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Questions about 12a tear down

Old 12-02-17, 07:18 PM
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WA Questions about 12a tear down

I recently picked up a used 12a that supposedly ran before it was pulled. Looking it over, it appeared clean and in reasonably good shape. I finally tore it down and I'm curious about a few things.

The housing look pretty good. There is no chrome flake and one housing is almost perfect. the other housing shows some chatter marks and I'm wondering if it's okay to reuse.





I'm also curious about the bearings. Every bearing appears to have this line in it. Is that normal?






The other ugly thing is the needle bearing. It looks like I'm gonna need a new bearing plate. Is this normal?



One last question, I made sure to account for all hard and soft seals, springs, etc. I am missing four of the rubber plugs from the corner seals. Is that normal? Do they burn up?

Thanks for looking. More pictures are available here: https://imgur.com/a/bIzq9
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Old 01-29-18, 10:53 PM
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looks like my bearings I have pulled two 12a engines and there the same lines has yours. how is your rebuild going? did you find a good source for parts. I have started the process of the 12a rebuild, would like any info you might have doing yours. my housings in same condition has yours and I was told there fine no flaking is good. please give me some input on your rebuild cheers
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Old 01-29-18, 11:34 PM
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i'd replace all 3 of those pieces pertaining to the thrust bearing. i see what looks like galling on that one plate and blueing of the needle bearings from heat, maybe lack of lubrication.
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Old 01-29-18, 11:52 PM
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If you look at the tech info on racing beats website they make mention of this line on bearings. It sounds like it’s from how the bearing is manufactured and then made round and concentric. Shouldn’t be an issue
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Old 02-03-18, 10:48 AM
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the bearings are made by bending a flat plate into a circle, plating it, and then honing it, which leaves the line, its completely normal, and i think even new bearings have it.

dead thrust bearings aren't really normal, but those are bad and you should just replace the lot of them, its cheap. be a little careful to set the end play, as it will be all new stuff.

those housings, for a 12A are perfect.
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Old 02-03-18, 11:03 AM
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Thanks for all the answers. I have purchased a new thrust plate and thrust bearings. I'm currently working on street porting the irons. I'm going slow since this is my first time.

Last edited by kippen; 02-03-18 at 11:20 AM.
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