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Rebuilding my A12, Need help.
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Hey guys hows it going :)

So since im doing a head gasket, for a extra $30 i was able to get a full gasket kit for rebuilding my a12 motor.

I also figured... since im going to pull it apart (which i have already done :P) ... i might as well replace the conrod bearings and crankshaft bearings and a few other things...

Now im only a 3rd year mechanic so im still slowly learning at the moment so rebuilding motors is still new to me... and i need a little help.

So i live in Australia and i need some parts for my motor obviously...

But i don't now what to buy?

Like do i need to measure and find out my oversize for my bearings and if i do what tools would be the best?

can i get any advice on this?


cheers

Posted on: 2016/1/8 6:50
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Re: Bearing Tools
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Quote:
do i need to measure and find out my oversize for my bearings and if i do what tools would be the best?
Tools:
* 2-inch outside Micrometer to measure journals (43 to 50 mm range required)
* feeler gauges to measure bearing crush and end-play
* Plastigage to measure clearance

The good news is that an A12 almost never needs oversize bearings. You already know this, but for the newbies reading this: only if the crankshaft is damaged, then the crank is machined smaller and oversize bearing fitted. So examine the crank journals, if there is no obvious wear then you can simply replace worn bearings with the same size.

To measure your crank to find out if it uses standard bearings or oversize, use a precision micrometer to measure each (and every) rod journal, and each main bearing journal.

Also see Bearings

Attach file:



jpg  outside_micrometer.jpg (3.98 KB)
174_568f67eb4367b.jpg 240X139 px

Posted on: 2016/1/8 7:37
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Re: Rebuilding my A12, Need help.
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Appreciate the help as always dd !!

I will buy some plastigauge tomorow and check out how it all goes !
will buy my own micrometer too ill need it in the near future anyways :)

anthh

Posted on: 2016/1/8 11:25
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Re: Rebuilding my A12, Need help.
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also one more question.

when i pulled apart my motor my block had M79 on it. but my 120y is a 1977 model.
isnt m79 a later 1980+ model block?

also my pistons are flat top, could this mean engine overhaul or engine replacement was done in the past?

Posted on: 2016/1/8 11:35
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Re: Rebuilding my A12, Need help.
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Flat tops indicate someone did an upgrade. Maybe they bought a "good used Japan motor" back in the 1980s and swapped it in. Or maybe they just fitted Datsun 1000 Coupe pistons for the extra hp. With the M79 block most likely a piston swap as only the A12GX and A12T came with flattops from the factory as far as we know

M79 -- I've never seen any Nissan documentation about this. And no Datsun block part number include M79 in it. But from photos and reports it appears that M79 was the 1979 casting. If it has a newer cylinder head on it (e.g. G25 instead of H74), that would be another clue

Posted on: 2016/1/8 22:15
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Re: Rebuilding my A12, Need help.
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thanks dd!

haven't had a chance to do any engine work, had family stuff on sat
and today i spent my morning taking a 4speed box out of a 1200 ute for my 120y :)
then more family stuff in the day of-course..

i did how ever get a chance to gurney my new gearbox and go buy some plastigauge(or flex gauge...)... i will buy my micrometer on Monday from the snap-on truck that comes around every week to work.

so hopefully i will be measuring it all and see how i go.

Posted on: 2016/1/10 6:42
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