Engine seized

[MoominPapa]

The point is that the valves must have been shut and therefore could not have been jammed open to now be hitting the piston, anyway,3/4 of a turn? nearly a whole turn I would say if it were a valve. Plus your post would have the rocker trying to push the valve open against the hydraulic "brick wall" at the top of the compression stroke? Yes something would have to give, the rod.

On these slowish diesels, the valve springs are quite weak: it's perfectly possible to depress the valves with a strong thumb. If the engine sat for weeks with water in the exhaust, that will have rusted up the exhaust valve guide. the camshaft would still be strong enough to open the valve and the crap in the guide and on the stem could then have jammed it open, with the spring not strong enough to close it again.

 

I've got some experience of this on the ebay-spare FR2, which has had water down the exhaust at some point. The inlet valves move easily by hand. The exhaust valves are siezed solid.

 

As everyone else has said. Really, spanner time is needed.

 

MP.

[Chris Pink]

I'm with Mr Papa on this, take the crankcase door and rocker boxes off, easy(ish) you should be able to tell what's stopping the motion.

[Sir Nibble]

On these slowish diesels, the valve springs are quite weak: it's perfectly possible to depress the valves with a strong thumb. If the engine sat for weeks with water in the exhaust, that will have rusted up the exhaust valve guide. the camshaft would still be strong enough to open the valve and the crap in the guide and on the stem could then have jammed it open, with the spring not strong enough to close it again.

 

I've got some experience of this on the ebay-spare FR2, which has had water down the exhaust at some point. The inlet valves move easily by hand. The exhaust valves are siezed solid.

 

As everyone else has said. Really, spanner time is needed.

 

MP.

The valve must have been open for water to enter the cylinder. The valve must have closed for hydraulic lock to occur. Ergo, the valve is not stuck.

[MoominPapa]

The valve must have been open for water to enter the cylinder. The valve must have closed for hydraulic lock to occur. Ergo, the valve is not stuck.

Alternative scenario: Valves were closed and exhaust manifold filled with water which rusted-up the exhaust valve guide, no water in cylinder. Engine turns and camshaft forces exhaust valve open against rust. Water enters cylinder. Spring not strong enough to close valve against rust, rising piston contacts still-open valve and engine stops with a clunk: water now in cylinder.

 

I think it's more likely that a con-rod has been banana'd, but I'm trying to keep hope alive here, OK?

 

MP.

 

Edited to add: My theory only really works if the valves are inclined: if the valves move on an axis parallel to cylinder then the rising piston would have smashed the exhaust valve closed again, even if the spring couldn't do it.

Edited January 28, 2010 by MoominPapa

[billh]

Tried to start the boat engine today; it turned briefly then stopped with a heavy 'clunk'. It's a Petter PH2W and what I fear is that water has got into it through the roof exhaust stack - it should have been covered but the cover blew off 2-3 weeks ago and I forgot to replace it.

 

To investigate further I took the injectors out and was able to turn the engine a bit with a stilson on the prop - water squirted out the rear injector injector orifice which seems to confirm this diagnosis. Eventually after turning the engine forwards and back again several times no more water came out.

 

I now have an engine which will turn pretty easily for about 3/4 of a crankshaft revolution but then stops solid with the real feel of locking up. I'm wondering what's stopping it. Would a bent valve give this symptom; a bent pushrod or what? I don't want to start stripping the head(s) off if the problem is elsewhere.

 

PS Just to complete the day from hell our car - a bloody useless Citroen C3 diesel - wouldn't start and I ended up being towed to a dealer by the AA!

 

Personal experience of Petter PH2 air cooled in a dumper. The engine often got water in the cylinders due to being left out in all weathers for long periods. Taking an injector out and turning it over only gets rid of some of the water and it can still hydraulic lock when you put the injector back. You don't say if it is locked with the injectors still out - if it is there is a mechanical problem. Bent valves are unlikely , they are vertical above the piston and bent con rod also very unlikely- the PH2 is a robust engine and a starter motor or handle isn't going to bend the rods. Have you considered the possibility that a foreign object has got onto the top of a piston? Nut, washer , small stone?I had this a while ago on an Enfield diesel, a nut had somehow got into a cylinder and caused the engine to lock up(after 3/4 turn)

Bill

[Sir Nibble]

Ice?

[steamraiser2]

Oh Dear!, Firstly dont despair as the PH2W is a very robust engine and is easy to fix. You appear to have suffered a hydraulic lock caused by the rain water which will probably have bent a conrod if you have tried to crank it over. The head and cylinder barrel are easy to remove from this engine as is the crankcase door. Drain off the oil and take the head off, remove the barrel and undo the big end. It all comes out of the top. On the outside of the barrel assembly are two push rod tubes, you will need to remove these... note which way up they go as they will pour out oil if re-fitted incorrectly.

 

Don't try and straighten a bent rod. Some of the engine remanufacturers can take slight bends out of rods with a purpose built rig but its far better to replace it. This is where you can get lucky. Although the PH2W is not that common its air cooled sister the PH2 is still a common engine and often come up on Ebay ex dumpers etc. If my memory proves correct they are the same rods. You may be lucky and track down a new, old stock item ( try Sleeman & Hawken in Teignmouth who hold a large stock of obselete Lister / Petter stuff). Check the bumping clearance on the head as you reassemble as the rods can vary slightly. Other than that its a simple enough job. Oh..one more thing... cover the exhaust before you go home!

[Chris Pink]

Personal experience of Petter PH2 air cooled in a dumper. The engine often got water in the cylinders due to being left out in all weathers for long periods. Taking an injector out and turning it over only gets rid of some of the water and it can still hydraulic lock when you put the injector back. You don't say if it is locked with the injectors still out - if it is there is a mechanical problem. Bent valves are unlikely , they are vertical above the piston and bent con rod also very unlikely- the PH2 is a robust engine and a starter motor or handle isn't going to bend the rods. Have you considered the possibility that a foreign object has got onto the top of a piston? Nut, washer , small stone?I had this a while ago on an Enfield diesel, a nut had somehow got into a cylinder and caused the engine to lock up(after 3/4 turn)

Bill

 

I was wondering whether there was still water in it. Decompressors?

[steamraiser2]

Good point Chris..best to decompress the engine and take the injectors out and wind it over just in case some water remains

[soldthehouse]

Good point Chris..best to decompress the engine and take the injectors out and wind it over just in case some water remains

Already been covered

 

Good point Chris..best to decompress the engine and take the injectors out and wind it over just in case some water remains

Already been covered

[Chertsey]

Probably at least a month I have to admit - and of course we've had plenty of snow and rain in that time. (Hangs head in guilt and shame...)

So leaving one like that for eight+ years isn't a good idea then?

[MoominPapa]

So leaving one like that for eight+ years isn't a good idea then?

Different problems. After eight+ years the pistons will be seized in the bores, so there's no chance of getting the flywheel moving with enough kinetic energy to bend the rods.

 

Pick your poison: new rod, or (maybe) new cylinders and liners.

 

MP.

[billh]

Different problems. After eight+ years the pistons will be seized in the bores, so there's no chance of getting the flywheel moving with enough kinetic energy to bend the rods.

 

Pick your poison: new rod, or (maybe) new cylinders and liners.

 

MP.

Neither is there enough kinetic energy to bend the rods with a starter motor or handle. The only way the rods would bend is if the engine seized suddenly , say by a dropped valve, at full power . Even then it's more likely the piston would be smashed before a rod bent. Have you seen a PH rod? My guess is there is still water in it, or as someone suggested, solid water (ice). We are talking about a 1950's designed British engine here , made to withstand all sorts of abuse , including getting water inside, not some flimsy automotive-derived modern disposable.

Bill

[LEO]

Neither is there enough kinetic energy to bend the rods with a starter motor or handle. The only way the rods would bend is if the engine seized suddenly , say by a dropped valve, at full power . Even then it's more likely the piston would be smashed before a rod bent. Have you seen a PH rod? My guess is there is still water in it, or as someone suggested, solid water (ice). We are talking about a 1950's designed British engine here , made to withstand all sorts of abuse , including getting water inside, not some flimsy automotive-derived modern disposable.

Bill

 

Hi, are talking about a push rod or a con rod?

 

Leo,

[billh]

Hi, are talking about a push rod or a con rod?

 

Leo,

 

Con....... a push rod could be got straight enough to work ok in a vice with a nammer!

[soldthehouse]

Neither is there enough kinetic energy to bend the rods with a starter motor or handle. The only way the rods would bend is if the engine seized suddenly , say by a dropped valve, at full power . Even then it's more likely the piston would be smashed before a rod bent. Have you seen a PH rod? My guess is there is still water in it, or as someone suggested, solid water (ice). We are talking about a 1950's designed British engine here , made to withstand all sorts of abuse , including getting water inside, not some flimsy automotive-derived modern disposable.

Bill

Without repeating my previous comments I agree with your conclusions in the main with one exeption. The stress at slow speed is likely to affect the valve train, The rockers donot apply pressure in a completely downward movement there is always some lateral movement that is ultimately put on the guides causing wear. With a worn engine this sideways movement under the kind ofpressure involved in a hydraulick situation will bend the valve stem. Another cause as was mentioned briefly by the op could be pushrod, camshaft or cam follower failure. I agree that a bent rod is usually due to an engine coming to an abrubt halt from high speed...

Edited January 28, 2010 by soldthehouse

[LEO]

Con....... a push rod could be got straight enough to work ok in a vice with a nammer!

Sorry, but I have seem con rods bent by hydraulic force exerted by the starter motor and a decent battery on an areo engine.

 

We also see it on the communal motor mower on the moorings when someone takes on a mooring ring with the motor going flat out - the ring wins.

 

Water and especially oil don't compress much and a big flywheel provides a lot of Kinetic energy, GU mooring rings are pretty solid and easily beat a Briggs and Stratton.

 

M

[Thewatchmaker]

Yes but Briggs Stratton rods are brittle cast alloy.

[billh]

Without repeating my previous comments I agree with your conclusions in the main with one exeption. The stress at slow speed is likely to affect the valve train, The rockers donot apply pressure in a completely downward movement there is always some lateral movement that is ultimately put on the guides causing wear. With a worn engine this sideways movement under the kind ofpressure involved in a hydraulick situation will bend the valve stem. Another cause as was mentioned briefly by the op could be pushrod or cam follower failure. I agree that a bent rod is usually due to an engine coming to an abrubt halt from high speed...

 

But,but, but, the hydraulic lock due to water occurs on the compression stroke when both valves are shut and because of that the water has nowhere to go and is incompressible, that's why it appears to go "solid" at the top of the stroke. There is no extra stress on the valve train because the increased pressure is all on the valve head and seat . If the OP is saying that the engine is still seized, with *both*injectors out then I agree, something is very wrong. Possibly frost damage as it's water-cooled?

 

Sorry, but I have seem con rods bent by hydraulic force exerted by the starter motor and a decent battery on an areo engine.

 

We also see it on the communal motor mower on the moorings when someone takes on a mooring ring with the motor going flat out - the ring wins.

 

Water and especially oil don't compress much and a big flywheel provides a lot of Kinetic energy, GU mooring rings are pretty solid and easily beat a Briggs and Stratton.

 

M

 

An aero engine will have lightweight conrods and a chuffing powerful starter motor - fine in normal circumstances . I'm not going to comment on B&S lawn mower engines ,my contempt for them knows no bounds!

Petter PH is in the same league as Lister SR etc. That is the Bomb-Proof League.

Bill

[ditchcrawler]

I'm not going to comment on B&S lawn mower engines ,my contempt for them knows no bounds!

Petter PH is in the same league as Lister SR etc. That is the Bomb-Proof League.

Bill

Bent the crank on mine when I hit a bit on concrete

[Timleech]

Without repeating my previous comments I agree with your conclusions in the main with one exeption. The stress at slow speed is likely to affect the valve train, The rockers donot apply pressure in a completely downward movement there is always some lateral movement that is ultimately put on the guides causing wear. With a worn engine this sideways movement under the kind ofpressure involved in a hydraulick situation will bend the valve stem. Another cause as was mentioned briefly by the op could be pushrod or cam follower failure. I agree that a bent rod is usually due to an engine coming to an abrubt halt from high speed...

 

I agree valve stems can and will get bent even if they are square to the piston top.

I've seen it with big Kelvin diesels, a couple of times.

One one occasion, not relevant here but may be of interest, on a T6 where the valve had been 'lightly' sticking just now & again, it started to display strange symptoms where it would actually open slightly during the firing stroke. I eventually worked out that the stem was very slightly bent just enough that the valve face couldn't seat properly, and the geometry was such that the rush of gases between seat and valve face was lifting the valve off its seat.

Also, on my 'to do' list tomorrow is to source an exhaust valve for a TASC8 to replace one with a significantly bent stem, probably the same cause though I don't know the exact history of that engine.

 

 

Tim

Edited January 28, 2010 by Timleech

[soldthehouse]

But,but, but, the hydraulic lock due to water occurs on the compression stroke when both valves are shut and because of that the water has nowhere to go and is incompressible, that's why it appears to go "solid" at the top of the stroke. There is no extra stress on the valve train because the increased pressure is all on the valve head and seat . If the OP is saying that the engine is still seized, with *both*injectors out then I agree, something is very wrong. Possibly frost damage as it's water-cooled?

 

 

 

An aero engine will have lightweight conrods and a chuffing powerful starter motor - fine in normal circumstances . I'm not going to comment on B&S lawn mower engines ,my contempt for them knows no bounds!

Petter PH is in the same league as Lister SR etc. That is the Bomb-Proof League.

Bill

I think you like me faced with the same problem would go about a diagnostic process and come up with a solution in a relatively short time. It is another world trying to diagnose something with only limited facts at hand, who knows there might be a game show to be devised out of this type of situation,, diagnosing a fault blinfolded and only given a small number of factswith no history. the mind boggles.......

 

 

I agree valve stems can and will get bent even if they are square to the piston top.

I've seen it with big Kelvin diesels, a couple of times.

One one occasion, not relevant here but may be of interest, on a T6 where the valve had been 'lightly' sticking just now & again, it started to display strange symptoms where it would actually open slightly during the firing stroke. I eventually worked out that the stem was very slightly bent just enough that the valve face couldn't seat properly, and the geometry was such that the rush of gases between seat and valve face was lifting the valve off its seat.

Also, on my 'to do' list tomorrow is to source an exhaust valve for a TASC8 to replace one with a significantly bent stem, probably the same cause though I don't know the exact history of that engine.

 

 

Tim

I, sure someone on ebay was selling some used pistons out of a tasc8 they may have a previously owned valve, or are parts more readily available than that..

[Timleech]

I think you like me faced with the same problem would go about a diagnostic process and come up with a solution in a relatively short time. It is another world trying to diagnose something with only limited facts at hand, who knows there might be a game show to be devised out of this type of situation,, diagnosing a fault blinfolded and only given a small number of factswith no history. the mind boggles.......

 

........and we're all unknowing participants..........

 

 

Tim

 

I, sure someone on ebay was selling some used pistons out of a tasc8 they may have a previously owned valve, or are parts more readily available than that..

 

I could phone Kelvins (British Polar) and have one here next day, but it wouldn't be cheap and I'm not in that much of a hurry

 

Tim

[starman]

Personal experience of Petter PH2 air cooled in a dumper. The engine often got water in the cylinders due to being left out in all weathers for long periods. Taking an injector out and turning it over only gets rid of some of the water and it can still hydraulic lock when you put the injector back. You don't say if it is locked with the injectors still out - if it is there is a mechanical problem. Bent valves are unlikely , they are vertical above the piston and bent con rod also very unlikely- the PH2 is a robust engine and a starter motor or handle isn't going to bend the rods. Have you considered the possibility that a foreign object has got onto the top of a piston? Nut, washer , small stone?I had this a while ago on an Enfield diesel, a nut had somehow got into a cylinder and caused the engine to lock up(after 3/4 turn)

Bill

 

 

Wow! Thanks for all the advice. I've come in after being away all day to three pages worth. The spanners come out tomorrow so I may have more to report.

I must say it does seem a little odd to me; the engine can be spun round easily (when decompressed) for just over 3/4 turn and then stops so abrptly it is exactly as billh says as though it's physically stopping against something. There's a clunk and that's it. Curious because nothing has been done to it - it was running fine; I drained the coolant out to replenish the anti-freeze and then left it to its fate!

But, as many have said, enough of theories, only the spanners will reveal the truth.

At least it should be easier then the bloody broken down car - while being towed to the garage I charged my flat phone battery via my car charger. Result - somehow - a completely knackered phone and a whole string of fault codes in the car computer because some weird voltages somehow were going through from the cigarette lighter socket. The garage is baffled to say the least!

[starman]

Well the spanners have revealed the depressing but predictable truth. A considerably bent con-rod (and a bent exhaust pushrod on the same cylinder). The offending cylinder is now stripped down and the rod removed.

I haven't looked at the other cylinder yet - I'm hoping it ought to be okay because the piston was down while the damaged one was up and also the damaged cylinder is the one which was full of water - nothing came out of the other when the engine was turned. I guess I ought to have a look but annoyingly getting the crankcase inspection cover off means removingthe starter and the boat's fast filling up with dismantled pieces of engine.

 

So the hunt is on for a new con-rod - the Petter service manual say the two should balance to 7 grams; I don't know if that will cause any problems.