A Full Guide to Owning or Buying a 320si with Costs

The 320si is BMW’s homologation special for the 2006 WTCC S2000 race series. BMW was left in need of developing a handful of these limited edition cars in order to meet the regulations for the WTCC series.

With 2600 ever made and only 500 coming to the UK market these cars soon became collectors cars found in the hands of enthusiasts.

The 320si boasts unique 18 inch wheels, bigger brakes (300mm front and rear), a quicker differential ratio and a couple of interior touches like the limited edition stop start button to name a few. Most notably however was the engine, this N45B20S (S meaning it was developed by BMWs M division) was specifically designed to rev higher, increased bore and valve sizes. This engine is made immediately recogniseable by the carbon valve cover it boasts, a lovely touch to its motorsport heritage as well as weight saving. This engine is capable of pushing 170hp at 7k rpm.

Sounds fantastic so what’s the problem?

The cylinder liners in the N45B20S are made from aluminium, something almost unheard of for a road car engine and for good reason. With improper warm up and poor care these liners crack, causing a loss of compression and occasionally chunks of liner can come off and wreck havoc in the engine too. There’s only one real solution to this, to resleeve with steel liners, as should have been done from factory. Even with gentle driving, all original aluminum liners will fail at some point in the car’s life.

Has my car got steel liners?

If you have a 320si with a decent number of miles on the clock, over 80,000, chances are that the previous owner has already had this work done. We have seen cases where they have failed as early as 40k and some not until 80k and beyond. If you experience a loss of power or compression and starting problems, I would recommend getting this looked at by a specialist ASAP before it fails on you.

With an endoscope it is quickly apparent whether the car has steel or aluminum liners, cross hatching is a very tell tale sign of steel liners. Dull grey color, with no markings and perhaps cracks if you’re unlucky will indicate original aluminum liners.

It is worth mentioning that even if you have the upgraded steel liners, sometimes they don’t stand the test of time. We have seen several cars suffering from poor resleeving work, causes by errors or lack of knowledge in these engines from the machine shops.

How much does it cost to rebuild with steel liners?

We won’t beat around the bush here. Machining and resleeving cost for the liners is in the region of £1500. Using a mixture of aftermarket parts where possible, and OEM genuine parts where they are not available is about £700, assuming no major damage has occurred. For an entire rebuild, expect it to set you back about £3-4k. This will be less if we rebuild just the engine, with no engine removal and installation required from the car. Every engine rebuild is different and special consideration is taken with each to make sure any parts with undue wear or damage are taken care of. We always warranty our engine for a full three years after any rebuild, we are confident in our workmanship and the quality of parts used.

Yes it’s not a cheap rebuild but there is good news. These cars will keep there value. At the current market a 320si with good history and condition with steel liners will fetch £5000 easily and can even reach £7000 for a very clean rebuilt example. Whereas cars with failed cracked liners will go for nearer £1000 or £1500.

Rebuilding and resleeving to steel liners

Here at Element Performance we are proud specialists in the 320si and as owners of them ourselves we love these cars as much as you do. We offer full rebuilding services as well as resleeving options to the upgraded steel liners. We work alongside some of the best machine shops in the UK to deliver this service. We carry out a range of work, from diagnosing problems to servicing requirements such as valve shim adjustments, which are often overlooked on these cars. Unfortunately we see a lot of problems created by garages being unfamiliar with these engines, so if you own a 320si we would highly recommend seeing a specialist or seeking advice from one.

320si Servicing and Valve Adjustments

The N45B20S shares a drivetrain similar to that used in the E46 M3, S54. These shims need regular adjustment otherwise they can fall into the engine, causing many problems. If neglected the finger rockers can experience bad wear as pictured and will need replacing.

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