MD7A progressivley slow to start

[nickdick]

My previously faultless MD7A now suddenly takes 20 secs to start from cold, on one cylinder initially. When warm it starts immediately. I suspect it`ll be a non starter before long. Where do I start ? Local diesel engineer, who I respect, says lower than normal compression may not help but he`ll need £ 500.00 plus Vat to find out. Injectors calibrated last winter. I know most of you will suggest burial at sea but before I commit to that, is there anything simple I can check ?

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[Birdseye]

£500 to investigate is laughable - does he think he's a dentist or something?

I'm not an expert, and you follow the procedure below entirely at your own risk . take care with your own safety and get a knowledgeable friend to help.

all a diesel needs to start is a supply of atomised fuel, air, compression, and someone, or something, turning the engine over fast enough. you need to check all these points.

start by making sure the battery is good and the engine is turning over fast enough. clean and remake all battery and earth connections.

am not familiar with this particular engine. does it have glow plugs to help starting? if so, then check the plugs and their electricity supply.

then check the fuel system for air leaks. try bleeding the fuel system before you start the engine. can you get any air out of it? does it start better? if so, cure the air leaks.

then take the injector(s) out of the engine and turn the engine over on the starter with them still connected. are you getting a good fine spray of fuel from both? (dont get face anywhere near).

by this stage you should know that the engine is turning over properly, the glow plugs are working (if present) and the fuel is getting through. assuming all these are ok then check compression. the fact that the problem has arrived suddenly suggests that it is one of the above causes. bore wear is gradual.

best way to check compression is with a compression testing guage. failing that, remove the injectors and put a squirt (maybe a teaspoon max) of engine oil down each bore. briefly turn engine over to spread oil. replace injectors and start engine. did it start better? if it did, this is a crude indication of bore wear.

at this stage you have two choices - hire someone to do the job for you, or do it yourself. the latter is much more satisfying and really quite easy if you buy yourself a workshop manual and take it steadily and in easy stages. you need to remove the cylinder head and check the valves - low compression can be either valves worn / not seating, or bores / rings. valves are easier to deal with so check them first. whilst the head is off, beg /borrow/ steal an internal micrometer to check the bores. there will be an engine machine shop near you whop will do any machining work at reasonable cost.

i dont know about the price and availability of volvo spares, but i stripped, rebored and reconditioned a V8 stag engine for not much more than £100 which is why his £500 is so silly.

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[Jcorstorphine]

Why high cost on Volvo, reason Spares prices

Pistons about £250 each
Rings about £60 a piston set.
Main Bearing about £70 each
Top gasket set about £100
Bottom gasket set about £90

Ex Volvo owner



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[Davy_S]

If you need any spares it might be worth a look back on the for sale forum.
Oldestgit has a complete engine for spares MD7B (same engine).

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[castaway]

Check that the exhaust is clear. Had similar problem with my Sabb.. Turned out the exhaust was blocked with carbon.

Regds Nick

<A target="_blank" HREF=http://www.yachtsite.co.uk/fairweather>http://www.yachtsite.co.uk/fairweather</A>

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[Roberto]

aside question

<<then take the injector(s) out of the engine and turn the engine over on the starter with them still connected. are you getting a good fine spray of fuel from both?<<

How can this be done? I have a perkins 4108 but I reckon the problem is similar in most engines : the injectors are supplied through a metal pipe (from the injection pump) and in the manual it says "whenever removal of the injectors is needed disconnect the metal pipe first, to avoid bending them or stressing the joint", it is often advised to have spare pipes as bending -stressing is unfortunately easy.

When you have removed the injector, how can it be tested if the metal pipe cannot accept even the slightest bending ?

rob

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[Birdseye]

Re: aside question

cant give you ananswer without seeing the engine, but on my yanmar i loosen the pipe joints at the pump, and rotate the injectors away from the head re-tighten pump joints and off you go.

volvo will not make their own bearing shells, or ball bearings and probably not their pistons. go to an engine re-conditioner (there is at least one in most big cities) and they will have the manufacturers catalogue of things like bearing shells. they're not silly prices. they may well be able to get suitable pistons even.

in any case, difficulty starting could be no more than rings or valves ie no need for pistons or shells.

but the real point here is simple. if you dont try to understand things yourself, and get to the point where you can do most yourself, then you are at the mercy of tradesmen. even the best of them cannot afford to take the care and time you would do, and the worst will simply rip you off. ok , there are some jobs that are difficult to do yourself. and you may well earn so much in the city that you dont have to bother and dont want to. but you will never be worse off by knowing what the tradesman is doing.

does that sound pious? probably does. but in my trips further afield, i have seen countless boats disabled because the skipper didnt know how to do simple jobs like lifting a cylinder head and changing a gasket. some are even proud of it! (like they're proud of not being able to do mental arithmetic. )

must stop - i feel a meldrew coming on.

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[Roberto]

Re: aside question

i loosen the pipe joints at the pump, and rotate the injectors away from the head re-tighten pump joints and off you go.

thanks I ll try your method next time an injector check is due

r

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[oldharry]

Starting on only one cylinder then picking up on the other suggests there is a problem either with any cold start device fitted (pre heater of some sort, such as a glow plug failed, or some sort of extra fuelling device), or the compression is down on the one cylinder for some reason.

Pre heating devices, particularly electric ones are quite vulnerable and do fail regularly. They are usually simple to replace and should cost very little.

Have you already had a compression test done? If so, this still may not reveal which cylinder is in trouble. If the fault has started suddenly, (i.e.not getting gradually worse over the season) then it is unlikely to be a major wear or piston fault. Far more likely is something like a leaking head gasket, or a valve not seating properly due to carbon build up.

The fact the engine starts on one cylinder means that one is probably ok and the fault is limited to the 'lazy' cylinder, therefore not likely to be blocked exhaustr or air intake.

First thing though is to have the injector out and have it checked. Any diesel specialist will do this while you wait - it only takes minutes.

A HEALTH WARNING: reversing injectors to 'see if they are spraying properly' is VERY DANGEROUS. The velocity of the ejected fuel is such that it will penetrate your skin and introduce diesel fuel into your blood stream which leads to potentially fatal blood poisoning. So dont risk it! In any case even a trained operator will have difficulty in telling whether the spray is correct when tested this way.

No apologies for this particular rant - it IS very dangerous and people still die doing it.

Once you are sure the injectors are OK, then you must look for a mechanical fault. A compression test is the first step. If it is down then the fault is unlikely to be pistons or ring wear, which rarely shows up on compression testing. This simplifies matters as the fault is in the cylinder head which is easy enough to remove and deal with. If the compressions are near enough the same then the fault is more likely to lie with the (expensive) piston and rings assembly: but it will be accompanied by increased 'blow by' where fumes and sometimes engine oil are blown out of the crankcase breather with the engine at speed, and if the breather is blocked off crankcase pressure builds up. If there is no blow by, then the chances are the pistons/rings are OK.

Have fun - but dont throw too much money at it unless you are reasonably sure the fault has been identified. Cut off point depends on the condition of the rest of the engine. Is this the first of a series of annoying and possibly expensive faults as the engine begins to wear out?



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[dickh]

I understod there is a certain starting procedure on these old engines. A friend I knew some time ago had one and he also had difficulty starting until another boat owner showed him the correct sequence and it started immediately!
Try the <A target="_blank" HREF=http://www.volpen.org.uk>http://www.volpen.org.uk</A> for more info

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I'd rather be sailing... /forums/images/icons/smile.gif

 

[ranald]

Last boat had MD7B sail drive It to was hard to start
this was primarily caused by running the engine for long priods charging the bateries cuasing the barrels to glaze if not bady glazed you should be able to remedy this by running the engine under load ie motoring at about 2700rpm for several hours checking engine temp and exhaust colour if stiuation dose not improve then read on
some disel basic fault finding
since you had injectors serviced last year have noticed any increase in the oil level in the sump if not, good
when engine eventualy starts is it smokey if so what colour blue oil, black is exsesive fuel and white could be blocked air filter or bad combustion

if blue and clears after engine is warm no problem if it continues worn engine or glazed barrels

if black and clears when engine gets up to speed this is ok
but if it continues this could be caused by a leaking injector this can hapen if water has gone though the fuel line during combustion the heat and the steam can cause the the injector to block one of the 3 or 4 jets or at wost burn the point of the injector
if you have non atomising fuel this can wash the oil from the sides of the barrels and as a result can lower compression and hense bad starting.
all diesel engines like petrol engines nearly always are easier to start when warm

white smoke can be caused by insuficient air or exsisive and i mean lots of fuel being pumped into the engine through a leaking injector ( this is into the combustion chamber ) you would also get a rise in oil level due to the diesel being pushed past the piston and it would smell badly of diesel

have you checked the valve clearences and the decompressor is off
and the engine stop is pushing the lever on the pump to its stop


an aside I was told after I sold the boat if you put the throtle 1/4 ahead and pull the stop fully up and push it fully home and start the engine this ensures that you get excess fuel to start ( like a choke on a petrol engine) I never tried this to see if it works but it does on other Volvo's

Thought has ocurred to me your fuel may be contaninated with the dreaded bug check colour of the diesel if brown or conserably darker than fresh dump old and clean tank

ps I had A worn engin I had it re-sleeved and bought lada 1500 piston rings for a fraction of the price no problems after that well I saved £250 per piston not bad but I had to buy some gaskets from volvo but I used rhodeseal instant gasket this is the stuff Citroen Pugeot and renault use on thier engines I have used this for 5 years on a few engines

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[DavidGrieves]

Hi Nick

I have a MD7A in my boat, and very reliable it is...
Just to correct some previous posts it has no cold start device fitted, be it glow plugs or excess fuel. Nobody has mentoned it but dont spray that "magic start" stuf into it, it will become hooked on it.

I had the injectors out of mine last winter and when I refitted them it was bugger to start, sometimes on one cylinder. On close inspection I noticed compression gasses (fuel & air) leaking out from round the injector. I couldn't get them fastened any tighter because the three plates that hold the injectors down had been bent into a slight curve, the ends of the plates were making contact with the top of the cyl'head before sealing properly. I took the plates off ( 6 in total ) straightened them with a hammer and a vice. Engine starts first touch every time. I think this type of engine has a sleve type liner that the injectors fit into, these can be replaced to give you a nice mating surface for the injectors to seat into, but I'm only guessing it would be expensive.

When you removed the injectors last winter you probably cleaned them and removed some carbon that had built up over the years which may be causing compression gasses to escape. After 20 seconds or so on the starter the engine will be starting to warm up, expand, and re-seal any leak path.

Hope this helps. Keep us informed of any developments.


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[philwebb]

Why strain the metal pipes to check your injector ? Take the injector to a commercial
diesel specialist and they will check it for you for little more than a contribution to
the tea fund. I had some problems with my MD5 at the start of the season. I had a
leak between the injector and the copper sleeve. This meant taking the head off, so I had the head skimmed and put in new valve guides and springs at the same time.
Get the work done (eg valve seat cutting) by engineering workshops that do work on car engines their charges are usually reasonable. After reassembly my engine has been
as good as gold this year.


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