Hi all,
ok whilst putting my bigport together, when it came to putting the rods and pistons in and bolting them in, i noticed when any of the pistons are on top dead they stick out above the block deck. They stick up about 13 thou.
Is this normal? If not what size metal head gasket will i need to negate the higher compression?
Cheers again
Dan
I didn't check closely, but I think when I was doing the same thing recently the pistons were slightly below the block deck.
Have a word to Terry from Road and Track in Ipswich QLD. I'm sure he can steer you in the right direction and even source the right gasket for you.
Hen
are they std or higher comp pistons?
yes i would say thats fairly normal
these are high comp
heeey not a 4age piston!!! whatever it is it must have a pretty shit combustion chamber shape. From the piston alone I can tell that its limited in its hp/L
Dan: could you please tell me what that is in current measurements please?
30kw club
yeah not a 4ag, 3t-c bottom end with cut-outs for a 2tg head
just using to demonstrate what a higher comp piston would look like.
it's .3302mm
that cant be right, that would reduce the squish down to less than 1mm and theres no way the factory would do that, any signs of the block being shaved?
30kw club
on a 4AG with flat-top pistons, the crown usually sits about 030" below the deck surface. there is no way you want them protruding, especially on an old engine that has head shaved several times, otherwise your compression ratio will be too high. You can correct it with a thicker head gasket, but its not ideal. what we often do for such cases, is machine a squish ring on the piston crown, say take 020" off a small ring around the outside. .
To give you specific advice, I need the exact data on pistons, head chamber volume etc.
terry
Yeh i had the block and head only skimmed by my engine mob but because the engine was rebuilt in japan im not sure wat they did over there. The pistons are just standard Toyota with the valve cut-outs.
can you post a picture?
Terro has some excellent points, it may well be you need to get a thicker gasket to correct the piaton to squish area clearence
30kw club
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