The correct battery for a Murena (and a Bagheera) is an '049' battery.
This code denotes the physical dimensions, the types and positions of the terminals (as on the right here)the clamping arrangements, and possibly the power level. However, it is not very common judging by the number of stockists that keep it 'on the shelf'. The '048' (lower image) in fact tends to be much more common and more likely stocked. The only difference between the 048 and 049 is that the positive and negative terminals are reversed, so it will not fit without some minor modifications.
If you are prepared to do these modifications, you will have access to more batteries, as the MX5 used to fit an 048 and there are many of those around! The batteries are also slightly more powerful these days. The original battery was rated at 265 CCA (cold cranking amps) and 35-40 Ahr whilst the newer ones are up to 330 CCA (commonly 300 CCA) and 40-45 AHr within the same physical size case. This physical size is important. The Murena needs a battery that is no wider than 135 mm. Most common batteries are 175 mm wide and if you fit one of those you will not be able to fit the tools back in their designated place. To fit the '048' battery you will have to make up, or have made, a slightly longer earth lead and replace the original. Then simply shorten the positive lead and fit the 048 battery. Whilst shortening the positive lead you can eliminate that terminal for the lead to the circuit board and get rid of one potential problem area too.
Other possibilities are the 053 or 154 battery, which are very similar to the 048 but do not have the hold down strips along the base of the casing, which the original hold-down brackets clamp on. As these batteries do not have these ridges so you will need to devise another method to secure them. One suggestion is the 'L' shaped strip along the top edge and two hooked rods to clamp it, like you see on some other cars. You can often buy these parts as a kit from parts suppliers. Batteries should always be clamped as it reduces the wear from the heavy battery moving around and helps improve their life. The other possible difference are the terminals which may be the smaller Japanese terminal posts so you will need the converters to bring them up to the standard size.
Finally, if you don't mind paying more for a superior battery, you could go for an A.G.M. battery. The only one I know of in the U.K. that will fit is an Optima 'yellow top' YTS 2.7 coil cell design battery which has an even higher spec. and should last much longer as well as hold its charge far better. It is rated at 460 CCA and 38 AHr but will cost around GBP130 (in 2019).
The sump gasket is special on the Murena 2.2 and MUST have metal spacers in the gasket. So the gaskets are expensive for a reason. There are many incorrect ones listed so beware that even manufacturers often list the wrong type. e.g. BGA list the Tagora gasket for the Murena - WRONG.
Do NOT fit any 180/2-litre/Tagora gasket as it will not last any time at all, and since it is such a big job to change usually involving the engine out, you do not want to do this a second time because you used the wrong one!
First of all, if you examine the installation, the engine is mounted, not on the block like most cars, but on the sump and the gearbox. So think about it - since the engine is mounted on the sump not the block, the engine MUST be rigid with the sump, especially since the gasket is cork. If you only have a soft gasket (whatever type) it will soon get damaged by the power unit vibrational movement, and it will be leaking again in no time. So don't try to use the Chrysler 180/2-litre/Tagora sump gasket. If the engine is rigid with the sump, they will move together and preserve the seal between them.
You cannot simply drop the sump off to replace the gasket, like a conventionally mounted engine, without making alternative arrangements to suspend the engine! Since the long (RH) driveshaft runs in a bearing held in a non-removable sump casting, it has to be slid out which involves removing the RH trailing arm. If you decided to do the job, leaving the engine in and suspending it, before you drop the sump, you MUST remove the oil level sensor otherwise it is going to get damaged, and they are no longer available.
However, I have usually found that not only is the sump gasket leaking, but the timing case seal is often leaking too, and as you are removing the sump, you might think this is now the time to do it. Taking off the lower timing case involves removing the cylinder head and upper timing case too, as well as the water pump and crankshaft pulley, and the sump mounting normally gets it the way of the latter. You might wonder why you need to remove the cylinder head, and the reason is the way the head gasket is one piece incorporating the block and timing case, and compressed as the head is torqued down. Also the timing cases are dowelled to the block vertical face. You cannot refit a timing case onto these dowel sleeves certainly without being able to compress the gasket or damaging them. Removing the water pump means tilting the engine away from the RH inner wing, which is more difficult when you have the engine suspended, and since you really need the head off too, it is getting to be more of a full engine strip down.
To angle the powertrain, for the water pump to move away from the inner wing, you have to release the gearbox mounting and lower that end, and what you would now have suspended is no longer just the engine, but the complete powertrain on an angle! And you must remove the original air box on a Prep 142 or S, if still fitted, otherwise it will foul the fuel tank. Finally, removing the crankshaft pulley and the lower timing case whilst the engine is temporarily suspended in the engine bay, is not particularly easy either. Also, while you are fixing oil leaks from the engine, you need to check and make sure it is not leaking from the rear crank seal. This is not a lip type seal as with more modern engines, but a cord type seal set into a rear block housing cap; with a reverse scroll and thrower on the crankshaft to deflect oil away from it. (This is similar to old BMC engines if you have ever worked on them.) If you do have any leak at this point, then you have to remove the crankshaft to fit new cord seal halves, so you can see the job becomes one where removing the engine is definitely the easier option!
This is why I normally recommend you take the complete unit out. Yes, it becomes an even bigger job, but not by much, and you will be able to work on it much more easily, and you will be able to see ALL the things that need doing, and do them in one complete job.
The bolts are torqued up on the metal spacers, and the gasket forms the seal but does not take the load. This is why the sump gasket is special to our car and costs a little more. When the original supply of Murena 2.2 sump gaskets ran out, I had some more made up by Cooper-Payne but without the spacers - just the holes to take the spacers. You simply transfer them across from the old gasket to the new one. This is why my gaskets cost much less than others. Mine cost around 35 Euro plus post and packing, where I think you will find others cost much more, possibly twice as much at that time. Please check them out. The choice is yours.
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