Timing chains

BMW and MINI use Timing Chains in almost every model of engine that they produce but only a small number of engines are actually affected by an unpleasant metallic rotational grinding noise or worse failure.
The most common is the N47 4 cylinder diesel engine which is fitted to the following models:

• 118d
• 120d
• 123d
• 318d
• 320d
• 520d
• X3 2.0d

If you were to search the internet regarding this subject it will not take you long to realise that BMW have had their fair share of negative press, and the issue was brought to light back in June 2013 by Watchdog on the BBC. The engine in question was the 4 cylinder diesel designated N47 which is fitted to vehicles between 2006 and 2012 although vehicles outside of this production date can suffer failure too often caused by overdue engine oil servicing.

What exactly is a Timing Chain?
The timing chain connects the moving parts at the bottom of the engine to those at the top very precisely so that all components move in perfect time with each other. If the timing chain breaks the lower engine parts such as the pistons come out of time with the upper moving parts such as the valves causing extensive damage. Although an all round brilliant 4 cylinder diesel engine unfortunately the N47’s weak point is its timing chain and it has two - an upper and lower. The problem is not helped by the fact that they are positioned to the rear of the engine which is extremely inaccessible as the timing chain was not designed as a serviceable item and to replace them the engine should be removed.

Is it expensive to repair?
Each failure is different often depending on how fast the car and engine were moving at the point that the timing chain failed. The best case scenario is that if the car was moving at a slow parking speed and suddenly stopped the impact of the valves hitting the pistons may not have caused them to bend and usually the camshaft carrier cracks and the pistons are just marked. In this case all of the timing chain gear and tensioners will need to be replaced with the later modified type. This stage of repair will usually cost from around £1900.

Worst case scenario is that all of the 16 valves are bent and catastrophic damage has been caused to the camshafts, pistons, connecting rods and crankshaft – combined with metallic contamination to the complete engine oil circuit in this case the most economical repair can be to replace the engine complete. It is not uncommon for garages to charge anything from between £2500 to £5000 and even up to £8000 if the complete engine is required to be changed.

What’s involved in the repair?
At Turner Automotive we have over 20 years of BMW experience and have seen every possible type of timing chain failure. Our BMW Master Technician has a specific engine rebuild program that means we only repair what is required as we know exactly what the best repair is for the engine and for your pocket. Rectifying catastrophic engine damage is a very labour intensive and expensive task. As the timing chain is positioned to the rear of the engine near the bulkhead, the engine must be removed and completely stripped down to assess exactly what components are damaged and require replacing.

All damaged parts are replaced along with new genuine BMW modified chains, guides and tensioners. Each engine failure is different and individually assessed and depending on damage to engine parts, and fluctuations in BMW component pricing, the cost of repair will vary.

Can I prevent my Timing Chain from breaking?
If your timing chain is noisy and not broken you can take preventative measures. Often this complaint is described as a metallic “grinding” “rattling” or “scraping” sound heard mostly from inside the vehicle cabin whilst the engine is idling or at a speed of up to 2000 rpm. If this is the case you could save yourself a considerable amount of money by having the modified type chains and guides installed before they fail.

Beware of cheap remanufactured Engines and rebuilds
Be very wary of companies offering to repair or replace your engine cheaply as they may not be using genuine BMW parts. The timing chain, guides and tensioners are all modified and often second hand replacement engines will not have them installed so you may think you are getting a good re-manufactured power plant but instead it could be from a broken or salvaged car with old type components and you could suffer poor reliability or worse another failure. At Turner Automotive we pride ourselves on customer service and technical ability, our BMW Master technician has over 22 years of experience in the BMW dealer network including 7 years working at BMW’s head office. Feel free to call us or pop in and we will be happy to discuss what options you have to get your pride and joy back to being the ultimate driving machine.