Head gasket

I have always used the composite copper gasket with the flame rings, Buy from a good source.

I use two solid copper head gaskets sandwiched together.

I had troubles with using one copper gasket or a composite gasket with combustion gases escaping between the barrels and head (10 thou of hollow between the spigots on the barrels). 

After blowing 3 head gaskets and after much investigation it seems that modern copper head gaskets are made from much thinner material than they used to be and therefore have very little compression or 'give' to them.  Fitting 2 head gaskets will lower compression ratio very slightly, but I doubt very much if anyone could tell the difference. 

A little tweak on the tappet adjusters and checked the rocker geometry was still good and have never looked back.

This was done on a 99 and I guess the Mercury is spigotless? so go with what Robert advises.

Hi Bob,  I might try your dodge on the Atlas as a bit less compression sounds good.

I've never had any problems blowing head gaskets on my Mercuries (5). I always use the Hallite or Klingerite composite after John Hudson told me to do so.  He used them on his Mercury as well.  Remember to anneal the solid copper thoroughly before employing.......... By the way any engines after engine number 114870 would have used a spigotless barrel and cylinder head combination with the Hallite or Klingerite gasket.  Cheers, howard

I'm just in the process of changing out my 2nd blown head gasket, one composite and the other copper on my spigotless  1967 650 SS. Of course this was all my fault not the fault of the head gaskets. I found both the barrel and head not flat, just bought the bike recently. To correct the barrel  I had a friend surface grind it , had to remove .012 to get it flat. For the head I was able to lap it on a 4" thick smooth granite bench top . I suggest to people with head gasket problems to check their barrel/head fits. An easy way to do this is place two 3/8" -26tpi bolts on one side of the head next to the sparkplug hole, just nip them up slightly then measure any gap on the opposite site of the head with a feeler gauge, usually the high spots on both barrels and heads is the center section of each. If the gap is .0025 or more corrective action should be considered. Hope this helps someone as I learned the hard way!

If it is a head gasket blowing there is usually a trace of oil running down the fins on the head and the barrel.  If it's blowing oil out with the exhaust gasses it's usually going down the valve guides or pressure keeping the oil in the head instead of draining it down the drain holes back to the pump.  Some people have fitted Commando type oil seals to the top of the valve guides on the  Mercury because of over-oiling problems.  You could fit a bolt in the timing cover in place of the banjo for the oil-feed to the rockers and then go for a ride   (several miles will be OK).  If the oiling from the exhaust stops then you'll know.  Sometimes a badly made head gasket allows mis-alignment of the drain holes and the head retains too much oil eventually forcing it down the guides and past the rings.  Similarly the cylinder base gasket drain hole must be clear to allow the passage of returning oil.  Good luck, Howard 

It might not be a blown gasket at all.  so a little more detective work may be helpfull before you pull it all apart . Nothing worse than a strip and rebuild  to find the problem still there.   Done that!,.Seems likely its got to come down but  something like a blocked breather or sump filter is worth checking first.