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Old 03-11-2016, 01:35 AM   #1
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Default Miata Motor Murder Mystery!

Let's play a game of "What Happened to Kill my Car First?"

A couple of days ago I ended up on the side of the road with my car making a lot of really bad noises and refusing to run. I realized pretty quickly that something was not happy in the bottom end and had it towed home. Here are some video clips of the sounds it was making.

http://youtu.be/zYXohZ92qIc
http://youtu.be/M7120YYj8sY

Knowing I'd need to get into the oil pan, I broke out the hoist and pulled the motor. This is what I found once I got inside.



A chewed up thrust bearing.




A whole bunch of paper thin chunks of metal and a thorough coat of metal shavings along the bottom of the oil pan. Also 1 broken off oil squirter nozzle.




One of these things is not like the others.

Then we have this gem.
http://youtu.be/IESNXkWRKeg




And that, boys and girls, is what it looks like when a rod bearing disintegrates...

So! Now for some information.
This motor was completely rebuilt last spring and has roughly 1k miles on it with new forged rods, pistons, rod bearings, main bearings etc.

Here is the build thread for full details. https://www.miataturbo.net/build-threads-57/k-bai-tale-one-mans-struggle-do-right-86250/

Everything else in the motor seems to be in really good shape. From the looks of things it's just cylinder 2 that had any issues.

So what the hell happened? I've seen other threads that talk about Wiseco pistons snapping oil squirters. Oddly enough that cylinder looks like the only one that touched and was broken. But it doesn't look like it got caught and screwed anything up.

The thrust bearing definitely got mangled by the crank but I'm fairly sure I installed it correctly, I rember reading up about it.

Or did that Rod bearing just seize first and start to screw things up? I can't think of any reason it wouldn't have gotten proper lubrication. I've got one noticeable oil leak but i changed the oil 3 times over the 1k miles it's been running....

So what gives? Let's hear your theories.
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Old 03-11-2016, 03:21 PM   #2
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Did you check crank endplay after assembling it? If the thrust bearing was the wrong size, the crank will touch the end caps, machine them down, filling the oil with iron filings. Crank moving forwards and backwards could move the piston a bit further than usual and might the oil squirter breaking off, and the filings will definitely destroy bearings.

When you say everything else looks OK, have you torn it down further? Did you pull the other caps to inspect the other bearings?

--Ian
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Old 03-11-2016, 04:20 PM   #3
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It was the butler in the library with a candlestick.
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Old 03-11-2016, 04:21 PM   #4
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Quote:
Originally Posted by Elfering View Post
Let's hear your hypothesis.
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Old 03-11-2016, 04:26 PM   #5
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Quote:
Originally Posted by codrus View Post
Did you check crank endplay after assembling it? If the thrust bearing was the wrong size, the crank will touch the end caps, machine them down, filling the oil with iron filings. Crank moving forwards and backwards could move the piston a bit further than usual and might the oil squirter breaking off, and the filings will definitely destroy bearings.
I agree with this order of events. Thrust bearing failure > iron filings > spun rod bearing > broken rod bolts > broken piston/squirter
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Old 03-11-2016, 04:56 PM   #6
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I agree with this order of events. Thrust bearing failure > iron filings > spun rod bearing > broken rod bolts > broken piston/squirter
That sounds very probable. I never checked the end play during the original assembly. This has never been something I've ever really had to consider with other motors =/.

I haven't taken the motor down any further so my initial statement of "everything else looks good" may have been premature, but on the surface that seems to be the brunt of the damage.

I haven't touched the crank journal on cylinder 2 just yet but as of now I'm crossing my fingers that the crank/block will be salvageable. This being my first spun bearing i'm not quite sure what the typical course of action is for a spun bearing. I'm going to pull the crank, clean it up, plastigauge it with the new rod/bearing and possibly take it to a machine shop I guess we'll find out soon.
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Old 03-11-2016, 05:21 PM   #7
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I'd take the crank to the machine shop to be checked for sure, take no chances imo.

Was that a mazda thrust bearing?
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Old 03-16-2016, 01:29 PM   #8
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I'll be taking the remains of my old motor to a machinist this weekend to see if its salvageable. In the mean time, I've begun searching for replacement motors and have come across 2 options for roughly the same price and would love some input to help with my decision.

Option 1 is a VVT 1.8 out of an 02 NB Miata

Option 2 is a BPZE 1.8 motor out of a 95 NA Miata. (Should be exactly the same as the one I just ruined)

My question is: Is the added benefit of VVT/the slightly improved intake manifold worth the added complexity and hassle of the additional modification that will be required for me to run that engine over the BPZE that im already familiar with and should plug right in?

I've read that wiring the actual VVT portion isnt overly complicated but im mildly worried about tuning it as I've never used VVTuner before. My findings have also been less than clear about wiring the ignition coils on the VVT motor, I really have no desire to change my ignition setup and would happily run the NA coil setup if its an option.

Any educated opinions on Miata VVT motors would be appreciated!
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Old 03-16-2016, 01:49 PM   #9
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We have a huge VVT swap thread as a sticky. Go read it. You have an MS3, I assume it is an MS3x or a MSlabs, or a MSPro of some sort. In that case you want the vvt, it is worth the extra hassle. Wiring it in is not to painful. The following plugs need to be changed cam, crank, tps, idle valve, and vvt wires. All of it is explained in the sticked thread.

As for the coils on the VVT motor. You can look at the install instructions from FM for their LS coil big spark setup for how they handle it. Basically you get rid of the hard line and run a -4an oil line from the side of the block to the vvt feed.
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Old 03-16-2016, 02:02 PM   #10
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It's easy to swap in VVT.

Or get the singular coil mount and keep the hardline.
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Old 03-16-2016, 05:35 PM   #11
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If you're not worried about smog restrictions, then I'd definitely get the VVT motor over another 94-97.

--Ian
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Old 03-16-2016, 06:06 PM   #12
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If you're not worried about smog restrictions, then I'd definitely get the VVT motor over another 94-97.

--Ian
There's a little worry, fortunately I'll be moving to Boise, Idaho soon and emissions are a lot easier to work around there than Denver. I did just find a really good deal on a local 95 engine that I think I'm going to jump on. I'll cross the VVT bridge when the time comes I guess. Thanks for the input though fellas.

Now hopefully the machine shop doesn't take forever and a day to do the bore I need.
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