Thrust Bearing Failure - Help to Diagnose Cause

Information on the naturally-aspirated KA24E and KA24DE engines.
Palmetto Owner
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Joined: Thu Aug 23, 2018 4:10 pm
Car: 1994 Nissan Pathfinder
1993 Nissan D21 Truck

Thrust Bearing Failure - Help to Diagnose Cause

Postby Palmetto Owner » Sat Jun 18, 2022 6:54 pm

There is a lot of detail here, but the real question is, "Can I reuse my Exedy Stage 1 clutch on a stock engine rebuild if my thrust bearing failed?" Some people say this kind of failure is due to no lubrication on the thrust bearing surface on start up with the clutch in. Others say the plastic timing chain tensioner failure clogged up the oil passages.
Details follow: Please offer advice (and thanks for reading all this).
My truck is a 1993 D21 with the KA24E engine. The odometer says 160,000 miles but I always thought it was more because the body and all is pretty rough. I bought it used and the clutch was slipping and since I use the truck to haul construction materials I thought it made sense to install an Exedy "Stage 1" clutch and a new flywheel. Exedy says "These clutch covers are designed to achieve a clamping load that is approx. 40% higher" but they also claim "Pedal efforts will be slightly higher" and "Drivability is similar to the stock clutch."
So i didn't anticipate any problem.
Next issue was: The plastic timing chain tensioners shattered. No problem... no complaining... I expected to work on the truck when I bought it. So I replaced the tension piston device, tensioners, timing chain, new timing gears and while I was at it, new rocker shafts and rocker arms. Also dropped the oil pan and cleaned it out real well. It was a real pleasure to drive... ran like a top.
Then one day, maybe six months later, oil pressure dropped to about 10 psi so I parked it at home immediately.
I took off the valve cover to be sure nothing was loose in there (from my work) and then dropped the oil pan to check rod and main bearings. Everything felt real solid and there was no visible metal in the oil but when I checked the forward and back clearance it was .060". The backside of the thrust bearing (on the center main) was almost worn through (photos attached) and the crank is slightly damaged on the thrust surface, but she didn't turn or destroy any bearings
I would do a proper rebuild but the local machine shop has a three month waiting list. I need the truck and I posted a question about "rebuild or buy new or used." It got lots of views but zero replies. So I have decided to R&R what is possible. I need a new crank and bearings. Maybe con rods too if the shop needs three months to recondition them as well. I have a new standard Hitachi oil pump I had planned to put in hoping it would "fix" the oil pressure. I'll check for a ridge at the top of the cylinders; I'll run a ball hone through it, install rings, plasti-gauge the bearings and drive it. I've done this before.
Thank you for reading this far. The question is, have any of you installed an EXEDY or similar stage one clutch on a stock engine. Assuming you treat it properly, starting in neutral, etc., has it given you good service? Or do I need to go back to the original style clutch. BTW I adjusted the clutch pedal very carefully to dis-engage near the top (about 3/4" clearance) and disengage fully, per Exedy instructions.
Don 't hold back with your opinions... I can take it! Thanks in advance! (wouldn't mind some opinions on the other post too. thank you in advance 2)
Section thru Bearing.jpg
Not worn through so bearing cap is till good.
Front (good side) of Thrust Bearing.jpg
Good side.
Back of Thrust Bearing.jpg
Bad side that takes clutch thrust?

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Re: Thrust Bearing Failure - Help to Diagnose Cause

Postby VStar650CL » Sat Jun 18, 2022 8:16 pm

The KA has only the one thrust bearing and the max end play is ~0.012". There's a lot more metal missing than 0.012", and the fact that there's virtually zero wear on the opposite side and a healthy-looking load surface makes me think the end play has been past tolerance for a long time. That makes it unlikely clogged passages are the reason. It also seems unlikely that the higher clutch plate pressure could have worn it out in 6 months, so my guess is it was already far gone when you bought the truck. You probably know, once a bearing hits a "critical mass" of bad clearance the wear accelerates enormously, so I think the new clutch simply accelerated the trip from already-bad to much worse.

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