Head gasket for Atlas

Use the 750Commando Flame Ring head gasket, as the solid copper ones tend to leak. The later part number is 063844 as this replaced the earlier 064071.This later flame ring head gasket is installed with out gasket cement. This as per the Service Release number 3/74 subject Head Gasket,on19/2/1974. If you have the earlier 5/16 head bolts, by the spark plug holes,convert them to the 3/8 head bolts, as this makes for a better head gasket sealing. Torque them to 30 ft lbs.

Use the 750Commando Flame Ring head gasket, as the solid copper ones tend to leak. The later part number is 063844 as this replaced the earlier 064071.This later flame ring head gasket is installed with out gasket cement. This as per the Service Release number 3/74 subject Head Gasket,on19/2/1974. If you have the earlier 5/16 head bolts, by the spark plug holes,convert them to the 3/8 head bolts, as this makes for a better head gasket sealing. Torque them to 30 ft lbs.

I hate to put a spoke in the wheel in this thread but some of the good advice will only work with particular models of Atlas cylinder head.

If the cylinder head and barrel are both from the early spigotted type then you are going to have a problem converting the headbolt holes up to 3/8". If you keep the barrel spigot then you will have to also open out the gasket holes to match the bolts. This will take out gasket material where you need it most and leave the whole area vunerable to leaks. This was one of the reasons that the early Atlas engines had 5/16" headbolts. You could not have a spigotted cylinder head plus 3/8" headbolts. The head gaskets leaked or blew out. Even with the 5/16" bolts many owners found that they got oil leaks through the gasket. Many tried torquing down the head further and promplty snapped a bolt or two.

If you go down the route of having the spigot ground away then you can look at 3/8" headbolt holes. But........if the cylinder head is still the spigotted type then you must get hold of a set of the steel conversion rings (p/n25494)that sit inside the combustion chamber and help seal the headgasket. Aluminium ones appear to work just as well.

The attached pic shows 3 varieties of later Atlas/Commando cylinder head gaskets plus a 650 type. I could not find an early Atlas gasket for a spigotted head to show how absurdly thin it is in places. But if you look at the top right version and take away the flame ring you will get a reasonable idea.

Like so many other owners, I thought that a solid copper headgasket would solve all my oil drip problems. Not so......both my 650 and 750 motors dripped/blew through the gasket sides despite annealing them carefully. The problem with annealing is that you can over-cook the metal and it actually vaporises away leaving thin parts even thinner. The most vunerable sections are by the pushrod tunnels and the rear head bolts.

Attachments
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Previously phil_hannam wrote:

I hate to put a spoke in the wheel in this thread but some of the good advice will only work with particular models of Atlas cylinder head.

If the cylinder head and barrel are both from the early spigotted type then you are going to have a problem converting the headbolt holes up to 3/8". If you keep the barrel spigot then you will have to also open out the gasket holes to match the bolts. This will take out gasket material where you need it most and leave the whole area vunerable to leaks. This was one of the reasons that the early Atlas engines had 5/16" headbolts. You could not have a spigotted cylinder head plus 3/8" headbolts. The head gaskets leaked or blew out. Even with the 5/16" bolts many owners found that they got oil leaks through the gasket. Many tried torquing down the head further and promplty snapped a bolt or two.

If you go down the route of having the spigot ground away then you can look at 3/8" headbolt holes. But........if the cylinder head is still the spigotted type then you must get hold of a set of the steel conversion rings (p/n25494)that sit inside the combustion chamber and help seal the headgasket. Aluminium ones appear to work just as well.

The attached pic shows 3 varieties of later Atlas/Commando cylinder head gaskets plus a 650 type. I could not find an early Atlas gasket for a spigotted head to show how absurdly thin it is in places. But if you look at the top right version and take away the flame ring you will get a reasonable idea.

Like so many other owners, I thought that a solid copper headgasket would solve all my oil drip problems. Not so......both my 650 and 750 motors dripped/blew through the gasket sides despite annealing them carefully. The problem with annealing is that you can over-cook the metal and it actually vaporises away leaving thin parts even thinner. The most vunerable sections are by the pushrod tunnels and the rear head bolts.

from the gist of this discussion I'll need some guidance. My Atlas is a '63 model, obviously a very early run, with the spiggoted head. I am having head gasket problems ie those my supplier has sent are a very poor fit. As my Commando is running, I likely should plan the removal of the spigots and conversion the 3/8 head bolts over the winter. Please inform as to the correct procedure for removing them (I will engage a machine shop).

thanks

Ernie

Phil mentions the rings to fill the gaps where the spigots were designed to fit. But wasn't there a thread a year or two back where the rings had self-destructed and ended up inside the cylinders? Like metal worms...?

Previously David Cooper wrote:

Phil mentions the rings to fill the gaps where the spigots were designed to fit. But wasn't there a thread a year or two back where the rings had self-destructed and ended up inside the cylinders? Like metal worms...?

I never had a problem with either my 650 or Atlas engines once the spigots were removed. You generally have to do this with the 600/650 barrel, if you rebore to +60", as the spigots become too thin and soon break.

My Atlas rings were alloy and supplied by John Hudson. They were one piece and once inserted never came loose.

I took my barrel to an engine specialist who recut the four threaded holes to 3/8" Cycle...charging me £30. Because both the 5/16 & 3/8 are 26tpi this could possibly be a DIY task.

from the gist of this discussion I'll need some guidance. My Atlas is a '63 model, obviously a very early run, with the spigotted head. I am having head gasket problems ie those my supplier has sent are a very poor fit. As my Commando is running, I likely should plan the removal of the spigots and conversion to the 3/8 head bolts over the winter. Please inform as to the correct procedure for removing the spigots (I will engage a machine shop).thanksErnie

Hi I have read the posts and was wondering why my atlas has an alloy head gasket. Should I replace this with the the Commando flame ring gasket (063844) or with another alloy one as I read somewhere the alloy ones were used to reduce compression. Any advice/clarification would be appreciated.