Keeping a head

[fweddy]

I'm out of commission with a blown head gasket

Nice timing with the couple travelling in the Morris Oxford coming from Oxford UK to Oxford NZ 40mins up the road from me on Sunday. There's a big classcic car event focusing on Morrises.

Never mind there is hope yet. I'm wondering what blew my gasket only a couple of months after replacing it - maybe the head wasn't flat - warped or something.

But my real question is what are the pros and cons of putting on a mini cooper small-bore head and 1.5" carb while I'm at it? I have a reconditioned head sitting here (well my brother does) and my dad has a 1.5" carb. Will the std headgasket do or are there any mods needed? I understand a set of flows would make the carb more effective but I don't have any flows at present.

[Cam]

If you use a copper head gasket it will be fine. A cooper head and 1.5" carb will give you a noticable power boost, so if that's what you want then go for it!!!

Erm.......... what's a 'set of flows'???

[fweddy]

Thanks for the info Cam

If you use a copper head gasket it will be fine.

Did that - still blew!

what's a 'set of flows'???

Free flow exhaust - in relation to the carb, I understand if you are enhancing the input (carb) if you also do the output (exhaust) it makes better use of the increased input - make sense?

[ianselva]

If the gasket blew , the head or the block or both are probably not flat. To check the head , take it off , clean the face and put a steel straight edge across and end to end - there should be no gaps more than a couple of thou anywhere . Check the block the same way. Obviously machining the block face true again is a major rebuild job. They both normally bow between cylinders 2 &3 in either case.

[Cam]

Well, clearly (as Ian says) you have problems with the head/block faces being out of true. If I were you, I would get the head (and block if it were me) checked, otherwise you'll keep blowing gaskets!

Free flow exhaust - in relation to the carb, I understand if you are enhancing the input (carb) if you also do the output (exhaust) it makes better use of the increased input - make sense?

Right! I had never heard of the term 'flows' before! Well, yes a decent exhaust manifold will make a difference. You can think of the engine as an air pump. The more air you can get through, the more power you will extract. Obviously then if you restrict the outlet you will decrease the power but not as much as if you restrict the inlet!

Thinking of the engine in this way also allows you to see how a small cc engine with high revs can produce equivalent power to a larger cc engine with lower revs as the same 'air' is being pumped through!

[fweddy]

If I were you, I would get the head (and block if it were me) checked, otherwise you'll keep blowing gaskets!

Exactly the plan! I'm hoping only for the head to have a problem, as the mini head should solve the problem. I'm looking at getting the current head planed and I need to do the exhaust valves too. I have a (suspected) Marina head here - are their exhaust valves larger and therefore suitable to put in as over size ones in my old head? Its obviously had a few grinds in the past.

[ianselva]

Some part numbers would be useful in answering that question . The number is cast into the top face of the head. Probably the Marina may be better than the mini one.

[fweddy]

Probably the Marina may be better than the mini one.

I think marina (1300) is big bore as oppose to the 1098 small bore so the head mightn't work properly. And info would be appreciated.

Also the Mini head is cooper spec (dle valve springs, etc)

[Kevin]

The combustion chambers will be a different size as the marina head is a 1275cc
The 1098cc engine has bore dimensions of 2.543" (64.58) and the standard head is numbered 12G202, with the larger valve version numbered 12G295.
The 1275cc engine has bore dimensions of 2.78" (70.61) and the standard head is numbered 12G940.
The larger head can be fitted but often requires the block to be pocketed so the valves dont hit the block.

[Peetee]

Just to expand on Kevins info, you may also come across a 12G206 head. This, the 12G295 and 12G202 heads will all fit on a 948 or 1098cc engine with a standard gasket for that engine.

[fweddy]

Thanks for the info chaps

Fortunately I was able to get my ute going for Sunday. (temp fix) Had a good turnout of about 90 Morrises, 42 of which were minors. See thread on Oxford 2 Oxford for pics.

Now I need to assess what I'm going to do with my head. Dad still talking of doing his minor and using the cooper head so I may go with planeing mine and putting bigger valves.

Would I be better off with the marina head if it fits (12G206, 12G295, or 12G202) or my std minor one planed and bigger exhaust valves??

I'll have to see if I can find the code on it.

[Cam]

To fit larger exhaust valves you will need to have the seats re-machined and not just try to grind them in as you wil be there forever!!

Fitting larger exhaust valves won't do a great deal in terms of performance but fitting larger inlet valves will.

To be honest, I would ask myself what the goal is? Improving the power slightly or keeping things standard? Then you will be able to make the choice on which head to use. To be honest I would probably stick to the standard head with standard sized exhaust valves and if you are wanting a little power boost then fit larger inlet valves and perhaps port the head slightly (if you wish).

[ianselva]

I don't think you would gain much from a Marina 12G940 head on an otherwise standard engine . You would have to shave it to get the compression ratio right and I think the vakves would possibly be too big if you're still using standard inlet/exhaust manifold and carb.

[rayofleamington]

I don't think you would gain much from a Marina 12G940 head on an otherwise standard engine . You would have to shave it to get the compression ratio right and I think the vakves would possibly be too big if you're still using standard inlet/exhaust manifold and carb.

The 12G940 has valve sizes are approx the same as the much sought after / expensive 12G295.
With a standard manifold and exhaust you are making it very coonstipated ;-) but it will rev more freely.
If you also go for an uprated exhaust and a marina carb and manifold you will find it a dream.

[fweddy]

To fit larger exhaust valves you will need to have the seats re-machined and not just try to grind them in as you wil be there forever!!

I had my head looked at by a local mechanic who did his time on BMC stuff. He suggested that it's had too many grinds in the past and the valves are seated too low so ideally needs the larger valves etc to get it up to scratch.

[bmcecosse]

The marina 12g940 head is the way to go ! It does NOT need skimming - the combustion chamber size will just nicely lift the compression ratio. You should grind small pockets in the block under the exhaust valves - you may JUST get away without doing this, but I don't advise it. It's a far better head than a 129295. You must use a 1275 head gasket - and the 1275 rockers to align correctly with the valves. You can re-align the original rockers on the existing shaft - takes time and patience. With a bigger carb and a decent exhaust you should get about 60 bhp.

[Peetee]

The marina 12g940 head is the way to go

Thats all very well if you have the facilities available to you to pocket the block - not a job for your average car owner!
For a reasonably competant mechanic with a limited budget a 12G295 with 1.5" SU, alloy inlet manifold and good exhaust should give you plenty of bang for your bucks.

[bmcecosse]

Indeed it does - but it needs to be skimmed at least 100 thou to get a fair compression ratio. The block pockets take an hour to do (assuming head already off) using mounted points in an electric drill. Not difficult to do. The 940 head has bigger valves and much bigger ports - and needs no skimming !