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My mercury 500 thunderbolt needs a head gasket

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Kanook450

New member
As the title says I need to replace the head gasket on my thunderbolt. Not quite sure of the year but serial number 2516794. I have a small drip coming from the cover while running. The question I have is do I have to remove the motor to do this or is there a way to access all the bolts with the motor intact? Or what needs to be removed to do the gasket? Thanks in advance
 
That is called a water jacket cover there is no head on that engine. If you can get all the bolts out without breaking any you do not need to remove the powerhead. Use the serial number and find the range to look up parts here inder mercury 500
 
Get a can of permatex aviation gasket maker and brush a light coat on both sides of the gasket and just get the bolts snug do not use a torque wrench. Use a center out bolt pattern and just pull it down slow and even i put the gasket maker on the bolt threads as well. Gasket part number 27-78026 let it cure for at least 24 hrs before you start it up.
 
Thanks for the speedy responses.
It does look like some items do need to be removed to get to the bolt heads?The rear cowl support it looks like it’s called. And obviously the plug wires.
 
Success. I got the water jacket cover off. About half the bolts did snap off but they had nuts on the back side so I could just push them out the back. The exhaust manifold side was a little more tight so I used my dremel with a small cutoff wheel to trim the broken studs flush with the case. This made them short enough to get past the exhaust manifold cover.
 
Nice i forgot you can just remove the broken bolts without using a easy out. What condition is the water jacket? Maybe replace the telltale hose and rod out the fittings then once you get it running put it in a barrel of water and pour in a gallon of salt away and let it high idle for 1/2 hr or so. Keep an eye on the exhaust cover is not getting hot. If so you will need to do the same thing to open the cooling circuits. Running in a barrel will also tell you the water pump is working properly before you take it out on the water. The muffs give you a false pos as it pressurizes the system.
 
kimcrwbr1 said:
Nice i forgot you can just remove the broken bolts without using a easy out. What condition is the water jacket? Maybe replace the telltale hose and rod out the fittings then once you get it running put it in a barrel of water and pour in a gallon of salt away and let it high idle for 1/2 hr or so. Keep an eye on the exhaust cover is not getting hot. If so you will need to do the same thing to open the cooling circuits. Running in a barrel will also tell you the water pump is working properly before you take it out on the water. The muffs give you a false pos as it pressurizes the system.
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It doesn’t look as nasty as I thought it would in there so that’s good. I did clean out the tell tale it had some gunk at the very end but now is clear.
Thanks for the tip on running the salt away. I’ll just need to find a big enough bucket once it’s all back together.
 
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