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MG Midget and Sprite Technical - 12G295 Head Valves

Can I pick your brains on valve sizes. I have a 12G295 Head with 31mm inlet valves, having lapped the valves the seat is only a couple of millimeters wide. The inlet diameter is 29.6mm Is this correct or has the head been modified for larger valves. I have attached a picture.

Andy Potter

It could be a no lead kit....just guessing
prop

Valve seats may have been recut at a single angle thus making it seem like a bigger valve installation. The biggest problem with the 295 is the valve throat is too wide and gives a 1mm seat width from new. We fit inserts in the inlet so we can narrow the throat and produce 'proper' three angle valve seats.
You should have 31mm inlets and 25.4 exhausts. 29.6 inlet is 12G202 or the rare 12G206.

Peter
Peter Burgess Tuning

Thanks Peter, it does sound like everything is correct. Doesn't give much to play with then as standard does it. There are two angles on the head and the 29.6mm dimension is the actual bore of the inlet. Would this have been standard fitting on 1966, 1098 cc car?
Andy Potter

Hi Andy

I am not an expert on what should be fitted for each year to be honest. I tend to just know the heads as they sit on the bench. It is a shame the inlet throat is so wide but it is good that power can be gained by doing the inlet insert work. Mini Spares used to sell oversize inlets for the 295 which sorted the problem but they have had such little demand the product has slipped away.

Peter
Peter Burgess Tuning

The 295 was fitted to the later 10CC prefix 1098cc engine. These engines were stronger than the earlier 1098cc 10CG prefix engines using 2" rather than 1.75" main bearings. They were fitted to Spridgets with wind up windows and semi elliptic rear springs so yes it would be standard for your car. Later in 1966 the factory started fitting the 1275cc engine.

The 295 head is still usefull and is a favourite with Mini owners with 998cc engines.
Bob Beaumont

This thread was discussed between 22/05/2016 and 23/05/2016

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