Well i put together my shortblock tonight and it "seems" like my piston is coming out of the deck ever so slightly

Just a small history:

i got this block in trade and it was a 355 at the time.....but it was blown up pretty good when someone had it a 383 (i could tell because they grinded the block to fit the crank) It was freshly bored over and more than likely decked

I got it and had it honed, align-honed, plugged the deck and restricted the coolant passages, and decked it flat

I asked if possible to leave .010 on it, well its either @ zero or its coming out of the deck a little. I have to mic it out to be sure

The combo is a stock 3.48" stroke, 5.7" rods and TRW blower/turbo pistons

What kinda problems or things should i look into since i think the piston is popping out the deck a touch

thanks in advance
jim

 

Mic it out & try'n keep it below .050 clearance and above .038"... go see what the damnable thing is at

 

Jim,
They probably decked it as little as possible, that would clean everything up. Like Skarodo mentioned, if your quench is between .038 and .050, I wouldn't worry about it. If it's below .038, You might want to run a slightly thicker head gasket or fly cut the top of the pistons slightly. Shaving .015 off the pistons shouldn't be too terrible, but the upper ring land will be *slightly* thinner. Take a depth mike, and check it for real.

Andris

 

I am with these guys. Alot of people have the piston .020 in the hole, a .051 head gasket an dthat puts the pistom .071 away freom the deck surface of the head. Hottible quench. If the piston is .005 or less out of the hole I would still run the .041 head gasket. If it is .015 out of the hole I would run the .051 gasket. If it is over .015 out of the hole check your parts (rod length, piston heighth, etc.) and see why and make sure thay are matching pieces. I am not sure what piecs you have but also make sure the piston package is not too close to the top of the block. If the distance from top of piston and the head is .035-.050 these are the #s I have allways heard of as optimum. If these are aluminum rods (again , I do not know what parts you have) or a very high RPM motor than you will need more clearance for rod stretch and piston rock but a 6500 rpm LT1 with steel rods these #s should be fine.

NightTrain66

 

i have CAT h-beam 5.7" steel rods

i'll go and measure it and see what i find

thanks for your opinions

my head gasket is a 1010 for aluminum heads...has the copper ring

i believe compressed thickness is 39

 

Do you happen to have the block height (about 9.0xx") and piston compression height measurements? We can then figure it all out:

(Block Height + Gasket Thickness) - (Rod + Stroke *.5 + Compression Height) = Quench

Here are my numbers:
(9.027+.039)-(6.000+3.75*.5+1.151) = .040 Quench

HTH!

Andris

 

Well thanks for asking andris but i'll let you know after my machinist gets done shaving off the top of my piston

I went home and mic'd it out and its @ .015 at the highest and .012 @ the lowest (lowest meaning as straight in the bore as possible and highest meaning as far as i could rock the piston)

so WHOOHOO

i get to take it all back apart

 

Or you could do like some guy in LT1 tech a long time ago... doing a head/cam swap, to clean up his deck... he used an orbital sander

D'oh.. oh well.. it's only time.. and money.. :-/

EDIT: Didnt you mention a .049" compressed gasket? .037 ... Dunno how i'd feel about that, TRW's are heavy... and though alot of race motors actually allow the pistons to touch the head (hey, its going awful slow at that point & about to change direction)... it might cause some issues with the knock sensor etc.

IMO.. i'd rather be safe than sorry... argh

 

Im pretty sure its .39 compressed...its a fel-pro 1010

I'm having the heavy slugs cut down on the top to get it to about .005 out of the hole per my machinist

orbital sander......NICE

i have a FAST system with no knock sensor.....but i dont want my pistons touching my nice heads that i have almost $3000 into

thanks for the laugh

 

I try.. i thought you said something about a .049" compressed gasket.. all ive used on lt1 stuff has been the .039" felpro's and the impala stuff

The pistons touchin the head comment was completely serious though . Scary thought, but eh.. works. Engineering something that tight though... not something I'm gonna dow hen i rebuild.. theyll get close, but I'm not that serious

EDIT: I think i remember the guys name who used the orbital sander.. but I'll play nice and not mention it.. everyone makes mistakes.. but boy that was a funny one. IIRC, he also ran his car without exhaust manifolds etc. to see what it'd be like... and without coolant..

Ahhhh.. the internet..

 

__________________________________

^^^Flatlined

 

why take that back part? Your most likely going to hurt the pistons more and lose valuable piston deck thickness (maybe not with a 5.7" rod) get a .060" thick gasket from someone like SCE and forget about it. that will get you to .045 Quench and that will be pretty dam good.

Bret

 

I would leave the piston out of the hole and run a thicker head gasket.

FWIW I have ran a steel rod 383 at 7,200 with .029 piston to head clearance with no problems.

 

Honestly.. if it were my car.. and a blower motor.. I'd be awful tempted just to leave it alone.. .035" is probably enough.. those rods shouldnt stretch too much.. and since its a blower motor.. i'd assume you arent gonna spin it too far..

*shrug*

 

hmm......OK

i'm a little confused but am seeing where this is going.....how do i check the clearance between the head and the piston?