Hi All,
I am about to have hardened seats fitted to a head I’ve been working on, but recall reading somewhere that there is a risk of hitting the water jacket when they machine for the inserts?
I’ve removed the rings / ridges around the valves in the chamber so am a little worried about depth?
How low can you go before hitting water?

I don't know about the clearances involved in fitting seat inserts, but thought it worth saying that they are very marginal in reducing valve seat wear. I have 1 car with the inserts and 2 without them. Also stopped using fuel additive years ago - more through laziness. There has been no noticeable effects on valve clearances or seat wear, either with or without the inserts.
One less thing to worry about? Just a thought.
And most minis travel much shorter distances now.

There must be a limit to when hardened valve seat can be fitted. The experts on here can advise.
When reconditioning my 9FXEY Cooper S engine, I found that it was not possible to fit hardened valve seats to the head, as it was running 1.308" inlet head dia & 1.212" exhausts.

I did have a Mk1 S head where the valve seats were recut when the head was reconditioned and I ended up with a very small pin ning nong hole into the water jacket. The 12G940 heads seem to have much more thickness and don’t seem to have the same issue. Agree with the inset comment. Both my 1275 engines have no inserts and going fine so far. Occasionally I put a bit of additive in the fuel but not religiously

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Hi, I am 100% with Bill. My own experiences since ULP was introduced, that most of us thought was going to produce lots of burnt valves etc, is that ULP seems to be much better than Leaded in a mini . I do not believe I have had an engine that I or my staff had built that suffered valve or seat issues. I do have people think I am mad for not fitting hardened seats. My favourite reconditioner expression ... measure with a micrometer...mark with chalk...cut with an axe ... can apply to fitting hardened seats... it is a very exacting process .... it is a tight fit......potentially catastrophic.failures if they fall out ... I have seen 8 seats fitted to a 1275 where the second seat into one cylinder turns the first one into a D shape, and loses half of its interference fit..... I have definitely seen them fall out..... Obviously there are people who can fit them accurately and know what they are doing with cast iron. I know some will totally disagree with me.... Engine combustion temps and parts quality can have an effect so proper tuning is a requirement not too rich not too lean not too advanced not too retarded All my cars go on a gas analyser on the road, under conditions of how I drive it ... I think maybe Bill does the same Cheers Lindsay Siebler Rover did fit hardened seats to late A plus ...maybe if you intend to do huge mileage at high speed it could be a bonus , but thats why you have late model car to wear out

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1959 Austin A40 Farina fun car
1965 Mk1 Cooper S restored
1970 Colt 1100F SS restored
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project

HI Frog Johnson
To answer your question the seats that I fit are .250 deep you will not hit water at that depth.
If you are just doing normal driving and not reving the hell out of them and using heavy springs you can get away without seats.
I fit seats to the MK1 cooper S heads both inlet and exhaust, 90% of the time you will hit water with the inlet seat but that's not a problem have a special sealant that fixes that, I have saved a lot of these heads, even the ones that have cracked between the two valves.
I put exhaust seats in all my race now using 8000 RPM and unleaded fuel with heavy springs the valves will pull into the head half a MM in a couple of race meetings.
I have never had a seat fall out yet I use .005 to .007 interference fit.
Graham Russell

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"It's better to be not informed than ill-informed"

So what point would you call the springs heavy - 200lb? More/less?

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Hi, not trying to back track on my comments, but I also agree with Graham. I assumed we were talking about the category of normally driven road cars, and I dont believe inserts are necessary there. but Graham is one of the people who knows cast iron and how to fit inserts . Race applications, retrieving special rare castings, absolutely necessary, but not just fitting them because you think we must with ULP. cheers Lindsay Siebler

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1959 Austin A40 Farina fun car
1965 Mk1 Cooper S restored
1970 Colt 1100F SS restored
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project

HI Timmy
200LB springs are ok it's so much the spring pressure it's more the RPM,in formula Fords if you don't fit exhaust seats to them one race meeting and the valves will pull down up to 1.5mm and they only use 6800/7000 RPM as I said if you are not going to thrash the day lights out of them you won't need inserts.
Graham Russell

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"It's better to be not informed than ill-informed"