Volvo MD6A will not rotate

halcyon

halcyon

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Just spent two years on and off finishing fit out on the boat, including changing it's Sabb for the MD6A. When obtained the engine ran sweet, during it's layup I have kept it turing over by hand to move oil round, and check compression was still there.
Last three months bolted it down, wired and plumbed it, yesterday tried to wind it up and see if we got any pressure on gauge. But after half a turn the engine stopped dead with a mechanical clonk. Doing some checks I find that I can turn the flywheel easly from 12 o'clock round to 11 o'clock, with this solid clonk at each end.
The only thing that strikes me is something in the cylinder, though a stuck valve but they look free.
Any thoughts out there ?

Thanks

Brian
 
You are right it sounds like something in the cylinder, probably water. Can you turn it over with the decompressor activated? I am not familar with the MD6A, but if there is no decompressor you should be able to press the exhaust valve down against its spring to expel any water while rotaing the flywheel. Any sign of water in the oil? If it is water, you will then have to trace the source: head gasket, exhaust system, cracked head? Do you have an anti-siphon device in place between the exhaust manifold (or wherever the water exits the engine) and the exhaust injection elbow? If not and the boat is in the water this could be the problem - water siphoned into the exhaust and filled it up and then entered the cylinder through an open exhaust valve. You have my sympathy, my engine used to suffer the occasional water-lock until I sorted out the exhaust system.
 
I assumed from halcyons question that the engine has not been near the water since being installed.

The fact that it is free except for the bit presumably around TDC and comes to a halt with a sudden clonk at about TDC would make me look more closely at the valves. It does rather sound as though one is stuck open. We do not know which part of the cyle of two revs we are in. If it is the power and exhaust parts of the cycle it should be possible to see the exhaust valve opening as the piston rises, if the rocker cover is off. If it is in the induction and compression parts of the cycle then it should be possible to see the inlet valve open as the piston goes down. When both are closed, on the compression or the power stroke, the tops will be level if they are closing properly and it should be possible to detect the clearance between the rocker and the valve stem. If either is more than the small clearance specified then it indicates that that valve is stuck open. I would say that if a valve is stuck it is more likely to be the exhaust one.

Another possibility is that there is a ring of rust on the cylinder wall very near the of the stroke but that is unlikely and would not result in such a sudden stop with a clonk.


If I am wrong about the engine not having been near any water then check the above but then go for cindersailor's lines of thought.

I know the MD11 rather than the MD6 but the 11 is just like two 6s stuck together.
 
Engine and boat have not been in water.
Engine is on flex mounting, has flex coupling, and has the problem in neutral, forward and reverse.
Removed rocker cover, there is a clearance on all tappets, all valves move freely.
No water has been in engine for last year.
It appears thet it is No 1 cylinder that is stopping on compression stroke, but I hope to take injectors out to-morrow to check TDC, I hope?. Number 2 appears to be going through TDC.
Have been turning engine over.
It has decompressor lever, makes no effect.

Brian
 
[ QUOTE ]
all valves move freely.

[/ QUOTE ] But do they all close fully. Could it be that one of them is sticking before it is fully closed and remaining open just enough for the piston to hit it. The decompression lever only opens the valve a little, not enough for the piston to hit it.

Sorry I was thinking the MD6 was a single cylinder engine. I get in a bit of a muddle with the number system!
 
Pointless speculating. Whatever it is you need to have the head off and have a look. I hope for your sake it is in the top end somewhere.
 
Have you had the injectors out since it last ran? I assume you could have put oil in during the lay-up?

I once saw a piston with a perfect shape of a nut stamped into the top.

I would check that there was not any unwelcome guests in there. Even a small piece of metal in the inlet manifold could do it.

I cannot tell if yours is a direct injection (End of injector is inside cylinder as opposed to a cavity in the head). If the nut falls down into the hollow of the piston top and the you manage to start the engine it could suddenly stop with alarming consequences.
 
It is direct injection or so says the info you can access at http://www.volvo.com/volvopenta/global/e...engine/inboard/

The point is the engine was, we are told, running well but after a couple of years during which time it has sensibly been rotated from time to time it now will not turn over.

If it has been kicking around with the air cleaners off or the exhaust manifold off then a foreign body could have got in but I assume that is not the case.

Boatmike may have a bit of a point in saying that it is pointless speculating but I would want to determine with some degree of certainty where the problem is before dismantling things, if only to save the exhorbitant cost of gaskets unnecessarily! I assume this is like other similar VP engines in having two separate heads so one would want to know which one to remove for example.


BTW Brian,
If it is similar to the MD11 you will find an oil feed pipe to the rocker shaft which has to be disconnected and bent out of the way a bit to lift the head off. Treat it gently, we broke one once and then to remove it and repair it the whole cylinder block had to come off, or at least be lifted clear of the top of the crankcase.
 
Take out injectors. Rotate engine stick pencil down't ole to see whish pistin is upperds. Then remove offendin 'ed.
This is a perticlularly nice Merlot y know. Hic! Why am I on this compooter talkin about engins in me drinkin time?
 
Been down boat, removed injectors, number one cylinder is not going over DTC as thought. It's a one piece head, Key part are qouting around £35 head gasket, £55 decoke set, plus vat and p&p, looks £70 to find whats in there !!!!!!!!!

Thanks for comments.

By the way, don't put a pencil down the hole, it will break the end off, then you have two items down there, I used a bit of stiff wire.

Brian
 
I believe that the current rocker cover gasket is thinner than the origional and that you need to use two to obtain the correct clearance for the decompression lever.

On one occasion when I had a problem with the dynastart/regulator, I was turning the hot engine over by hand with the engine decompressed when it jammed solid - I thought that it had seized but eventually found that rotating the flywheel backwards slightly freed it up and it was then normal. I believe the decompression gear can jam it all up. I knew of another engine where the decompression mechanism for one of the cylinders was broken.

I would suggest that youn ensure that the decompession gear is in the normal run position and try turning it over - easy if the injectors are still removed - otherwise turn using the flywheel rather than the starting handle.

Ash
 
Re: Volvo MD6A will not rotate update

Many thanks for last post, I wondered why there was two rocker cover gaskets in the decoke set.

Have removed head, found solid carbon the thickness of the head gasket. At some point a bit of rust/cast iron had fallen from inside the exhaust manifold, and through the exhaust port into the engine. This was sitting ontop of the solid carbon, thus stoping the piston going over TDC.

What else have I found, other Volvo owners may find it interesting, or not as the case maybe.
/forums/images/graemlins/mad.gif
Two waterways between the head and block were solid, no hole at all.
Three more were 90% blocked.
The remainder were 20-50% blocked, only two large ones nearly clear.
Engine block to exhaust manifold, three water ways blocked, only large water way open.
Thermostat has no closing disc, therefore will no block water flow, I am assuming the disc is missing?,as a 7 mm pin in a 16 mm hole looks wrong.
The return hole from thermostst to exhaust manifold is blocked solid, so if themostat was right, the water has no where to flow too!!!!.
/forums/images/graemlins/laugh.gif
Good points,
Cylinder bores look undamaged, no score marks, and there is no step so little bore wear.

Many thanks

Brian
 
Re: Volvo MD6A will not rotate update

Thanks for reporting back.

The state of the water passages sounds typical for a seawater cooled engine of that age and is certainly in line with our experiences with an MD11c dating from circa 1977. I hope you are going to be able to clear them.
Fitting two rocker cover gaskets is a funny idea. You would think they would supply a single gasket of the correct thickness.

Look critically at the valve springs. If there is any surface rusting it can lead to their failure. We believe that was the cause of ours dropping a valve into a cylinder. That really made a mess of things!
 
Re: Volvo MD6A will not rotate update

Thank you for the valve spring info, just put head back on. Have a feeling that one was a bit rough on the ground half turn on the end, now waiting for the bang !!!!!.

Found today, the flange that moves to open and close the thermostat has been removed. To compensate, they filled in the water way that allows a feed to water injection elbow, from thermostat with a cold engine until thermo opens. I think this has resulted in the exhaust elbow to cracking the casting.

Off to get a mortage to buy a new thermo from Volvo, may try Keypart though, hopefully a little cheaper. Then try and open up a port through the blockage.

I'll be were I was a fortnight ago then, might still make a launch for the 28th Aug, just hope for a late summer this year.

Brian
 
Re: Volvo MD6A will not rotate update

When you look at the face of the thermostat cover - what looks like a small port below the themostat - isn't. The hole is there as part of the manufacturing process, then blocked off with a brass plug. Not sure why the volvo manual then shows that it needs a small o ring.

With the thermostat closed, the water flow is along the lower pipe, into the stat cover, across the smooth face of the stat, and out to the top pipe.

When the thermosta opens, water is induced by themal circulation into the waterways from the tee piece in the bottom pipe, cilculates, and exits the block at the capsule side of the stat, thro the stat and out of the top pipe.

Ash
 
Re: Volvo MD6A will not rotate update

Spent ages trying to unblock that on a MD11C. No brass plug just no hole.
 
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