1.8 bmc diesel engine cautionary tale

[Frank mellin]

My boat is fitted with a 1.8 bmc engine which has been regularly maintained and oils checked and changed.
the other day i was running the engine prior to a trip out when it suddenly started to increase speed until it was screaming like a banshee with plenty of smoke.
I managed to stop it before a rod came through the side.
I took some advice and was told most likely cause was air breather problem that resulted in oil being drawn into combustion.
Checked all pipes and filter no problem.
Then decided to dip oil level and horrified that level was twice as high as should be!
On investigation realised that approx gallon of diesel fuel had contaminated oil which had resulted in the subsequent detonation problem.
How did the diesel get into the oil I asked.
Turns out that the lift pump main diaphragm had failed without any warning and had then dumped fuel into the sump.
Replacing the lift pump is a cheap repair but the potential to destroy the engine horrified me.
Will probably replace with an electric pump to ensure that this problem never occurs again.
Had I have been out at sea the implications dont bear thinking about!

 

[Jim@sea]

Regarding BMC 1.8 Diesel Engines, obviously you know they are all probably around 56 years old.
In the early 1970's at my garage we were dealing with a fleet of 1960's Austin J4 Diesel Vans which were fitted with these engines some had extreme mileages 350.000 miles We found with these lift pumps that the metal of the arm which rested on the camshaft was (deliberately) made of softer metal so that the arm would wear rather than the camshaft lobe, with the result that a lift pump with a worn arm was not giving a full rise and fall so that not all the fuel which could be pumped was being supplied.
I recently mistakenly bought a boat with a 2.5 BMC Diesel Engine (Thornycroft) thinking that like MGB engines, parts for these BMC Diesels would be easy to get. I was mistaken
Try and get a Water Pump to have as a spare. I could not get one. I could have mine serviced bit to get one as a spare was impossible.

 

[Frank mellin]

Hi
interested to hear from someone who has knowledge of these engines.Obviously to achieve starship mileage they must have been fairly robust if primitive in their engineering.
From your experience with them did you ever come across the lift pump leaking fuel into the sump as it seems to be an absolutely ridiculous design fault.
I was surprised that you cant find spares for your engine as lots of sites seem to cater for these engines and people like asap seem to stock lots of bits.

 

[Jim@sea]

Hi
interested to hear from someone who has knowledge of these engines.Obviously to achieve starship mileage they must have been fairly robust if primitive in their engineering.
From your experience with them did you ever come across the lift pump leaking fuel into the sump as it seems to be an absolutely ridiculous design fault.
I was surprised that you cant find spares for your engine as lots of sites seem to cater for these engines and people like asap seem to stock lots of bits.

With the lift pump, isent the Diaphram a rubber thing moulded to cloth. If these engines were made today they would probably have service replacement schedule of replacing it at 5 years.
Although its a few years since I had a garage, when I bought this boat with the BMC diesel knowing how easy (simple) they were to work on I thought that as I was intending to sail the boat to Brittany where I had a mooring I would get a second hand engine, get it bored, new pistons, shells, have the crankshaft checked and ground (if necessary) new cam followers, oil pump, water pump, everything to make a good replacement engine.
And after spending 25 years with a garage doing engine repairs and a lot of what I did was sourcing parts, I felt confident that I could get all the bits I needed to put together a Replacement Engine. But I was wrong. I did not feell happy about Motor Sailing all the was to Brittany with the existing engine which was new in 1986, I sold the boat.
In hindsight in 1982 I bought a 1973 Nauticat with a Perkins 4236 Diesel Engine and since then having had Massey Ferguson Tractors fitted with the same 4236 engine these parts are available virtually off the shelf.