Bukh DV20 woes... hard to start, and now....

[ghostlymoron]

There's plenty of videos of runaway engines on YouTube. BTW stopping a big engine by putting your hand over the air inlet could result in serious injury.

 

[No Regrets]

At the age of 15, I was apprenticed to a shipyard in the motor sheds. Subsequently permitted by the relevant authorities to stand as Engineer Officer on any British registered ship. It is doubtful if you have experienced what you have claimed. Never in 55 years I have experienced a runaway. Most stories are sheer fiction.

Were you the apprentice tea-boy? :ambivalence:

Seen several. The Detroits sounded the most impressive in fairness, but cars and boats with over-filled sumps or knackered turbo's are surprisingly vulnerable..

 

[<152587>]

Were you the apprentice tea-boy? :ambivalence:

Seen several. The Detroits sounded the most impressive in fairness, but cars and boats with over-filled sumps or knackered turbo's are surprisingly vulnerable..

Your inane comments contribute nothing to this thread. I accept that runaway can occur but the original post concerned mixing oil and diesel to flush the sump cannot cause runaway unless the mix migrates to the combustion space. The engine will NOT continue to increase in speed ad infinitum as valve float will restrict the revolutions eventually. All runaways involve some failure of the injection or turbo system or excessive wear between pistons and bore. Just ask yourselves out of all the Taxis, trucks, vans ,cars ships etc powered by diesel, how many runaways are witnessed in the high street everyday. As your mother taught you, believe only half of what you see, funny how most of you tube videos have a camera running to record instant disaster.

 

[RichardS]

Just ask yourselves out of all the Taxis, trucks, vans ,cars ships etc powered by diesel, how many runaways are witnessed in the high street everyday.

I'm just asking myself how many of those taxis, trucks, vans, cars and ships have a sump half full of diesel?

Richard

 

[<152587>]

I'm just asking myself how many of those taxis, trucks, vans, cars and ships have a sump half full of diesel?

Richard

Richard, we are talking of a 5-10 minute run here not the Paris to Peking.

We agree that a CI engine will run on lube if, say, turbo seals fail. As in normal operation the crankcase contains a mist of oil droplets which do not migrate to the combustion chamber. Please enlighten us all as to adding a quantity of diesel to the lube can now magically cause migration.

Maybe you could enlighten the forum via your vast diesel knowledge as to the cause and possibility of crankcase explosion whilst flushing heavy contaminants from the sump.

 

[RichardS]

Richard, we are talking of a 5-10 minute run here not the Paris to Peking.

We agree that a CI engine will run on lube if, say, turbo seals fail. As in normal operation the crankcase contains a mist of oil droplets which do not migrate to the combustion chamber. Please enlighten us all as to adding a quantity of diesel to the lube can now magically cause migration.

Maybe you could enlighten the forum via your vast diesel knowledge as to the cause and possibility of crankcase explosion whilst flushing heavy contaminants from the sump.

I can't really express this any clearer, Third Engines, but to run a diesel engine with a 50:50 mixture of engine oil and diesel fuel in the sump is total madness. It is so far beyond the realms of sanity for so many reasons including lubricity, viscosity, flammability etc that I cannot believe that anyone who has the slightest knowledge of internal combustion engines would even countenance it. It's not even as if it's a significant cost saving as 5 litres of cheap supermarket oil which would work well as a flushing oil is barely any more expensive than diesel.

I've no idea what your last sentence has to do with this discussion.

Richard

 

[rotrax]

I can't really express this any clearer, Third Engines, but to run a diesel engine with a 50:50 mixture of engine oil and diesel fuel in the sump is total madness. It is so far beyond the realms of sanity for so many reasons including lubricity, viscosity, flammability etc that I cannot believe that anyone who has the slightest knowledge of internal combustion engines would even countenance it. It's not even as if it's a significant cost saving as 5 litres of cheap supermarket oil which would work well as a flushing oil is barely any more expensive than diesel.

I've no idea what your last sentence has to do with this discussion.

Richard

Well Richard, one dayin the late 70's while practicing for a big motorbike race I dropped a valve in No 2 cylinder. It wrecked the combustion chamber and piston, plus dropping loads of hard pieces of silicon piston alloy into the sump.

My mechanic changed the piston and fitted a spare head, but we ran out of time to remove the sump and flush the lube system through.

A mixture of lighter oil than we normally used and parrafin was put into the sump after draining it and changing the filter.

We then ran the engine for ten minutes, at high RPM, and drained the sump.

The race oil was installed and we made the start and I had a respectable finish considering the opposition.

So, in a highly tuned petrol engine-an 8 valve air cooled 100 BHP plus Kawasaki Formula 1 engine by LEDAR-nothing untoward happened running with a sump of half and half oil/parrafin.

We did flush enough crap out of the engine by doing this to ensure a finish.

Now Richard, something that nobody with design and manufacturing experience has ever been able to explain satisfactorily to me-in a conventional loop scavenge two stroke the explosive fuel mixture travels into the crankcase before going up the transfer ports into the combustion space.

Why does the occaisional piston blow by of combustion flame-which must happen as the rings are pegged-not cause this crankcase mixture to burn?

By the way, I am a 50 year plus time served mechanic with experience of engines from 50cc twins to large marine engines.

I would have no problem with running a diesel with a 50/50 oil/diesel mix in the sump at light load.

I would not punch into a headwind and foul tide, but I would happily run it under light load-and for some time.

My two pennyworth anyway.............................

 

[stevie69p]

Anyhooooo....

To get back to thee original post....

I removed the head at the weekend. Starting by removing the exhaust elbow flange, when it was taken off, water dribbled out of the exhaust manifold. When the manifold was removed, water could be seen dribbling out of the exhaust port of number 2 cylinder, so it's looking like the head is cracked, probably at the exhaust valve guide. Also, once the head was removed it could be seen that 2 of the holes which carry the cooling water round the head (the ones next to each of the exhaust valves) had completely crusted over.

So...

I have sourced a head and am just in the process of taking out a second mortgage to buy the head set from Bukh lol...

The sump has the 50;50 mix diesel and engine oil in it at the moment, but I'll drain this off before rebuilding. Fingers crossed that it all works out.

 

[RichardS]

Why does the occaisional piston blow by of combustion flame-which must happen as the rings are pegged-not cause this crankcase mixture to burn?

By the way, I am a 50 year plus time served mechanic with experience of engines from 50cc twins to large marine engines.

I would have no problem with running a diesel with a 50/50 oil/diesel mix in the sump at light load.

I would not punch into a headwind and foul tide, but I would happily run it under light load-and for some time.

My two pennyworth anyway.............................

There is a big difference between a combustive mixture being compressed into a tiny space and then fired with a spark or compression and a combustive mixture in an uncompressed state residing in the crankcase where it is shielded from the spark and not compressed enough to self-ignite.

Feel free to run your diesel engine on a 50:50 mixture of diesel and oil. Just make sure that you have the video running.

Richard

 

[<152587>]

I can't really express this any clearer, Third Engines, but to run a diesel engine with a 50:50 mixture of engine oil and diesel fuel in the sump is total madness. It is so far beyond the realms of sanity for so many reasons including lubricity, viscosity, flammability etc that I cannot believe that anyone who has the slightest knowledge of internal combustion engines would even countenance it. It's not even as if it's a significant cost saving as 5 litres of cheap supermarket oil which would work well as a flushing oil is barely any more expensive than diesel.

I've no idea what your last sentence has to do with this discussion.

Richard

So come on, what has this to do with your original statement on runaway? The forum is still waiting for your explanation on how the fuel is delivered to the combustion space from the crankcase.

 

[RichardS]

So come on, what has this to do with your original statement on runaway? The forum is still waiting for your explanation on how the fuel is delivered to the combustion space from the crankcase.

Errrrrr ..... from the diesel mixture in the sump/rocker box then through the crankcase breather would seem the most direct route. But it depends upon what you mean by "what has this got to do with your original statement on runaway" as that's another sentence which has left me completely confused.

Richard

 

[Milestone]

I can't believe what is being said, I have witnessed many run aways or the aftermath of run aways from the failure of a tandem pump, (combined vacuum pump and diesel pump running off the camshaft), which led to diesel mixing with the engine oil.
I'm with Richard, and would definitely not start an engine on a mix!

So back to the thread, how much are they stinging you for a head set?

 

[stevie69p]

It's about £260 for a head set! Mental...

 

[rotrax]

There is a big difference between a combustive mixture being compressed into a tiny space and then fired with a spark or compression and a combustive mixture in an uncompressed state residing in the crankcase where it is shielded from the spark and not compressed enough to self-ignite.



Richard

But as I said, two stroke rings are pegged so they stay still and dont rotate. If they do they catch in the ports and disaster occurs. Some high performance ones only had one ring. When these were dismantled it was clear that the flame front of combustion burning HAD transfered past the ring and down the side of the piston from time to time.

The Works CZ Motocross mechanic Jiri had the most likely explanation, but purely seat of pants. He assumed that it did burn off some of the fast moving gas when the flame front passed the piston/bore clearance, usually towards the end of a Moto-30 minutes plus 1 lap-and was reported as a missfire or " Holding back " by the rider. He had had the odd crankcase seal failure during a long season when maintenance had been neglected which he put down to wear and tear plus this phenomena of piston bypass burning. The seals would turn inside out, just as if there had been a sudden increase in internal crankase pressure-such as by a fast burning gas incident.

These were all old tech air cooled simple engines whose bores would change shape significantly in use, due to having a cool, dense air fuel mixture one side of the cylinder and a red hot exhaust the opposite side. Some years later water cooling allowed much tighter control of these internal tolerances.

 

[RichardS]

But as I said, two stroke rings are pegged so they stay still and dont rotate. If they do they catch in the ports and disaster occurs. Some high performance ones only had one ring. When these were dismantled it was clear that the flame front of combustion burning HAD transfered past the ring and down the side of the piston from time to time.

I think you're confirming what I said although I'm not sure of the relevance of the non-rotating rings. If there ever is any combustion in the crankcase, although it's not a phenomenon I've ever been aware of, then there would be a world of difference between the combustion of a highly compressed fuel air mixture which has been heated by compression in the cylinder and the combustion of a non-compressed and much cooler fuel/air mixture in the crankcase.

Richard

 

[rotrax]

I think you're confirming what I said although I'm not sure of the relevance of the non-rotating rings. If there ever is any combustion in the crankcase, although it's not a phenomenon I've ever been aware of, then there would be a world of difference between the combustion of a highly compressed fuel air mixture which has been heated by compression in the cylinder and the combustion of a non-compressed and much cooler fuel/air mixture in the crankcase.

Richard

You are obviously unaware that a conventional motorcycle type Schnurle loop scavenge engine DOES compress the gas in the crankcase. When tuning a Villiers for higher performance stuffing blocks of alloy, balsa wood or cork would be fitted to reduce the internal volume, so increasing this primary compression.

To be fair, it was rarely, when measured, more than 4:1.

Non rotating rings-or in many cases ring-could leave a route for combustion burning to pass down the side of the piston into this area of possibly 4:1 compressed gas. The rings had to have a gap to avoid siezure, of about 6 thou per inch of bore in a tuned stroker. So, one or two rings, with gaps, staggered to clear the inlet port in most, but not all, cases.

The combustion burn can, in theory, and probably in practice, get past the piston skirt by passing through the ring gaps.

Diesels usually have no air intake control. The BMC engined london black cabs were an exception-they had a butterfly to allow manifold vacuum to assist the brakes through a conventional servo. Without intake manifold control, a runnaway is of course possible when burnable mixture from the sump is drawn into the intake manifold by knackered piston/bore clearance and faulty breather valves. That is not in dispute.

But suggesting using a 50/50 oil/diesel mix in the sump is a total no-no, when being done for another particular service purpose, is patently incorrect.

I and I suspect many others have done it without problems.

 

[PaulRainbow]

Diesels usually have no air intake control. The BMC engined london black cabs were an exception-they had a butterfly to allow manifold vacuum to assist the brakes through a conventional servo.

Some older diesels also had a butterfly in the intake manifold which acted as the throttle, rather than the more common fuel pump control.

But suggesting using a 50/50 oil/diesel mix in the sump is a total no-no, when being done for another particular service purpose, is patently incorrect.

I and I suspect many others have done it without problems.

My concern with putting fuel in the oil was not centered around an engine runaway. I'd prefer to use cheap oil/flushing oil, rather then pumping a fuel/oil mix through my bearings etc. As a general rule it's not a great idea to pump poor oil through shelled bearings. Deliberately making contaminated oil even poorer by mixing in fuel doesn't seem like too sound a policy to me.

Confucius say, oil is cheaper than metal

 

[<152587>]

Some older diesels also had a butterfly in the intake manifold which acted as the throttle, rather than the more common fuel pump control.

You do rather come out with some nonsense at times!

The idea of a butterfly in the inlet tract is to create manifold depression. The vacuum then produced controlled the fuel pump rack ala Mercedes OM.

CI engines do not work on carburettors you know.

 

[RichardS]

You are obviously unaware that a conventional motorcycle type Schnurle loop scavenge engine DOES compress the gas in the crankcase. When tuning a Villiers for higher performance stuffing blocks of alloy, balsa wood or cork would be fitted to reduce the internal volume, so increasing this primary compression.

To be fair, it was rarely, when measured, more than 4:1.

Non rotating rings-or in many cases ring-could leave a route for combustion burning to pass down the side of the piston into this area of possibly 4:1 compressed gas. The rings had to have a gap to avoid siezure, of about 6 thou per inch of bore in a tuned stroker. So, one or two rings, with gaps, staggered to clear the inlet port in most, but not all, cases.

The combustion burn can, in theory, and probably in practice, get past the piston skirt by passing through the ring gaps.

Diesels usually have no air intake control. The BMC engined london black cabs were an exception-they had a butterfly to allow manifold vacuum to assist the brakes through a conventional servo. Without intake manifold control, a runnaway is of course possible when burnable mixture from the sump is drawn into the intake manifold by knackered piston/bore clearance and faulty breather valves. That is not in dispute.

But suggesting using a 50/50 oil/diesel mix in the sump is a total no-no, when being done for another particular service purpose, is patently incorrect.

I and I suspect many others have done it without problems.

Talk about sucking one's Grandmother to suck eggs, Rotrax, I stripped down and rebuilt my first 2T single-cylinder engine in 1967 although I had done plenty of work on 4T engines before that.

I keep trying to explain to you that combustion conditions in a 2T crankcase are nothing like the combustion conditions in the cylinder which probably explains why I have no personal experience of crankcase combustion although I also keep saying that it may well be possible, but you keep contradicting me ..... and then changing your mind again.

Whether 2Ts have one ring or two or pegged rings or not seems, to me, to be an irrelevant detail in the circumstances where we are simply talking about whether blow-by in a 2T, for whatever reason, can cause crankcase combustion and we both seem to agree that it is presumably theoretically possible although neither of us appear to have any personal experience of it.

For the third time, I have no problem with you running an elderly diesel engine with 50% diesel in the sump and I look forward to seeing a list of knowledgeable web links where this is a recommended technique ..... but, if you try it, please make sure the video camera is rolling. :encouragement:

Richard

 

[RichardS]

My concern with putting fuel in the oil was not centered around an engine runaway. I'd prefer to use cheap oil/flushing oil, rather then pumping a fuel/oil mix through my bearings etc. As a general rule it's not a great idea to pump poor oil through shelled bearings. Deliberately making contaminated oil even poorer by mixing in fuel doesn't seem like too sound a policy to me.

Confucius say, oil is cheaper than metal

Indeed Paul. I keep repeating the mantra of lubricity/viscosity/flammability but I don't seem to be getting through.

Richard