misbehaving MD2B

[hamishnf]

Hi everyone,

I have recently assembled and installed an old md2b in my westerly windrush. It starts easily and runs fine in/out of gear with just a tiny puff of blue smoke from the exhaust. It responds well to the accelerator and doesnt make any nasty noises. Today I ran it for half an hour at lowish revs in gear without any problems whilst it warmed up. Trouble is that as soon as the engine comes up to its proper operating temperature the following happens:

It starts to puff out white smoke from the exhaust. Then it starts to lose power, the revs drop away, it doesnt respond to the accelerator, then it slowly stalls. By pressing the cold start button I can get it to restart again, but it soon slows down and stops again, and eventually it refuses to start at all, just turns over on the starter. If the engine is allowed to cool for an hour or so it starts up again and runs perfectly.

I have checked the fuel system. The lift pump pumps clean bubble free fuel right up to the injector pump. Plenty of diesel squirts out the injector unions when they are loosened off. When the cold start is depressed black smoke belches out the exhaust from the over rich mixture. So I'm sure the issue is not fuel related.

The air filters are clear, the exhaust manifold is clear (if a little sooted up).

I changed the oil/oil filter, the oil pressure is fine.

I have checked the valve clearances when the engine is hot (as it says in the manual), they are fine.

The engine pumps plenty of water out the exhaust, all cooling passages were cleared before I assembled the engine, A temperature probe reads 80 degrees centigrade on the front block. The engine isnt overheating, the problems occur when it reaches its proper operating temperature.

When the problem occured today I tried re tourqeing the cylinder head nuts and restarting the still hot engine. (the nuts had loosened up a bit) This seemed to stop the white smoke, but the engine soon slowed down and stalled again.

When I originally assembled the MD2B I used proper new head gaskets, and torqued them to the figures in the workshop manual. I visually inspected the valves, they looked to be seating ok, but I lapped them very gently with some fine paste anyway. I did not replace the piston rings, as they looked ok, I simply freed them up in their grooves.

Why is my engine running perfectly when its cold, but failing when it comes up to temperature? Any advice would be apreciated as its driving me bananas!

 

[VicS]

80C is a bit hot isn't it. ( but if it was indirectly cooled it would run that hot)

The thermostat should start to open at 60C and be fully open at 74C

You say 80C for the front block did you check the rear one ? They can be different.

I think I'd measure the head temps if possible. Can you get probe onto the coreplugs?

you say all waterways clear ... that includes the small passages in the exhaust manifold that take the water to the heads ?

No signs of water in the engine oil ?

 

[Jcorstorphine]

Options

Having rebuilt one of these engine from crankshaft up, the following comes to mind.

Leaking head gasket. It might be that it starts to leak when the engine gets hot as the bolts expand.

Cracked head, again this may only happen when hot.

Crack in exhaust manifold but then even though that caused the steam, it would not stop your engine.

Any chance you have a blockage in the exhaust which is collapsing when the system gets hot.

Other point is that when you had the head off, did you lift the blocks to clean the rings, if so did you check the piston protrusion and use “leads” to determine the final piston to head clearance. The clearance is adjusted using crankcase gaskets of differing thickness.

You said that the engine reaches 80oC. This does seem rather hot for a direct sea water cooled engine as I think this could cause silting up with salt. Are you sure all the waterways are clear all the way round and right down to the drain holes.

Have you tried to isolate which cylinder is causing the white smoke. Just as it starts to smoke it might just be possible to have someone watch the exhaust while you slacken the fuel pipes one cylinder at a time. You could use the decompressor to achieve this but this is frowned upon as it still fires unburnt fuel into the engine and the valves can get a bit fried.

I had problem with my engine with the water pump seals failing and pumping seawater direct into the sump but this was very evident from the state of the emulsified oil.

 

[david_bagshaw]

have the head bolts got to the point where they keep stretching?

had this happen on a farryman where the head had been removed 3 times to my knowledge.

 

[hamishnf]

Thanks for the quick replies guys. There weren't any shims under the blocks originally. If the bump height was wrong on one/both cylinders I would have thought the engine would run rough from cold, not run perfectly from cold then smoke, slow, and stall, as it heats up? But if I get a chance I will check with leads.

If a head was cracked or warped then presumably it would only affect one cylinder, this problem seems to be affecting both. I am pretty sure both cylinders are working spot on when the engine is cold, then they both lose power as the engine heats up.

It is possible that the engine is overheating. When I ran it yesterday the temperature guage stubbornly stayed in the cold position all the time, then when the engine heated up and finally stalled the guage shot up. The sender for the guage is in the 'hot' part of the thermostat housing so if the guage isn't getting hot then the thermostat isn't either, even though the blocks and heads are. Also I'm fairly sure the pipe that runs from the thermostat housing to the exhaust inection elbow is staying cool even when the engine is hot, which makes me suspect that the water is bypassing the engine regardless.

I might try removing the thermostat and closing off the pipe between the T piece under the manifold and the thermostat housinf to force all the water through the heads/blocks all the time. I will also remove the manifold and re check the waterways in there.

The engine sounds great when it works, so it would be a shame to pull the thing out again!

 

[Bilgediver]

Thanks for the quick replies guys. There weren't any shims under the blocks originally. If the bump height was wrong on one/both cylinders I would have thought the engine would run rough from cold, not run perfectly from cold then smoke, slow, and stall, as it heats up? But if I get a chance I will check with leads.

If a head was cracked or warped then presumably it would only affect one cylinder, this problem seems to be affecting both. I am pretty sure both cylinders are working spot on when the engine is cold, then they both lose power as the engine heats up.

It is possible that the engine is overheating. When I ran it yesterday the temperature guage stubbornly stayed in the cold position all the time, then when the engine heated up and finally stalled the guage shot up. The sender for the guage is in the 'hot' part of the thermostat housing so if the guage isn't getting hot then the thermostat isn't either, even though the blocks and heads are. Also I'm fairly sure the pipe that runs from the thermostat housing to the exhaust inection elbow is staying cool even when the engine is hot, which makes me suspect that the water is bypassing the engine regardless.

I might try removing the thermostat and closing off the pipe between the T piece under the manifold and the thermostat housinf to force all the water through the heads/blocks all the time. I will also remove the manifold and re check the waterways in there.

The engine sounds great when it works, so it would be a shame to pull the thing out again!

It sounds to me like overheating however DO NOT play with the tee piece but
find out why the water is not going through the engine. The bypass to the thermostat housing is there to keep the exhaust cool when the thermostat is closed.

You may have one of two problems. Either the heated water is unable to circulate to the thermostat and heat it. I have in the past drilled a small hole in the thermostat to allow a trickle of water at all times to stop this. say around 2mm. Some thermostats come with a hole drilled.

You should also check you have the exhaust manifold gaskets seated the right way round as they may obstruct the water passages.

Your white smoke will probably be steam which is probably being generated in the blocks due to a lack of circulation.

You can easily check if it is overheating by running without the thermostat.

 

[scottie]

Two quick thoughts

You must have at least one but usually more cyl base shims which are more like gaskets than the later model which are metallic your compression will be way out without and cyl base sealing very iffy

The manifold has a blanked off connection to the thermostat housing which looks as if it should be open but the water supply to the manifold was rerouted to a hose under the manifold the engine should run about 60 +

 

[Kurrawong_Kid]

Thanks for the quick replies guys. There weren't any shims under the blocks originally. If the bump height was wrong on one/both cylinders I would have thought the engine would run rough from cold, not run perfectly from cold then smoke, slow, and stall, as it heats up? But if I get a chance I will check with leads.

If a head was cracked or warped then presumably it would only affect one cylinder, this problem seems to be affecting both. I am pretty sure both cylinders are working spot on when the engine is cold, then they both lose power as the engine heats up.

It is possible that the engine is overheating. When I ran it yesterday the temperature guage stubbornly stayed in the cold position all the time, then when the engine heated up and finally stalled the guage shot up. The sender for the guage is in the 'hot' part of the thermostat housing so if the guage isn't getting hot then the thermostat isn't either, even though the blocks and heads are. Also I'm fairly sure the pipe that runs from the thermostat housing to the exhaust inection elbow is staying cool even when the engine is hot, which makes me suspect that the water is bypassing the engine regardless.

I might try removing the thermostat and closing off the pipe between the T piece under the manifold and the thermostat housinf to force all the water through the heads/blocks all the time. I will also remove the manifold and re check the waterways in there.

The engine sounds great when it works, so it would be a shame to pull the thing out again!

Reads to me that you have got one or both of the exhaust manifold gaskets the wrong way round so water is not circulatin properly

 

[hamishnf]

Hi all.

went down the boat again today...

Took the manifold off, some debris in the passages that take water from the manifold into the heads, so I hooked as much out as possible, strapped the manifold back on, removed the thermostat, and clamped the hose that runs from the t peice to the thermostat housing. This shuts the bypass, and forces the water through the engine proper and into the exhaust.

Engine started and ran fine for 30 mins medium revs in gear. the back block stayed cool to touch, the front one went up to 60oC and stayed there (still some debris in the front head probably). Plenty of water out the exhaust. Whilst it was running I slackened each injector union in turn, so the engine ran on each cylinder, a bit of white smoke came out regardless.

Then after 30 mins the engine lost power and stalled, same as before. I started it again, and it lost power and stalled almost immediately.

I loosened the injector unions, whilst cranking, plenty of fuel came out.
I turned the engine over by hand with the decompression levers up, nothing had seized.
The compression felt fine with the levers down.
No funny noises.
Oil pressure fine.
The problem cant be caused by overheating in the heads or blocks.
If the bump height was wrong, I cant see how the engine would run fine for 30 mins, then just stop on both cylinders, regardless of the temp in the heads and blocks.
The manifold gaskets are the right way round.
There is some blow by round the piston rings. Could this cause excess heat in the crank case and timing case.
If the injection pump was partially worn out, presumably it would squirt fuel out of the loosened injector unions, but when the unions are tightened up it wouldnt have enough pressure to break the injectors. Would a hot injection pump generate less pressure than a cold one, especially if it was partially worn out?

Could excess crank case heat cause the push rods to expand, reducing the valve clearances and preventing the valves from closing properly?

Any ideas welcomed.

 

[Stemar]

Could excess crank case heat cause the push rods to expand, reducing the valve clearances and preventing the valves from closing properly?

I don't know about that, but too small a valve clearance could work fine when cold but prevent the valves closing properly, hence loss of compression. The workshop manual says to do them with the engine hot. Doing them cold, as you'd have to when rebuilding, may well leave them too small when hot. There's an adjustment on the decompressor as well, I don't know if that would have the same effect.

BTW, the manifold gaskets should have the "ears" up and the high narrow hole facing the flywheel.

 

[GrahamM376]

80C is a bit hot isn't it. ( but if it was indirectly cooled it would run that hot)

The thermostat should start to open at 60C and be fully open at 74C

You say 80C for the front block did you check the rear one ? They can be different.

I think I'd measure the head temps if possible. Can you get probe onto the coreplugs?

you say all waterways clear ... that includes the small passages in the exhaust manifold that take the water to the heads ?

No signs of water in the engine oil ?

I agree with all the above, it sounds like overheating to me. Does the MD2B have wet liners like the 11C? Have you had them out and cleaned the water jackets?

The manifold and cylinder head passages are favourite for blocking and core plugs need removing to clear the heads out properly.

 

[david_bagshaw]

does this engine have a mechanical lift pump? may be it is sticking when the crank case is hot?

if the valves were sticking, or open due to clearance there would be black smoke for inlets or may be grey / white for leaking exhausts as it slowed.

leaky inlet could starve the working one of combustable air, but I would have expected it to die with black smoke, but you could hear it ''chuffing " in the induction manifold.

 

[hamishnf]

Hi guys,
When I tested the engine today with the thermostat out and bypass closed the forward block and head went up to 60oC and stayed there (see my last post). The rear cylinder stayed luke warm. But the engine slowed and stalled after 30mins same as before. So the problem can't be caused by overheating of the blocks or heads. The crankcase is not watercooled, and could easily be overheating from the exhaust gases blowing round the piston rings. This could lead to overheating of either the lift pump or injection pump I suppose, When I hand pump the lift pump it seems to work well enough. I will get the temperature probe on both pumps next time this happens, I have heard that old injection pumps can fail when they get hot, anyone heard of this before?

 

[hamishnf]

The engine only puts out black smoke when the cold start is depressed during running. I suspect that the inlet valves may be seating imperfectly, (despite my amateur attempts at lapping). But presumably that won't cause the engine to run fine for 20mins then slow and stall on both cylinders at the same time?

 

[david_bagshaw]

could do as the running cylinder could be choked by leaking combustion products from the other.

next time as it dies crack an injector pipe, that will show if it is fuel related.

supose you have checked the stop control is definately in the run position? if not electronically controlled, or not moving etc.

If you think the crank case is overheating due to exhaust gasses, where are they going? is the dip stick being blown out? is the crank case vent blowing?


A good check on cc pressure is to remove the oil filler while the enging is running, and putting a hand over the filler, shouldnt develop a high umph when removing hand.

 

[hamishnf]

Ok, so went down the boat again and think I have the problem. Engine only started and ran on the front cylinder. Im sure it was only running on the front cylinder yesterday, although it was definitely running on both the day before that, as I had it running with the front cylinder decompressed (not best practise, but there you go). Today the engine made a banging noise and a big puff of white smoke came out the back every few seconds. I suspect this was diesel accumulating in the rear cylinder, eventually building up and creating compression, and firing. I checked the bump heights with the engine hot and I had a whopping 3mm on the rear cylinder, and 1.2mm on the front one (which was running well). It seems strange, that with only a thin paper gasket under the blocks and a standard head gasket, the gap between the pistons at TDC and the face of the heads could be so much. The cylinder blocks obviously haven't grown over time! I'm pretty sure that the small ends are perfect because I removed the gudgeon pins during assembly and the fit was nice and tight. But there was a very small amount of vertical movement in the pistons (much less than a millimeter) so I suspect the big ends need replacing, or possibly even the main bearings. There was no knocking during running though. Why would the clearance between the piston at TDC and the face of the head grow over time?

 

[Bilgediver]

Why would the clearance between the piston at TDC and the face of the head grow over time?

There can be a couple of reasons for the large clearance. Either someone has faced of the spigot part of the head which sits in the bore though I can not think what as usually it is the gasket surface which needs sorting and this can reduce the clearance.

The other reason is a bent con rod. Have you looked to see if this is a possibility. This may be caused by water in the cylinder which cannot be compressed hydraulic locking the engine on start up. If the con rod is bent then the piston will sit low in the bore.

 

[ianat182]

Does your engine have a watercooled gearbox fitted and is the water flow through it clear. Are you running the engine in gear at all times.

I think you need the shims to be fitted on the high gap block to match the other one.

I also used to have problems with the decompression lever setting when I'd stripped down and rebuilt my MD1B, almost a trial and error, and a wrong setting can damage the valve arm itself.

ianat182

 

[scottie]

Can't remember and do not have access to figures for bump hight but would suggest that maybe the block without shims has been fitted by someone without knowledge of them and or scraped them off one but not other.

 

[alahol2]

From a complete numpty on the internals of engines... Could the pistons have been put back in the wrong cylinders? And would it make any difference anyway?