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no fun in straight lines
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696 Posts
Discussion Starter #1
im doing a rebuild on my rb25det. n
eed pistons as my own are cracked between the rings,(what causes this) anyhow what is the standard size of the pistons?and standard size of the bore as iv no micrometer or vernier gauges

i seen a set on egay for £500 but they where 87mm, if i go for 87mm pistons i'll av to bore her out then, will boring her out give me any gains performance wise??? and with reboring will a standard nissan head gasket do???
 

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Track addict
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4,907 Posts
Cracks are caused by detonation, i have just rebuilt my engine for the exact same thing, crank case pressurising, oil blowing out the breathers etc etc.

I got a set of wisco pistons off ebay, shop called ericsperformanceparts reasonably priced but took a loooooonng time to arrive.
These were 87mm so the block req boreing to suit. I paid £200 to have the block bored and honed and also the head pressure tested and checked for straightness
Std pistons are 86mm btw.

Obviously by boreing the block you will increase capacity, i think 87mm makes it about 2558cc instead of the std 2498cc. You will notice no difference in performance though.

I wouldnt bother using a std nissan hg, far better off getting a greddy/trust stopper mhg in my opinion. I used a 1.6mm for my rebuild, but i plan to run more boost over std. So you are best off choosing a gasket to suit your needs.
 

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no fun in straight lines
Joined
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696 Posts
Discussion Starter #3
cheers m8 boring her out to suit 87mm pistons would hardly make any performane difference as you are slightly increasing the cylinder cubic capacity would it??
 

·
no fun in straight lines
Joined
·
696 Posts
Discussion Starter #4
Cracks are caused by detonation, i have just rebuilt my engine for the exact same thing, crank case pressurising, oil blowing out the breathers etc etc.

I got a set of wisco pistons off ebay, shop called ericsperformanceparts reasonably priced but took a loooooonng time to arrive.
These were 87mm so the block req boreing to suit. I paid £200 to have the block bored and honed and also the head pressure tested and checked for straightness
Std pistons are 86mm btw.

Obviously by boreing the block you will increase capacity, i think 87mm makes it about 2558cc instead of the std 2498cc. You will notice no difference in performance though.

I wouldnt bother using a std nissan hg, far better off getting a greddy/trust stopper mhg in my opinion. I used a 1.6mm for my rebuild, but i plan to run more boost over std. So you are best off choosing a gasket to suit your needs.

well here is what im doing/over hauling/changing for my rebuild
new big ends,
new mainshaft bearings,
new pistons,
new rings,
new oil pump
head skimmed as its marked

i forget any thing
 

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Track addict
Joined
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4,907 Posts
Sounds good so far mate, what bearings are you going to use. I used nissan ones on mine as you can get a finer tolerance, i also plastigauged everything too just to make sure it was all spot on. I changed the water pump on mine also. I would strongly advise you got the proper nissan sealer for the sump, water pump etc. It is very very good stuff, although expensive £20 for a small tube, i was very impressed with it. Only use a very fine bead around the sump as it will be squashed out when you torque it down, and it can fall into the sump and could block the oil pick up. A quick tip is to pre fill as much of the oil ways as you can, fill the pump before fitting, fill the oil filter use a syringe to squirt it into the oil ways, just try to get as much oil into the engine as possible. You want to be renewing things like oil pump gskt, oil filter housing gskt, rear main oil seal etc Basically the only gskts i reused were the cam cover gskts and the top plenum gskt, the rest were replaced
 
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