Piston To Bore Clearance, Hks Pistons

[Denver]

Just wondering, if anyone has in there grasp, and english version of the HKS install instructions for a set of 87mm pistons to suit an rb26dett

Ive got the kit, but the info is in jap, so just wondering if anyone has some specs on what the piston to bore clearances should be machined too, ive deciphered all the other info, just need that last little nugget of info..

cheers

[ylwgtr2]

you can make it out from the jap sheet......i have these pistons...i will check when i get home

[The Dan]

I would assume they would still have an equation to work it out. Math is the universal language.

I would think that you would need around 5-6 thou clearance but it will depend on what the instructions tell you.

Do you happen to have a camera you could take a photo of it with?

[Mik]

I would assume they would still have an equation to work it out. Math is the universal language.

I would think that you would need around 5-6 thou clearance but it will depend on what the instructions tell you.

Do you happen to have a camera you could take a photo of it with?

<{POST_SNAPBACK}>

It should be 2 thou...nowhere near 5 thou!

[T04GTR]

i had the same drama with my trust ones.

look at the instruction for some numbers. mine had a dodgy diagram and .05mm amongst it all.

which is 1.9 thou(2 thou) very important because they dont use "file back" rings

[The Dan]

forged pistons will need a much greater clearance than cast pistons

But it all depends on what the manufacturer specifies for them

Hence my previous remark

6 thou is not excessive for piston to bore clearance. 2 thou is extremely close. But like it was said...fileback rings do make a difference.

Edited December 12, 2005 by 3lit3 32

[mitchy_]

XRW - i made up an RB bore page a little while ago...

http://members.westnet.com.au/taffyt/RB%20...over%20bore.htm

87mm pistons on a RB26 requires a 40thou overbore.

[The Dan]

XRW - i made up an RB bore page a little while ago...

http://members.westnet.com.au/taffyt/RB%20...over%20bore.htm

87mm pistons on a RB26 requires a 40thou overbore.

<{POST_SNAPBACK}>

That is correct but your RB20 info is wrong. They are a 78 X 69.7.

[mitchy_]

heh, they are too..

i have used 78 for the dimensions too, else it would give me a wrong calculation, i just put the wrong numbers at the top

cheers

edit: tis fixed now

[Denver]

forged pistons will need a much greater clearance than cast pistons

But it all depends on what the manufacturer specifies for them

Hence my previous remark

6 thou is not excessive for piston to bore clearance. 2 thou is extremely close. But like it was said...fileback rings do make a difference.

<{POST_SNAPBACK}>

6 thou is the sort of clearances id expect on poorly made forged pistons, not properly made hks stuff..

the factory specs for stock cast pistons indicate .035-.055 mm as clearances, i wouldn'ty have expected much more than the factory specs for HKS stuff, or anything japanese really..

4-5 thou and more and you get a very slappy motor..

which means it'll be a breather,, something im not really looking at building..

[proengines]

I did an engine not long ago with HKS pistons. They were used but not really worn. At the nominal bore size they ran under .0025" clearance. If you bore and hone your block to the nominal size you should find that you have just over .002" clearance. Pistons are usually made with the clearance built in to them, meaning that the pistons will be whatever the clearance is smaller than the nominal size.

At 87mm (3.4252") the piston should measure 3.4232" +0/-.0003-4" about .250"-.300" from the bottom of the skirt. Remember that the skirts are tapered slightly, smaller at the top of the skirt.

Any extra clearance you give the piston will increase your ring gap by a factor of Pi, meaning that for every .001" extra size on the bore you will have .0031" extra ring gap (using Pi x diameter).

Edited December 12, 2005 by proengines