Head gasket

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Something I wouldn't try but might be interesting is to skim 20 thou off the top of the cylinder except for the channel area. That way they lock into each other some even with preload and a thin gasket. Not sure if there's enough room in there for the plug to clear, if I'm looking at it correctly.
Machining swirls usually go around a pressure source, but in this case you don't have much of a choice.
I don't know... But I always use 120 grit sandpaper (and 150 with less surface contact) and it's always good. and I will certainly never assemble an engine with a surface like the in Gordon's picture
Certainly that needs some touch up. Since I am preparing for some brazing repairs, I'm wondering if Gordon could braze some material on the end of that then trim it up? Of course photos never show what one can see with the bare and present eyes so the onley one who could say for sure is Gordon.
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Resurfacing on the lathe doesn't necessarily mean flat.
I always flatten by lapping after machining and check the mating faces with micrometer blue. I then simply use an oil soaked paper gasket. Never had one leak yet.
here is a head held on with two bolts and it seals fine with liquid gasket. All my engines including this one just have the turned finish to head and cylinder top as I have never had the need to do anything else to them as I don't get leaks.

I lap mating surfaces much finer than others are suggesting. Either use fine grinding paste (I have some 600 grit) on a glass plate or wet-or-dry paper on a surface plate. For that I use 800 or 1200 grit and stick the paper to the plate, and lubricate, with paraffin (kerosene). That gives a matt grey surface on aluminium (as seen at the bottom of this page: Seagull Engine Construction Diary - Assembly). It is very important that the paper is flat on the plate, otherwise it will round over the edges. Also, move the part in a figure-of-eight motion, and change its orientation regularly. My Westbury Seagull has the heads fitted with Wellseal (which I prefer to Hylomar) and no gasket. But it does have plenty of bolts.
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Blue Hylomar used by Rolls Royce and the CEGB on power-station equipment was always applied ton surfaces that were properly flat and finished to quite fine tolerances. It won't CURE ALL bad surfaces in any way. Also, all those machines and engines were "properly" bolted and torqued, where an adequate set of bolts were provided.
For all our clever ideas and alternatives that work on other engines, the immediate problem is advice on what we can see with these parts that don't work successfully. The comments about the line/groove at the "joint" between cylinder and side block seem most pertinent. The whole NEEDS to be "groove-less" - or filled with a suitable material (for temperature, expansion, gas pressure, joint pressure, etc.).
Putting it simply. The pressure (average) between the joint faces (applied forces from bolts divided by contact area) must be GREATER than the max pressure of combustion gases when the ignite at max compression. Suppose you have compression at 6:1 (measured). Then you heat the gas in the confined combustion chamber to (say) 800deg, C. You start with 6 bar pressure, then by "PV=RT" (Gas laws) you get maybe 24 bar pressure in the cylinder. Any "soft" gasket goo will extrude at that sort of pressure, given time. Suppose we have a joint face 1/8" wide by 1.5in long: I~.E. area 0.1675sq.in. Then we need a force of over 4.5lbs from the 2 bolts to withhold the gases at the joint. So I suggest you work-out what the bolts are doing on your joint area... They should be adequate, if to a proven design.
Personally, I think a setting gasket material may resolve the issue, but head gaskets are normally in a "hot zone" so destroy gasket goo by cooking it and breaking it down into rubbish. Paper (cellulose fibres from trees) can withstand the temperature better, but need no deep scratches or grooves in the surfaces. try applying the thinnest goo on the cylinder side, paper gasket on top and then fix the head on, The goo should only fill the scratches in the surface, the paper gasket seal over that, and hold the viscous goo from extruding.
OK Back in the shop. I had taken a light cut across the face of both the head and the cylinder. Since some folks seemed to think that the surfaces should be rough I did not lap them on my flat plate. The next thing to try is to try lapping the surfaces. If all else fails I will either add head bolts or use a gasket sealer.

PS: The side nub on the cylinder is attached with screws and JB Weld so it is not leaking at that joint.
OK So this is the result after removing all tool marks with 1200 sandpaper. Same as before. Leaks all around the side nub and not around the main cylinder. Teflon gasket and both cylinders leak at the same point. This is with 20PSI.

You know, I reckon there is no contact on the side nub? Or at least no pressure of the gasket there. It appears that as the side nub is "glued and screwed" then perhaps it cannot take the stress of the head and gasket pressing on the sealing face, and is "deforming" out of the way of that pressure.... so the lower contact pressure of the joint is leaking. There is some stuff called "Fuji Paper" that is commonly used to understand the pressure in joints. Inserted instead of the gasket, it makes a "contact print" where the pressure exists, and no print where there is inadequate pressure. But I bet if you used a piece of ordinary print paper, but used a pencil to "dirty" the surfaces with graphite, blew away the dust and then carefully made the joint, upon dismantling you will probably get a witness mark where there is high pressure (around the cylinder) but not where the nub exists?
Personally, I HATE any epoxy or other organic material in a joint, unless the structure is designed for it. Maybe the JB weld is to blame? Or the bolts inadequate to hold the nub properly tight?
A silver soldered joint would not do what you are seeing here, I reckon.
Any other ideas? - As I am just guessing really.
I have always just used Form-A-Gasket #2 (non-hardening) and not worried about surface finish. I dilute the F-A-G 50/50 with ethanol (denatured alcohol) so I can paint it on in a very thin layer. always works for me, and when I finish my Hansen Diesel that's what I'll use there too.
1: Can you put some blue on your surface plate, then show us how flat the cylinder is after blueing from touching the surface plate?
2: Another check: get some cigarette papers, (Cheap but very fine and thin paper) and place some around the joint instead of gaskets, no overlap (gaps are OK). Clamp as designed. then carefully try and pull the cigarette papers out of the joint. Where fully clamped they will tear at the edge of the clamped zone, but where not adequately clamped they will pull-out and not tear cleanly as the edge of the joint.
BUT you know from your leak check that the Nub is relaxing away from the joint, so maybe ignore my advice (55 year old training) and just fix that?
3: joining aluminium is as easy as electrical soldering with modern alloys: e.g. Type this into Ebay and see what it shows?:-
Durafix Aluminium Welding Rods Wire Filler Brazing Easy Solder Temperature.
The stuff I have has no flux, it is something like 95%aluminium and 5% silver, and simple to use. (Like lead soldering copper, just hotter). I make small 1mm thick enclosures from folded and soldered sheet aluminium with these rods. Are you in the UK? - Send me some details personally, and I'll send a rod. All you need is a gas blowlamp, and care. = Clean off the JB weld, chamfer the edges of the nub, reassemble with bolts and tighten, heat, apply solder all around, then let it cool. It just may be stronger and stiffer than JB weld?
I'm running short of ideas now...
Anybody against using Indian head sealant on the head gaskets. Or permatex high tac in the spray have had great success with both of these. Also you do not want your surface to be a mirror finish you will be better off roughing it up with some 120 - 220 grit this will give the head gasket something to bite into and seal
Although I usually use sandpaper and stick it on the glass to grind, one thing it can't make a 100% absolute flatness - but it's good enough.
Apply pressure near the center of the workspice , so that the workpiece presses evenly on the glass
Make a good surface before thinking about head gasket or glue....
Anybody against using Indian head sealant on the head gaskets. Or permatex high tac in the spray have had great success with both of these. Also you do not want your surface to be a mirror finish you will be better off roughing it up with some 120 - 220 grit this will give the head gasket something to bite into and seal
Precisely my thimpfking
Cylinder and head are aluminum so using silver solder is out and I have no way to weld aluminum.
Would a copper gasket possibly work ? What I'm thinking is if you took a fine strand (0.010" maybe) of copper out of a multi strand wire and coil it two or three times around in a single layer in the appropriate spot. A dab of grease might help hold it during installation.
Just an idea with no knowledge to base it upon.

John 🇨🇦
Lots of suggestions, but if the Nub isn't solidly held onto the cylinder so it can withstand the gasket pressure it will always leak - as in the photos of it leaking. Maybe some clever ideas of how to replace "JB" weld with a more solid fix would help Gordon?
My suggestion is "Aluminium solder"
We do not know how many and what size of bolts you have to hold the Nub in place? Please can you tell us or show a picture?
Have you checked the head for flatness after the test.
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I saw that but didn’t watch it, just figured the guy doesn't know much or he's never heard of exhaust valves. Maybe it's just me, I have been known to exhibit a little cynicism from time to time.

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