less, glorious blue skies, ideal top down motoring to enjoy consuming a fine bowl of Cullen Skink in Cullen and watch for basking sharks in the Moray Firth.

The car now performs admirably after its head and needle change - accelerates up hills in 5th no less, but I have noticed a distinct rattle - which has I am sure become a little louder over the miles.

It does sound a like a tappet, and only occurs under load, so I have carefully adjusted all of them to 16 thou - as per the engine rebuild spec sheet - twice now over the past 600 miles or so. However, the noise still seems to be present.

Therefore, in turning to other possible explanations

What are the sypmtoms of a slack timing chain and how can you verify for certain that this may be the problem? - without taking the whole thing apart that is!

Oil level is fine, and pretty sure it is not pinking.

Any other possible causes?

Thanks as always

Mark





Mark O

"rattle.... only does it under load...."
'pretty sure it's not pinking...'

How/why are you so sure?
David Smith

David

It is not overly advanced
It rattles even when retarded
It doesn't run hot
It rattles under even moderate load
It doesn't sound like it.
Mark O

minor exhaust leak ?

Are you certian its the engine, and not everything else

Does it do it standing still, get one of those cheap mechanic stethoscope ... that looks like a doc only with a long spike test the engine with that feeling around

If we can localize the noise to a certian area, then we can freak you out much better with dome and gloom

Im putting my bid in early ahead of the crowd and.saying its a connecting rod bolt thats streatching out...life of engine 260 miles tops

Haha

Prop
Prop and the Blackhole Midget

I have a rattle like you describe - like persistent moderate tappet noise. No amount of tweaking with the feeler gauge got rid of it completely.
My stethoscope found it - a bit of wear on the rocker shaft. It's so minor I haven't fixed it yet.
On your engine I'd imagine the bush would wear before the shaft. The Triumph doesn't have bushes AFAIK.
RS Hughes

Why 16thou?
Lawrence Slater

I'd put a hazy vote in for exhaust leak too.

Checking the t/chain is a case of moving the engine forwards/backwards in rotation and seeing how far you can go before the valves/dissy 'catch up'. I don't have an ideal amount of degrees for you, but it shouldn't be too far before something happens.

A long screwdriver placed on the t/cover (or anything else you suspect) and your ear will help pick up noise in lieu of a stethoscope. Just don't get it jammed and be careful not to damage your ears.
Roadwarrior

As it is a Triumph engine, with its oil supply problems, it could be a small end (gudgeon pin) rattle or if heavier, a big end rattle. Both are noticable under load.
JB Anderson

Or piston slap?

But, a good starting point in tracing engine noises is to take the fan belt off. Its surprising how much quieter it will be and it makes it easier either to eliminate the sound, or to make it clearer to locate. You can even go for a short test drive - but not too far as you will have no water pump function.
Guy W

Noises that occur only under load are usually ominous as per last two posts :-(
Slack timing chain is usually most noticable at idle or just off idle. It's chain you hear a dull-ish clattery noise is the best way I can describe it, but others may do better!
Paul Walbran

If it is something heavy internal, pulling a plug wire and test-driving could isolate it to a single cylinder. Which leads me to a question. If you have an electronic ignition and you want to pull a wire for test purposes, do you have to ground the wire to avoid damaging the electronics?

Charley
C R Huff

Charley

It shouldn't have any effect on the electronics, although I have blown a rotor arm by running with a plug lead disconnected.
Dave O'Neill 2

My midget has what I think is piston slap. It goes away when the engine warms up, and doesn't appear to make any difference to performance.
Lawrence Slater

Chaps

Thanks for the comments, though quite where the hideous notion of a Triumph engine came from I know not - It is a 1275 A series - albeit somewhat modified.

Exhaust leak - no, deffo from inside the engine - somewhere

Piston slap - possible I guess....

Lawrence - you raise a valid point ref why 16 thou. Basically because that what it says on the engine rebuild sheet, I assume something to do with the modifed cam fitted, but quite why that should affect valve clearance I do not know - I know Haynes says 12 thou.....quite a difference....

Anyways now set to 14 thou as a compromise. Can't say whether it improves the rattle, but very slight improvement in performance....

Will remove fan belt and try harder.....

Many thanks

Mark

Mark O

I guess you should go back the engine builder and quiz them on the requirement for 16 thou. Esp if you've noted a performance improvement at 14 thou. Whose cam is it? Look in their website for the specs and setup of their cam? at least it would elliminate that from the speculation.
Lawrence Slater

Lawrence

Good advice - will ascertain exact cam and report back.

Pretty sure it is a Kent cam - not quite sure precisely which one.....

Rebuild in 2003 - not quizzed builder.....

Cheers

Mark
Mark O

You need to know which cam in order to determine valve clearance.

Also, if using high lift rockers, clearances need to be increased appropriately.
Dave O'Neill 2

2003? I had it in my head it was a new build. I Don't know where I got that from. So if you've had it at 16thou for all that time, and the rattle has only just started, I reckon the gaps are probably not the cause. Must be wear elsewhere.

But if you think the noise has lessened a little, by reducing the gaps, then maybe it's wear in the rocker bushes/shaft/rods?
Lawrence Slater

Lawrence

It has always been there in a lesser or greater degree. It is not - I hope! - of a "Good grief I must do something about that" magnitude, rather a persistant, possibly even inherent, noise. Yes, rocker bushes and shafts did spring to mind....but perhaps I am worrying over nothing.....
Mark O


My 948 had an odd rattle. When I did a rebuild, I found the distributor drive gear to be terribly worn, to the point where the gear teeth were razor sharp. I replaced the gear and the noise disappeared.
HTH
Tim
T BURSTON

If it's an identifiable tick, you could time it. I did that when a rhythmic noise appeared after a rebuild, and after counting teeth and links, it had to be the timing gear. I replaced the whole set (which did the trick), then spent many an evening passing that chain through my fingers while watching television, and I never found the slightest blemish in it or the sprockets.

Another mystery.
Nick and Cherry Scoop

Checking with Kent cams website, clearance for the installed fast road cam is indeed 0.4mm or 16 thou - so adjusted them to suit.

It doesn't sound like timing chain - feeble I know - seems to come from the head area. Favourite so far is rocker ....somewhere.....Very tempted by the old saying of if it ain't broke.....
Mark O

with engine running and rocker cover removed, slide in old 12 thouish feeler gauge one by one and see which one/s go quiet then adjust em.

Peter
Peter Burgess Tuning

Peter

To clarify please, insert 12 thou feeler, and if it goes quiet, adjust? To what? Do I also adjust with engine running?

Kent cams specify clearance of 16 thou cold.

Cheers

Mark
Mark O

Adjust with engine off and find loosest point ot he one to adjust, cams, especially if reprofiled ones, can vary to find the loosest point. Then try 16 thou then reduce to say 14, then 12 till tappet nosie goes away. Those are cold setting starting points, if hot I would start at 14 thou.

Peter
Peter Burgess Tuning

You said this noise has always been there scence 2003

Do you have an aftermarket valve cover?

Ive got an aftermarket with the cooling vains on top, I had to grind the inside down in several spots as the valve and rocker gear where briefly making contact

Might try the orginal factory valve cover and see if the noise goes away

Prop
Prop and the Blackhole Midget

Well l for one wouldn't worry about it, if it is valve tappet noise. I would far rather have them slightly slack and a little noisy, than too tight and end up with burnt valve seats.
Guy W

Could be worn rocker arm bushes. When I replaced mine it was a lot quiter and felt better when adjusting.
Alex G Matla

Guy...

"noise valves are happy valves"

I wish that was mine, it belongs to trevor jessie

Prop
Prop and the Blackhole Midget

Peter

Understood, but my worry in nipping up the clearances is that I would be deviating from Kent cams specs, that I would burn out the exhaust valve and would compromise performance.

I have fiddled about a bit further re-adjusting back to 16 thou - rattle still present but possibly reduced. I think I can live with it.....
Mark O

If the cam isn't ground to perfection it already deviates from Kent specs. closing down the noisy one/ones minimum to cut noise has never caused us a problem in all the years we have been doing this. But, this is done finding the biggest clearance as you rotate the cam, a problem induced by the grind. Not all things are black or white...at least fifty shades of grey :)

Peter
Peter Burgess Tuning

"Chatty tappets are happy tappets" is the version I like.
Nick and Cherry Scoop

This thread was discussed between 10/04/2015 and 15/04/2015

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