Melted Piston #1 and #4
 

Hi all, I have a turbo mx5 1.6 running Megasquirt (DIYPNP) Supra 312cc injectors. But is more or less stock other than these.

Since ownership I had a series of problems with it:

- The water pump was leaking a bit so this was replaced in addition to doing the cam-belt whilst the water pump was off.

- The cam belt was about a tooth out on the inlet and outlet and this was rectified when fitting the new belt.

- However we were ignorant with Megasquirt and didn't know you then had to sync the timing with Megasquirt.

- We did a trackday in it the following day (Another mistake...)

- Noticed some slight rattling/possible pinging at high revs and should have probably stopped but hey-ho, you learn ay!

- On the trackday the car was overheating a bit (Getting about 3/4 on the temp gauge and bubbling back into the expansion bottle).

During the trackday it began smoking quite badly which we though was the turbo going. I've chucked a new turbo back in the car which has significantly reduced the smoke. However it is still letting out a small puff of smoke occasionally; although quite often this is under load. I also think the car was loosing a tiny bit of coolant and needed topping up occasionally.

We took the head off and were presented with the following:

http://imgur.com/a/dILYK

Basically, pistons #1 and #4 have melted on the Intake side.

We just can't figure out why those two and not the others? Any suggestions?

So far we think it may have been a combination of the timing being a bit out, overheating and possibly causing detonation.

Is this what you'd expect from detonation, or is it more likely due to running too lean? If so what would cause this problem on just those pistons?

PS the piston crowns are shiny from the wet compression check thats just wet carbon


Cheers for any help/ideas :)

Edited to attach the map

I had a turbo setup years back, would do the same thing, 1 and 4. Never figured it out, always blamed it on the manifold.

Massive detonation damage resulting from a bad tune. You abused the car.

How much boost were you running?

The amount of boost isn't necessarily a factor in making pistons look like that... It's the lacking of all those other things that need to go along with the boost that did that. You can melt pistons like that with any amount of boost really... Or even.. without boost at all, if you are really trying...

Yeah just gonna change the engine out

Hear what your saying Sav, I think the tunes OK as its run for a year but our ignorance :noob: on the timing being out was likely the major factor. You live and learn could have been worse :giggle:

Very True and your right boost wasnt an issue at a lowly 6 Psi

Yep, detonation. Massive detonation.

20 bucks says your injectors need cleaning...

+1

I've come across too many people that are content to simply throw in used injectors without knowing if they have recently(or ever..) been cleaned/flow tested. Your AFR gauge might as well not even be there if you don't know that all injectors are flowing properly.

What made you think the timing belt was off a tooth on both gears?

Please read up on how to check and set timing or this will happen again and again.

Jumper the correct pins in the Dia box and use a non-advance timing light.

Good luck.

o lawd those pistons took more pounding than hustler on a weekend

As evidenced by the condition of your motor, the tune is very clearly not OK. There is absolutely no way that a mis-aligned timing belt can cause that kind of damage. What kind of AFRs were you seeing?

Thx for all the comments
The injectors were professionally cleaned and flow tested prior to fitting this time last year.
We had a garage change the cam belt and it seems it was originally misaligned (E&I Cams not aligned correctly) unfortunately we did not at the time know you need to tell Megasuirt the timing has changed (Nothing to do with jumpering the pins)
This is ultimately what melted the pistons with a combination of timing out/ then overheating and cooking.
Subsequenty timing was set correctly and whilst the damage had been done the knock was removed.
Saying all this apart from some smoke the car still ran and pulled well so looking forward to getting it back bigger and better.
Thanks for comments it all helps the learning process :)

that looks familiar to me. Bad tune, timing, and abuse.
https://www.miataturbo.net/attachmen...ine=1355472275


I learned the hard way when I first boosted.

The car has been turbod from new 1992 and covered just over 100k
Attached the map for anyone thats interested

I believe you when you say it still pulled with all the carnage done to the block. Mine when it was opened, 2 of the spark plugs were gone, I mean melted, and still it ran and pulled pretty good. I bet you it would have been a B18c1 Honda engine, would have stopped right away.

There were other factors involved in mine, lesson learned, stay away from machine shops. The f_tards used locktyte on the head and main rod bolts (but this is subject to another thread).

What I find strange, and I am glad it happened to you, that always 1 and 4 were the ones to go first. I like Mazda blocks, you can get them a dime a dozen from junkyards real cheap.

Yeah I know what you man I have since found a few people that have ended up with 1 & 4 fooked
And yeah engines are cheap on this side of the Atlantic tho a bit more than a dime :)

the mazda engines are awesome, I still got home from sacramento with my melted pistons with no smoke, it covered 160 miles after it overheated, just felt like a loss in a bit of horsepower.

However my tune was poor. I was running band aids and abusing my car like the little 18 year old ricer I felt i needed to be. I however did manage at least 10k miles on the band aids and poor tuning skills. I learned my lesson and wise about it. The miata was boosted happily for years after that with a MSPNP later on, until my financial decision to part out.

Time to build my miata back up to par.