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MG MGB Technical - Timing chain rattle?

Hi, my 67 MGBGT has an awful rattle when first starting up and ceases when oil pressure builds up. I only really hear it again when accelerating at about 60 but soon goes away - it is not 'pinking', sounds slightly different. It does not sound like big ends either. Is it the timing chain/tensioner - I read previous questions that said the tensioner is spring loaded and also oil pressure assisted, or have I read it wrong?
Can members please suggest and answer?
If it the chain or tensioner, do I replace both at same time.
Appreciate your thoughts
Pete
Pete Dyble

Pete - the chain stretches and up to a point, the spring-loaded tensioner takes up the slack. There comes a time for change.
Roger W

The 'start-up' rattle doesn't sound like the timing chain, if it goes when the oil pressure builds.
Dave O'Neill2

To answer one of your questions - the chain tensioner is definitely not oil-assisted! Obviously oil splashes around, which will have some effect, but I don't think it is chain/tensioner either. Could be tappets loose in the bores, or rockers loose on the shaft.

Does it do it after being switched off just for a few minutes? Or only overnight or longer?

You could also try cranking with the coil disconnected until you get oil pressure, then start, and see if you get the rattle or not.

One would normally change the chain and cogs, maybe the tensioner, but a slack chain usually shows itself as timing jitter when using a timing light. Mind you that will also happen with slack anywhere in the path from crank to distributor rotor.
Paul Hunt

Pete You could try removing the fan belt,and starting the engine, if the rattle is still there you know it is not the Dyno. or water pump. My roadster recently developed an engine rattle, turned out to be a bearing in the alternator.
Trevor Harvey

What kind of oil pressure readings are you getting from your gauge while cranking the engine before startup? What are the readings when the engine starts and what are the readings when you're doing 60? Depending on your readings, this could indeed be rod bearings on the way out. I have a twin cam Ford Escape, in the driveway right now, that was making a bit of noise, was down on power and was using a lot of oil. After dropping the pan and removing the balancer shaft assembly, it was obvious that number three rod bearing cap was nowhere to be found. However, there were two holes, one in each side of the engine, where the rod had gone through the block rendering it useless. Please, don't let this happen to you! Track down that noise before it's too late. RAY
rjm RAY

The tensioner is supplied with oil under pressure and that does have some effect in pressing the slipper against the chain.

Rattles rarely come from the chain - far more likely to be rocker shaft noise.

Chris at Octarine Services

The tensioner is supplied with oil under pressure, both to lubricate and tensioner assist. I've also had a new tensioner last less than 2000 miles. That poor product issue again!!
Make sure you using an oil filter with a good non return valve. Mann seem to be the best. If the oil drains back it takes a frightening time to build up pressure and cut the rattles.
Allan Reeling

"The tensioner is supplied with oil under pressure"

Well you learn something every day. Was this a mod to later engines? The Workshop Manual only talks about an "Oil bleed to chain".
Paul Hunt

Chris,
Since this is a relevant to the issue under discussion, I am going to suggest that the chain tensioner is spring operated - at least mine is. The oil line provides lubrication and perhaps a damping effect.
Pete,
As others have suggested; a long screwdriver and your Mk1 ear while someone starts the beastie for you - will tell if the problem is on the rocker shaft. Only be careful ( a stethoscope is better if you know a doctor).

Pse let us know the outcome
Roger W

No - the oil has always been supplied to the tensioner and yes it is spring loaded but the oil must add something as there is only a small bleed hole in the face of the slipper. Rough guess as I have never measured it I would say the oil pressure off the front cam bearing is around 25psi which would result in about 5 lbs of force at the slipper plus whatever the spring contributes.
Chris at Octarine Services

As I understand it the slipper rests on the chain. Unless there is some part of the chain blocking the hole you won't get any pressure in the hole, it will just dribble or bleed out over the chain as it passes by.
Paul Hunt

Hi all and thanks for all your comments.
I have taken the rocker cover off this morning and checked the tappet clearance and was suprised to find that all but one was quite loose and two had clearances where 0.25" feeler easily went in. Adjusted them to 0.15" slide fit and rattle radically reduced on cold start. There is still noise, not excessive, when on tick over, but I think it is an accumulation of wear throughout the engine system. RAY, the oil pressure roughly is 65-70psi when cold, 50ish when hot at about 60mph and it drops to some 25psi on tick over - does this seem OK?
Thanks ALL for help.
Pete
Pete Dyble

It's perhaps a little low hot running - the book quotes 50 to 80, but given the hot (I assume) idle of 25 which is good (book quotes 10 to 25) the lower hot running is more likely to be the pressure relief valve opening at too low a pressure. Could be a weak spring, or a poor seat.
Paul Hunt

Those pressures are very good. But keep a close check on the rocker clearances, 25+ thou is a tad gappy, depends how long it took to get that large. Also have a look at the rocker pads, if they are worn even using the correct feeler gauge can still result in too large a gap. I've also found that the "rule of nine" method doesn't always result in correct, back of the cam lobe, clearance.
Allan Reeling

Pete, your oil pressures are in the safe range. Most likely, the culprit is your oil filter which is allowing the oil inside it to drain back into the sump overnight. When you start the car the next morning, the filter housing is empty and the oil pump must first fill it before the rest of the engine sees pressure. You're hearing the big end bearings rattle due to lack of lubrication and the rotors, in the oil pump, are starving for oil at the same time. I replaced the stock oil filter on my '678 B with the later style inverted spin on filter due to similar problems and the noise went away. RAY
rjm RAY

bit late now, but anyway........I thought I had a chain rattle, but turned out I didn't. I do have the 3 blade metal fan (73BGT). The wee rubber bushes have perished away (those that the studs that hold the fan on the pump), and this makes the fan make a horrible noise at idle - sounds really serious. Check to see if your fan has a little play - it doesn't go anywhere, just makes a nasty noise. Well, when i say nasty, its not so bad as I needed the excuse to convert to an electical fan anyway - just couldn't see my way to getting rid of somehting until it was misbehaving!
Mick Rae

Thanks for reply Mick, but I have an electric fan installed already.
I am very interested in RAY's point about oil draining away and starting dry before oil pressure builds up. I get the rattle after only a hour or so standing before pressure build. My oil filter is paper and the canister is upright next to the engine via a aluminium casting connected to where the canister was fitted to engine downwards. My previous MGB engine was like this and I was pleased when I go this engine that it was mounted upwards, but I did notice when I took it off there was no oil spillage as it had drained away. Surely there must be a non-return valve to stop oil draining away to prevent dry start up? Is it best to remove casting and fit oil filter canister upwards into the engine - this would ensure oil is always in filter? What do you Guys think?
Many thanks for comments, Pete
Pete Dyble

personally I when I had a paper cartridge type I swapped it straight away for a spin on disposable, changing oil is messy enough as it is without farting around with the older type of filter
Nigel Atkins

Pete,

What filter are you using. Some have the anti-drain valve, some don't, and some have them but they don't work. Can you get a Mann W-917 filter? I have had good luck with them. Check to make sure that it works on your filter head. Also, do you have the stand pipe in your filter base?

Charley
C R Huff

Nigel, I am not worried about mess, it is only once a year, what I am concerned about is no oil at start up. Is it normal for either paper or spin on to drain on standing so the oil pump has to fill the filter before the oil gets to the bearings on start up? What else causes the bearings to rattle for 2 -3 seconds before quieting when the oil pressure builds.
Charlie, It is just a paper element and I am not sure if I have a stand pipe or not. It is just an aluminium outer case with a long bolt through the middle and it houses the paper filter.
Thanks Pete
Pete Dyble

Pete,

I guess I took a wrong turn somewhere. I thought you had a spin-on conversion that sat with the closed end of the spin-on pointing up so that it was prone to draining.

If you have the cartridge type that has the open end up, and the closed end with the bolt head pointing down, then I would not think draining would be a problem.

Got a photo?

Charley
C R Huff

I'm confused now. You say "the canister is upright" but do you mean hanging i.e. with the body of the filter below the head attached to the block, or inverted i.e. with the body of the filter above the filter head attached to the block. The book shows the replaceable element with the bolt going through the middle as hanging, it is the later cartridge type that were inverted, with a few months of being hanging for some reason.

The hanging filter can't empty (unless it is dripping on the ground), but if it only takes 2-3 secs for the rattle to stop that is just refilling what has drained out of the ports.

The inverted will drain if either or both of the anti-drainback valve inside the filter - visible through the holes around the edge of the base-plate, or the stand-pipe pressed into the filter head, are missing. The former stops oil draining back through the pump, the latter through the bearings. Removing one of those, especially hot, should make quite a mess after the seal in the filter comes away from the head. The attached shows the stand-pipe.

An empty filter takes quiet a bit longer than that to refill. Having said that 2-3 secs if it has only been off an hour is longer than I would expect, pressure on the gauge should be virtually instantaneous. What does you gauge register in relation to this noise stopping? A rattle while pressure builds is indicative of bearing wear somewhere.

Paul Hunt

Thanks for photo Paul, I have attached two of my oil filter for clarification. The first is how it is in engine and the second shows it open after 1 day standing, i.e. dry. It does not look your photo Paul. is there something missing on my casting?
On start up, it is about 5 seconds without reving before the oil gauge starts to rise.
Again, my question is - should there be oil in the filter canister, if so, is the 'extension casting' faulty or am I wise to remove the casting and screw the filter canister directly up into the engine?
Appreciate all your comments and time.
Thanks
Pete
Pete Dyble

Having trouble uploading photo's, may have to upload them twice.

Pete Dyble

Second photo

Pete Dyble

There were three types of filter fitted - early ones were like the MGA and hang down with a paper (originally felt) element inside a steel case with centre bolt.

Then they moved to an upright filter of the same type - also shared with the MGC.

Finally they went to the upright screw on disposable type that has the stand pipe fitted to the adapter to reduce drain down.

The middle type does suffer drain down and there is little you can do about it, but I really would not worry too much as long a oil pressure comes up in a few seconds.
Chris at Octarine Services

Not seen the inverted element type before. Unless there is an anti-drainback valve in both ports of the filter head that type is likely to empty the filter when switched off.
Paul Hunt

This thread was discussed between 08/09/2013 and 30/09/2013

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