Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement

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Fri 16 Apr 2021 18:48
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - David Berrisford

So the other week I changed my head gasket and timing belt as I had all the classic symptoms; milky coolant., white exhaust, low coolant. I changed the gasket and timing belt, as well as flushing the coolant and the engine seems happy. The idle rpm is stable and sounds normal.

HOWEVER, it definitely still hasn't got all the power it used to (not that there was much to begin with). With my foot on the floor in 4th gear it takes an absolute age to get to 60 mph, like probably 30 seconds. Are there any ideas on what is causing this? Cheers!

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Fri 16 Apr 2021 19:38
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - elekie&a/c doctor
Check your camshaft timing . If this is wrong , then the ignition timing is also out . Low power on these was often caused by a faulty maf sensor .
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Sat 17 Apr 2021 12:35
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - David Berrisford

The timing looked well aligned to me, and the idle sounds normal to me. I can try the MAF sensor though.

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Thu 10 Jun 2021 18:48
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - David Berrisford

So reviving this topic again. There's definitely an issue with low power, as I also get much worse mpg than I used to (40-45mpg down to 30-35).

I've just checked the timing belt and both marks are aligned correctly. I have also since got a torque wrench, and although torquing the spark plugs up to the specified torque helped somewhat, it certainly hasn't solved it.

Any advice very welcome!

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Thu 10 Jun 2021 19:05
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - elekie&a/c doctor
Did you replace the maf sensor ?
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Fri 11 Jun 2021 06:52
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - Railroad.

Does this engine use a mass air flow sensor? I would've thought it would use a MAP sensor in the inlet manifold. Check to see if it's not blocked.

If not I would definitely revisit the valve timing. You say the timing marks line up, but are you certain that the pulleys are sitting correctly on their shafts, most importantly the crankshaft pulley? Check to make sure the slot and key are in good condition and not worn. Incorrect valve timing by only a few degrees will have a massive effect on performance. You can also verify this with a vacuum gauge. A low reading of 10 - 15 in-hg indicates Incorrect valve timing. A normal reading would be 19 - 21 in-hg.

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Fri 11 Jun 2021 08:30
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - Topdude

"I have also since got a torque wrench" ?

This statement puzzles me, do you mean you didn't have a torque wrench when doing the head gasket ?


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Fri 11 Jun 2021 12:03
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - edlithgow

"I have also since got a torque wrench" ?

This statement puzzles me, do you mean you didn't have a torque wrench when doing the head gasket ?


Also slightly hard to believe that "torquing the spark plugs up to the specified torque helped somewhat" unless it was loose enough to be actually leaking compression, which I'd think would mean it was not much more than finger-tight.

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Mon 28 Jun 2021 21:55
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - David Berrisford

So I borrowed the torque wrench for doing the head gasket but didn't use it to do the plugs.

I think it's reasonable that I did only do the spark plugs up hand tight as I didn't want to wreck the threads so basically just nipped them up.

I have since retorqued the head bolts to confirm they are done up nice and tight.

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Mon 28 Jun 2021 21:53
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - David Berrisford

So this has a MAP rather than maf. I've tried running it unplugged and it runs horribly, so it's definitely working better than the default ecu values (if this engine even does that). I'm pretty confident the pullies are seated correctly. The notch seems good on the shaft for the lower one.

I'll look in to getting a vaccum gauge to check the pressure. Cheers!

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Fri 11 Jun 2021 12:13
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - edlithgow

While valve timing is probably the way to bet, are you sure your head was un-cracked, un-distorted and torqued correctly?

Head gasket failure can involve distortion and/or cracking of the head which isn't fixed by a replacement gasket, which may not last long as a result.

Edited by edlithgow on 12/06/2021 at 03:07

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Mon 28 Jun 2021 22:18
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - David Berrisford

I torqued it correctly that's for sure. I used one of those metal block things for trying to get yhr head flat again (can't remember the name for the life of me) and didn't notice any cracks. Not a guarantee that it isn't cracked though...

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Sat 28 Aug 2021 18:08
Corsa B 1.2 C12NZ - Corsa B - Low power after head gasket replacement - David Berrisford

Just to tidy this up, I've resolved this issue. Although I checked the timing of the timing belt, the timing was off on the distributor. I adjusted it and am back up to full power.

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