- My model of MX-5 is: 2006 1.8 NC
- I’m based near: _Gloucester _
- I’m looking for technical help or recommendations on: __I’m well into my engine strip down now to cure the excessive smoking - my thought was the rings are clogged! However, having removed the head I have found piston damage. So I’m in bit of a conundrum now, do I carry on and repair (if it is repairable) or stick a new lump in.
Any thoughts?
I think that’s showing the early signs of piston crown damage possibly due to ring problems. Are all cylinders the same and have you removed the piston yet. You need to do this to see what the piston / ring condition is.
In any case that is not normal.
It’s just No3, which was the cylinder that had the lowest compression. As I mentioned I had suspected the rings were clogged due to the amount of oil it went through. I guess No3 rings finally gave up.
Pistons will come out tomorrow if it stays dry/warmish. Not sure if the bore is salvagable though using a Honing tool or if needs Re-boring.
Put a new lump in it !
Hello richj870
If you do need a replacement engine, or more advice contact Roddisons Motorsport,
ask for Paul, 0114 244 5300 Sheffield S9 1US.
Cheers
Keith
That looks like scrap to me, it certainly is if you can feel the bore scoring with your nail.
It would be useful to know the orientation of that piston, i’m assuming you were stood at the end of the block to take that pic and the inlet/exhaust are left and right? If so what do the squish pads on the head look like?
What is the history of this car/engine?
The piston is No3, the photo is taken standing at the front of the block so as you look at the picture the inlet is to the right, exhaust to the left.
I don’t know the history. I bought the car cheap (£1000) knowing there was a problem as it smoked and drank oil.
But with a years MOT, 50k miles, no rust and in very good condition it seemed a worthy project.
After having 4 previous Mk2 projects I fancied a change and a bit more refinement.
Where on the head are the squish pads. I haven’t really paid much attention to the head yet, only a quick glance to make sure all the valves are in tack and mo other damage.
The squish pads are opposite where that damage is so will likely also have some damage or maybe just faint witness marks on them.
My first guess is that a foreign object has found its way in there.
Need to see what that piston looks like.
Here’s a pic of No3 piston. It looks like a partial seizure to me. Clearly something has been bouncing around in the chamber and it’s also damaged the head. The rings are not broken which is what I was expecting but they are seized. In fact the oil control rings on all 4 pistons are clogged and stuck in.
Not sure where to go with this now - hone it out, stick 1 x new piston in and a set of rings then bang it all back together.
Or as there are only a couple of bell housing bolts & a starter cable left connected - pull the block out?.
Well it’s a re-bore and new piston(s) job so it’s up to you. That’s if you can even buy oversized 1.8 pistons.
If you buy another used engine you’ll have to strip it, fit new rings etc and rebuild it too before fitting it.
It’s likely it’s been run dry of coolant and overheated. It’s got all the hall marks, look at the way the pistons been nipped. Did the original green coolant come out?
Really you should have dropped it out as it’s quite often the crank will have taken a swipe at the rod bearings too.
The photo of the cylinder head makes me think that it’s almost certain that something like a metal fixing, such as a hexagon nut or a screw has found it’s way into that cylinder. It’s been trapped between the top of the piston and the squish area and that’s distorted the piston causing the ring lands to be compressed.
I wonder if one of the screws from the “flaps” in the intake manifold has come off and found its way in there.
To me the marks are too defined and concentrated in the 2 areas to be a foreign object. If it had been a screw or other fixing then the top of the piston, the valves and the spark plug would have been showing signs of damage. This is more likely the effects of stuck or damaged piston rings allowing blow by from the crankcase and combustion products to leak causing local overheating due to poor combustion and melting of the piston crown plus further damage to the rings. Eventually the top piston land will melt leading to more piston and bore damage.
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That was my thought Alben.
When I got the head off I was convinced a ring had broken up but with the piston out I found the rings in place albeit seized.
There is no evidence of debris damage in the inlet manifold and all flaps/screws are in place.
I still believe the root of the problem stems back to poor maintenance leading to lack of oil and the oil control rings flogging up and sticking in the grooves.
Agreed.
This happened on the Kent engine in my old bitsa.
A nut holding down the air cleaner on top of the 32DFM Weber was “ingested”;
bang-bang-bang…bang-bang-bang
and then spat out.
Evidence was all the nut prints on the piston rim and two bent valves.
After that we needed a new 7" strainer for the kitchen because I stole the old one’s nicely shaped stainless mesh to protect the carb top from a recurrence.
What you are talking about is ‘detonation’ and it does indeed destroy pistons like that. The thing is though it’s a stock engine so i’d be surprised if it is. If it had been suitably modified to enable huge amounts of det’ then it would have been more likely.
What also leads me to think it isn’t det’ caused by low octane fuel in the chamber is that det’ usually happens around the inlet squish pads and to the side of them on the piston, not at both sides of the chamber like that and generally not on the exhaust side either.
It also breaks the ring lands which it hasn’t there.
I wouldn’t rule it out, just think it’s less likely.
A spark plug earth strap could cause damage like that, it’s small enough to get trapped there, but not big enough to hit anything else.
The skirts have rubbed the bores indicating overheating.
If I had it in front of me i’d probably make a better diagnosis, but it’s difficult from a few pics.
The jury is still out for me and it could be more than one problem at once.
You haven’t said what coolant is in it yet.
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The coolant was dark green in colour (see photo)
There is no evidence on the rest of the engine to say its been cooked, ie discolouration of metals on block/head , the coolant smelt of coolant - no oil or burnt smell etc.
I think my question now to the many SMEs on this forum is what would be the best option now?
Is it salvagable in situ or do I need to pull the block out for some kind of repair?
I’m not keen to get a 2nd hand donor engine as I could end up with a dud. Also I don’t want any ‘big bore go fast turbo 300bhp’ mods done - just plain and simple as standard as possible.
Has anyone any ideas for costs of a recon short bock or cost to repair mine ?
Ideally I want to do the rebuild myself - just for the satisfaction really 
Thanks to all
I have no idea what an SME is, but you’ve had my overview as a professional engine builder and i’ve done a lot of these.
Read that again and act accordingly. The 1.8 is the runt of the family, most people just bin them so parts (pistons) are difficult, if not impossible to find. I’ve just looked in my parts cat and they don’t list a piston for this at all, others may do, but I doubt it.
I think that I’d be looking for a decent lowish mileage 2.0 from a write off with a known history. Transfer all the 2.0 unique bits over and take it from there. If you get lucky you may find a 3.5 or 3.75 motor with the mods. Otherwise how about a 2.5L motor?
Your lump is effectively a write off, it will cost more than it’s worth to rebuild and even then it is what it was.
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