Crank Walk
#1
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.
#10
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.
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.
#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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