FWIW, My brother 30 years engine build experience including high performance. Uses sprays light coat of aluminum paint on the gasket then dry assembles. Swears by it.  Gooping anything on gasket would ensure failure IMO.

Ok guys from all the info I can gather from the previous owner this is the stock head. Looks like it was milled once before- but very little. I ordered a Fiber Gasket, and New Fastners. Studs, Nuts, and Washers. Will install Head Dry, run dry and retorque. I hope this is the one. 

To blow out at the end of the head like that, either the head or block is not flat, or the head gasket is rubbish. As you have blown a few gaskets I suspect the former. 
As others have said, bin the cheapo nyloc nuts. you want real grade 8 head nuts.

Meh. Small bores can run ridiculous levels of boost (compression). The chambers don't look that shallow-- No shallower than a big bore head-- and that's an 850 bore and stroke. The schmutz on the gasket and the nylocks are the biggest contributor to non-seal and consequent blow-out.



[tangent: I brought up the 112g940 head because there's a mismatch of water jacket sizes between small bores and large bores and for THAT I can maybe understand some sort of jacket sealant. Plus as I recall a small bore gasket on a large bore head had the fire ring hanging over the sealing edge and halfway into the head chamber. But it's been a while since I have looked at it. Nevertheless if that were the case, fire ring hanging into the burn chamber, that makes the blowout/burnthrough all the more understandable. But, as was made clear, this isn't a big bore head so all of this here parenthetical drivel is simply some internet idiot trying to hang his knowledge-sack out for all to admire, not unlike some other forum contributors]

Looks like a 12G295 or similar. You need to cc those combustion chambers as you may need a special thickness gasket made up to compensate high c/r or a different head. 

Frankly, I'm now wondering how the Mustangs are running.

yup. Didn't notice that.

Based on the third picture above, this should not be a 1275 head.  The heater valve is parallel to the back of the head and not angled. 

I only use cometic gaskets these days. They need perfect prep but I've never had a failure yet (touch wood!)When Rover went away from the steel shim to the composite type it cured a lot of in service problems but personally I think it was just lack of prep work as to why the shim gaskets failed. As in all things mechanical there are a miriad ways to **** it up but if you do it right it works. Remember do it right the first time!

Spank is onto it!  Look at how shallow that combustion chamber is!  You are running extremely high compression... I bet it ran great for a while! If indeed running a 1275 head, I think you need a 1275 head gasket with possibly some work on the deck water ports as the 850 bore is less than 2.5 inches!  Small bore heads have way larger combustion chambers to go with the way smaller valves.

Also, I've harped about this before... head gaskets out of England have been neutered by what I can only guess are the asbestos lawyers. In particular, the small bore type.  The ONLY gasket I really trusted was the Australian C-AEA647, and it's no longer available.

I have not tried the 'Rover Black Composite type'....  Way more expensive, but so is the work of doing it again!  Anyone try these?

I'd put a bit of assembly grease on the studs before seating in the block. Agree on ARP hardware. One thing not mentioned is any re-torquing of the head after getting the motor to operating temp. Also suggest that, as you may be surprised what it takes to re-torque.

Additional note about Husky tools from Home Depot: as I was buying a bunch of them for a Road Kit our club prepared as a raffle gift, the checkout lady told me, "These are guaranteed for life, just like Snap-On, so if something breaks, bring it back and get a new one, no questions asked." Another advantage is that wrenches and sockets can be bought individually, not in the sets sold at, say, Ace Hdwe.

Smearing a head gasket with that much copper grease will affect the clamping pressure - you compress the grease and then it melts, along with all your clamping force.

Trying to torque down anything using nyloc nuts is about as much use as doing them up finger tight - you're only measuring the grip of the nylon on the studs...

Buy some proper head nuts (or even just some grade 8 nuts and hard washers) and put it back together again with a shiny new gasket without any additional product.

That is my understanding for the method to use on the coated gaskets like the Payen BK450 for 1275s.  It didn't look like the failed gasket above had that type of coating.  Personally... I've never had the guts to start an engine dry.  I do however start them with water instead of anti-freeze.

Regardless, MustangMechanic, don't use RTV on the head gasket.  I have used copper coat on laminated copper gaskets for non-Mini cars but I have always put A- and B-series heads on "dry" as Spank said.

If your new stud kit does not include nuts, look at the ARP nuts from Summit that I mentioned earlier.  The thru hardened washers from BP Northwest that I mentioned are optional and beneficial when you are using "plain" hex nuts.  If you buy the ARP nuts, they have flanges so hardened washers aren't really needed.

Yea, that's not a stock small bore head. 

And looking again... that gasket doesn't even take up the whole head surface.

What is your head casting number? I'm gonna guess it's 12G940...

If my guess is right, you should be using a large bore gasket. But let's not go there, yet. Just report back what your head casting number is and post up a pic of the block surface, too. [edit-- my guess was WRONG]



Speaking in generalities-- you do NOT put anything on a new modern head gasket. Put it on dry and clean.

We all have our own superstitions for how to torque it up and what socks we should be wearing and whether nor not we should be wearing lace-up or velcro shoes while torquing the head down. Personally, I like to get it all torqued down with NO coolant in it. Then start it up and let it run til it's warm to the touch. Maybe a minute maybe 3. Let it normalize for like 15 min. Then do a hot retorque. Then let it cool fully. Then add coolant. My theory is that the shellac or coating on the gasket gets warm and mushy and the retorque pushes the goop to fill in any miniscule voids.

Yes we used copper coat and rtv around the water jackets and oil galleries. I have ordered a new arp stud set and a new gasket. Head is decked and at some point someone did some work to it I don't know what. So you guys think dry installation is best? I tried it dry the second time and the pressure blew right thru the water jacket.

Mike, I'm thinking a combo of things led to the failure. The early 850 head studs were not a good quality part. The dimple studs followed and were better. Looks like they used a can of Copper Coat on the other side of gasket. Another thing to check is the rocker pedestals. Early ones were alloy and would crush under torque. It is hard enough to fix these things when you can reach them. Steve (CTR)

Is the concensus that the nyloc nuts moved and let the gap develop between the head and block?

I have a had a couple of small bore gasket failures for no clear reason. I sent the first head out for a light skim and replaced the gasket. Within 30 days it was back with another gasket issue. The second time I had a head completely worked with hard seats, new valves and guides. I also picked up a set of upgraded head studs and hardware. Second head surfaced as well. Removed all studs and counter sunk the stud holes and ran a tap in each. Worked the block surface with large sanding block and borrowed a straight edge from machine shop to check deck surface. 

It appears to me that you do not have an 850 cyl. head. It appears to be a 295 or a 206 casting. It also looks like some work has been done on it and it may be surfaced quite a bit. CC the chambers and do the math as to compression ratio. In the 60 s I built a very strong 850 with a 295 cyl. head and twin 1 1/4 SUs.

Yesterday I went for a ride in a early Lotus Seven that I built the 948 Sprite engine in. We followed the same build sheet as my old 850. Granted with 998 pistons on the new press fit rods it is in the 1015 CC range now while the 850 was only .060 O/S. While the engine in the Lotus had been built by a race shop, I could not understand the 7.8 to 1 C/R std cam and only turning to high 4 s low 5 s.  Yesterday it cranked first touch of starter button once warmed up it sounded perfect and revs cleanly to 7000 ( all his tach goes ) I told him I suspect it will keep pulling to 8000 plus. I also suggested he keep it on scale. 

I have an 850 coming in today for a rebuild, it will also get a four synchro converted to magic wand tranny. New head hardware is on the parts list and block and head will both be surfaced. Steve (CTR)

Regarding torque wrenches....
I bought the digital readout shown in the Amazon link below.  I compared the output of this device to the calibration standards we have at work.  I was very pleasantly surprised at how accurate it was.  If you need to buy a torque wrench, this is a good alternative for 90% of the jobs on the Mini.
https://www.amazon.com/ACDelco-ARM602-4-Audible-batteries-included/dp/B004VYURT0

Agree with all the points above. Also consider making sure the block is straight with a straight flat piece of steel or whatever you have that is level and straight along with some well lubed wet/dry sandpaper. It is a bit tight but can be done in the car you may find that as the studs have probably stretched they have a mushrooming affect around the base where they screw into the block so you need all this to be straight and level. Get the head skimmed correctly just enough to take out any flaws.
I thought you replaced the carb with twin HS2's not 4's ? These would not be the cause of gasket failure.
What is that copper looking substance in the water ways some kind of radiator sealant ?