Page last updated July 17, 2008



Mercury Gasket Replacement

I have several pages entailing the gasket replacement process for these particular Mercury Models (650 - 700).

Some are easy to get to and some of them are difficult and can at times cause additional problems. The exhaust cover gaskets or head gaskets gave a problems on both engines. It was so long since those areas were serviced, the headbolts were solidly corroded in place. Both ended up having broken headbolts in the same place. I'll upload pictures of locations soon. If you have a similar engine design, be weary of these head bolts. They may give you the same problem. See top menu for quick access links to common gaskets.

Gasket do not require you to screw until you can't screw anymore. Apply the proper torque according to the manufacturer recommendations. I have found that if you hand tighten the bolts (all of them) and then apply a small amount of torque past hand tight. It should suffice. Too much torque will result in a blown gasket. In order to hand tighten torque, you may need to CLEAN bolt holes with a tap set. By "cleaning" bolt hole, it will allow to hand tighten bolts, while you are at it, make sure you clean bolts with a dremmel or wire brush.

Exhaust cover gasket - This area has 2 gaskets and two plates; one gasket inbetween each exhaust cover. If you have a thermostat, this has a rubber ring that needs to be

replaced as well as the housing that it sits against. Those may or may not come with your gasket set.

There are 2 bolts that hold the exhaust cover in the center that may give problems (see pic to the right). Both Mercury Outboards that I worked had the same problem. Bolts were solidly corroded in place and broke off easily. Be careful, apply some WD-40 or similar item and maybe you'll get lucky. Water circulates around these bolts and so they are exposed to lots of moisture. The bolt in between thses two bolts gave me no problem on both engines.

Be careful. If you break them, you will need to bore them out with a press or better yet, take to a professional to bore out. They have the proper equipment for the job.

Also, inspect all parts that are removed for hairline cracks. The exhaust cover to the right had a hairline fracture

on the top left bolt hole. It was over torqued and cracked the cover. Luckily, I already had a replacement cover. You may also want to sand the cover until it is flat with some sandpaper. Glue a sheet to some thick partcle board (the smooth type) and slide cover over it until all high spots are gone. Through the years, the covers warp due to heat. If the cover is warped, you may or may not get a good seal when you try to install a new gasket .

The fuel side has 3 gaskets. It requires that you remove all electrical parts to get to them, and if that area leaks, might as well replace gasket do be on safe side.


Search Ebay for gasket sets

More to come. A complete layout will follow with proper links.


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