Duplex timing chain fitment

[Mr Spigot]

I am looking at fitting a new duplex timing chain to my 1275 midget engine as the current one is rattling and I want to fit a tensioner as well. I have looked at many of the posts on here and replacing the actual gears and chain seems straightforward, but I am not sure if I need to replace the backplate if I fit the later timing cover to accommodate the tensioner (see photos of existing). I know I will have to flatten the breather cannister to clear the fan, but am not clear about the tensioner fitment and how it will work with the existing backplate. Any advice/photos appreciated. Thanks.

[philthehill]

If you want to fit a timing chain tensioner you will need the timing chain cover to suit.
Whilst some fit the tensioner pivot pin without drilling the front engine plate it is best if the tensioner is fitted as per the factory i.e.
the head of the pivot pin is fitted into a drilled hole in the front engine plate. The body of the tensioner keeps the pin in place.
With some 1275cc Midget front engine plates you may have to remove part of the front engine plate strengthening 'U' bar so as to allow the new timing chain cover to fit.
You will need to drill at least one extra hole in the front engine plate to accommodate additional holding bolts for the new timing chain cover.
You will need to fit and Loctite in place countersunk screws to secure the bottom of the front engine plate. They replace the two 1/4" UNF bolts.
The fitment of the duplex chain and sprockets is a simple job helped if the front engine plate is removed to drill and countersink the required holes.
Grease the front plate gasket before fitting.
Below is a 1275cc front engine plate with all the required holes drilled, countersunk and the strengthening 'U bar shortened.

Front engine plate 1.JPG (929.07 KiB) Viewed 1103 times

You may have to remove the dimple from under the timing chain cover ignition timing sensor bracket and the baffle ring inside the timing chain cover as per timing chain cover below.

Timing chain cover 1.JPG (1.27 MiB) Viewed 1097 times

Timing chain cover 3.JPG (1.3 MiB) Viewed 1097 times

[philthehill]

Tensioner as per photo below:-

Tensioner 23.JPG (638.94 KiB) Viewed 1090 times

Duplex and timing chain tensioner as fitted to my 1380cc 'A' Series engine:-

timing chain tensioner (1).jpg (1.18 MiB) Viewed 1084 times

[Mr Spigot]

Thank you Phil. That is just the information I needed. Would it be easier to prepare another engine plate first and then swap them over?
Looking at the tensioner, it seems to consist of 3 parts, the rubber tensioner, the base bracket and the pin. Is there a spring as well?

[philthehill]

I would recommend that you obtain a spare front engine plate and modify it prior to fitting. It makes the job so much easier.
There is a spring but it is part of the rubbing pad.
You fit the tensioner assembly and then tension the pad against the timing chain. It does not have to press hard against the timing chain just firm pressure. If the pad is pressed hard against the timing chain then rapid wear of the pad will occur.
Having a classic Mini 'A' plus front engine plate helps as you can hold it against the plate to be used and it will then give you the location and size of the additional holes required.
The classic Mini 'A' plus front engine plate cannot be used for anything other than a pattern as the plate does not have the two engine mounting lugs.
Below is a 'A' plus front engine plate which shows the additional holes required for the tensioner and cover.

A Plus timing gears.jpg (87.48 KiB) Viewed 1027 times

[Mr Spigot]

Many thanks. A clear and very helpful explanation. I can now prepare a shopping list!

[svenedin]

Phil,

I have read this and previous similar threads with interest.

Can I ask you a few points about this please.

1) Can a Duplex chain be used with the tensioner or is the tensioner (12G2621) only for a Simplex chain?
2) Will the timing chain cover with the squashed breather canister (LJR10168) fit behind a standard 1098cc metal fan or will the fan collide? If so should the cover without canister CAM4904 be used instead?
3) What is the advantage of a tensioner set-up as compared to an ordinary Duplex chain? Is it that the chain is less likely to rattle about as it wears?

Stephen

[philthehill]

To answer the above questions.
1. The tensioner can be used with the duplex set up - see my photo above.

2. a. If you fit a non squashed breather/timing cover the fan will hit the breather.
b. You can use the non breather timing chain cover but it is better if the cover has the breathing facility.

3. The advantages are:-
a. The timing stays correct for longer.
b. The timing chain/sprockets last longer.
c. The timing chain noise is reduced.

The tensioner presses on the return side of the timing chain so removing any possibility of chain slack due to wear.

[svenedin]

To answer the above questions.
1. The tensioner can be used with the duplex set up - see my photo above.

2. a. If you fit a non squashed breather/timing cover the fan will hit the breather.
b. You can use the non breather timing chain cover but it is better if the cover has the breathing facility.

3. The advantages are:-
a. The timing stays correct for longer.
b. The timing chain/sprockets last longer.
c. The timing chain noise is reduced.

The tensioner presses on the return side of the timing chain so removing any possibility of chain slack due to wear.

Thank you for a very clear explanation.

When my engine is rebuilt which is hopefully quite soon I will seriously consider these modifications. My engine has a duplex without tensioner at the moment and I would certainly not go back to the simplex and all of that awful rattling.

Stephen

[Jim McCrae]

The fan clearance issue can be simply resolved by fitting a spacer as used on the classic mini.
https://www.minispares.com/product/Clas ... o%20search

[philthehill]

Not absolutely true
The spacer can bring the fan forward to clear the breather canister but it brings the fan very close to the radiator core and if the engine moves forward under braking the fan can rip into the radiator core with disastrous results.
It is better to have the squashed/modified breather or do away with the timing chain cover breather completely and fit a breather canister to the unused mechanical fuel pump aperture (if it has one).
The classic Mini engine to radiator clearance is fixed due to the classic Mini radiator being attached to the engine/gearbox by appropriate mounting brackets. With the Minor the engine to radiator clearance is not fixed as the radiator is fixed to the body and the engine is able to move forward (under braking) on its engine mounts.
The main reason that the gearbox steady cable was fitted was to stop the engine moving forward under braking and fouling the radiator.

[Jim McCrae]

Phil
I don't see that is an issue. I have this fitted to my 1275 engine, A 4mm spacer gives adequate clearance for the breather and is still 40-45mm from the radiator. The engine steady and gearbox restraint should restict engine movement and prevent any contact with the radiator (in normal use at least).
Jim

[philthehill]

Jim
You are right in that it will fit and clear the radiator but be very close.
Saying that -not all engine steady bars and gearbox restraint cables are in good condition. Also not all engine mount towers are the right way around which can push the engine forward by 20mm.
Care must be taken if fitting a fan spacer and if it works very good but it does not always work out that way.
It would be very remiss of me not to point out the possible effects of fitting a fan spacer.
Phil

[Sleeper]

... and then you have the different thicknesses of the radiator cores...

John ;-)