Cylinder head measurement
Discussion
i recently got myself a 12G940 head.
It's appear the head has been ported flowed etc but i dont know the valves sizes.
i measured it appeared 35mm inlet / 30mm exhaust?????? while the valves are shut. the valves are like 2mm apart from each other. the bottle neck in the head (kinked camber seem be gone really smooth in there)
the bypass hole is there. a flat thermostat area.
i think it came from mini 1275 not mg metro according to ime.org.uk
Anyone know how to measure the valves etc and id the head correctly
Anyone would know the valves sizes etc on 1992 mini sprite unmodifed head?
THank you
Jay
It's appear the head has been ported flowed etc but i dont know the valves sizes.
i measured it appeared 35mm inlet / 30mm exhaust?????? while the valves are shut. the valves are like 2mm apart from each other. the bottle neck in the head (kinked camber seem be gone really smooth in there)
the bypass hole is there. a flat thermostat area.
i think it came from mini 1275 not mg metro according to ime.org.uk
Anyone know how to measure the valves etc and id the head correctly
Anyone would know the valves sizes etc on 1992 mini sprite unmodifed head?
THank you
Jay
35.6mm/29.2mm are the standard valve sizes for the MG Metro head and the Mk3 Cooper S. And probably the old 1300GT as well.
Mk1 and Mk2 Cooper S's had 35.6mm/31mm valves but were prone to cracking between the seats, the primary reason for making the exhaust valve smaller on the Mk3.
1275GT's, standard 1275 A+ heads and the Metro Turbo head have 33.3mm/29.2mm sized valves.
Mk1 and Mk2 Cooper S's had 35.6mm/31mm valves but were prone to cracking between the seats, the primary reason for making the exhaust valve smaller on the Mk3.
1275GT's, standard 1275 A+ heads and the Metro Turbo head have 33.3mm/29.2mm sized valves.
Jay,
Take the valves out, clean the outside diameter and measure with a digital vernier or a 1" to 2" micrometer.
The 35.6 in and 29.2 ex will be the best for you. The biggest you can get without offsetting the valves is 37mm/31mm. I have these in my 1964 car, but with this you can only run leaded fuel. The heads that used to crack were the original 163 type. the later 12G940 is much more tolerant, although i have known them to crack if they overheat through incorrect setting of mixture or ignition.
If the head has been opened out, especially in the combustion chamber area, the chamber volume and hence the compression ratio will be important.
I've seen many people not get this right and after fitting a gas flowed head they find the car goes no better because the c.r. is actually lower than with the standard head.
Do you know how to measure the c.r? If you don't, let me know and I'll post the formula on here for you (and others who may be interested). You use this to work out how much to grind, or not grind, off the face of the head.
I was asked to look at a 998 Wolseley Hornet recently. It had a full 998 Cooper spec engine including the super 12G295 Cooper head. Apparently it seemed slow. I took the head off and did all the measurements and the c.r.was about 8.2:1 which would have made it well down on power. I am having .060" machined off the head face, having opened out the chambers to 'de-mask' the valves a bit more, and I'm fitting slightly larger valves both in and ex. With its slightly modded head, twin 1.5 SU's and 510 Cooper 'S' cam I am expecting about 60 bhp at the flywheel. I doubt if it had more than 45 before.
Take the valves out, clean the outside diameter and measure with a digital vernier or a 1" to 2" micrometer.
The 35.6 in and 29.2 ex will be the best for you. The biggest you can get without offsetting the valves is 37mm/31mm. I have these in my 1964 car, but with this you can only run leaded fuel. The heads that used to crack were the original 163 type. the later 12G940 is much more tolerant, although i have known them to crack if they overheat through incorrect setting of mixture or ignition.
If the head has been opened out, especially in the combustion chamber area, the chamber volume and hence the compression ratio will be important.
I've seen many people not get this right and after fitting a gas flowed head they find the car goes no better because the c.r. is actually lower than with the standard head.
Do you know how to measure the c.r? If you don't, let me know and I'll post the formula on here for you (and others who may be interested). You use this to work out how much to grind, or not grind, off the face of the head.
I was asked to look at a 998 Wolseley Hornet recently. It had a full 998 Cooper spec engine including the super 12G295 Cooper head. Apparently it seemed slow. I took the head off and did all the measurements and the c.r.was about 8.2:1 which would have made it well down on power. I am having .060" machined off the head face, having opened out the chambers to 'de-mask' the valves a bit more, and I'm fitting slightly larger valves both in and ex. With its slightly modded head, twin 1.5 SU's and 510 Cooper 'S' cam I am expecting about 60 bhp at the flywheel. I doubt if it had more than 45 before.
I'll do a 'thingy' on this and post it as a new topic asap. Probably not tonight though.
It's not as difficult as you might think. You need a 5cc shringe which you can buy from Boots, a digital vernier caliper (or you can get away with a set of feeler gauges, but they are not quite so accurate) and a steel rule.
It's not as difficult as you might think. You need a 5cc shringe which you can buy from Boots, a digital vernier caliper (or you can get away with a set of feeler gauges, but they are not quite so accurate) and a steel rule.
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