BMC 1500 will not start when hot

[Bobby b]

Good evening 

New to the forum and after some advise on an on going problem I have we BMC 1500 - a brief history 

Brought a boat as a restoration project  with a BMC  1500 and as matter of course sent for overhaul to local engine company, turned out to be in good order, an overhaled injection pump was fitted also as a matter of course, this engine than ran for about 100 hours in 2021 faultless but  towards the end of the season it would not start when the engine was hot,  if you left in 20 mins to cool down it would start fine, since then the following work has been done on the engine.

 

• compression check  all around 400psi when hot or cold 
• Head removed and inspected [by the company that overhaled the engine] no damage noted 
• lift pump replaced 
• injector pump replaced [another overhaled one]
• injectors checked for correct opening and spray pattern
• new combustor washers fitted  
• fuel filter replaced and water trap cleaned 
• NRV on fuel filter injector pump return line check for correct operation 
• calibrated hole in the banjo bolt on the top of fuel filter checked 

 

Thought it was all fixed until out on the water yesterday and same problem !

 

Engine is turned by a new battery and starter motor which turns fast enough (in my option) 

Temp gauge shows 80 deg which L would say is roughly right, measuring with a infa red gun, cylinder head is around 85 deg, injector pump is about 65deg.

This engine is not fitted with an oil cooler like some I have seen - does it need one? 

 

The thinking is the fuel is too hot and the injector pump can not make the pressure to open the injectors when been turned by the starter motor - possible ? 

it has a 75 deg thermostat fitted - if this is removed the engine runs a lot cooler and starts - (not the answer) would like to get to route cause of this issue  and would like your options please.

Photo for reference 

Thank you Bob 

[john.k]

My guide for worn rotary injector pump is starts coldOK,but wont start easily  with pump and fuel heated to running temp...........however ,two reco ed pumps should eliminate that.........but another however.........the tiny 1.5l motor is lower limit for an effective fuel charge from a DPA pump,and very slight internal leakage has great effect ,than say a DPA pump on a 11.3 l AEC...(upper limit of DPA is around 2 litres per cylinder.)....................when faced with a worn DPA pump on a small motor (4/108 Perkins),my first move was to reduce the set pressure of the injectors.....sometimes considerably ...like down to 1000psi ,and see if that helps ............the other factor is time.....in other words ,starter performance ......try one of the Taiwanese geared starters ,which do whiz over at a much greater rate than a sickly M45G....................EDIT.....to eliminate internal wear leakage in a DPA requires a new "hydraulic head"......this is the black steel part the fuel lines screw onto.......a fairly costly repair......................and finallly ,the Hartridge pump test machines do have facility for heating fuel (and pump) to engine operating temp ,so ask this to be done during test .

Edited April 10, 2022 by john.k

[Tony Brooks]

It this is a sea boat and is used for long periods at high speeds/powers then an oil cooler might be a good idea.

 

The deck boarding looks a very good fit so does it have any vents and have you thought about a bilge blower.

 

Is there any chnace the valve clearances are too tight so the valves are being held open when hot? If so it probbaly would run but not start and possibly not idle.

 

[Tracy D'arth]

The oil cooler often seen on these engines is most likely for the hydraulic gearbox, if yours is a mechanical box it won't have one. Unless it is a sea going engine that gets thrashed as Tony said.

I would suggest that the governor in the pump is not going to full fuel position when stopped so the engine is starved of fuel on a hot start.

A diesel engine only needs compression, fuel, warm air and to spin fast enough to start hot or cold.

Check the valve clearances, hot. Is there a fuel line twixt lift pump and injector pump that is getting hot say close to the exhaust or cylinder head causing fuel to vaporise?

Does it start with the throttle wide open? Many don't start at tick over.

[Bee]

I think I would start with carefully bleeding it just to see if there is some sort of tiny air leak that occurs when its hot and cooling down, My engine used to start OK from cold but restarting after lunch it could be a bit reluctant, the filter had a bit of air in the top, checked all the conections and it has 99%  cured it but I never really identified the actual leak despite a lot of searching. Nice looking installation by the way.

[Tony Brooks]

Agree about the nice installation.

 

An even longer shot idea that for a few minutes work will be ruled out. Has anyone checked the non-return valve on the filter head where the return from the injector pump enters. I have seen the odd one choked with muck (not sure how the muck got past the filter and the strainer in the pump). I can't see how this could cause the symptoms  unless the body of the pump is pressurizing to the degree the governor valve can't work.

[Bobby b]

Thank you all so much for quick feed back, i can confirm a few of the comments

• It had new geared type start motor fitted at the time of rebuild and spins over fast (quick enough to put the oil pressure light out)  
• It is 28ft 1950s river boat and cruises around 1800 -2000 RPM 
• valve clearance were one of 1st thinks we checked and were within limits and of course were done when the head came off 
• none return valve (NRV) was checked for correct operation 
• once it starts in in tick over at 700/800 RPM fine 
• It is under a deck which does get warm with qty 2 -  4 inch  air vent (as said it ran for 100 hours with no issues) with same vents 
• does not matter what position the throttle is in - will not start 
• we did suspect a build up of pressure in pump body but releasing the top banjo bolt on filter housing fuel comes out under a little pressure but makes no difference to starting 
• Fuel system has been bleed many many times 

I do deep down think we have fitted another duff pump and as one of one mentioned not making enough pressure to open the injectors with hot fuel , thanks again for all your comments 

[john.k]

A simple way of checking the pump is to dump a couple of gallons of oil into the fuel tank.........Its also possible to test injection pressure on the motor by simply spudding into the fuel lines with a Hartridge gauge set.......mines called a Hartridge "Spotcheck"

[john.k]

A  way of cooling the pump may be to fit an electric lift pump,so that it circulates cold fuel thru the pump,or at least thru the filters.

[Tracy D'arth]

30 minutes ago, john.k said:

A  way of cooling the pump may be to fit an electric lift pump,so that it circulates cold fuel thru the pump,or at least thru the filters.

The standard BMC filter housing should be bleeding fuel constantly back to the tank from the top banjo union in the return line. That is the purpose of the small drilling in the union.

What ever the solution is when you find it please let us know, its an intriguing fault.

[StephenA]

Does the injector bleed rail actually go up in the air before going to the top of the banjo bolt? Or is is an optical illusion?

 

[Tracy D'arth]

I once had a return rubber hose from the filter head banjo collapse internally, closing it completely, This caused some odd running problems as there was no leak off or return to the tank.

 

It does look as though the leak off pipe rises considerably but I can't see that being a problem.

[NB Esk]

I think what appears to be the fuel leak off is in fact a morse control cable, it’s an optical illusion.

 

 

 

[StephenA]

22 minutes ago, NB Esk said:

I think what appears to be the fuel leak off is in fact a morse control cable, it’s an optical illusion.

 

 

 

I mean the copper in the middle of the cropped picture - running from the last injector back to the banjo

[john.k]

We used to get this problem with trade in Bobcats with 4/108 Perkins motors.........a replacement DPA pump would eliminate the profit on the transaction,and besides the hydraulics were just as worn .......but you cant sell a machine if it cant be started,so I would first lower the set of the injectors .....not below about 700psi ,though or cylinder pressure would blow into the nozzles stopping the motor..

Edited April 10, 2022 by john.k

[Bobby b]

Hi well noted you are correct  in thinking the spill rail pipe does (did) loop up in the air and that has now been removed  as we thought  the same that this could cause a vapour/air lock of some kind. See photo below, just before the rail is refitted, thanks again  for all the comments  it does seem to point to another pump 

[Tony Brooks]

Even if the loop did vapor lock, but I can't see how with diesel because of the much higher vaporization point, it would not stop the engine starting. All the flow in that pipe is back to the tank, either from injector leak back or the small hole in the filter banjo.

[john.k]

In general with DPA pumps,if there is an air leak,the motor will start ,run for a couple of seconds,then stop...........not whats happening here.................... n any case,at this point ,the immediate cure is a more viscous fuel......which is easily done by tipping some oil into the fuel tank.

[Tony Brooks]

22 minutes ago, john.k said:

In general with DPA pumps,if there is an air leak,the motor will start ,run for a couple of seconds,then stop...........not whats happening here.................... n any case,at this point ,the immediate cure is a more viscous fuel......which is easily done by tipping some oil into the fuel tank.

 

I am happy to accept the theory behind a worn injector pump might be correct, but it seems unlikely as this is the second pump. I am far from convinced that pouring lubricating oil into the fuel tank is a good idea. It is known that when run on plain vegetable oil there were lubrication problems with the rotor bearings that necessitated a helix being machined on the shaft to assist lubrication.

 

The point about having the pump tested again with heated fuel in the test rig seems a far safer option to me. I also have reservations with the advice to reduce the injector break pressure, it might work for a time but I think it may also lead to poor atomisation, bad starting and smoke. I also have concerns it may cause the auxiliary spray hole in the pintaux nozzles to not spray properly so again it may hinder cold starting.

[john.k]

Im not suggesting the OP reduce his set pressure.........for the reason he may  not have the technology to set and reset the pressures..........if he does have an injector pressure tester ,then different story..................We might look at the situation when he bought the boat.......it ran and started OK for six months,then no more hot start......this period may well coincide with all the oil the previous owner added to the fuel being used up.

[john.k]

Just noticed  a restrictive looking sports aircleaner off  a car on the engine......wonder if its had the element cleaned  or replaced.

[john.k]

Do you get summer and winter diesel there?.........winter diesel supposedly has the wax removed ,and maybe if the OP gets a tank of summer diesel ?

[StephenA]

4 hours ago, john.k said:

Just noticed  a restrictive looking sports aircleaner off  a car on the engine......wonder if its had the element cleaned  or replaced.

 

I can understand a clogged air filter causing poor revving and poor burn but stopping enough air that it can't start, but only when it's hot, sounds unlikely

[Tony Brooks]

5 hours ago, john.k said:

Do you get summer and winter diesel there?.........winter diesel supposedly has the wax removed ,and maybe if the OP gets a tank of summer diesel ?

 

We do,  but both should have a 32 second viscosity.

[StephenA]

is it a manual stop or electronic?