Crankcase breather smoke

[Guest]

We recently purchased a 1984 Hallberg rassey 42 with a Volvo MD31A engine (62HP non turbo). All is well at 2500rpm but when we exceeded this smoke came from the crankcase breather. Is the engine knackered? The boat has hardly been used for the last 12-18 months and is filled (slightly over) with cheap halfords oil. I intend to get it pressure tested but hopes for some ideas? Could it just be burning off? am i over revving? coolant problem? Rings? If it is the piston rings will I have to have the engine removed to replace them?

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[Avocet]

Hard to say. Is the smoke black or blueish? If it's black, it could be one or more injectors not sealing properly and giving too much fuel. If it's blue, It's probably oil and piston rings would seem like the first things to try. A compression test would show this up if you know what the cylinder pressures should be on that engine. Getting injectors cleaned and tested is cheap - only about £15 per injector at your local Lucas shop. Replacing rings shouldn't be done without at least honing the bores so a satisfactory job ought to require taking the engine out. You won't do it any harm running it like this (as long as you don't run out of oil!) The worse that will happen is that you get a dirty transom. If the oil level drops after a few hours running, it's probably the cause of the smoke.

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[aztec]

wasn't gonna post, as i'm probably wrong. but i'd be looking at possibility of broken rings, or rings that've been overheated. you should have this confirmed by going a leakdown test. any good diesel mechanic should be able to oblige, i'm not convinced that a compression test at cranking speed would show a problem up. may also consider a head gasket blowing across to a drain/pushrod hole.

is this a "new" problem or one that has developed?

hope i'm wrong, steve.

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[faustina]

With the greatest of respect..........................Dont worry about the colour of the smoke (even if you can identify) If itscoming from the crankcase breather, its almost certain to be coming through the bores. So worn rings/bores I'm afraid. Unlikely head gasket without other symptoms but just possible

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[bigmart]

Clutching at straws I notice that there has been no mention of valve guides. Whilst I too am inclined to think that the bores are the most likely culprit the Valve guides & seals are a possibility.

Martin

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[david_bagshaw]

you said smoke, how much?.

vast billows & clouds..... expensive trouble

small wafts, that barely fall of the end of the pipe, ..... no problem


What colour is the exhaust gas above 2500

Not knowing the engine , do you have to run abobe 2500, or is it nearas damit max any way.



<hr width=100% size=1>David
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[oldharry]

Almost certainly ring trouble of some sort. They may be worn, sticking, damaged, or there may be bore glazing. Whichever, the pistons will need to come out to ascertain and fix the problem. Dont waste too much time and money trying to get a diagnosis - there is no way of finding out without removing them, and replacement is the only remedy anyway!

A compression or leakdown test will cost and not tell you anything you you dont already know. i.e. that there is a ring fault! It will not tell you whats gone wrong. Compression testing at cranking speed rarely shows up ring faults, unless they are very bad indeed in which case its unlikely the engine would run at all.

A much simpler and more realistic check for compression blowby and which will tell you immediately if the rings are in trouble is to block off the breather system altogether, remove the oil filler cap and fire up the (previously warmed up) engine. Wearing a rubber glove, put your hand over the filler orifice for 5 - 10 seconds to seal it. The engine should be ticking over at normal speed. If there is any noticeable build of pressure - a puff of air when you remove your hand - then there is definitely blowby, and the pistons and rings need to come out for replacement/repair. Do not allow the pressure to build up or you may do other damage.

An engine with blowby may start and run quite happily, except that at higher speeds as you have seen there are excessive breather fumes, and engine oil can be blown out which is both messy and dangerous. More seriously, at speed the pressure can build up in the crankcase sufficiently to blow the oil seals out. Much more mess and more cost!

Why has the previous owner used 'cheap Halfords oil'? Is the because the engine was changing its own oil so quickly it wasnt worth putting proper oil in? Or was he just a skinflint and thought cheap oil was a realistic saving? If so, thats why you have problems now....

Whichever way - major engine repairs are called for now - and it might be worth considering the cost of replacement against that of a major overhaul. Consider: you replace the rings and possibly the pistons - could well need a rebore as well. New crank? Cost with labour could run to 30% of a new engine. Thats without looking at the cost of checking and renewing the valves, the cam shaft and followers, the lube oil pump, the water pump, the injectors, the injection pump, main bearings, cam bearings, the alternator, and the starter - all of which may be nearing the end of their service lives.... and any of which may be waiting to spring a nasty on your newly rebuilt engine.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by oldharry on 31/03/2003 09:36 (server time).</FONT></P>

 

[oldharry]

And....

.... if there is no pressure build up in the crankcase when tested the way I suggest, then the rings are OK. Before you order your new engine, have the head off and check for bore glazing - the bores will have the appearance of being varnished with a honey coloured glaze. Its still expensive to fix as the pistons must come out, but theres a good chance the rest of the engine will be OK.

Another thought - you just bought the boat - the Surveyor should have spotted this fault - should you not refer back to him? After all, a knackered engine is not exactly a minor fault....

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by oldharry on 31/03/2003 09:42 (server time).</FONT></P>

 

[stubate]

its blow by going past the piston rings, take no notice of the boing boings boinging from one solution to the next, color of the smoke etc, could be this or that. really.
if the engine hasnt done a lot of use recently, it could be the rings are "gummed up" and a bit of use will free them up. however first things first, do a definitive test on it with a compression tester, i know its difficult and a pain but its the only way.
stu

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[vyv_cox]

Have to agree. But check that the crankcase breather is working correctly and not blocked or broken. Some smoke will almost always be produced but is not obvious if the breather is functioning.

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[oldharry]

Agreed Stubate, but why mess about paying through the nose for further tests, unless he happens to have a compression tester in his kit? If there's crankcase compression, the pistons have to come out to find out why. And if its not glazed, then its knackered.

SWMBO reckons she can tell my mood by the colour of the smoke from my pipe..... so it is a diagnostic tool, but not in this case.


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[stubate]

cut the crap and get to

the root of the prob
doing the armchair bit, just a chance the underuse could be the cause and got stuck rings
stu

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[stubate]

and one other thing

is the blow by that bad?
me along with a few others on the forum could look at it and say oh thats not to bad leave it for now,
people tend to navel gaze too much especially if they are not experts, if you are looking at a couple of grand and are really worried about it pay a little to be sure before paying out
stu

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[JEG]

Re: and one other thing

I am not an expert, but, might an oil test [£15] show a large amount of soot caused by failed piston rings?
Good luck

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[JEG]

Re: and one other thing

I am not an expert, but, might an oil test [£15 approx] show a large amount of soot caused by failed piston rings?
Good luck

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[Weatherlawyer]

You don't say it but your engine is a deisel.

You don't say how you know what oil is in the engine. Didn't put it there yourself did you? Cheap (rock oil?) engine oil is not designed for deisels. You should be using high quality high detergent deisel lube.

Since the engine has been standing, it may just have picked up condensation. How much water was in the fuel tank? Or rather, what condition was it in if it had been drained by the previous owner?

If the smoke comes out of the exhaust you have valve trouble. If it's a cracked case or cylinder head it will mix the oil and water (eventually the 25:1 compression will blow out all the coolant straight away.)

Out of the breather it could be anything or nothing. You are not going to be going far in an untried boat (are you?) you should be alright pottering about while the engine cleans itself of the condensation/gum/cheap oil.

If it gets worse you will at least have one season to get an idea about what you want to do with it. If you are not going out on the rolling deep a ropey engine might last a life time. Good luck.

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[vyv_cox]

With all due respect, I should stick to lawyering, if I were you.

<You don't say it but your engine is a deisel.> Most experts are aware that the Volvo MD31A is a diesel.

<You don't say how you know what oil is in the engine. Didn't put it there yourself did you? Cheap (rock oil?) engine oil is not designed for deisels. You should be using high quality high detergent deisel lube.> Not the case. Use of a top-tier lubricant in a non-turbo engine may well be the cause of this problem. Most oils to API CD, i.e. as sold in many car parts shops, are perfect for yacht auxiliary engines. As recommended by Yanmar.

<Since the engine has been standing, it may just have picked up condensation. How much water was in the fuel tank? Or rather, what condition was it in if it had been drained by the previous owner?> What's water got to do with it? It smokes at higher revs.

<If the smoke comes out of the exhaust you have valve trouble. If it's a cracked case or cylinder head it will mix the oil and water (eventually the 25:1 compression will blow out all the coolant straight away.)> Valve trouble does not normally cause smoking. Where did a cracked head come from? No evidence whatsoever. Cracked heads have totally different symptoms.

<Out of the breather it could be anything or nothing. You are not going to be going far in an untried boat (are you?) you should be alright pottering about while the engine cleans itself of the condensation/gum/cheap oil. > Based on what has been said, likelihood is that the bores are worn, although as suggested earlier it might be sticky deposits on rings. Engines no worse than this have run for years at the cost of rather more frequent oil top-ups.



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[tcm]

from what you say, and other posts below, the engine seems ok - there's only smoke above certain revs. For a start, there's nothing much to lose by changing the oil. I would consider using flushing oil to give a good cleanout inside, and then perhaps do it again. Things like redex additive to the fuel are also suposed to have lubricating de-gunking qualities.

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[vyv_cox]

I realise on re-reading what I posted previously that I had been less than clear. Crankcase breathers are normally vented via the inlet manifold, where the reduced pressure draws any fumes out. It is not normal for full vacuum to be applied to the crankcase, as all sorts of sealing problems might result. There are two approaches in my experience but this may not be the total. I don't know your engine so not certain what is used.

One is that a small orifice is drilled from the manifold to the breather connection, limiting the flow rate. This orifice can become blocked with sludge and can usefully be cleaned. This is a known problem with Bukh engines.

The second is that a rubber spring-loaded diaphragm releases crankcase vapours to the manifold when their pressure exceeds a certain value. The diaphragm can tear, the spring can break or the cone valve can stick in its seat.

Rocker cover fumes are often not vented separately but if they are they may go direct to the air cleaner. Again, the small orifice can become blocked with sludge.

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[oldharry]

It all depends on the degree of blow by thats taking place. Basically if oil is being blown out of the breather then there is a problem which needs dealing with before long. If there are just rather more fumes than is nice then it may well be the breather system needing cleaning out as Vyv suggests, and the engine may have several more seasons useful life left in it.

Armchair experts are disadvantaged by not actually being able to SEE what is going on..... puff! puff! choke....

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