Possible gearbox trouble - oh woe

[Robert Wilson]

Now THAT would be good news because I have a brand new spare lift Pump, which I meant to put on in2015 but decided to give the old one a stay of execution.

Tranona,
Starts fine and runs nicely either on tick-over and throughout the range.
And presumably a fair bit of smoke - which there isn't.

 

[RichardS]

I wonder whether it could be worn valve stems / guides / seals? That would not lead to a loss of compression so starting would not be affected and not too much smoke but worn valves seals might lead to over-pressurisation of the rocker box which might well result in oil in the air intake depending upon the breather design.

Richard

 

[Robert Wilson]

Now then Richard, you have introduced another scenario just when I thought I was getting to grips with the problem.
Your idea makes sense. I shall have a word with my friendly auto mechanic and see what he thinks about it.
I'm beginning to think that I'll put up with the problem for what's left of this season, have a good strip down in the "off" season and hope for a belter next year.
I'll be poking an endoscope up the exhaust on Saturday, if it's calm enough to get across the Loch. Tomorrow does not look nice at all.

Thanks.

 

[Baddox]

Damaged or worn valve stem oil seals would give smoke on startup. There would be enough pressure in the cylinders to keep the oil out when running but when the engine is off, the lack of pressure will let the residual oil drain down into the cylinders. It will burn off at startup with a puff of blue smoke and then the extra pressure bleeding past the seals will get to work as Richard mentioned.

 

[anoccasionalyachtsman]

What's your typical engine use pattern, and would you have noticed that it was consuming oil more quickly?

If it's been inhaling the stuff in the filter I'd have expected you to see smoke, and also lots of burned and part burned in the exhaust pipe - so I think changing that will be enlightening.

If the new pipe helps, and it's thought that it is wear that's the cause you won't do much harm getting the season out of it if you're sympathetic. Stop if it starts to rattle. The only caution would be to carry something to block the intake with should the worst happen and it start to run on the oil mist (not wanting to scaremonger - either drain the filter regularly or divert the breather to a bottle to recycle into the engine).

 

[Robert Wilson]

Damaged or worn valve stem oil seals would give smoke on startup. There would be enough pressure in the cylinders to keep the oil out when running but when the engine is off, the lack of pressure will let the residual oil drain down into the cylinders. It will burn off at startup with a puff of blue smoke and then the extra pressure bleeding past the seals will get to work as Richard mentioned.

There is a very small amount of bluish smoke on start-up, but it hasn't got any worse in the six or so years I've used the engine (since buying the boat).
What is baffling me, as said in previous posts, is that all was well until haul-out in Autumn 2105 and then on re-launch in May this year.

Would warn valve seats cause this lack of mid/top end revs/power?

 

[Robert Wilson]

What's your typical engine use pattern, and would you have noticed that it was consuming oil more quickly?

I only use the engine for calm days to make a moderate distance and occasionally for on/off the mooring. In 2015 going round the UK I had motor/motorsail rather a lot.

If it's been inhaling the stuff in the filter I'd have expected you to see smoke, and also lots of burned and part burned in the exhaust pipe - so I think changing that will be enlightening.

First approx. 60cm of pipe is solid (stainless) then proper hard rubber exhaust hose. I can't change the s/s pipe as it's "part of the engine". This is the section I hope to investigate with the endoscope.

If the new pipe helps, and it's thought that it is wear that's the cause you won't do much harm getting the season out of it if you're sympathetic. Stop if it starts to rattle. The only caution would be to carry something to block the intake with should the worst happen and it start to run on the oil mist (not wanting to scaremonger - either drain the filter regularly or divert the breather to a bottle to recycle into the engine).

I'll keep an eye and ear on the noise and filter. As said replying to Baddox, I don't use the engine a great deal, in normal use. The engine doesn't appear to use very much oil in normal use, but a day-long motoring would use a bit. Difficult to quantify because I've never had to take much notice. I check oil and water levels about twice a month - of infrequent use.​

Thanks

 

[PaulRainbow]

Would warn valve seats cause this lack of mid/top end revs/power?

The discussion was about valve stem seals, not seats. Stem seals will behave as Richard and Baddox explained above, seats are an entirely different matter. Worn valve seats will usually mean a loss of compression, not an increase in blue smoke. They will cause a loss of power.

 

[Robert Wilson]

Gotcha, thanks.
I misread their posts. Doh!

 

[anoccasionalyachtsman]

I wonder whether it could be worn valve stems / guides / seals? That would not lead to a loss of compression so starting would not be affected and not too much smoke but worn valves seals might lead to over-pressurisation of the rocker box which might well result in oil in the air intake depending upon the breather design.

Richard

The stem seals aren't there to hold exhaust pressure back, they're just supposed to allow a dribble of oil into the guides. Pressure (and excess oil) in the rocker box comes from worn rings allowing gas into the crankcase which blows up the oil passages, reversing the downward flow of oil from rocker gallery. Worn stem seals just let too much oil down the guide, and it will run on down the valve stem either into the cylinder or back of the valve head if it's closed. Hence the puff of smoke on start, but for oil to get through the seal and out to the air filter would take a flood of oil and/or a very strange inlet tract.

 

[Robert Wilson]

So if I understand you correctly worn stem seals are not the likely culprit causing oil in the filter housing?
Likewise, worn/cracked piston rings are not the culprit?
But they (rings) might cause of the lack of mid/high revs under load?

Potentially two problems.

 

[macd]

Likewise, worn/cracked piston rings are not the culprit?
But they (rings) might cause of the lack of mid/high revs under load?

I think occasionalyachtsman (if that's who you were responding to) was saying the opposite. Anything that increases crankcase pressure can cause excessive crankcase breathing. Piston blow-by is the usual suspect. Assuming the breather routes into the air-cleaner, that could be the cause of your oily problem. Clearly rings which don't seal well enough to prevent crankase pressurisation, also don't seal well enough to make the most of combustion = less power. As suggested, though, if they were particularly bad, you might also expect starting to have deteriorated.

P.S. this is from the school of daft questions, but how's the oil level? A seriously overfilled sump could cause similar symptoms.

 

[Robert Wilson]

OK Got that, thanks.

Oil in sump is another weirdo.
After draining the sump before re-launch servicing I reckon all the oil was drained.
Fresh oil was put in, up to the mark on the dipstick.
So far so good

Ever since I bought the boat in 2010 checking the oil has been "odd" :-
If the engine has stood idle for a good while the dipstick comes out clean as a whistle, but on re-dipping the oil level shows between low/mid to full (depending on hours' use).
Immediately on re-checking several times the level is still as the "re-dip".

I am very careful to check water in the header, oil in the sump and fluid in the gearbox - perhaps not every time before I use the engine, but often.
As said above, I don't use the engine very much in ordinary day-to-day sailing.

 

[RichardS]

The stem seals aren't there to hold exhaust pressure back, they're just supposed to allow a dribble of oil into the guides. Pressure (and excess oil) in the rocker box comes from worn rings allowing gas into the crankcase which blows up the oil passages, reversing the downward flow of oil from rocker gallery. Worn stem seals just let too much oil down the guide, and it will run on down the valve stem either into the cylinder or back of the valve head if it's closed. Hence the puff of smoke on start, but for oil to get through the seal and out to the air filter would take a flood of oil and/or a very strange inlet tract.

I know all that .... but I'm trying to deduce a way in which oil could find its way into the inlet tract without the loss of compression caused by blow-by which someone suggested might not apply to Robert's engine.

If an inlet system is designed in such a way that oil could find its way into the inlet tract through the breather as a result of piston blow-by, then oil could equally well find its way into the inlet tract as a result of rocker box pressurisation.

I agree that piston blow-by is the most likely cause of crankcase/rocker box pressurisation but, if blow-by is excluded, what other explanation is there other than exhaust pressure leakage up the valve stems?

Richard

 

[anoccasionalyachtsman]

So if I understand you correctly worn stem seals are not the likely culprit causing oil in the filter housing?
Likewise, worn/cracked piston rings are not the culprit?
But they (rings) might cause of the lack of mid/high revs under load?

Potentially two problems.

Yes. stem seals won't force oil into the filter.

No, I'm saying worn rings could well be causing oil in the filter.

Worn rings loss of compression will cause low power. Very easy to test if you can borrow a tester.

But worn rings won't cause the sudden drop in power, so I'm still backing the blocked/disturbed exhaust theory others have suggested, especially since we now know that burned oil could be going out that way.

 

[anoccasionalyachtsman]

I know all that .... but I'm trying to deduce a way in which oil could find its way into the inlet tract without the loss of compression caused by blow-by which someone suggested might not apply to Robert's engine.

If an inlet system is designed in such a way that oil could find its way into the inlet tract through the breather as a result of piston blow-by, then oil could equally well find its way into the inlet tract as a result of rocker box pressurisation.

I agree that piston blow-by is the most likely cause of crankcase/rocker box pressurisation but, if blow-by is excluded, what other explanation is there other than exhaust pressure leakage up the valve stems?

Richard

Short of it being a sidevalve , exhaust over inlet design or an engine mounted on its side, I can't think how there could be a realistic chance of oil getting out that way. And for there to be any exhaust pressure^* the engine must be running, and that means there will be an irregular but healthy breeze through the inlets which would surely waft the oil through too.

^*Exhaust pressure wouldn't normally be more than a few psi above atmospheric in a non turbo engine although if the exhaust is blocked it'd be a different story, but I'd bet on the breather blowing off if it was significant?

 

[RichardS]

Short of it being a sidevalve , exhaust over inlet design or an engine mounted on its side, I can't think how there could be a realistic chance of oil getting out that way. And for there to be any exhaust pressure^* the engine must be running, and that means there will be an irregular but healthy breeze through the inlets which would surely waft the oil through too.

^*Exhaust pressure wouldn't normally be more than a few psi above atmospheric in a non turbo engine although if the exhaust is blocked it'd be a different story, but I'd bet on the breather blowing off if it was significant?

I agree that it seems unlikely in a normally-aspirated engine unless the exhaust pressure was raised by a downstream constriction ..... although this possibility is also part of the scenario under discussion. I also understand your point about the inlet valves but my assumption was that only the exhaust valves would be worn. In practice, my experience is that exhaust valves, guides and seals do wear more quickly than inlet valves which is presumably why they sometimes have thicker stems.

Richard

 

[Robert Wilson]

Update:
I was recommended to check fuel line and filters (2) for possible ingress of air upstream of the injector pump.
This is done and I'm confident that no air is being sucked into the fuel/injector pump..

The breather hose I was taking about is from the rocker box, not sump. Sorry if I misled folks.
I have changed the air filter (for new) and run the engine. No oil now seen in housing after running twenty+ minutes at mid/high revs.

No noticeable change in revs/power output under way.

Question.:-
I have two CAV type filters, first is 30 micron second is 10 micron. IF by mistake I have put two 10micron filter elements into the system, would that restrict the fuel and cause fuel starvation under load?
I only thought of this on the way back in the dinghy

P.S. Just asking, but what if one injector was mis-performing? Could this be the cause of the problem?

 

[macd]

1. The breather hose I was taking about is from the rocker box, not sump.
2. I have two CAV type filters, first is 30 micron second is 10 micron. IF by mistake I have put two 10micron filter elements into the system, would that restrict the fuel and cause fuel starvation under load?

1. Depending on the architecture of your engine, it's probably still a crankcase breather. Ever wondered how the oil you pour into the rocker cover gets to the sump...?
2. If they're clean, probably not.

 

[Robert Wilson]

1. Ah. the logic escaped me...…
2. Certainly clean, brand new in May and tank drained and cleaned.

Force4 are sending up a new exhaust hose but it won't be here til mid week, and I'm not going to start hacking-off the existing one til a new replacement is to hand

If the exhaust is clean, then I think it can only be injector(s) or injector pump.

Time will tell.

Thanks