Head gasket mismatch 1275 on 1098

[ed8die]

In my Minor I am fitting a 12G940 head on my 1098 block. I have already done all the adaptations from the forum here so I expect everything should be fine.
However when fitting the 1275 head gasket on the 1098 block I notice that two of the oilways do not line up exactly on the gasket. They are partly covered. Would this be too much and can I expect problems? What would you advise me to do?
Please take a look at the pics. Would this be a problem?
The gasket is a genuine 1275 Minispares one for metro/maestro and was advised for the 1275 head.
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[MarkyB]

Doesn't look right at all, how does it look on the head?

[ed8die]

I haven't put the gasket alongside the head before fitting it to the car, but from pics I took of the head earlier, the oilways on the head seem to be in the same place as on the block.

[MarkyB]

Wrong gasket then, fit a 1098 one.

[mike.perry]

I cannot see any point in fitting a 1275 gasket to a 1098 block, surely the idea of the gasket is to get as good a seal around the bores as possible, especially between 2 and 3. Having said that, I am no expert on A Series heads, so if the 1275 combustion chamber is wider than the 1098 bore then maybe a 1275 gasket is necessary

[rayofleamington]

General advise is to use the gasket that matches the head - some swear by this rule, but only out of naivety.
The reasoning is to get the cylinder chambers to be sealed in the 'normal' position around the combustion chamber cavity (different sizes and shapes) - this is pretty sound reasoning except when the other features don't match.

As you've found (and so have others) the 1275/1098 combination is not always a simple one.

What I'd recommend (from personal experience) but isn't guaranteed:
Get a good quality 1098 gasket (not a cheap generic 948/198 one) - prefferably (but not neccessarily) a 1970's old stock one!
Check carefully that all the chamber seals are sitting on a good surface on the head when aligned by the bolts.
If the chamber seals are going to work, check the remaining features.
If there's no obvious issues, it's the one to go for.

As well as that issue, valve lift is another issue. A 1275 940 head will often have the face of the valves too close to the block, and the valves will overlap the block. This does not give sufficient clearance for full valve lift If the head has been skimmed the situation worsens.
The most common workaround is to recess the valve seats - thereby increasing the distance between valve head face and block face.
Another alternative it to recess (pocket) the block - but that needs engine strip & machining. Reworking the head is less time & effort.

[Alec]

Hello Ray,

"Reworking the head is less time & effort."
that seems to be the favourite trick but I don't like it very much, as it affects the gas flow as the valve is shrouded a lot more and (Nit picking) affects the valve timing also.

Alec

[bmcecosse]

Everyone I know (including myself) has used a 1275 gasket - it works. I doubt a 1098 gasket will seal around the larger combustion chambers of the 940 head. What else have you done? Have ypu removed some metal from the top flange of the water pump? Have you checked there is sufficient clearance for the exhaust valves? And do you have a set of 1275 rockers to use with this head - or are you re-arranging the 1098 rockers on the shaft so they line up EXACTLY over the valve stem tips??

[ed8die]

Back to my original post, my problem concerns the 1275 head gasket. Is the overlap of the oilways too much and can I expect to run into problems with what is shown in the pics? Has anybody experienced this problem before?

I am wondering if maybe the 1275 gasket exists in different versions, meant for different 1275 cars? Would anybody know about this? I understand a 1098 gasket will definitely not be correct when using a 12g940 head (judging from all the posts I have read on this forum during the past few weeks)

I have sunk the valves (32 thou), filed the top flange of the waterpump and used the 1275 sintered rockers with the 1098 push rods. So all this should be OK.

[ed8die]

Could a possible solution be to enlarge the holes in the gasket a little or will this affect the seal between the various passages.

[chrisryder]

if you put the gasket on the head, do the holes that are 'shielded' by the gasket present in the head?

i only ask as i think there are some holes in the block that don't pass through to the head, they're just there from when the block was cast. it's only a vague recollection, and it could infact be the other way around, with holes in the head not passing to the block resulting in a little pile of 'silt' on the block when the head and gasket are removed.

the holes you have aren't oil holes, they're water. oil only passes through the gasket in one place, and that's the front right one (in your 2nd picture).

[Alec]

Hello Ed8die,

that would be a solution. As Chris says they are water holes but why they are copper ringed I don't know, the others are not.
I would give that a shot.

As they say in this part of the world 'you've got two chances'

Alec

[bmcecosse]

They are water ways - not oil ways - the single oil passage is perfect. It's never been a problem for me - certainly don't modify the gasket by cutting in to the rings! Smear of grease and clamp it down - torque to 44 ft lbf in easy stages. Retorque after the first heat cycle - and then reset the valve gaps to 12 thou inlet and 15 thou exhaust. Did you put 32 thou shims (washers!) under the exhaust valve springs to compensate for the 'sinking' ?

[Alec]

Hello BMCE,

personally I'd cut the rings out, as they are sitting half across the hole it will upset the seal around that passage.

Alec

[linearaudio]

For goodness sake don't go taking bits out of the gasket!!
The only passage of any possible concern is that oil feed.
Though it doesn't get mentioned in the "how to" description, I carefully chamfered the hole in the block to unshroud it on mine, it is not a high-volume feed, but I felt it sould have as good a chance as possible of aiming the right way.
If you do this, then push a screw of kitchen towel down the hole first, so you don't get iron dust in the feed.
After doing it, I removed the paper, then cranked the engine over a bit to get some oil pumping out of the hole before assembling it all.

[bmcecosse]

Pocketing the block is a messy business (I first did it 4o+ years ago..) - and it exposes the rings to the combustion gases. Sinking the exhaust valve is an easy/quick/inexpensive process, and certainly doesn't affect the valve timing! The local area around the exhaust valves can be teased away using a small grinding stone to negate any 'masking' effects. A certain 'well known KC ' Mini modifier actually claimed that sinking the valves INCREASED the engine power. I 'hae ma doots' as we say up here! But the very limited masking that may be caused by the sinking that has to be done here to run a 940 head on a small bore engine is far far outweighted by massive increase in gas flows from using this excellent cylinder head.

[rayofleamington]

Everyone I know (including myself) has used a 1275 gasket - it works.

Had this fail more than once. The waterways that OP mentions can cause problems

Back to my original post, my problem concerns the 1275 head gasket. Is the overlap of the oilways too much and can I expect to run into problems with what is shown in the pics? Has anybody experienced this problem before?

yes and yes as per my post. Oilways were never an issue - just the waterways you've highlighted. The minor block must have differences to the Mini blocks that others 'never' experience problems with. Personally I wouldn't even try that 1275 gasket you've got, however that doesn't mean you'll have a lovely big water leak like I did - (on a 948 and a 1098).

ps - 940 head is a great mod and worth the effort. Not had to put one on a small A-series for ages, but only because I've mostly had 1275's

[linearaudio]

Can we answer the original question??
As I see it there are two shrouded holes that you are showing in the original post. The hole in the first picture is the oilway. This is what I suggested blending with a dremel or similar to give the oil the easiest route to the rockers, though as I said it is not a high volume feed anyway, so blending it in the block or not is a nicety.

the second picture shows a waterway. As someone pointed out, some of these are blanked by brass inserts in the head anyway, in which case it is irrelevant.

Either way, mine, and many others', 940 headed 1098's have been thrashed around regardless and had no overheating or oil starvation problems!

[ed8die]

Here are some pics of the gaskets on the head. The top pic is the 1275 gasket on the 12G940 head. (I do realise it’s the wrong way up but since it’s symmetrical the effect is the same - honestly I checked when I noticed it in the picture just now)
The second and third picture are of a 1098 gasket on the 12G940 head. You can see that the gasket overhangs the combustion chamber between 2 and 3 just a tiny bit, so I would hesitate to use the 1098 gasket - although I am not sure if this would be too much and would cause problems.


As already mentioned, I read up on the subject of changing the 1098 head on the Minor for a 12G940 one during the past couple of weeks and I thought I had everything covered - I even bought Vizard’s bible - so I am a bit confused about this one. And yes, I also put shims under the exhaust valve springs to compensate for the 'sinking' of the valves.[frame][/frame][frame][/frame][frame][/frame]

[bmcecosse]

The 1098 gasket must not be used - it will burn away in no time. My 940 head has been on my 1098 engine for 6+ years now, no oil or water leaks - nor has it ever 'blown' . And the 1098 block is no different to the Mini 998 block on which many many folks have fitted the 940 head. It works.
I would just say though that I used a 'copper' head gasket rather than these cardboard gaskets......