Pushrods

[Onne]

I ahve just trial fitted the 12G940 to my 948 block, using the 948 pushrods and rockerthingies.

The pushrods seem a tad short for the job, about 5 mm or so.
Is this just adjustment, or do I need different ones?

Now for a question about the valves

How clear is if the valves ARE hitting the block?

One final thing, how well will this all run on the standard carb?

Onne

[Alec]

Hello Onne,

pushrods, too short to adjust with the tappet screws?

Do not try and run the engine unless you are certain that there is clearance between the valves and the block. Turn it over by hand, if you feel any mechanical resistance, stop. If that is OK, turn each exhaust valve to fully open in turn (tappet clearance correctly set if pushrods allow) and try to move the valves further down and see how much available travel there is. (You could try pushing in a knife blade or the like between the rocker and valve stem).

I would say that you will lose a lot of the benefit of the head unless you increase the carburettor size.

Alec

[Onne]

I think the pushrods will allow a bit more adjustment.
I am going to try and use the blue tack method.

The mechanical resistance, is that very clear to feel?

[bmcecosse]

You just use the standard pushrods. You need to use 1275 rocker gear (and a 1275 head gasket of course) - or - re-align your rockers on the shaft (with shims and some filing) so they are acting directly over the exhaust valves. The inlets will be fine. If you have the standard 948 camshaft - it has slightly less lift on the exhaust lobes and you MAY just get away with doing any sinking or pocketing. But for me - it is just that - 'getting away with it' and the valves will be very close to the block face. I urge you to sink the exhaust valves by 40 thou. If you have fitted the 1098 camshaft you will NEED to do this !! It has more lift on the exhaust lobes than the standard 948 cam. The standard 948 carb is a pitiful wee thing - there is no point doing this conversion unles you upgrade to a 1.5" carb - the HS4 will bolt on your manifold (you still need to open the big hole up) - far better to get an MG Metro alloy inlet manifold - and use an HIF 38 carb on that.

[Packedup]

the HS4 will bolt on your manifold (you still need to open the big hole up)

And turn the carb though 45 degrees!

Unless I have only seen mystic special low spec HS2 carbs and inlets, or hitherto unheard of HS4s with diagonal mounts, the 2 and the 4 are NOT INTERCHANGEABLE ON THE SAME MANIFOLD!!!

The HIF 38 and 44 will most certainly fit the HS4 inlet (though there may be issues with bore size when putting a 44 on a 1.5" inlet, negating any real advantage) but o course they'll only use two out of their 4 mountings.

I'm not really convinced the 12G940 is worth messing around with on a 948 using an HS2 or 4 carb and 1098 cam - If there's a 206 or 295 kicking around I reckon that would be the better option as it doesn't require working the block or valves. Plus it's going to be plenty good enough in terms of flow for a very mildly tweaked small bore lump I'd've thought....

[Onne]

I might now go for a mildly tweaked 1098, and donate this engine to Jonathon.

[bmcecosse]

I was assuming the later manifold with the diagonal studs - this takes the HS range of carbs. The earlier north'south studs manifold is for the H range (2 or 4). That' s why I said HS4 ! The HIF hole spacing is not quite right for diagonal mounting - but the holes can be easily filed out to fit.
I took a well modified 295 off my 1098 earlier this year and fitted a 940 head. Much much better. It's also a much less expensive head - the 295 is really getting expensive now - there are 940 heads on ebay right now for £10 - and it's a way better head that needs NO skimming. A 295 needs skimming for use on 948 or 1098 engine.