BMC 1.5 Oil Loss

[jacksonp_uk]

Hi

 

My BMC 1.5 Diesel narrowboat engine has started to lose oil via the exhaust main outlet pipe 4 hole flange gasket. Once the enigine is up to temp the oil almost sprays out! If i remove the oil fill cap the flow is reduced and also the breather pipe from the push rod cover. However it does not stop altogether. The engine runs and starts very well and the head gasket is ok. It is also not apparently burning any oil. I did a top end overhaul about a year ago as it was burning oil due to the valve stem seals. Any suggestions welcome please.

 

cheers

 

Paul Jackson

[cereal tiller]

Hi

 

My BMC 1.5 Diesel narrowboat engine has started to lose oil via the exhaust main outlet pipe 4 hole flange gasket. Once the enigine is up to temp the oil almost sprays out! If i remove the oil fill cap the flow is reduced and also the breather pipe from the push rod cover. However it does not stop altogether. The engine runs and starts very well and the head gasket is ok. It is also not apparently burning any oil. I did a top end overhaul about a year ago as it was burning oil due to the valve stem seals. Any suggestions welcome please.

 

cheers

 

Paul Jackson

first thing to check would be the crankcase breather,they can get clogged over time.

[Chalky]

I had this on a petrol 1.8 B series in an MGB. I had a failed piston ring and fortunately was able to replace the rings and fix the problem.

 

As said previously check the crank case breather. It's the cheapest solution and if your lucky it'll fix the problem. If your getting lubricating oil into the combustion chamber there are only 5 places it can come from:-

 

• 
   
  
• It can get in through the crank case breather. The breather is designed to burn blow by fumes. If it's blocked these can be excessive.
  
• It can leak through a blow in the head gasket between the oil gallery and the cylinders. I've had this on a B series petrol and an A series petrol. In both cases there was no leakage into the water jacket so no water in oil. Check the compressions. A head gasket can be done in situ.
  
• It can leak down the valve guides. If you're lucky its a set of valve stem oil seals otherwise it's a new set of valve guides and valves (head rebuild). You'll need the head off to change the oil seals.
  
• It can get past the piston rings. If you're lucky its a set of rings, otherwise its a bottom end rebuild (engine out in both cases - can't get the sump off in a boat, just possible in an MGB).
  
• It can get in through a crack in a casting. Unlikely but a possibility if the engine has been frozen without antifreeze in the coolant.
   
  

 

If in doubt find a mechanic to look at it. If the lubricant is getting into the combustion chamber you need to be aware of run away. That happens when the engine starts to burn its own lubricant as fuel and there is very little that can be done to stop it other than stalling the engine. (in a car put it into gear and drop the clutch - not possible in a boat). If this happens its usually terminal for the engine.

 

The fact that removing the cap slows the rate suggests something pressurising the crank case. The petrol B series filler cap has a wire gauze inside that acts as a vent for the crank case. Check that for cleanliness. On the B when the ring went I has 4 jets of oil vapour coming out of it.

Edited January 21, 2012 by Chalky

[Geoff Taylor]

Hi Paul,

Does your engine oil seem to be rising above maximum on dipstick lately and seem thinner than usual as it could be diluted due to fuel leaking into it via lift pump diaphragm or injector pump seals,does it smell of diesel?, if so the thinner oil mixture could cause this.

Did the problem happen suddenly or coincide with any maintenance or repairs?.

[Mike Jordan]

Hi Paul

I note that you have had the top off the engine before the problem started. I think you may have made one of the classic mistakes with the 1.5 - Did you put valve stem seals on the exhaust valves? If so these can , if you are unlucky, weld themselves onto the valve stem while the engine is hot and the exhaust valve stems even hotter! The result is that the rubber seal moves up and down with the valve stem and makes a near perfect pump to force oil mist and drops down the exhaust valve guides. If you take off the rocker cover and use a torch you should be able to see if the seals are stuck to the stems. If this is the case just post again and I will detail a method of removing the seals without taking the head off again.

Mike.

[jacksonp_uk]

Hi Paul

I note that you have had the top off the engine before the problem started. I think you may have made one of the classic mistakes with the 1.5 - Did you put valve stem seals on the exhaust valves? If so these can , if you are unlucky, weld themselves onto the valve stem while the engine is hot and the exhaust valve stems even hotter! The result is that the rubber seal moves up and down with the valve stem and makes a near perfect pump to force oil mist and drops down the exhaust valve guides. If you take off the rocker cover and use a torch you should be able to see if the seals are stuck to the stems. If this is the case just post again and I will detail a method of removing the seals without taking the head off again.

Mike.

 

Hi Mike

 

I'm afraid I did put seals on all the valve stems! Your advice to rectify this would be appreciated. This sounds like a logical explanation to the symptoms to me.

 

cheers

 

Paul

[Mike Jordan]

Hi Paul

Don,t feel to bad about it, I'm sure you can guess how I found out!It's possible to get the engine onto top dead centre on two pots at a time by looking at the crankshaft front pulley, you should find two small holes in the web, when these are horizontal two pistons should be at the top. With the cover off and the rocker shaft removed, its possible to use the bolts projecting from the head with washers and nut to secure a ring spanner. A second open ended spanner can then be used to press down on the valve spring to release the collets.(its a sort of three handed job) Obviously you need to turn the engine 180 degrees with a spanner to do the second pair of pots.

On the occasion I had to do the job, I used the winter cover to ensure that nothing got thrown over the side if the spanners slipped off.The system worked for me but it took several days of cruising before the oil drips from the exhaust joints stopped. A little of that sooty oil goes a long way!

One final point, the boat safety scheme requires the exhaust to be lagged for safety,unfortunately "oil soaked lagging" is a prime cause of fires in big ships. I strongly recommend you remove any insulation until the engine is running clean again.

Very best of luck with the job.

It would be interesting to hear how it works out.

Mike

[RobinJ]

The engine runs and starts very well and the head gasket is ok. It is also not apparently burning any oil. I did a top end overhaul about a year ago as it was burning oil due to the valve stem seals. Any suggestions welcome please.

So you replaced the valve stem seals then!

Don't forget there are 2 types the rubber rings and the neoprene seals.

 

Sounds to me as thought you are loosing a fair amount through the exhaust valves into the exhaust. I have to admit BMC's normally show leakage through the inlet and the air intake?

Edited January 23, 2012 by RobinJ