Drivetrain Cooper S engine works

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Mar 2, 2019 | 06:55 AM

snowsports1

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Cooper S engine works

Hi this is my first post, i have found the forum to be quite useful and active with gen 2 minis. Hi everyone. My R55 cooper s has broken a piston which i have come to the assumption was pinking, super knock code was present. Piston 1. Luckily the piston broke it skirt and didn't cause any cylinder damage . So i have removed the head and pistons. I am rebuilding the head and am now at a point of ordering new pistons. I suspect the previous owner has chipped the engine. i have a few questions i would really appreciate some advice;

1) i have measured the cylinders for roundness, this is 0.00025 inch. Which to me seems ok, but i dont have the engine spec for this, i want to avoid a rebore if possible.
2) The shop selling the supertech pistons are offering 10:1 (JCW) or 10.5:1 (cooper S) compression forged pistons. I am thinking about going for the lower compression (JCW) to avoid pinking under the assumption that my turbo is running at higher boost than a standard cooper S and this may have caused the piston failure. Is this a good move?

Mar 2, 2019 | 10:57 AM

oldbrokenwind

6th Gear

Joined: Mar 2011

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From: Northern NV

Time for you to learn about the repair instructions web site --- NewTIS. Here's a link to the applicable specs for my N14 --- https://www.newtis.info/tisv2/a/en/r...-block/6OUaMyN --- I suggest you get familiar with this site, 'specially if you plan on DIY projects. Use your own VIN (the last seven characters) to ensure proper specs.

If you believe your turbo is producing boost comparable to a JCW, then by all means, go with the lower CR pistons --- all four, don't even think of running with a mix of CR's. Personally, I'd do a rebore if replacing all four pistons. Getting rings to seat might be a problem, even with cylinders in spec.

Mar 2, 2019 | 11:21 AM

snowsports1

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Thanks for the reply I am planning to change all 4 pistons. Could the standard Cooper s be chipped to increase turbo pressure to be comparable to the standard Jcw pressure? The problem I have is I don’t know what was modified with the chip. I am planning to get a manic stage 2 chip once this is done with a switch to allow standard Cooper s programme.

Mar 2, 2019 | 11:49 AM

oldbrokenwind

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From: Northern NV

Can't help you with the chip --- no experience. BTW, Manic doesn't use a "chip", your ECU will be reprogrammed. I suggest you find out what, if any, mods you have installed before going too much further. And if you have a chip, lose it!

Also, going with the lower CR will minimize future reliability problems, as the mod bug gets its teeth in you.

Mar 2, 2019 | 12:19 PM

snowsports1

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I can’t find a chip, but I am assuming the ecu has been reprogrammed. Because it seemed to be very powerful and there are signs an intercooler was fitted then removed when I bought it. The main thing to decide at the moment is whether to reduce the compression by using the jcw pistons, I need to buy pistons and they are the same price. I’m pretty much decided on the jcw pistons now unless anyone gives me a good reason not to. Will the engine run right with lower compression and no other ecu programming? I am plannning to get it dyno tested while the manic stage 2 is flashed to the ecu but I need to drive the car there