Thornycroft BMC 90 1.5 Diesel

[BMC90]

Hi, im new member here. I´m Kenneth from Denmark.

I have a Thornycroft BMC 90-1.5 Diesel, in my boat. The engine runs great, but leaks oil from the crank behind the flywheel. This engine have no oil seal. Is there anything i can do to make it stop leaking?

Is there some kind of an oil seal kit that could be mounted?

Sorry for my bad English :-)

 

Greetings, Kenneth

[Crow]

It's a long time since I worked on a 1500 BMC , I thought when you remove sump there will be a 180 deg square section cork gasket

That fits round the main bearing in a groove,I'm sure there should be a o ring seal that fits in back plate and to o/ d of crank

[The Bagdad Boatman (waits)]

Look for a haynes manual for the 1.5 bmc.

[cereal tiller]

The BMC 1.5 has an installation angle limit of around 12 degrees,if the angle is greater they do tend to weep oil

 

Try reducing the Oil level a bit.on narrowboat installations the engine is usually fairly level,so less of a problem

 

the 1.8 can be inclined at 25 degrees as it has a Lipseal at the flywheel end of thr Crankshaft

 

CT

[Tony Brooks]

As CT says above many have no rear crank oil seal and there is a chance your engine is set at too greater an angle. However I think that some 1.5s did have a rear main bearing oil seal depending upon their original purpose so email Boats@Calcuttboats.com and ask. However that would mean a change of engine block and probably a full rebuild unless they can supply a rebuilt short motor. I may be wrong about this though so you need to ask. Calcutt are probably the UK specialists in these engines.

 

It will also be worth keeping an eye on the sup oil level because as CT implies if its too high it will leak. The change to low sulphur diesel has done the ageing 1.5s no good at all and with increasing frequency I am hearing of them with leaking injector pump shaft seals that dilute the engine oil and overfills the sump. If you are suffering from dilution it could also be a lift pump problem.

[BMC90]

Okay, thanks a lot. The latest build 1.5 engines has a rear main bearing oil seal. I dont think I have a leaking injector pump (yet) The engine oil was not thin, and did not have a smell of diesel. I will contact Calcuttboats, if they have any suggestions.

Reducing the Oil level sounds as an good idea.

Do not know if the angle is over 12 degrees, the boat is an LM27.

 

Kenneth

[Canal Cuttings]

BMC cars of this era often did not have a rear oil seal. Instead, they had an "archimedes scroll" which gathered up oil as it was thrown off from the crank, and as it revolved the spiral shaped groove re-delivered the oil back into the crankcase. Of course, for this to work the spiral has to be revolving, so when the engine is at rest there is nothing to stop oil leaking out, especially if the engine is tilted. There were companies that could machine a groove and insert an aftermarket seal, but this could fail: the original system was poor but foolproof.

It is worth taking professional advice that your engine is properly vented. If air pressure builds up inside the crankcase it will blow oil out through any aperture.

[BMC90]

I separated the engine, and it is as you describe it. Perhaps I should change the valve stem o-ring seals, and new piston rings to avoid pressure indside the crankcase,while I have the engine almost separated.

The engine will be tilted a bit in this boat, an engine oil will be sloshed around in heavy seas :-O