The BMC 1.5 was the most favoured engine for inland marine propulsion from the 1950s, through to the early 1980s. Its simple engineering and solid construction made it hugely reliable and dependable with many people using terms like “bullet proof” to describe its suitability for the task.

So good were these engines that they are still performing today. Heavier and slightly noisier than modern-day replacements, they’re surprisingly frugal on fuel and, given the honest option to install a modern Nanni or Beta engine or a rebuilt BMC 1.5, we’d install the English engineered engine without hesitation.

The BMC 1.5 is a great engine, but it needs regular serving and maintenance to keep it in good condition

Whilst some parts are now getting more difficult to come by as new items, the BMC 1.5 Diesel is still highly regarded with many sources for second-hand parts. But there are some that believe that these engines are virtually unbreakable. They are not. Abuse will see the untimely death of a BMC 1.5 whilst regular care and maintenance it likely to see such an engine easily reach its 60th Birthday, and quite possibly without multiple rebuilds.


Overheating any engine is never a good thing. For many modern alloy engines, overheating can signal a swift death as the heads are prone to cracking, particularly with Kubota v1505 derived engines. Overheating a BMC 1.5 to the point of heat seizure is bad. Whilst we would not fully expect the head to crack at this point, it’s quite likely to warp slightly. Worse, you’re in danger of damaging the crank shaft which may flex slightly. Once cooled down, the BMC will probably run again and likely with no obvious running defects. But, the flex in the crack shaft will introduce a weakness and, possibly, at some point in the future, the crank may snap. Always keep an eye on your temperature gauge and if you haven't already fitted overheating warning lights and buzzers, seriously consider it.

Timing Chain

The timing chain in a BMC 1.5 is built to last many years but with so many moving parts, wear is inevitable. For the majority of its life, the tensioner on the chain will take up the slack and wear will not be noticed. However, when chain is so worn that the tensioner can’t make it tight enough, the engine is likely to be very smoky, particularly at cold idle and less so under load. No adjusting the injection timing adjustment will cure this. Truthfully, you’ve gone beyond the point of the timing chain needing replacement and should get it attended to before one of two things happen; either the chain will break or there’s a danger of the chain jumping a sprocket. Both of these outcomes will wreck the engine.

A replacement timing chain and tensioner arrangement are inexpensive spare parts and in many engine compartments, there will be enough access to change the timing chain without removing the engine, though this is never guaranteed.

Fuel Filters

All engines need clean fuel and the BMC is no different. Always replace fuel filters on a regular basis as the tiny non-return valves in the fuel pump will fail if they have some crud lodged in them which will signal a breakdown and likely need for a replacement fuel pump (which is often cheaper than trying to service the existing one).

Injector Pump - Important

In recent years, petroleum manufacturers have modified the ingredients of red diesel and it’s additives now have an adverse effect on the seals within a BMC’s injection pump. Leaks are growing in number and you need to keep an eye on this as a leaky pump may not be obvious.

  • Keep a regular check on your engine oil.
  • Does the level appear to be rising?
  • Is there more of a Diesel smell to it?

Often the first seals that begin to leak are those on the injection pump drive shaft as this is under constant pressure. The problem is that the leak is straight into the oil sump and can go unnoticed for some time. Too much diesel in the oil could cause the engine to “hydraulic”. This means that the engine will begin to run on the oil in the sump rather than the fuel. The result is that the engine increases speed, often very quickly, and it can easily spin out of control. Once the lubrication in the sump has been burned as fuel, the engine will seize and in some cases may destroy itself by throwing a connecting rod out of the side. None of these scenarios are pleasant and can be very dangerous. The only way to stop it, if you dare, is to starve it of combustion air.

BMC diesel engine fuel pumps are prone to this failure with modern fuel. If you have not had your injection pump serviced in recent years, you should seriously consider this.

Having the injection pump serviced is not cheap, but the replacement seals will not be attacked by the modern fuel and, at the end of the day, if your pump is original, it’s already well overdue an overhaul.

Kingfisher Boat Services offers a pump reconditioned BMC 1.5 Fuel Injection pumps on a service on a service exchange basis at a very competitive price. However, there are many variants of pumps in use and only the most common will be offered on an exchange basis; older type units can be reconditioned but with a delay for the work.

We'd be happy to carry out the removal and fitting work for you if you would prefer not to do this yourself.

Contact Us for Pricing