Yanmar - cranking damage

[Halo]

There is a good Yanmar website at

http://psyberspace.com.au/yanmar/anatomy.htm

Amongst other things It says that if you are cranking over a Yanmar and it does not start you should stop the seacock to prevent water getting into the cylinders. This seems logical but has anyone had a problem ?

Martin

 

[prv]

Amongst other things It says that if you are cranking over a Yanmar and it does not start you should stop the seacock to prevent water getting into the cylinders. This seems logical but has anyone had a problem ?

Yes - someone who posted a couple of weeks ago having knackered his engine in exactly this way.

It's not specific to Yanmars, by the way.

Pete

 

[VicS]

not only Yanmars. Almost any engine with a wet exhaust system can be similarly affected.

 

[LP1]

How would sea water get into the cylinders during cranking but not in running the engine? The cooling water runs only in the part of the engine it's supposed to unless there is a fault?

 

[prv]

How would sea water get into the cylinders during cranking but not in running the engine?

Because when the engine is running, it's producing exhaust gas that will blow the water out of the exhaust.

If it's not running because of some problem, the water pump still operates when you turn it over on the starter motor. So with each starting attempt, you pump a bit more water into the exhaust system. Eventually it reaches the engine, and floods into the cylinders through the exhaust valves.

Pete

 

[lpdsn]

How would sea water get into the cylinders during cranking but not in running the engine? The cooling water runs only in the part of the engine it's supposed to unless there is a fault?

Because there isn't the exhaust pressure to force the water out of the exhaust when the cylinders aren't firing away. Compare the level of the exhaust outlet to the position of your engine compartment. In theory the water in the exhaust system could reach this level.

In practice you have to crank it a helluvalot to pump that much water through into the exhaust so that it floods back into the engine.

 

[lpdsn]

Because when the engine is running, it's producing exhaust gas that will blow the water out of the exhaust.

Beat me to it.

 

[LP1]

Surely though the 'cranking' would provide the sufficient thrust to eliminate any seawater from back entering into the cylinders? That would be a serious design fault to allow flooding of cylinders on 'cranking' of engines or am I misunderstanding something here???

 

[Tranona]

Surely though the 'cranking' would provide the sufficient thrust to eliminate any seawater from back entering into the cylinders? That would be a serious design fault to allow flooding of cylinders on 'cranking' of engines or am I misunderstanding something here???

No, as the others have said it is the exhaust gases that expel the water, not the cranking of the engine without it starting and producing gas. The water collects in the water trap in the exhaust system and as the outlet is higher than the engine (or has a loop in it) the excess water goes back up the exhaust into the engine.

 

[prv]

That would be a serious design fault to allow flooding of cylinders on 'cranking' of engines

Well, the seriousness is a matter of opinion, and you'd have to crank away for quite some time to fill the average exhaust system all the way back to the engine. But it's certainly a possibility.

Note the warning under the starter button on my previous boat's engine panel:

Pete

 

[ianabc]

Wet exhaust

ALTERNATIVE SYSTEM

STAND PIPE SYSTEM

without exhaust pressure forcing water out of the system

is possible

I know as we made one ourselves.

Basically it's the engine exhaust entering a can from the bottom through a pipe almost to the top of the can.

Inside is an stainless disc covering the exhaust,

cooling water enters and leaves the can at differnt heights ensuing that there is always water but never over the exhaust which is the very top.

Engine pressure never ever required.

 

[prv]

Basically it's the engine exhaust entering a can from the bottom through a pipe almost to the top of the can.

Inside is an stainless disc covering the exhaust,

cooling water enters and leaves the can at differnt heights ensuing that there is always water but never over the exhaust which is the very top.

I can't really visualise this - but it's irrelevant anyway as nobody likely to suffer from this problem will have such a contraption. If they were knowledgeable enough to fit one, they wouldn't make the mistake of pumping a conventional exhaust system full of water either.

Pete

 

[ianabc]

http://www.moyermarine.com/forums/attachment.php?attachmentid=3409&d=1297312493

STANDPIPE EXHAUST DIAGRAM

 

[pcatterall]

Any one had a stab at putting a figure on this ( I know each system will be different).
I only crank for 3 lots of 10 seconds, am I being overcautious?

 

[prv]

http://www.moyermarine.com/forums/attachment.php?attachmentid=3409&d=1297312493

Thanks. The "New" version appears to be essentially the same as a conventional exhaust elbow, just constructed a little differently.

Your claim that it never needs exhaust pressure to push the water out only holds true if the exit pipe remains lower than the can all the way to the skin fitting - no swan neck. That in turn means that, to keep waves out, the can has to be mounted as high as possible - if it were an off the shelf system, this would be called a high-rise elbow. Swan necks in sailing boats generally run up to deck level, so for equivalent safety your dry rising pipe and can must do the same. But unlike a loop of rubber hose, or a pre-formed plastic swan neck, the dry pipe and can are hot. This will limit where they can be mounted, preferably inside the engine space, which in most yachts doesn't reach up as high as the deck. A cool rubber pipe in a locker or void space somewhere in the stern is much more flexible (in both senses!). The dry pipe also has all the problems of a dry exhaust stack, in terms of corrosion, lagging, vibration-proofing, etc.

Alternatively, you mount the can immediately above the engine, without a tall rising pipe, and then you need to have a loop or swan neck in the exit hose to keep the sea out. Then you rely on the engine pressure to push the water up over the hump, and you're in exactly the same position as a conventional system with regard to filling the hose, then the can, then the cylinders, if the pump runs but the engine doesn't.

Pete

 

[MagicalArmchair]

Gosh prv, love the panel :encouragement: - mine is made up of stickers, plywood and some of Maplins best toggle switches at the minute

 

[RichardS]

Any one had a stab at putting a figure on this ( I know each system will be different).
I only crank for 3 lots of 10 seconds, am I being overcautious?

I think that was the recommendation from the Beta manual I quoted a week or two ago. After that you are right to close the seacock. It's not usually too difficult to get at - well at least mine aren't - and then you're 100% protected against hydrolocking!

Richard

 

[lpdsn]

Any one had a stab at putting a figure on this ( I know each system will be different).
I only crank for 3 lots of 10 seconds, am I being overcautious?

10s is an awfully long time to crank for. Even if I haven't bled the injectors (which is usually the case coz I'm lazy) two or three cranks of a couple of seconds is sufficient.

 

[pcatterall]

10s is an awfully long time to crank for. Even if I haven't bled the injectors (which is usually the case coz I'm lazy) two or three cranks of a couple of seconds is sufficient.

Yes it is a long time. My engine usually starts within 2 seconds. But on the occasions that I have had to bleed her it can be 10 seconds though I have not used a stop watch ( as I usually have not got a spare hand)