K11 micra: project nastily aspirated

........put new pistons on..........check all C.R. measurements, tweek maps.......and try again?


*......and ring gaps 👍

Here we go dadstaxi...

Jeezlus,okay you have ringland failure from severe knock and a material strength issue as a possible secondary factor. Still gonna need pics of the tops, underneath and other thrust face to get a better picture.

Failure is going to be due to any or all of;

Excess ignition timing
Lean fuelling
Insufficient octane petrol
Too much CR.

I'd go with all 4

I don't see a piston/bore clearance issue.




Hold your horses.....................

You've got bore damage on at least one bore



I can't tell from the pics how deep bad and if it can be honed through.

You're going to need to check the bore diameter at the top, middle and bottom of the cylinders in an north south and east west orientation for all four bores with a precision dial bore gauge that reads to at least 0.01mm to establish the level of bore distortion/wear/taper.

You're going to need examine every bearing and bearing surface for damage due to a) knock & b) debris of the piston ring lands circulating in the oil system.

You need to check the block deck & cylinder head surface for straightness.


If that all checks out you can think about new pistons. If you are going to reuse the rods and pins you need to check those as well for pin bore damage/elongation and pin condition.

I think what I am trying to say is have the wrong gudgeon pins been fitted so that the little ends are partially seizing through lack of lubrication and so causing the heat build up and sideways drag on the pistons leading to ring failure?

Interesting point however the skirt is cut away beneath the gudgeon pin holes. It would be useful to see if there are any signs of localised overheating or even wear / deformation around the pin holes though.

Cheers people👍👍

Got some homework to do then 😂


The pistons came out of the cylinders whole/intact , the parts that are broken off are from when I was removing the rings.......hopefully this has kept much debris from floatong about 😬

The pistons I bought last time came with the rings, and pin, so il just get a complete set of those again (£35 for piston/ring/pin)

I picked up another head the other day, so il get my new valves cut in to that one......do away with the decomp plate.

Il get a proper burette this time rather than a syringe to take C.R. measurements

With regards to fuelling, only thing that’s changed with this engine from the last, was that I polished the ports in the head.......could that of thrown the fuelling out that much ?

One thing I haven’t done though is had the injectors tested, so might get those sent off and cleaned/tested


.......main concern is the bores, il try and dismantle it all later and take some pics, I don’t own the correct tools to measure the diameters precisely 😕


Isn’t learning fun.....and curse word expensive 😂👍😎

You'll get there eventually bud, we've all blown a few up in out time!

With regards polishing heads and fuelling requirement, if you actually mean literally JUST polishing, then no, polishing does absolutely nothing for flow or power. (Surface finishes can do trick things with boundary layer conditions but that's WAY beyond the scope here)

If you mean porting then possibly, depending on what you're using to measure load on your EFI system.

Are you datalogging or at least monitoring mixtures? You at least need a wideband AFR gauge plumbed up in the car whilst you're getting it up and running well.

I’ve got an afr gauge, but it’s built into the ecu so have to run with the laptop plugged in.

And using a map sensor 👍

Yeah, I only polished the ports last time.

I agree..... though not necessarily in that order. I've seen 12:1 mentioned. Unless very long duration cams, that's much too much. Have a careful look at your ignition map - just one or two wrong numbers in a bad place can do that......

Nick