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Old 05-20-2014, 01:39 PM   #1
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Default Thrust bearing fail

Only 600 miles on motor. End play when we put it together was .005 endplay now is at .057 and crank pulley moves visibly. What could have caused this? We found small metal strips in oil this morning, cams were ok, and then observed the movement.

The driveshaft ujoints were loose but I don't see that vibration going all the way through to the thrust bearings.

HELP!
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Old 05-20-2014, 01:41 PM   #2
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they could have possibly been installed wrong. Very easy to mess up.
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Old 05-20-2014, 01:46 PM   #3
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You're sure you used the later design?

This is '99 vs. '01 thrust bearings, which one did you use?

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Old 05-20-2014, 01:49 PM   #4
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My mechanic thinks we may have used the top. I recall it being the bottom. Will check against a spare I have at home. I have an 04 MSM.

We installed them with the pictured edge towards the crank and the flat part towards the slot.
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Old 05-20-2014, 02:00 PM   #5
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That's part of your problem. I'd have to read my manual, but I think that's backwards. The crank is the surface spinning, so I think the oil grooves face the crank. It's been a few weeks since I've read and installed a thrust bearing though.

If you used the one pictured above, that's your very obvious reason for failure.
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Old 05-20-2014, 02:04 PM   #6
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Pictured edge (with the oil grooves) faces the crank. I've seen them installed backwards and actually weld itself to the crank.
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Old 05-20-2014, 02:36 PM   #7
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We did use the big bearings.

Oil pressure is up with rotella t6 (maybe the low killed bearing before). At idle with the fan on it's about 2 needle widths higher on my gauge.
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Old 05-20-2014, 02:44 PM   #8
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Part number for bearings used.

ZJY1-11-SJ0

Engine isn't making any strange noises at idle or while driving. Waiting for a spot at the shop to open so we can drop subframe and pan.

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Old 05-20-2014, 03:32 PM   #9
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Its not until .250" that it's seriously bad, and most likely completely missing a thrust bearing. At .057", you can probably replace the thrust bearing and be ok, but that's about .05" out of spec. Which is still a lot.
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Old 05-20-2014, 07:36 PM   #10
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Oil filter didn't have big stuff when we cut it up. I hope I can just replace bearings....didn't see crank but cams looked normal.
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Old 05-21-2014, 08:17 AM   #11
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Are thrusts supposed to be put in and crank laid on top or can they safely be slipped in with crank already in place, and then cap tightened?
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Old 05-21-2014, 09:57 AM   #12
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Remove #4 cap and you can slip them in. Grooves out!
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Old 05-22-2014, 10:40 AM   #13
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That's basically what we did last time and pushed them around till they were flush with a screwdriver.

What kinds of things can cause a thrust bearing(s) to fail?

Prolonged cranking? we had some because of a tune problem where the car just would only start after 20 secs or so of crank

Driveshaft inbalance? had a u-joint with about 5mm of play in it that I replaced, don't know if this can cause problems like this though.

Clutch inbalance? we didn't have an alignment fork for my disk so we installed it and measured around the disk at 4 points the overlap of the pressure plate vs the disk and it was even, but perhaps not even enough?

"Pop-starting?" at times my car would die when I put it into neutral so if I was still moving I would put it in gear and slowly release the clutch to get it to fire up again.

Low idle Oil Pressure? I don't know what the deal is, but I switched to Rotella T6 the day we found crap on my drain plug and measured endplay, but my idle oil pressure with T6 was significantly higher than with other oils used up to this point. With Amsoil Signature Syn 10W-30, and the way I have my gauge set, the needle would sit right on the "low" line. When the fan would kick on, the needle would sit right below that line. This doesn't mean pressure was "low" but just how I set my gauge to read. With the T6, and the fan on, the needle sits right above the low line, and with the fan off, even higher than that. Cruising oil pressures seemed the same with both, but at that point I was limping home a car with a known thrust bearing issue, so I wasn't really trying to drive any kind of fast.

I am hoping that at my wristpins I have at least .057 of clearance side to side otherwise my rods will surely start pushing my pistons side to side in the bore. IIRC there was a fair amount of room there, certainly nothing to measure in the thousands. The motor runs very quiet, no knocks or anything, so I am a bit hopeful, but I think it's gonna come out through the top and block will once again get a teardown, but quicker this time. Last thing I want is to assume all else is OK and then have it fail again.

Would compression or leakdown tests indicate anything at this point?
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Old 05-22-2014, 12:15 PM   #14
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All those things should be fine. I've taken thrust bearings out of 70,000-100,000 mile engines, they all have very little wear, and measure right at the factory rating of .100 (I think), and the cranks have .005-.007" end play. Something serious happened for one to fail by .050" within a few hundred miles.
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Old 05-22-2014, 07:18 PM   #15
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Sorry to interrupt, but are the thrust bearings block dependant or crank dependant?

Example: I have a BP from a 2000 that I will be rebuilding, can I use the obviously superior 01+ thrust bearings?
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Old 05-22-2014, 09:07 PM   #16
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I believe they're block dependent. That's where they sit, and you'd have to mill a larger recess to have a '01 thrust bearing sit.
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Old 05-22-2014, 10:56 PM   #17
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Well crap, I hope I ordered the right one. Its an ACL so it should be easy to finger out. Thanks Curly.
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Old 05-23-2014, 02:42 PM   #18
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I wonder what prompted the larger bearing on 01+ cars.

Maybe wear was an issue with the smaller surface. Maybe beefier clutches or maybe they were thinking about future MSMs....
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Old 05-23-2014, 02:49 PM   #19
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Quote:
Originally Posted by Sparetire View Post
I wonder what prompted the larger bearing on 01+ cars.

Maybe wear was an issue with the smaller surface. Maybe beefier clutches or maybe they were thinking about future MSMs....
Probably had something to do with all the failed thrust bearings in the 99's

ACL lists one thrust bearing for Miatas: 1T8353H

According to 949 that PN covers: Mazda B6, B6-T, BP, BP-T, ZL-VE, ZM-DE & 90-05 Miata MX5, all




ACL Thrust Washer Miata
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Old 05-23-2014, 02:49 PM   #20
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No, they were thinking about all the failures of the smaller thrust bearings with pathetically weak Miata clutches.

They were half wearing, half just plain falling out. They were poorly held in place, and once worn would rotate 180* with the crank and fall into the pan. Occasionally catching the crank on the way out, ending like this:

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