Piston Damage
 

My engine is a built 1.8LVVT with an FM turbo kit, GT2560R, 3" exhaust running 10psi or 14psi depending on my mood. Pistons are SuperTech 84mm 9.0:1 installed about 50K miles ago. The head needed a shave to return to flat, resulting in 9.4:1CR.

The engine started burning oil in the fall of 2020. This past summer, oil consumption got ridiculous, about a quart every 300 miles if I was enjoying the turbo. Teardown photos are below. Pistons 3 and 4 have a spot below the oil ring in the wrist pin area where the aluminum melted away. Number 4 was the worst with damage to the oil ring. Number 3 has the same spot but it did not break into the oil ring groove. You can see particle damage in the side pocket for the wrist pin. The wrist pins in both 3 & 4 do not turn in the piston, they will need to be pounded out with tha drift. The rod bushings also have play in them, we assume from heat.

My engine builder believes the damage was caused by heat. I have a 949 coolant reroute on the engine for the past 20k miles or so. I also have an oil cooler. Oil temps regularly ran at 240°F during the summer and water temps in the 215°F to 220°F range all the time. This summer I installed hood vents and replaced the 195°F thermostat with a 180°F thermostat. Both oil and water temps are lower, but this damage was done before those mods could have had an impact. What stumps my engine builder is the loacation of these melted spots. How can a piston have a hot spot in the pocket for the wrist pin?

If anyone has experience with this or ideas, please share. I'm rebuilding. The block is scored so we are going up to an 85mm piston. I sure would like to avoid this in the future.
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Are you still running the piston squirters?

Yes, squirters still in place.

WOW, that's the only thing I could think of that might cause the melting you are seeing. If the squirters are still working I don't have a clue and am VERY interested in what the final diagnosis is.
Since it's all apart anyways I'd test the squirters. Most squirters have a pressure check valve in them. They will not squirt below a specific oil pressure but above it they should work fine.
I think the Mazda ones fire at 30 psi but I'm not 100% sure. Another member may have a more accurate pressure.
Some folks disable them and I'm not sure how they are oiling the piston pins as the rods themselves do not have oil squirt holes in them.
By the time that heat from the top could trash the pin bore as your pictures show I would expect significant damage to the tops as well.

You has "double-headed weird" going on right here.
I hope someone else posts with better suggestions.
Sorry I couldn't help...

My first thought was, "There was something in the cylinder that got trapped in the wrist pin area". But if it happened on two cylinders, that would be kinda unlikely. I got nothin' but am curious as to the cause. I had a ST piston fail in the the top ring land in the area around where the valve relief was. But that's on the topside, and not the lower oil control ring.

We had initially thought trapped contaminates as well, but looking closely at the failure point, it looks like the result of intense heat at that spot.

Tom disassembled the rods and pistons today. Wrist pins 4, 3, and 2, were broken inside the rod. He tells me the rods can be saved by replacing the bushings. The pins had to be pounded out of these 3 pistons.

https://cimg8.ibsrv.net/gimg/www.mia...37f9e55a0e.jpg

WOW, even more carnage.
And those are not the cheapo rods, those are GOOD rods IMO.

Still looks like excessive heat on the bottom of the pistons to me.
I wonder if the heat damage came after the pins failed?

Is #1 piston still perfect or does it have heat damage as well?
And then how in the hell can you break 3 ridiculously strong piston pins without trashing other things???

Waiting for the light bulb to turn on in my head, still waiting...

Holy crap! This is the first time I think I've ever seen a wrist pin break. I can't imagine the kind of forces needed to do something like that. I'm thinking a cyclical twisting moment from the small end of the rod, but what could cause that?

I'm intrigued...

Due to the price of new Manley rods I'd not re-use the ones you have now. I'd be worried about whatever heat treating they have done to them has been altered.
That's just me being conservative but the rods are less than $100 each...

Are the bearings OK? I'd expect trashed rod bearings al least.

Before I ever re-assembled that I'd test the crap out of the piston oil jets. I'm still leaning towards an oil jet issue being the root cause.
Might try swapping the main bearing shells upper to lower to block off the mains. If that doesn't work I'd put a piece of aluminum "duct" tape over each main bearing oil hole and put the bearings back in. You shouldn't even need the crank installed. The main caps alone should hold the shells in just fine.
I'd find something to plug the VVT supply hole.
I'd find something to stick into the oil feed hole for the head. Something tapered like an ice pick. A big "tooth" pick or maybe a sharpened golf tee and just hold that in during testing.
I'd fill the main bearing journal up with oil (through the center pipe for the oil filter) and apply air to it. Watch what is happening with the jets. Did they spray the ceiling of your garage? Well then I'm even more confused.
#1 sprays but the others don't. Target DOWN and you've diagnosed your issue.
Please keep us informed. Intrigued and confused...

I wouldn’t give those rods to my enemy. IMO they are cheap rods, just like k1, eagle, etc. “expensive” rods are Carrillo, no? I don’t think some crazy force broke those, that looks like a metallurgy issue. Replace rods and pistons, good opportunity to upgrade to wisecos.

I would not re-use any of that. But that's just me. I've looked it over, agree with everyone that it's weird, hoping to have a better post for you in the morning after I've had my quad shot espresso.
It's almost like the bores were oval or something

So did the heat break the wrist pins, or did the wrist pins break first and generate the heat?

--Ian

A bit of clarification. Tom removed material from the pistons to allow the wrist pins to slide out. No force was used to remove them. The 3 wrist pins were broken inside the rods.

I wonder if the broken pins in #3 and #4 caused heat that traveled down the pin to the end were it concentrated on the bottom of the piston creating the failure we see.

Now that I think about this more, I agree with Curly. These rods are only $400 a set. If they were $1000 Carillos, I would look into rebushing. But for $400, I'm just buying another set of Manleys.

can we see what kind of timing you're pushing at you peak loads?

also, I recall at least a handful of discussions over the years about defective supertechs, here's some quick search hits
https://www.miataturbo.net/engine-performance-56/concerns-about-supertech-pistons-38232/

https://www.miataturbo.net/engine-performance-56/vvt-supertech-pistons-%3D-interference-engine-44493/

https://www.miataturbo.net/engine-pe...8l-dohc-65235/

also here's a discussions about rods.
https://www.miataturbo.net/engine-pe...na-rods-93041/

https://www.miataturbo.net/engine-pe...-honing-42619/

Also also, I recall a few discussions (I'll have to find them) about rods being out of spec, specifically the small end. So I'm trying to kill 3 birds with 1 stone:
1) did the timing grenade your pistons/pins
2) were the rods out of spec causing the pin damage which caused piston damage due to heat? were the pistons defective and melted?
3) was this your builders oversight and bores were out of round/spec

Based on my vast experience in engine building/re-building - over 3 (re-)builds done in the past 7 years (that's a joke, guys) - I have come to the considered opinion (everyone has one, just like everyone has an asshole) that those rods were out of spec in some manner; not straight, or some error in the small end dimensions. That error over-stressed the wrist pins (long-term cyclical fatigue, or during multiple detonation events producing high shock loads) and they snapped like store-bought pasta going into a boiling pot. This either; a) dislodged a piece of the pin into the bore which wedged into the ring land and melted it and the ring land into oblivion, or b) caused excess heat in the pin bore through friction and/or rocking of the pin in the piston which caused the ring land to melt.

I've had "good luck" with Eagle rods absorbing my inexperience / laziness / stupidity and I just put some Manley rods in (after "banana-ing" a stock rod in my "alternative block"), so I'm hoping that defect in yours was an anomaly. But, as my old boss used to say, "Hope is not a strategy".

I'm in for the true cause...

Thank you for the links. I have some reading to do.

Here is my ignition map. I finalized this in February 2019 when I did the Skunk2 manifold testing. I did not touch fuel or timing numbers after that exercise. I tuned the ECU for the Skunk2 with spacer to AFR at 12:1 at 174kPa and 11.6:1 at 195kPa. After that, I just enjoyed driving the car.

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174kPa is my low boost setting. 195kPa is the high boost setting. I used 195 most of the time. Fuel was always 93 octane found in Pennsylvania and the east coast. This car went to MATG and Florida several times.
Looking at my data sheet from the engine build, the bores are all documented at 3.308" with 0.003" clearance on all 4 cylinders. We installed 84mm pistons.

If it were mine, I'd send one set of rods/piston to each of the rod and piston manufacturers, and ask their opinion.

And I would be buying new rods and pistons from different suppliers, partly for insurance, partly in protest. The latter may be pre-emptive, so be it.

Also in for knowing the roundness of the bores - those bores!

definitely wasn't the timing. so I'm in agreement with the others:
likely 1) rod defect
less likely but possible 2) piston and/or bore defect

I keep looking at the picture. I don't think I have ever seen cleanly snapped pins like that before. at least not without crazy hot spots and all sorts of other damage.

After reading the links 18psi kindly provided, I'm getting frustrated. Pulling out my soap box. Most businesses in this country have sold our soul to the Chinese Government. In the name of cheap labor, we have endured shit quality control from those unscrupulous slanted-eyed, commie bastards. They will think nothing of providing samples of a product exactly as specified, only to later substitute lower quality materials to save themselves money and not alert, or lie to the US customer. Manufactured in China has fucked me on my valve stem seals, my pistons, my rods and they are currently fucking me with storage batteries in my day job. Rant over. And if I offended any Chinese people, get over it. If you don't know every word above is true, you're an idiot.

A truly appreciate everyone's input on this issue. I will check with my engine builder on the roundness of my cylinders, but I doubt this is the issue. He is an ASE Certified Master engine builder and has built engines his entire life. Unless more information presents itself, I'm thinking the wrist pins broke because of shit, Chinese material. This created heat in the bottom of the piston causing the failure. I'm buying 100% American parts to rebuild my engine for the second time. I'll be buying Carrillo A beam rods.

Now I have to find pistons. My block is already at 84mm with scored bores. I need at least an 84.5mm piston, but would like to go up to 85.0mm for the extra displacement. If I have to buy a new block, I'm going to loose my mind.

Did your engine builder provide a sheet of all measurements when he assembled it? Bore taper, ring gap, scraper ring tension, etc.?

Weird.

I don't have much to add other than saying that those temperatures are regularly achieved on track by both stock cars like spec Miata and higher power boosted Miatas as well. Quality synthetic oil is fine up to nearly 300F, modern engines like the Ford Coyote run 260F+ all the time even with massive coolers, and 220F coolant is not really a huge issue either. Definitely not enough to cause a meltdown.


Also for the rebuild, keep in mind if you'd like to make more power in the future, smaller diameter piston bore means thicker cylinder walls, thicker cylinder walls means stronger block.

When I had to rebuild my motor after a throttle body failure a few years ago (wow, closer to 10 years at this point now that I think about it) it was cheaper to buy another block than to pay the premium they were charging at the time for 84.5mm pistons. Dunno if that's still the case though.

I have also read that not all blocks can be bored that large, some of them will break into the water jacket.

Carrillo A-beams are great, I've been very happy with mine.

--Ian

Once again, I agree with the guys Ken: unless you intend to sonic test the current block, you probably don't want to hog out a block you are planning to keep for a long time.

It's a crappy situation, and often times people call it excessive, but in the business of engine building you really gotta have everything perfect to meet the standard you're setting.

Wow! that's an impressive failure. I would be curious as to metallurgy of the wrist pins. How much crankshaft thrust clearance did you have?

I'm definitely seeing the light here. My engine builder is giving me a fresh OEM block to bore out to 84mm. I have ordered 9.0:1 CP pistons, Carrillo A beams and ACL Race bearings.

For those asking about various measurements in my engine. Attached in the blue print from my build. My engine builder is Tom McCulley at https://mccullyracingmotors.com/ His website is geared toward Ford V8s, but he builds plenty of BP engines as well.

Perhaps I'm looking at this from the wrong perspective, and given my lack of engine building experience I don't want to throw around any accusations here, but first impression seems like some of those measurements are "too round". Just from a Gage R&R perspective, with micrometers that read down to 0.0001" (which I'd like to think is common for master engine builders), I'd probably expect more variation for items like the bearing and piston to wall clearances.

Looking specifically at the wrist pins, and pulling from 5X's product pages, if I'm reading things correctly the called-out clearance would be 0.0011" not 0.0005" (0.7881" rod wrist bushing bore dia - 0.787" wrist pin dia). Gut feeling, 0.0005" of clearance seems like a rather tight/almost transitional fit, but I could certainly be wrong. Perhaps someone else can chime in if they recorded their wrist pin specs from a previous build?

https://cimg7.ibsrv.net/gimg/www.mia...b14bec2b3b.pnghttps://cimg0.ibsrv.net/gimg/www.mia...a646c1b147.png

Anyway, just food for thought. Best of luck with the new build.

So the motor ran for 50k (as in.... fifty thousand, five zero thousand) miles.

And it's the *insert racist bullshit* people's fault that it failed at that point?

You are a racist piece of shit.

^^^^^ Ben (Concealor404) has the gift of stepping back and seeing the big picture. ^^^^^

There is a cause for the failure, but the built and driven hard motor did last 50K / 5 years..

Right on the money. 90% of "blueprint" or "spec" sheets I see online are garbage. As someone with a metrology and engine building background, I get incensed by these things. Regardless of the called for tolerances in this specific application, there's a number of red flags:

1) Piston to deck height only provided on piston #1. These heights are NEVER identical across all pistons unless you specifically mill piston tops or take other action to make them so. This tells me the others were never checked. Granted you're running an exceptionally large piston to head clearance so I wouldn't anticipate issues, but it certainly is indicative of the lack of attention to detail when the entire task is inherently based in detail.

2) Bearing clearances provided with .001" resolution..0025" and .0034" round to .003" but are very different in terms of bearing fit. Same thing with piston to wall clearance.

3) Literally zero variation cylinder to cylinder anywhere on the sheet. This is not possible in reality, no way, no how.

I'd like to see all of these measurements taken again as part of the post-mortem. Your "engine builder" may have all the credentials to absolve him of any blame in your eyes, but these numbers are all fabricated. Someone probably eyeballed most of them to be "close enough" and filled in the ideal numbers to make you feel warm and fuzzy about the build sheet. The fact that you got 5 years and 50,000 miles out of this engine is astonishing already.

twopointwo..... this is a great quote: ...but it certainly is indicative of the lack of attention to detail when the entire task is inherently based in detail.

Is the crankshaft still in the block or has crank been removed and shortblock completely disassembled? If its still in the block can you measure the thrust clearence? If Its removed how did the two thrust bearings look?

Something extraordinary happened in that engine to snap 3 out of 4 wrist pins. Whether the root cause was manufacturing defect, assembly error, or (hard) usage has yet to be determined. To @twopointwo 's point, the builder spec's can be questioned and a reality check there can help the OP identify a possible root cause.

I'd like to know what kind of forces (dynamic and static) would destroy a wrist pin like that - out of curiosity. For me, that's something that just doesn't happen. I would expect a piston, or rod to fail well before a pin would snap in two. For me, that points to a manufacturing defect - just my $0.02.

Fascinating carnage with a side of political commentary. Lovely.

I won't get into whether or not you actually had those measurements, but personally your rod and main clearance is too large, I usually see under .002" for both, you're at .0025 main, .003 rod. I've never an issues for me to desire larger clearances. Except the ridiculously low oil pressure of a BP, especially at idle, which would only be exacerbated by larger clearances.

Ring gaps look ok. Maybe a few thousands small on the top ring, few thousand small on the bottom ring. I did .019/.022, but that's cutting hairs at that point.

I would NOT run ACL race bearings if you are not racing. IMO there's too much debris in the oil of a street driven car for the race bearings. I would even suggest stock bearings if you raced it. Some of the quietest (knock), cleanest (inspecting cut open filters), and highest HP builds I've worked on (330, 320, and 360hp) have all been stock bearings. Love your choice in rods and pistons though.

looks like the wrong pin spec and they broke. throw it all away rods also and get new. move on.

I have a set of pistons laying around here with identical damage from crap machining; an ovaled bore and too tight clearance. Possibly end gaps too tight as well.
I would lay the blame on the machinist, especially given their demonstrably false “build sheet”.

Personally, I’d be inclined to believe that the pins broke as the pistons seized in the bore at TDC/BDC.

Of course, this thread makes me not have much sympathy for you…

Way to show your true colors Ken. I had respect for you, at one point, as a Miata tuner who knew what the hell he was doing, being the go-to guy for FM back in the day and all that.

One post and that respect is out the window and unlikely to come back. Go post your narrow-minded hate elsewhere.

As someone who has extremely high quality items manufactured in China, you know whose problem this is? The US customer's. See your engine builder's spec sheets for an example of how this happens. Round off a number here, check only one of the pistons, "close enough", "pretty much", all of these are shortcuts that, as you found out, can bite you in the ass. Not doing the labor is the fastest way to save money on labor, no matter where the work is being done.

Incoming Quality Control is a thing, as is Supplier Quality Assurance, Authorized Supplier Lists, etc. Maybe in the Joe McCarthy-fellating past you miss so much, these checks weren't formally identified, but they existed. You didn't buy from so-and-so because they sent you a bad batch one time. Your source is always going to look for ways to cut their costs without raising their prices. That's as capitalist as you can get, maybe even in your befuddled mind that's as American as you can get. If the company putting their name on the white box from China isn't checking the quality, blame them.

You want high-quality parts in a global economy? You're going to have to pay for the labor necessary to assure that quality.

As the guy who asked for your build sheets I am leaning towards advising you to investigate more into the quality checks that both you and your builder implement. "I checked a few measurements here and there" is simply not good enough for a customized engine, especially a high performance F/I street car. There are some excellent YouTube videos by Jafromobile on the attention to detail one should have on clearances.

Finally, as a career military veteran and foreign diplomat I would strongly encourage you to set aside your xenophobia and seek to understand your fellow man.