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Old 03-09-2010, 11:58 AM   #1
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Default Crank Walk

After rebuilding my motor my clutch started to pull out some and slip a little. So my shop re-adjusted he then tells me that he has had problems when building miata's and crank walk. I am unfamiliar with this term but states the thrust bearings are not full face and this causes an issue. He belives I have mashed mine down. Also when coming to a stop my oil pressure was droping way down and the car was wanting to die. He states that this is a problem with the 99 miatas and because of there not being a full face thrust like other vehicles we will have to send it back to the machine shop and have it machined to accept a full face bearing. Any ideas anyone with crank walk and or what is this drop in oil pressure. He says he might have to go outside of the box on this one. And that any time you put a large clutch in these they have this problem. Any help or info would be great thank you.
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Old 03-09-2010, 12:09 PM   #2
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Common problem on "7 bolt" 4g63s in the 90s. Basically the sides of the thrust bearing wear down and cause the crank to "walk" back and forth in the main caps. This causes all sorts of problems with uneven bearing wear, loss of oil pressure, and eventual engine failure.
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Old 03-09-2010, 12:15 PM   #3
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i dont think this is common with bp's. this is the first time i ever heard someone say this about a bp.
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Old 03-09-2010, 12:17 PM   #4
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i dont think this is common with bp's. this is the first time i ever heard someone say this about a bp.
Read up on the '99 thrust bearing problem causing "excessive endplay". That's crankwalk.
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Old 03-09-2010, 12:20 PM   #5
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I knew a DSM would show up in this thread... In the second post no-less.
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Old 03-09-2010, 12:22 PM   #6
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I believe it is a common issue with some 99's search miata.net, there are some threads about the 99 #4 thrust bearing failure
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Old 03-09-2010, 12:42 PM   #7
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seeing that now. So does anyone know if my shop is going to machine the crank to accept a full face will that fix it or does anyone have any ideas of how to fix this problem?

Last edited by mach5; 03-09-2010 at 01:03 PM.
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Old 03-09-2010, 12:43 PM   #8
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seeing that now so does anyone if we are going to machine to accept full face will that fix it or does anyone have any ideas of how to fix this problem?
I've never dealt with 1.8s, but if it were me, I would skirt the issue entirely and try to source a 94-97 block to use as a core.
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Old 03-09-2010, 12:46 PM   #9
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The thrust bearing issues actually began in 97 and potentially go through 00.
01-05 got a bigger bearing.
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Old 03-09-2010, 01:08 PM   #10
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Lots of misconceptions about crank walk.

Just to clairify, whats happening (from what you describe) is that the bearing that holds the crank in place axialy (as in in-out motion, not side-side motion) is wearing down. This allows for a lot of movement, and also essentially opens up a huge gap for oil to pour through instead of the tight clearance that should be there. This is why your oil pressure is fluctuating a lot. I bet you can control oil pressure to some extent with your clutch pedal hugh?

When you push in your clutch, it puts a lot of force (around a ton depending on what pressure plate you use) on the crank axialy. Hence the crank is moving around when you use the clutch and the subsequent oil pressure issues.

I actually had a crankwalking 6 bolt G4CS (esentially a 4G64) engine once. The asshat shop who shall remain nameless (I dont think I have ever seen them mentioned here) that built the shortblock put in ARP mains, when I specifically requested stock mains. They did not do a proper alighn hone on the new main studs. I had thrust bearing wear big time within about 8K miles. Not the blocks fault. The assembly was the problem. This was with a CFDF clutch thats basically about as mild as it gets for a non-stock unit.

Had a plain old 6 bolt 4G63 made after that, by a local I know and trust and its still going strong with an ACT 2600LB clutch.

A full-face bearing is great, but so is a good shop who knows WTF they are doing.
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Old 03-09-2010, 01:32 PM   #11
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There is a service bulletin out on this from mazda. Some of the cars had the short block replaced if they found out to late. I would take your vin to the dealer and see if it falls into this group. I had a 1.6 short snout that had horrible crank walk by the end and you could watch the crank pulley move front to back about 1/16 of an inch and the mains were shot. The last drive it made was to my buddies shop about 40 miles away and it blew up at the end of his street.
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Old 03-09-2010, 08:22 PM   #12
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so is there anything set in stone which blocks where affected? i dont have a miata i have a gtx motor its a bp2 stamped on the block
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Old 03-09-2010, 08:48 PM   #13
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Don't leave the clutch in at stop lights. My pops taught me that.
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Old 03-09-2010, 09:06 PM   #14
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lol nice. So thats where I have been going wrong. To think all this could have been avoided. I am seeing its a block problem but I have just spent a ton of money over boreing the motor can I just get an older crank and change out the bearings?
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