Scorpiokent
Member
I have a Single cylinder BMW D7 that sprung a leak on the head gasket so now full of water which has seized the piston, anyone got any good tips on the best way to un-seize this without causing any damage to the bore and piston?
Best way to unseize an engine
- Thread starter Scorpiokent
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TopDonkey
Well-Known Member
put a decent amount of plusgas into the bore, and leave it to sit for a couple of days, you will need to add some more each day as it will leak past the rings, but it eats rust and unsiezes engines very quickly, If you have more time, then diesel poured into the bore should unsieze it in a couple of weeks of keeping it soaked
Searush
Well-Known Member
On my old MD2B it was possible to remove the fanbelt plley & put a spanner on the crankshaft nut. Then lift the decompressors & apply a bit of force direct on the crankshaft. This would free seized rings & spinning it a few times would get it moveing freely again each spring.
jerrytug
N/A
Improvise with hoses etc a way of running boiling hot water through the cylinder cooling jacket,or heat it up with electric fires any way you can the hotter the better. And plus gas as above. And,via a wooden pad,tap the top of the piston down with a very heavy weight,much safer than trying to rotate the crank with a bar.let us know what works!
lenseman
Well-Known Member
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OK, have you fixed the head gasket leak and whilst the head was off drained out all the water. This is the first thing to do.
If and while you have the head off, you can add oil to the bore and allow the oil to seep down to the piston rings but I doubt it is 'seized'; I suspect you mean it will not turn over (with the head on) due to the non compressability of the water in the cylinder?
Whereabouts are you located in Portsmouth, it is a very big tidal lake?
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trapezeartist
Well-Known Member
Why do you think hitting the piston is "safer"? It's an impact, so you cannot know what loads you are putting on to all the components. If you rotate the crankshaft you will know how much torque you are applying (use a torque wrench on the crankshaft nut), so it is much more controlled. You would have to guess at how many times normal engine torque you might feel is a safe maximum. Remember that the big end and little end bearings would normally be subject to inertia forces far exceeding the actual expansion forces.
Scorpiokent
Member
OK, have you fixed the head gasket leak and whilst the head was off drained out all the water. This is the first thing to do.
If and while you have the head off, you can add oil to the bore and allow the oil to seep down to the piston rings but I doubt it is 'seized'; I suspect you mean it will not turn over (with the head on) due to the non compressability of the water in the cylinder?
Whereabouts are you located in Portsmouth, it is a very big tidal lake?
Ime in gosport but the yacht is in Kent near my father on a deep mooring, head is removed and in my shed awaiting new gaskets and a good going over with some wet and dry, also going to re seat the valves while its off, there is some rust damage to the injector so will need to dismantle that and see if its reusable, I've filled the bore with a lubricant for the moment but have not tried to turn the engine over, will top it up In a few days with some oil and diesel so it's well lubricated before I clean the bore and turn the engine over manually, thanks for the advice really helpfull.
Topcat47
Well-Known Member
Get yourself a sheet of 6mm float glass. Cover it with fine grinding paste and flatten the cylinder head.
I did my Yanmar 1GM10 head like this last year. Actually what I did first was to use Brasso. This showed up the low spots so I knew how much to lap off. There wasn't a lot so I got some spay adhesive and stuck a sheet of 1200grit Wet'ndry to the glass. Once I was happy with the flatness of the head, I polished it up with brasso directly on the glass. I couldn't do that with the block so I relied upon the new head gasket to cope with any unevenness there.
I did my Yanmar 1GM10 head like this last year. Actually what I did first was to use Brasso. This showed up the low spots so I knew how much to lap off. There wasn't a lot so I got some spay adhesive and stuck a sheet of 1200grit Wet'ndry to the glass. Once I was happy with the flatness of the head, I polished it up with brasso directly on the glass. I couldn't do that with the block so I relied upon the new head gasket to cope with any unevenness there.
TobyJug
Active Member
Having had some personal experience with this engine, and assuming it is raw water cooled, then please look very closely at the cast iron wall between the waterway and the exhaust port. This is the area where heavy corrosion takes place with the cast iron becoming porous.
This allowing water to pass into the cylinder via the exhaust valve port and then into the cylinder.The exhaust manifold is best removed from the head to allow a thorough examination.
BMW marinised the Hatz industrial engine and this special head is no longer available from Hatz ,the price when it was available was very expensive.
Hope this is helpful.
This allowing water to pass into the cylinder via the exhaust valve port and then into the cylinder.The exhaust manifold is best removed from the head to allow a thorough examination.
BMW marinised the Hatz industrial engine and this special head is no longer available from Hatz ,the price when it was available was very expensive.
Hope this is helpful.
Jim@sea
Well-Known Member
And dont forget that after doing that, when you try to move the piston you do it in the opposite direction, going down the cylinder bore, not up past where it seized, turning it over a few times before trying it in its normal direction.
William_H
Well-Known Member
Assuming the corrosion and seizing is in the actual piston to bore then provided the piston is somewhere mid stroke then hitting the piston top will direct the forces to the siezure without straining any of the crank gear. Indeed you can go to destruction of the piston without damaging the crank.
If the piston is right up or right down then more likely to get a lot of force via the crank but hitting will still help. good luck olewill
jerrytug
N/A
That's right,heat it up and batter that piston,it's what happens when she's running anyway!
Avocet
Well-Known Member
+1 for bashing the piston (assuming it's not at Top Dead Centre at present)! My D12 did this some years ago. You're much more likely to do it some damage by trying to turn the crank, to be honest. I had to beat the living daylights out of mine with a sledge hammer, but it did move eventually. Only thing I'd say was that I used a circle of wood about the size of the piston and hit that. Obviously, hitting the piston top itself with something sharp / hard is asking for trouble. Once the piston has started to move, just get it reasonably near the bottom of its stroke (don't hit it right at the bottom), and just pull the cylinder off it (very easy to do on a D12 and I imagine similar on a D7). You wll probably have to fit new rings and hone the bore afterwards.
I don't think the were prone to head gasket failure though. As TobyJug says, they were prone to failing due to corrosion between the water galleries and the exhaust port. If that's the case, it might be "game over" unless you can find a second hand head.
I don't think the were prone to head gasket failure though. As TobyJug says, they were prone to failing due to corrosion between the water galleries and the exhaust port. If that's the case, it might be "game over" unless you can find a second hand head.
KellysEye
Well-Known Member
I'd go with the Plusgas or WD40 for days before hitting the piston, hitting it is the last resort. One issue is if the cylinder is badly corroded it will be pitted, not good for the piston rings or compression.
lw395
Well-Known Member
I would apply plenty of heat along with plus gas or similar.
If you can heat the block and then cool the piston it may help.
When it comes to hitting the piston, you want to apply the force around the edge of the piston, you might shape a piece of wood or use a piece of strong plastic tube as a drift.
Pre-loading the crank with some torque from a spanner may help too.
Good luck!
If you can heat the block and then cool the piston it may help.
When it comes to hitting the piston, you want to apply the force around the edge of the piston, you might shape a piece of wood or use a piece of strong plastic tube as a drift.
Pre-loading the crank with some torque from a spanner may help too.
Good luck!
savageseadog
Well-Known Member
For a really serious and large case I suggested a hydraulic hand pump coupled to an injector or glow plug port.
Avocet
Well-Known Member
Sorry, forgot to say - bashing it PLUS some sort of penetrating oil and / or heat! I'd be really reluctant to bash round the edge of the piston though, in case it damaged it locally above the top piston ring groove. Obviously, when the engine is running, the piston loads are uniformly distributed across the whole surface, but it I had to concentrate the load, I'd prefer to do it nearer the middle, to be honest. Soft wood is best because it will locally crush to the shape of the piston crown.
Sandyman
Well-Known Member
Dont bother with all that expensive plusgas etc etc
Take yourself off to your nearest supermarket / shop & purchase some coca-cola and
fill the pots with that for 24hrs. Has to be the real stuff. Not diet.
It works. Has for me on a number of occasions.
Take yourself off to your nearest supermarket / shop & purchase some coca-cola and
fill the pots with that for 24hrs. Has to be the real stuff. Not diet.
It works. Has for me on a number of occasions.
lw395
Well-Known Member
The danger is that bashing the crown of the piston will cause it to spread and jam firmly in the bore.
If the bore has not been wet for long, it may well be just the iron rings corroded to the iron liner.
Transmitting the taps from the hammer as directly into the corrosion as possible will give you the best chance of cracking the oxide layer before anything else gets bent.
As it's a diesel piston, it's likely to be pretty tough, compared to the petrol engines I'm more used to.
Hitting one side of the piston might crack the oxide layers locally with less force, but there is a balance, you don't want the blow to be too localised for fear of bending the edge of the piston crown.
If it doesn't respond to a sensible level of 'persuasion' the bore is probably so corroded that a new piston and rebore will be needed anyway.
Sandyman
Well-Known Member
OK, have you fixed the head gasket leak and whilst the head was off drained out all the water. This is the first thing to do.
If and while you have the head off, you can add oil to the bore and allow the oil to seep down to the piston rings but I doubt it is 'seized'; I suspect you mean it will not turn over (with the head on) due to the non compressability of the water in the cylinder?
Whereabouts are you located in Portsmouth, it is a very big tidal lake?
With all due respect David, I hardly think you are qualified to make comment on diesel engines. Have you fixed your rusty donk yet ??? Must be getting on for 2 years since your flood.