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Username Post: Do I need to check clearance?        (Topic#285442)
tmsnyder 
Senior Member
Posts: 988
tmsnyder
Loc: Buffalo, NY
Reg: 06-13-06
08-11-12 06:05 PM - Post#2258262    

I have a 327 engine I rebuilt for my '56. At the advice of my engine builder, I put in Keith Black KB156 pistons which added 7cc to the chamber volume. I used a composite head gasket which is 0.035" thick I think. And I put in a L79 cam (221in 221ex duration @.050" .447" .447" lift 114LSA). The heads were 1.94 double hump heads, rebuilt.

I ran that for a couple years then put in a XE268H cam which has .477 lift.

I have some used Dart Iron Eagle heads that I'm putting on the car now. I had 0.020" taken off them to clean them up and I'm using thin steel head gaskets, they are 0.015 instead of 0.035" thick. So basically I've moved the valves 0.040" closer to the pistons than they would have been if I'd left the heads alone and used a thicker gasket.

Is that worth worrying about?

Do I need to check the clearance between the valves and the piston with these heads and the thin gasket on there? I don't have a pair of solid lifters around to be able to do this.





'56 Chevy 4dr 210 327ci
'97 GMC K1500 Suburban 6.5TD


 
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62chevy427 
"8th Year" Silver Supporting Member
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62chevy427
Loc: laurens sc
Reg: 04-13-06
08-11-12 07:53 PM - Post#2258291    
    In response to tmsnyder

it is probably not the correct way to do it,but i have checked clearance this way: it will get close. the closest is not cecessarily when the piston is at tdc,but also depends on cam timing.
i did this with hydraulic lifters.
get a rally weak spring,just enough to hold the valve up. install it and turn engine slowly while repeatedly pushing down on valve to see if it still has clearance. when it moves very little,try to find the least amount of clearance.
when found,put a dial indicator on the valve stem and measure amount of movement. this is clearance at that point in the cycle.
with the really weak spring,it should not collapse the lifter.if necessary,do it with the intake off and you can see if the lifter collapses.
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tmsnyder 
Senior Member
Posts: 988
tmsnyder
Loc: Buffalo, NY
Reg: 06-13-06
08-12-12 06:34 AM - Post#2258371    
    In response to 62chevy427

Thanks, that sounds like a good way to check.

I see sbc 383 builds with lots of compression and 0.600+ lift, and I understand that those might run into clearance issues. I'm hoping that someone will be able to say that with my modest <0.500" lift cam and only being 0.040" closer b/c of the head grind and thin gasket, that 'no', it's couldn't be an issue.

Obviously the right thing to do is check the clearance, but at some point someone has the common sense knowledge that for non-radical build there's no need to check if the build is mild enough. Hoping someone can support my laziness!
'56 Chevy 4dr 210 327ci
'97 GMC K1500 Suburban 6.5TD


 
MikeB 
Senior Member
Posts: 9472
MikeB
Loc: Plano, TX
Reg: 08-28-03
08-12-12 08:23 AM - Post#2258407    
    In response to tmsnyder

How far are the piston decks below the block deck? They're normally down around .025" unless the block was decked or the pistons have a non-standard compression height. And why did you decide to use a .015" shim gasket?

Also, which valve springs are you using?

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Edited by MikeB on 08-12-12 08:25 AM. Reason for edit: No reason given.

 
tmsnyder 
Senior Member
Posts: 988
tmsnyder
Loc: Buffalo, NY
Reg: 06-13-06
08-14-12 04:44 AM - Post#2259054    
    In response to MikeB

I broke down and bought a pair of solid lifters and checked the clearance with playdoh. Confirmed what I was expecting. There was tons of room, over 0.200" to the piston and over 0.100" from the valve edge to side of the relief in the piston (side to side). Lots of room.

'56 Chevy 4dr 210 327ci
'97 GMC K1500 Suburban 6.5TD


 
tmsnyder 
Senior Member
Posts: 988
tmsnyder
Loc: Buffalo, NY
Reg: 06-13-06
08-14-12 04:47 AM - Post#2259055    
    In response to MikeB

Block wansn't decked, the piston is down in the hole. I went with the shim gasket b/c I wanted that 0.5 bump in the compression ratio. Should be around 10:1 now, more like stock.
Valve springs are the ones that Dart shipped the heads with, they have a max lift of well over 0.500.

  • MikeB Said:
How far are the piston decks below the block deck? They're normally down around .025" unless the block was decked or the pistons have a non-standard compression height. And why did you decide to use a .015" shim gasket?

Also, which valve springs are you using?




'56 Chevy 4dr 210 327ci
'97 GMC K1500 Suburban 6.5TD


 
models916 
Special Birthday Week
Posts: 2578

Age: 63
Loc: Addison, IL
Reg: 05-28-10
08-14-12 07:25 AM - Post#2259101    
    In response to tmsnyder

25 in the hole and 15 on the gasket is a nice quench. Tighter may be a problem. How far in the hole is the piston? Something you need to measure with the steel gasket.

 
tmsnyder 
Senior Member
Posts: 988
tmsnyder
Loc: Buffalo, NY
Reg: 06-13-06
08-15-12 09:28 AM - Post#2259579    
    In response to models916

I'm still learning (at 40+) about this stuff, but yes quench was one of the things I was looking at. With 25 in the hole, and a 'normal' 35 gasket, that's 0.060" quench. That with the 8.5:1 CR, I wanted more pep out of my 327. I don't know if my +7cc piston buries it down further in the hole and I didn't measure it, but it did look like 0.025 or so.

  • models916 Said:
25 in the hole and 15 on the gasket is a nice quench. Tighter may be a problem. How far in the hole is the piston? Something you need to measure with the steel gasket.


'56 Chevy 4dr 210 327ci
'97 GMC K1500 Suburban 6.5TD


 
tmsnyder 
Senior Member
Posts: 988
tmsnyder
Loc: Buffalo, NY
Reg: 06-13-06
08-15-12 09:31 AM - Post#2259580    
    In response to tmsnyder

One thing I'm not sure about is what the effect of using compression lowering KB156 pistons along with grinding the heads 0.020 to counteract the pistons? I think I'd rather have the unmolested head and the stock style piston but I don't know, will this effect performance? Don't know.
'56 Chevy 4dr 210 327ci
'97 GMC K1500 Suburban 6.5TD


Edited by tmsnyder on 08-15-12 09:32 AM. Reason for edit: No reason given.

 
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