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MG Midget and Sprite Technical - modifications to fit a chain tensioner

Hi Chaps,
I am currently in the process of building up a 1275 engine for my midget rebuild.
I didn't have an engine with he car when I bought it. However I managed to pick up a Morris Marina 1275 engine and am building this up.
I have had the flywheel machined to fit the crank and have a Midget front and back plate and chain cover.
However looking over the engine tonight I noticed that the marina has a chain tensioner. I have heard that is a good addition to incorporate this into the engine rebuild.
However the only way I can see to do it is to use the marina chain cover. This fouls a reinforcing piece on the midget engine front plate (which I have to use as it has the engine mountings on it). I could modify the plate by grinding off about 1/2 inch of the reinforcement..
Is this a good idea, or should I ditch the tensioner and go with the midget chain cover?
Any help would be great
Cheers
Tim
T Dafforn

Iirc the biggest effect of the tensioner is reduced chain noise.
And thinking about it logicaly when the camshaft is driven you have torque from the chain working against the pressure of the valve springs, this guaranties that there is no (or as little as posible) slack in the timing.
This is also why you should only rotate your engine in the driven direction when setting up your cam timing.
Onno K

Hi I would stick to the standard duplex without the tensioner. The reinforcing plate is there to stop vibration of the front plate at certain RPM. I found this out the hard way when i used a earlier front plate when rebuilding my 1275 from a 1098cc engine and went through a whole series of cracked dynamo brackets and water pump lugs. This was despite having the crank rebalanced and the dynamo bearings replaced. Finally the front plate fractured around the dynamo bracket and I replaced it with a front plate from a 1275 engine with the reinforcing plate. Hey presto! no more problems. That was over 8 years ago!
The timing chain still does not rattle by the way!
Bob Beaumont

On a related question I have noticed that on the exploded views of the A-series engine there seem to be 2 rings either side of the sprocket on the end of the cam which are described as tensioners. There were no signs of these on my A-series, should I be worried?
Cheers
Tim
T Dafforn

which parts diagram are you using? They do not appear in the factory parts manual or the Moss website.
http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=1378#52
David Smith

The small-bore engines with a single row chain used two rubber rings on the crankshaft sprockets to provide some tension to the chain.

They were not used with a duplex chain/sprocket set-up.
Dave O'Neill2

Tim,

As Dave says, utem 25 shown here for a Classic Mini with a Simplex chain:

http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=18722&SortOrder=126
Doug Plumb

Anyways, in answer to your question: cut the reinforcing strip to size.
The tensioner helps take out slack caused by wear.
Alex G Matla

This is exactly what I have...Marina block, duplex chain, marina timing chain cover and a tensioner.

I acquired the engine already modified as such and saw no reason to change it when I rebuilt it.

More pics here
http://www.eatworms.org.uk/mg-midget/projects/94-midget-engine



Dean Smith ('73 RWA)

Dean

I see you don't have the generator mount reinforcement, as mentioned by Bob.

Have you not had any problems with it?
Dave O'Neill2

I cant say that I have - the engine came from a Minor enthusiast and I fully rebuilt it. I've done 5000+ since and I have no idea how many it had done prior.

Now its been pointed out I'll have a good look around next time I'm under the bonnet - but there were no signs of stress or cracks on the front plate at the rebuild.
Dean Smith ('73 RWA)

Ditto me too. Probably 15 years with Duplex and tensioner and nothing to report.
F Pollock

This thread was discussed between 19/02/2013 and 24/02/2013

MG Midget and Sprite Technical index

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