I have yet to order them but a machine shop told me they'll need to inspect it before anything but from what i described on the phone itll need .5 oversize.

pics of the top of piston number 3. Am i right in thinking if it was detonation they would be marks all over the piston instead of the edges?
https://cimg4.ibsrv.net/gimg/www.mia...89e909cd93.jpg
https://cimg5.ibsrv.net/gimg/www.mia...34dfb3f26c.jpg

I was saying that FOD = foreign object damage after someone asked what FOD means...


#3 looks like detonation, and exactly where you'd expect it.

https://www.miataturbo.net/attachmen...ine=1389248544


but it also does look like it could still just be FOD... especially with all the scratches over the spark plug.


can you post the MSQ file of your tune? did you have rods? you we really pushing the limits of a stock block.

oh okay i mistaken it for ' Full on detonation'. Thats a relief!...... kinda

I have a MS2pnp Extra and this is my tune.
Its got forged h beam rods.

also, with det, you start to see the edge wear down. you just have chucks missing:


https://cimg1.ibsrv.net/gimg/www.mia...e5f8f5b5dd.png

https://cimg3.ibsrv.net/gimg/www.mia...9eccf0bf57.png


see all the small pitting, and even melting the edge off. So mistaking det.


you will not mistake my FOD for det:

https://cimg8.ibsrv.net/gimg/www.mia...56209bfc5d.png

mine hasn't got any chucks missing and the edges don't look melted away, does this mean in my situation it's not det?

No one can tell you for sure. Either way, now you'll be a lot more aware and careful.

Great info on this thread! I hope to never melt my pistons lol
Good luck with the build!

Technically.

you've lost me now. One second people are positive it's FOD then say it's det, I really appreciate everyone's help I really do but I'm easily confused

read post #48

So ive taken the engine to an engine builder, theyve told me that its foreign damage, im glad about that! so looks like the bottom end is going to get a full rebuild inc new pistons and rings. gonna be pricey but at least its peice of mind that its been done.

your timing map is hella conservative...

https://cimg2.ibsrv.net/gimg/www.mia...25508dba8b.png


your fuel map is crazy...but rich where it counts


https://cimg5.ibsrv.net/gimg/www.mia...7926afbe0f.png


you're also using an injection timing table, yet setting it to 90°. should be like -350°

did you ever sync timing initially? i have a feeling your spark [and fuel] timing was incredibly off, which lead to det.

Hello everyone again sorry for the late reply, new job means barely any time for myself so I've bought a daily and been building up the mx5 bit by bit.
okay so today I've finished installing the engine.
new rings bearings crank reground down and low mileage block.
cometic headgasket, same cylinder head but skimmed and genuine valve stem seals and valve guides fitted.
started up had a slight misfire but after a few minutes I think the lifters set themselves up as it went away.
only problem is, it's still smoking very badly. It's getting alittle upsetting now. I'm completely lost. Anyone willing to give me any advice?
just a random thought could there be the possibility that the cylinder head might have a crack somewhere letting in oil?