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MG Midget and Sprite Technical - Timing chain

Chaps

What are the symptoms of a worm timing chain on a 1275 A series please. I am aware it rattles, but what kind of rattle, when, and how to definitively determine whether the chain is worn/requires adjustment. I can see no external adjuster so I presume it may be under the timing chain cover - which incidentally looks a complete pig to remove. The crankshaft pulley being about 10mm from the cross member with very little scope for getting a socket on and removing it to facilitate removal of said cover.
Oggers

No adjustment on a 1275 timing chain. Unless someone has fitted an adapted chain cover from a Metro which l think had a slipper
tensioner.

One means of verification of a worn timing chain can be assessed by the degree of scatter apparent when using a timing strobe, if the marks appear to dance around at constant revs this can indicate a worn chain.

Timing cover can be removed if you undo engine mounts and lift the front of the engine by a couple of inches with a jack under the front of the sump to give added clearance for removing damper pulley.
GuyW

Guy

Many thanks - appreciated. Somewhere on the build sheet it mentions vernier adjustment - cannot see it though.....

Sadly no strobe - any other reasonably reliable method for pinpointing timing chain issue would be most welcome. Rattle on overrun on bikes is a fair sign....
Oggers

Presumably the "vernier adjustment" is referring to it having a set of adjustable timing sprockets.

Yes, a worn chain will clatter on overrun but especially at the moment of changing from power on, power off.
GuyW

May we turn the question round - what symptoms or problem do you have?
davidsmith

David

Some ethereal rattling noise at speed from the front portion of the engine - which I am fully prepared to admit could also be valve clearances. Hard to define....
Oggers

There's a saucer shaped oil thrower inside the timing cover. Could that be rattling? As for the timing chain, as others have said there is no chain tensioner of any sort. It's a while since I looked inside an A-series engine, but isn't there a rubber ring round the camshaft sprocket to supposedly keep the chain tight? Or is that only on earlier engines?
Mike Howlett

The rubber rings were fitted with the single-row chain. Also, the oil thrower shouldn't be able to rattle, as it should be clamped between the pulley and the sprocket.
Dave O'Neill 2

I may be wrong with this, and the "pros" and anyone with proper knowledge of these things will provide the correct explanation. But unless you are into racing spec engines I have always thought that a slight to moderately stretched chain isn't likely to make much difference to the running of the engine. - Other than fact you can hear the rattling sound and it begins to bother you.

The reason I think this way is that the cam, and therefore the valve timing and the spark timing is pulled around by the chain, so the leading part of the chain is always under tension and this is what controls the crank / cam relationship. Any slack is on the trailing side of the camshaft. Being slack, that may thrash around and rattle, but isn't playing any part in turning the cam.

Put a new chain in when rebuilding an engine and it should last the life of the camshaft before it needs a new one - then replace both at the sane time. Between times, habituate to the noise, its part of the engine sound. Or wear ear plugs, which I always favour anyway, at the least on longer journeys, anything more than a few miles.
GuyW

I think Guy's summarised it well. Theoretically if the crank is 'pulling' the camshaft round and the chain is stretched then the timimng will run a bit late. The amount of chain stretch can be translated into angular cam degrees to actually measure it, however my gut feel is it's insignificant and 'isn't likely to make much difference to the running of the engine'.
If you can hear the rattle then put the roof down; if you can still hear it drive faster!
davidsmith

Does the chain ever get slack enough to thrash the inside of the cover?
Mike Howlett

I agree with the sentiments, and my concern was taking some preventative maintenance before something terminal happened. That said, the engine has had a rebuild and I appreciate the longevity associated with the chain. There is no detrimental effect to performance, but rather it is the slight increase in noise - rattle if you will - that is bothersome to me. Perhaps I am being over-cautious and perhaps it is the valve clearances in any event. Will check the latter out - easy to do.....
Oggers

On reflection, I have a sneaking suspicion it could be rubbish fuel and the sound is pinking. I normally use the best Shell, but last week I had to fill up at some filthy garage near Aviemore. They only had normal garde stuff and I had never heard of the make - wouldn't surprise me if it was paraffin. Will refuel soonest and listen again.
Oggers

Oggers

If you know for a fact that you have a venier sprocket and you are certian you will need to remove the timing cover,

Then you do have a rather easy fast alternitive approch to doing this

Get a 6 to 8 inch diameter hole saw and drill our the section of rhe timing cover that placed over the top of the viener sprocket. Then just make a secondary gap filler plate with some sheet metaal and gasket cork and gasket sealer nd assemble it back togather with some pop rivits

But by removing just that section of the timing cover you have easy acceas to the vienerr sprocket to adjust it without having to spend 2 days tearing the entire front of the engine off.... its a little bit involved taking and putting the timing cover on and off


I cant remember who bit they modifed 1275 timimg covers just like i said and sold them to racers that needee fast access to there viener tkming chaim sproket adjuster screws
1 Paper

The timing chain on the A series lasts 70,000 miles before becoming unpleasantly noisy. Best to replace when the engine is out. Replace the sprockets too as they are "wear parts".

The chains don't seem to ever fail. They sound like they are hitting the timing cover but don't make contact.

I have the impression that cheap, junko replacement chains are of superior quality to the original OEM parts. They seem to stay quieter, longer.
Glenn Mallory

This thread was discussed between 02/04/2017 and 04/04/2017

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