12g940 head

[bmcecosse]

Sounds like a pretty useless 948 head - maybe had larger valves fitted - but still pretty useless. You want a 12G 940 head - from a 1275 engine........

[horrace]

is a head off an ital 1.3 the same?

[bmcecosse]

Of course......

[horrace]

so we got the 940 head now, its already got unleaded seats in it, im wondering if there will be enough meat left in the seats when i have the valves sunk in so that i get the 320 thou clearance? gonna get it skimmed just to make sure its flat. if all goes well i will have a 1098 unleaded head with about 1000miles on it available to buy.

[bmcecosse]

Have you measured the clearance at the moment? Don't skim the head unless you have to - the CR will be high as it is.

[linearaudio]

Don't concern yourself with "what ifs"!!
If you really feel the need then pay someone £30 or so to skim the head, or else put a straight edge across it and look for light or try to pinch a 2 thou feeler between straight edge and head (should nip up!).
Then get a good Payen 1275 head gasket, and go through the "real-world" assembly of the head, as documented many times! With the head tightened, but not fully torqued( say 15 foot/pounds), assemble valve gear and set exhaust clearances at zero. CAREFULLY turn engine over by hand with plugs out. When each exhaust valve is fully open, ensure there is still some clearance, by trying to further depress the rocker with a lever/ large screwdriver. As long as there is still some movement, then your fears are nil, as you will gain another 15 thou x 1.15 ratio(around 20 thou/0.5mm) when the valve clearances are set. Obviously, if on careful turning, the crank hits a resistance, you know you have clearance problems, and should then, only then, start sinking the valve seats!
ONE BIG THING TO NOTE: The top of the water pump housing will probably need filing or a quick angle grind to make it level to the top of the engine block, as the 940 head will foul it otherwise. This is a 2 minute job, but stuff rag down the bores or duct tape over the top of the block to stop any ally dust getting down the bores as you do this.(remove the tape before assembly....!)

[Declan_Burns]

And don't forget that you will probably need:
1) A different thermostat housing for the 940 head. A pre 1967 MGB is not bad but Birminghamm Morris minor centre sell one with the correct angle- Part no. 12M220.
http://www.morrisminor.co.uk/index.htm
2) Modification to the heater valve stub.

[bmcecosse]

There will only be a 15 thou safety margin la - the gap is at the valve stem, so no ratio involved...... But I don't like this method because the gasket is not compressed - better to just measure that 320 thou clearance - if it's there, all's well. If not - make it so. The rocker gear MUST be the 1275 sinter type -OR - carefully re-arrange the existing presssed steel rockers on the shaft so they act directly over the valve stem tips. I use perfectly standard therm cover and heater valve without problem.

[horrace]

i was only skimming the head to make sure all was flat and level, seemed like good practice. just confirm the 1098 rocker gear is fine but i need to carefully re allign over the valves, ill check the thermo housing and assume the prob arises if studs in different places and also check the heater tap. id rather set the valves in 320 that take a put together and take a chance, they will need lapping in so might as well lap them in 320 thou!

[horrace]

have u a link to "real world" cylinder head fitting

[horrace]

with my limited engine knowledge im wondering if i will need to change the needle in the carb? with the bigger valved more free flowing head i assume the mixture will be leaner? i also noticed today that cylinders 2 and 3 were showing heat damage, near the exhaust valve, again i assume this is because they share the same exhaust port. the inlet ports are noticeably smoothed off. im getting it skimmed level (belt and braces) and then having the valves professionally sunk in the 320 thou, for £4 a valve it seems a worthwhile spend to get it done properly

[bmcecosse]

Assuming you will be using a 1.5" carb and a 'free flow' airfilter - try an AAA needle. You do know it's ONLY the 4 exhaust valves that you need to seat down to 320 thou - don't touch the inlets!

[linearaudio]

I'm getting a bit scared!! The 320 thou is from the cylinder head face to the exhaust valve head. The way it is being talked of is that you are going to get someone to cut the valves 320 thou deeper! That would spell disaster!
Hopefully I'm being thick & misinterpreting what Horrrace is saying, but just wanted to clear up that point!
Sorry about my lack of success finding the "How to" 940 fitting guide, but I can't get much sense out of the search function!

[horrace]

no i wasnt sure on only doing the exhausts so thanks for that that will be easier! i have an hs4 and maniflow exhaust setup with k and n type filter, will check the needle it might be an aau i think at the mo...
fear not mr linearaudio its my way of writitng! i understand its (just the exhaust valves) the measurement from the face of head to face of valve....phew!
think this covers it...
cut valves to 320
shim up springs
grind water pump housing
maybe adjust therm housing
maybe adjust heater tap
1275 payen copper gasket may need oil or waterway adjustment/enlarge to line up
pay attention to very meticulous rocker allignment if using 1098 rockers

cross fingers

enjoy a slight improvement in performance

[bmcecosse]

And you need to understand that whatever amount the exhaust valves are sunk - a shim of that thickness needs to be put under the exhaust valve springs to retain the correct spring compression. I used flat washers. At very worst the valves could be sunk by 40 thou, but often much less is required - even zero! DO NOT sink them any more than that!!!!

[horrace]

i have been following another thread about headgasket on the 1275 head on a 1098 setup, i have ordered a 1275 gasket. couldnt get a copper one but have ordered a payen one. what was the outcome re alligning the mismatched holes on the head/gasket?
also alligning the 1098 rockers, i notice they are held in place with springs, do you just slide the rocker bar over and then all will line up ok or how do you do each one indivually?

[Declan_Burns]

Read through this:
I did fit the pressed steel rockers in the end.
http://www.mmoc.org.uk/viewtopic.php?f= ... lan+rocker
Regards
Declan

[bmcecosse]

It's much easier to just fit a set of 1275 sintered rockers - if you want to use the pressed steel rockers then first you need to be sure the rocker shaft is not worn where the rockers are running at the moment - assuming it's fine (or you use a new one) , you will need to add washers/machine the sides of the rockers and/or the pillars until the rockers act centrally on the tips of the valve stems... It should be only the exhaust rockers that need moving - but the inlets can usually be 'improved' while you are in there.

[linearaudio]

^^^^ I'm with him on this one, especially given the level of ability you profess to have (no insult intended, honest!) For all practical intents, a set of sintered rockers will sort the job out for you- thats the main reason BL went to them- one rocker set fits all!!
I could guarantee (if I was daft) that you will not break one by over-revving- the crankshaft will say "enough" before you get to those sort of revs (assuming you are not going for a "wild" cam!!)They worked fine in the MG Metro after all!
Please, please, measure for that magic 7.8mm, don't just sink the valves unless you need to! It is quite likely that your clearance will be fine, which takes away the added worry of finding suitable shims for the valve springs!
The rest you have listed is pretty much it! The heater valve clearance is more to do with bending/thumping the battery tray locally, as there is not much scope for cutting bits off the valve due to its (probable) construction. I have never had any problems with the Payen gaskets, the 940 heads I have seen have had various of the waterways blocked off by BL with brass plugs, which I guess was to improve water circulation to some of the more critical areas in the transverse installation. This has not shown up as any problem whatsoever in the 15000 very hard miles since I did this conversion!
My only additional comment is a safety-on-assembly caution: Be wary when you slip the head on, as it is longer at the front than the 1098 one, there is not much gap as it drops down the studs past the fan guard on the top rear of the radiator. If on assembly your hands get between the two passing items it hurts!

[bmcecosse]

Ooouchhh