Wobbly MD7a

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Hamish1

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Had local chandlers look at my MD7a - two issues; one is that after a couple of motor trips there is a black/ oily (?) smudge under the exhaust outlet but also although, to me, she starts and sounds very sweet she does have quite a wobble at the idle (on her rubber mounts) - this almost disappears at revs.
They think the fuel injection pump (?) needs recalibrated and that the injectors are being over-supplied with deisel and are going to check out the injectors at the same time...... Meantime she powers the boat well and I get about 5 knots.
- any thoughts from those wise old men of the sea amongst you?
 
If it were mine I would not let anyone touch the injector pump or the injector. It is starting easily and not smoking badly under load so that strongly suggests that there is nothing wrong with the injection system.

Check to see that the mounts have not failed, if that the rubber has not separated from the metal or the studs are not broken.

But single cylinder diesels always jump around a bit at idle unless they have massive flywheels.
 
TQA said:
If it were mine I would not let anyone touch the injector pump or the injector. It is starting easily and not smoking badly under load so that strongly suggests that there is nothing wrong with the injection system.

Check to see that the mounts have not failed, if that the rubber has not separated from the metal or the studs are not broken.

But single cylinder diesels always jump around a bit at idle unless they have massive flywheels.
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I think you may find that an MD7a is a two cylinder engine and that it also has a fairly substantial flywheel

5997.jpg
 
Thank you for that - yes it is two cylinder and yes it has a big flywheel - I'm a little unclear how too much Deisel will cause it to jump around a bit but presume that MAY be the cause of the black streak under the exhaust - they ARE going to send the pimp off do calibration.......
 
Probably worth checking the mounts on an oldish engine, but 2 cylinder vertical engines are inherently not well balanced.
I'd see the black, oily discharge from the exhaust as more likely a sign of bore/ring wear than over-fuelling, especially if there's no smoke under load.
Are there any fumes coming from the rocker breather or wherever?
 
Generally, oversupply of diesel causes black smoke in the exhaust. White 'smoke' in the exhaust - actually steam - is caused by water in it, often from a blown head gasket.
What colour is your exhaust?
 
Also check the oil level in the sump. Even a simple thing like worn valve guides can feed lub oil into the combustion chamber. These engines also have a cold start device designed to feed extra fuel for winter starting. If it's jammed you'll get a bit of black smoke which is most noticeable at start or at tick over. It's a long time since I had an MD but the engine mountings were not 1st quality and even when new we're prone to early life failure of the metal/rubber bond.

Re-injectors, they really ought to be periodically serviced with their HP fuel pumps; it's a specialist job done in clean rooms so NOT something either to try yourself of consign to a local mechanic. I use Panda in Fareham, there'll be something similar in your area, too. With your name, I assume you're based in Scotland so it might be Glasgow, Edinburgh or Aberdeen, but most connurbations will have a local specialist.
 
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Hamish1 said:
Had local chandlers look at my MD7a - two issues; one is that after a couple of motor trips there is a black/ oily (?) smudge under the exhaust outlet but also although, to me, she starts and sounds very sweet she does have quite a wobble at the idle (on her rubber mounts) - this almost disappears at revs.
They think the fuel injection pump (?) needs recalibrated and that the injectors are being over-supplied with deisel and are going to check out the injectors at the same time...... Meantime she powers the boat well and I get about 5 knots.
- any thoughts from those wise old men of the sea amongst you?
Click to expand...

Sounds about right to me! I wouldnt be spending money on recalibration injectors and the pump on this evidence.
Stu
 
Ok spoke to them - going to leave the pump but get the injectors checked - -also spoke to "Paul" at Volvspec and he afvised
 
skipper_stu said:
Sounds about right to me! I wouldnt be spending money on recalibration injectors and the pump on this evidence.
Stu
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Compression test worth doing ?

More to check that both cylinders are similar ( within 10% of each other ??) rather than they they are still close to the original spec. Might show up dodgy head gasket or valves.
 
I have an MD7A in my boat, and it is normally pretty smooth at idle. Smooth as in not jumping around, and cannot tell from the foredeck whether it is running or not on tickover. Mine does smoke a little on start up (which once occasioned a loud comment from the next boat in a Marina, from 7yo lad - 'Dad, why has that boat got a stinky old diesel?' ) and the transom needs a wipe down every so often. But I dont get an oily streak below the exhaust outlet, so the symptoms suggest there is something wrong. If it is starting and running OK then its not very likely to be fuelling: injector faults tend to lead to noise (injector knock) and excessive black smoke or a greyish white very pungent smog of unburnt atomised diesel. (Steam is very similar but doesnt stink!).

Oily exhaust suggests an oil leak has developed somewhere: rings are less likely as the compression would be down and it should affect starting. Saying that I once had a Perkins Perama that started and ran faultlessly except for excess crankcase pressure. Run it too hard and it would blow oil out of the breather, which was connected to the air intake and could accumulate sufficiently for the engine to run away on its own oil until the manifold had been sucked clean. Scary? Very! When I stripped it we found the rings/bores were worn to more than twice the service limit, so compression must have been way down! I digress except to highlight that good starting and running does not always mean there is nothing wrong!

Has the oily streak and vibration built up over an extended period or is this something new? Valve stem wear or seal failure comes to mind as a possible cause for the oily streak. The engine would be largely unaffected, but oil is leaking past a valve(s) into the manifold. As suggested earlier the most likely sudden cause of vibration is a failed engine mount. Get a strong lever under the engine near each mount and carefully try lifting the weight off each mount. You will see soon enough if it has failed. Your Chandler (? why not use a marine engineer who should know what he is looking for, and not just be sending bits of engine off randomly for expensive checking?) will start with the fuel system as the vast majority of diesel faults are fuel system related. But unless one cylinder is actually not firing on idle which would make it jump around and smoke badly, I would be more inclined to look for a mechanical issue to see where the oil is coming from.
 
I think you'll find that every engine has a 'sweet' spot at which it vibrates, sometimes quite alarmingly, especially those engines with just one or two cylinders. If all else is good while starting and running, the vibrations go away when you increase the revs. The main solution is to avoid leaving the engine running at those revs.
As has been said, I would also check the rubber mounts, looking closely (1) for any dripping diesel getting onto the rubber and (2) checking that the mount itself has not been twisted (even slightly) when the nuts that hold the engine feet to the top of the mounting.
Both corrections are easy DIY tasks, IMHO.

p.s. If you find that the mountings need to be replaced, they do not need to be VP. You can buy perfectly good mounts from generic suppliers for a fraction of the price. All you will need to know will be the height of the mount and the weight of the engine; the catalogue will do the rest.
 
VicS said:
Compression test worth doing ?

More to check that both cylinders are similar ( within 10% of each other ??) rather than they they are still close to the original spec. Might show up dodgy head gasket or valves.
Click to expand...

On the evidence presented, doesn't sound like much wrong with the thing. Let's not forget it's a simple, old, dare I say, crude design? A bit of soot on the hull near the exhaust? Pretty normal from an engine of this era? To put it in context our Peugeot cars, not so long ago used to get a sooty backend after a blast up the motorway?
Wobbly on tick over? And?
If really concerned, check the mounts, suspect they might be original, (I've just changed mine on my md22, it's taken away an annoying rattle from the hand rail on tick over) They had started to delaminate after 17 years!
If he is really concerned then yes, a compression check will give him an idea of the general state of the bores etc. Let's not start him worrying too much by talking about blocked water passages!
Just for a heads up, the scrapper Maestro turbo engine that I refurbished for the PBO article, I took the injectors to Dr Diesel in Oswestry to check them, don't forget they were from an engine over thirty years old, albeit "low mileage" had never been removed, had lain in the scrappy for a couple of years, yet tested out ok! This mirrors my life experiences when I was head of maintenance for an oil major in Africa, although I had spare injectors for lots of the engines, we never used them. The land crisers did nearly 200,000 kms, the chassis rusted out to finish them off, yet we never touched the injection systems!
Stu
 
Check if there is a mount near or under the fuel filter that has fuel spilt on it
The engine is getting on and that means it is worn in places and the cost of spares is horrendous so avoid casual investigation
caleycruisers maybe a local option
I wpould live with or change it rather than start a long and expensive trail
 
Before doing anything too complicated if the injectors are removed, the tips cleaned and the spray pattern checked by a commercial diesel workshop. ( The guy local to me did this for free!) You may find that this on its own may clear the black smoke. It could be incomplete combustion due to poor spray pattern. The engine joggling about, first check that your engine mounts are not knackered, then increase the tick over very slightly and you will get past the resonance point.
 
Yes, check the mounts - and probably replace them at that age! If the injectors are giving a less than perfect spray it may well cause one cylinder to stop firing at tickover, which could give you all your symptoms. All the other checks 0 such as compression - may reveal whether the engine has enough life left in it to do any further refurbishment.

Rob.
 
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