So,
Long story short we are working on resurrecting #1 dependants 1275LS and have been trying to diagnose a significant miss under load.
Checked the usual suspects (Fuel, air, electrical etc) and sorted some issues but still no go.
Took the head off today and can see (Apart from lots of soot ) that there may be tracking between #2 and #3. See pic

Would appreciate thoughts from those more knowledgable than me if this is significant or minor.
There is signs of unburnt fuel/oil in #3 which may or may not back up my diagnosis.


Top of gasket #2-#3


Underside of gasket


Head


Block face

Sorry for all the pics. Seemed the easiest way to describe

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'78 1275 LS (Under Repair, Dependant #1's car)
'72 GT Powered Clubman (Mine)... Under (re) construction

Hi,

I've just gone through that same issue with that gasket giving way between No's 2 & 3 on my 1275. The engine had only driven 3500km since rebuild. After checking that there was no damage to the head or block, I replaced the old fibre gasket with a high performance copper/aluminium one. So far it's purring beautifully, having only driven an additional 800km in five months and I've re-tourqued the head twice just no make sure.

Sean

The gasket doesn't show any clear indication of blowing out, but there's a good chance while the head is off to look at other things, so no loss there. The gasket is thin at that point, so its normal that it will look a little different to the rest of the gasket, but if it was tracking there would be metal missing, especially under load as there is so much heat and compressed mixture flying about.

Your miss might be electrical, or fuel related still.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Was there a compression test done before it was pulled apart? If it was blowing between 2 & 3, the compression on both these will be down.

Compression was even across all 4 - ~ 150.
Wasn't expecting gasket issue. Was pulling down to view/check.
Thought there may have been something funky going on once it warmed up.

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'78 1275 LS (Under Repair, Dependant #1's car)
'72 GT Powered Clubman (Mine)... Under (re) construction

That is pretty normal having a bit more heat in that area. there are two side by side exhaust valves there. Speaking of exhaust valves, they do look a bit low down in the seats. I think you should consider inserts .

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DID I MENTION THAT I AM THE BEST SUPPLIER FOR MINI ELECTRICAL PARTS AND REPAIRS?
"Let us remove your "SHORTS"

If the valve guides are very worn then oil can leak through them quite a fair bit. While the head is off, take the springs off and check the valves one by one and see if there is any play on the valve guides. Good time to put new valve stem seals too. If you buy a head gasket kit it should come with all this.

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Lillee - 1969 Morris Mini K

take the studs out of the block and clean the face with an oilstone, get the head rebuilt & surfaced

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did I tell you that I won a trophy?

Then countersink the head stud holes in the block to avoid raising burrs against the gasket.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks guys.

That was the other reason for taking the head off. Gives an excuse to "refurb" the seals and/or the seats. (And maybe go a bit further for a bit of performance ) Just have to convince dependant #1 to fork over some cash. (Not sure where his scottish nature came from, oh wait my wifes maiden name was Ferguson ! )

I haven't pulled the valves out yet, or checked head for straightness. Will do that before sending off for refurb.

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'78 1275 LS (Under Repair, Dependant #1's car)
'72 GT Powered Clubman (Mine)... Under (re) construction

Stud removal and insertion method ? Just use 2 nuts ?

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'78 1275 LS (Under Repair, Dependant #1's car)
'72 GT Powered Clubman (Mine)... Under (re) construction

Thinking I should revisit Electrical.

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'78 1275 LS (Under Repair, Dependant #1's car)
'72 GT Powered Clubman (Mine)... Under (re) construction

Yes, especially as it happens under load. A blown gasket screws you over completely.

I like to do a clean sweep with rotor, cap, leads and plugs. Consider the coil too if its old. Maybe a module as well if you're still running points. Set and forget from one end of the year to the next.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Thanks Mick
We thought we had it running OK and then changed to a module in the dissie. Been chasing our tails ever since. Have swapped stuff around with known good stuff, but I fear we got lost along the way. So once we sort the head and take the opportunity to reco/upgrade, we will start from the beginning.

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'78 1275 LS (Under Repair, Dependant #1's car)
'72 GT Powered Clubman (Mine)... Under (re) construction

I have stud removers - looks like a spark plug socket but grips the stud below the thread. 2 nuts will work but you've gotta be really careful not to crush the threads

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did I tell you that I won a trophy?