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Old 05-18-2018, 06:08 PM   #1
OkeyDan
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Default Piston damage analysis

Hi,

I blew my engine and it would be awesome if we could put our heads together to do a bit of an analysis on why it happened.

Story: I've been running 1.5 bar, 21.7 psi boost for 6 months now with some Chinese T3 turbo, IPD turbo cam and using Megasquirt2 . Was running great, fun was had. Then the day came I had the brilliant idea to up my rev limiter a bit, until then I had it set to a conservative 6000 rpm but made the change to 6400, 200 more then stock still not shocking one would think.

Did a couple of pulls and all seem great, drove home for about half an hour (still going into boost every now and then) and only while idling in front of a traffic light I noticed it wasn't running that great. Turned out, smoke was poring from my breather and doing a compression test showed 5 bar compression on cyl 4, not good.

Pulled the engine out of the car and got it apart.
Here are some pictures https://imgur.com/a/iWHotiM sorry for the bad quality.

As you can see the pieces of piston between the rings are broken. The 1st ring is still in one piece, the 2nd and the oil scraper are damaged. Below the oil scraper is even a bit molten, you can see the molten pieces of piston on the ground next to the broken pieces of piston and rings.

The top of all the pistons look immaculate, same goes for the bores, not a scratch, you can still see the hone marks.

What do you think?
- Knock
- AFR
- Simply to much boost for a high mile engine (400000 km, 250000 miles)
- Something else

tldr: Blew up my engine, come take a look at my piston and give your opinion on why it went wrong.

Last edited by OkeyDan; 05-18-2018 at 06:28 PM..
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Old 05-18-2018, 06:45 PM   #2
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Detonation trashed the cast piston by breaking the ringlands
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Old 05-18-2018, 07:01 PM   #3
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Quote:
Originally Posted by eabras View Post
Detonation trashed the cast piston by breaking the ringlands


Hone, check bores for round, new pistons, file fit rings, new oil pump, and go go go bewsts again.
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Old 05-18-2018, 07:25 PM   #4
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Yeah the ringlands are supposedly the weak link in the pistons on these mobiles.
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Old 05-18-2018, 07:30 PM   #5
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Ringlands are almost always the weak link in the boost equation until you spend beau coup bucks on pistons from my experiences with these cars and EJ motors.
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Old 05-19-2018, 02:17 AM   #6
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Ok detonation it is. I was under the impression that detonation would also cause pits on the top of the pistons, seeing as they are all good I thought it must be something else.

This is a bit annoying though, I've heard it knock once, changed the timing a bit and never heard it again, thought I fixed it. But this must mean I still got knock somewhere without being able to hear it.

Quote:
Originally Posted by eabras View Post
Detonation trashed the cast piston by breaking the ringlands
Awesome b21 build you got, I got a HX35 sitting on the shelf waiting to go in if I choose to go down that rabbit hole:P.

Quote:
Originally Posted by centason View Post

Hone, check bores for round, new pistons, file fit rings, new oil pump, and go go go bewsts again.
I still got to measure the bores to check if the wear is more then 0.1mm, don't have an "inside of a hole meter" yet.

Really, all new pistons? Wouldn't it be wise then to have the block bored to the next size and essentially start again with a 0 mile motor. Seeing as the pistons are then the most expensive part.

Would you change the crank bearings?

Thanks guys for having a look.
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Old 05-19-2018, 02:37 AM   #7
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If it were me, I'd rebuild the motor. Take it to a machine shop and see if it needs to be bored. It might not need it, then again it might.
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Old 05-19-2018, 10:13 AM   #8
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Fix it right OP. Oversize. Forged Pistons on H-Beam rods. Do it once and enjoy for years.
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Old 05-19-2018, 10:28 AM   #9
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I don’t think upping the rev limiter was your problem. Knock is most dangerous around the torque peak which for an 8v red block is a little above 3000ish rpm. If you’re shattering ring lands you are either too lean or have too much advance.

Is this a +T or stock turbo car? How much advance are you running at 200kpa?

Post your msq.
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Old 05-19-2018, 11:19 AM   #10
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Quote:
Originally Posted by 740atl View Post
I don’t think upping the rev limiter was your problem. Knock is most dangerous around the torque peak which for an 8v red block is a little above 3000ish rpm. If you’re shattering ring lands you are either too lean or have too much advance.

Is this a +T or stock turbo car? How much advance are you running at 200kpa?

Post your msq.
Wat is normal timing for these engines at 200kPa?

14 degrees at 2500rpm up to 24 at redline? Ofcourse I realize this depends on more variables such as camshafts, head type etc. But I mean for a stockish redblock with a bigger turbo.
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Old 05-19-2018, 11:28 AM   #11
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20 psi on a chinese t3 turbo. I bet your inlet and combustion temps went up, ring gap was too small/detonation, followed by ringland failure.
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Old 05-19-2018, 07:29 PM   #12
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Ok, yes, I will take it to a machine shop to have it measured.

Do I already need forged pistons? I thought people were running 500 hp+ on the stock ones. But to be fair, if I indeed need 4 new pistons, switching to forged is probably a smart extra +-300 euros spent.

It's an original turbo car/engine. '97 B230FT

AFR was 11.1 - 11.5 the whole run, all runs, I was watching it closely.
This is my ignition table: https://i.imgur.com/5cxXQ5r.png (Don't mind the fun gear shift section)
Here is my msq: https://ufile.io/v8g2m

Inlet temps were pretty high indeed, so the ring gap could indeed also be wrong. Would that leave marks on the cylinder wall? I was thinking of upgrading the intercooler but after seeing it when I removed the radiator I'm kinda surprised about how big it is. I'm not going to be able to fit much more if any if I went with an aftermarket one. (still got a condensor up there too:P)
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Old 05-19-2018, 11:03 PM   #13
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Much to be gained with large intercooler. Seat of the pants power improvement + turbo could be heard to not be trying so hard to force air through the puny I/C core.
I got very close to ambient IAT using a Ford Powerstroke intercooler.
I've also fitted the I/C from an NPR diesel. Nice improvement over stock and easy fitment.
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Old 05-19-2018, 11:33 PM   #14
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If you have those little NPR box trucks over there. That intercooler as John suggests is a great fit into a 240 to replace one in the stock location.
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Old 05-20-2018, 03:39 AM   #15
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Been a long time since I've messed with a stock b230ft/fk, but that ignition map is perhaps a bit hot compared to similar setups?
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Old 05-20-2018, 04:44 AM   #16
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Particularly 2300 to 3500 seems quite advanced to me (210kpa). I'm running a couple of degrees less than that.
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Old 05-20-2018, 06:39 AM   #17
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No I don't think we have those trucks here. But it's good to know a bigger intercooler has a noticeable effect. I will try to find one that fits or maybe move the condenser out of the way or something.

Ok, could you share your ignition map?
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Old 06-05-2018, 07:49 PM   #18
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Little update:

Completely disassembled the engine block and brought it to an engine shop (a nice old one with pieces of bitchin engines laying everywhere:P). The bore wear was right on the edge so we decided to go with 4 new over sized pistons. We were gonna go with the (original) Mahle over size pistons but they were not available/in stock. He called me to tell me he found some pistons and told me this would bring my compression ratio down to 1:7.8 and he asked if he needed to shave some of the top of the block to get the compression ratio back to original. But with boost in mind I told him to leave it, 1:7.8 sounds nice, that's WRX territory.

Went and picked up the engine block today, all nicely cleaned, bored and honed and he surprised me with the pistons, turned out he was able to source a Wiseco FORGED piston kit for the same price as original pistons, nice, brought a smile to my face. Need to do a couple things to the block, like deleting the stupid pcv, and then it's time for reassembly.

While the block was in the shop I cleaned and refurbished the head a bit, new cam seal, new valve guide seals. I also cleaned the valves and used a bit of fine grinding paste to just touch up the valve to valve seat fitment.

In order to prevent damage in the future I plan on building a little amplifier which makes it possible to listen to the knock sensor output with a set of in ear head phones. Like some sort of electronic det cans. I think this should enable me to hear knock and better tune the engine. Sadly it seems that sharing tunes is not really a thing.

I just thought I'd write this update because it sucks whenever I read through a topic and it has an open ending, so I try to complete mine. I will post an update when it's running again and have done some tuning, hopefully with an updated ignition map, I don't mind sharing mine.

Last edited by OkeyDan; 06-05-2018 at 07:59 PM..
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Old 06-05-2018, 08:01 PM   #19
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What about ring gap on the rebuilt motor?
That's my primary failure suspect in your initial blow up. Root cause possibly hot charge, a boost curve that came on too quick or both. Look into water meth injector or a larger intercooler.
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Old 06-05-2018, 08:07 PM   #20
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He told me since he bored it to Wiseco spec it should be fine but it wouldn't hurt to check at least 1 cylinder. I'll probably check all, doesn't take that long and is nice to know for sure.

Thanks, yes, intercooler is on the todo list.
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Old 06-05-2018, 08:40 PM   #21
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I believe Harald built some home-made det cans like you're mentioning. Maybe check with him.
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Old 06-05-2018, 09:28 PM   #22
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Shame on me for thinking I had an original idea, punched in "electronic det cans" in google and sure enough, tuns out it has been done already. I don't know Harald, is he a user on the forum?
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Old 06-05-2018, 09:43 PM   #23
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timing was a little high compared to what I normally see, but perhaps not out of question. are the rods bent? 7.8 :1 is borderline anemic.
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Old 06-06-2018, 03:29 AM   #24
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Thanks on the timing feedback, I'll keep that in mind.

The compression ratio is theoretical, not measured. I still need to assemble the whole thing. I think this is the piston kit. As you can see, advertised as 8.0:1 compression. Don't know where my guy came up with 1:7.8, probably calculated, but that's near enough to call the same. Good for running a lot of boost.
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Old 06-06-2018, 10:39 AM   #25
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If by "a lot of boost" you mean, constantly over 30psi, sure maybe.

Nice pistons, I'd run a thinner hg and maybe skim off the head a little bit. Verify rod straightness of the rods. I'd personally just get a set of hbeams regardless and move on, but ymmv. These days, 9:1 is low compression, anything much lower than that is either very high output or just old.
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