Acl Forged Pistons

[R334door(s2)]

hi all ive been doing a fair bit off research on forged pistons but can not make my mind up on size.?

A: Should i go for standard forged size for rb25det,.?

OR

B: Get 20thou oversize forged pistons,.?

option A sounds easy thats if the bores are ok.

But then i can get it bored out the same size as the oversize pistons then i will have a nice smooth bore.?

if you can give me some advice that would be great.

Cheers

Allan.M

[NYTSKY]

Go the the next step up,so 86.5mm 20thou over.

[dangerman4]

forged pistons have a specific tolerance so i wouldnt recomend trying to stick with the standard size.

a nice fresh rebore to 20 tho will gaurentee the bores a perfectly round and the right size to suit the piston specs.

[Adriano]

Yep, i agree, i would never trust 15 year old bores to be as new, also you need to adjust the size to suit piston/bore clearance.

[Duncan]

dont go oversize unless you need to. lets you use the block again one day. your machinist will tell you if the clearance is too loose for standard

[R334door(s2)]

well the motor with standard pistons and rods is fine has not been boosted more than 8psi since i have had it so you think go with the standard size forged pistons then get my machinist to check out the bore then he will let me know if i need more clearance encase of scrubbing from the piston.

but wouldn't it be better to go that tad little bit bigger so there is a fresh new bore to work with.?

cheers

Allan.M

Now i need a rb25det block anyone got one in Adelaide.?

take my time and build it right.

[Bumblebee]

if the bores are around then why bother boring it out? boring it out doesnt make it "better" or "fresher" because after a bore, u hone it anyway. and ur going to hone the standard bores anyhow.

[R334door(s2)]

yeah true so do you think its still worth going the 20tho oversize pistons or stick to standard size.?

any advice will help me with this decision.

cheers

Allan.M

Edited April 7, 2008 by R334door(s2)

[Bumblebee]

get bores checked for roundness. if they are still perfectly round (which isnt uncommon) then stick with std size. but u will still need to get the bores machined out to suit the new forged pistons (even if its just .001 thou)

[R334door(s2)]

oh ok cool that sounds good is there anything else i should know off before starting the internal rebuild.? Just want to make certain thats on the "TO DO LIST"

[bloodzkull]

the bores on my rb26 where still showing the factory cross hatching. perfect round and no machining nessacary for a standard sized set of forged pistons.

well the front 5 where. number 6 had a broken ring land and ever so slight scoring because of it. a slight hone might have gotten ridden of the mark but decided not to take the chance.

[R334door(s2)]

yeah so did you get the standard sized forged pistons or did you go a tad bigger.?

[Adriano]

Its not so much the roundness, its the taper, as 99% bore wear occurs in the top 15mm. Anyone who has rehoned a second hand bore can tell you that its obvioius as the hone does the whole bore except the top 15mm. IMO if you are having to buy another block, then machine it out, its really not a lot of extra $$$, in the unlikely event that in the future you need to bore it out again twice, then buy another block then.

Edited April 7, 2008 by Adriano

[Duncan]

just get the machinist to check the block first, then get the smallest pistons you can to allow for future use.

no point buying 20 thou over pistons and then finding out you needed 40 thou oversize due to some problem

[R334door(s2)]

ok so ive decided to go standard size by what every one has said.I am looking at a block that a friend has and ill get it checked out to make certain the bore is all fine.

cheers guys keep the info coming.

cheers

Allan.M