Piston/Valve clearence
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From: New Zealand
Piston/Valve clearence Hi all,
What would be minimum safe piston to valve clearence ?
I have std LS1 block , TR 224 cam , ported LS1 heads 2.02 inlet , 1.57 exh , 61.5 cc chambers (bought heads second hand but reconditioned) and as near as I can tell have had 60 thou milled off them.
measured clearence as 135 thou exhaust & 50 thou inlet.
Do I have enough clearence on inlet side ? am considering using 0.020 "thicker Cometic gaskets to improve clearence
Cheers
John
What would be minimum safe piston to valve clearence ?
I have std LS1 block , TR 224 cam , ported LS1 heads 2.02 inlet , 1.57 exh , 61.5 cc chambers (bought heads second hand but reconditioned) and as near as I can tell have had 60 thou milled off them.
measured clearence as 135 thou exhaust & 50 thou inlet.
Do I have enough clearence on inlet side ? am considering using 0.020 "thicker Cometic gaskets to improve clearence
Cheers
John
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From: BFE
.050 on intake is suicide in M6 on the street. Why don't you get some intake eyebrows (flycut intake)
Though I would think that running a thicker gasket would improve your intake seating, but reduce your quench, SCR and power gain.
Though I would think that running a thicker gasket would improve your intake seating, but reduce your quench, SCR and power gain.
Originally Posted by PREDATOR-Z
Though I would think that running a thicker gasket would improve your intake seating, but reduce your quench, SCR and power gain.
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From: New Zealand
I'm running an M6 with ripshift and Textrailia clutch, limiter set at 6500 rpm.
I'm contemplating a cast block with 402 strocker kit and would fly cut forged pistons to suit even a larger cam. But would like to get it running as is for now without pulling pistons to flycut.
Cometic do 0.074" head gaskets, that would give me .070" inlet valve clearence , is that still cutting it fine ?
Could try retarding cam timing but I think that will just transfer the problem to exhaust valve
I'm contemplating a cast block with 402 strocker kit and would fly cut forged pistons to suit even a larger cam. But would like to get it running as is for now without pulling pistons to flycut.
Cometic do 0.074" head gaskets, that would give me .070" inlet valve clearence , is that still cutting it fine ?
Could try retarding cam timing but I think that will just transfer the problem to exhaust valve
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From: BFE
Very safe margins are .080 int/.100 ext
But you can run a little lower.
Retarding the cam is not a bad idea, if you have an adjustable chain, I would try that first. Try it on a 0 advance (I believe the TR cams have +4 in them)
But you can run a little lower.
Retarding the cam is not a bad idea, if you have an adjustable chain, I would try that first. Try it on a 0 advance (I believe the TR cams have +4 in them)
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From: New Zealand
Originally Posted by schpenxel
you don't have pull the pistons to flycut.. call LG motorsports, they will rent out the tool to do it
How deep can you cut the std pistons ?
Staging Lane
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not a clue how deep they can be cut... but I know you can cut them without pulling the pistons out, # should be on their website www.lgmotorsports.com they can ship you the tool as well 
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I wouldn't be that worried. First, you should have the factory fuel cut off operating at some safe RPM, so only an accidental down vs. intended up shift can cause over revving, and if you do that at high RPM, your engine's toast regardless.
Next, consider what it takes to eat up that 0.050" clearance on the intake side:
1.You over rev bad enough for the lifters to pump up 0.030" or more (allowing 0.020" for rod stretch, etc.), putting the valves into the pistons next time around. Cure: Use only 0.010" hot preload.
2. Unlike the exhaust, where the piston is approaching TDC as the valve is closing, on the intake the piston is maybe 120 degrees down the bore at IVC. It's going to take one hell of a float to get the two together and the exhaust is bound to get nailed first...
Next, consider what it takes to eat up that 0.050" clearance on the intake side:
1.You over rev bad enough for the lifters to pump up 0.030" or more (allowing 0.020" for rod stretch, etc.), putting the valves into the pistons next time around. Cure: Use only 0.010" hot preload.
2. Unlike the exhaust, where the piston is approaching TDC as the valve is closing, on the intake the piston is maybe 120 degrees down the bore at IVC. It's going to take one hell of a float to get the two together and the exhaust is bound to get nailed first...
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From: New Zealand
OK an update !
Played around with cam timing today (TR 224/112lsa) ,I beleive cam has 4deg adv ground into it.
cam timing -- exh valve/pston clear -- inlet valve/pston clear
0 deg -- 0.136" -- 0.049"
-2 deg -- 0.126" -- 0.058"
-4 deg -- 0.120" -- 0.073"
so is 0.073" enough on inlet or do I need to try -6 deg.
I'm thinking -4 will be ok, and any lose of bottom end power due to retarding cam should be more than made up for by added compression and better flowing heads.
Thoughts anyone ?
Played around with cam timing today (TR 224/112lsa) ,I beleive cam has 4deg adv ground into it.
cam timing -- exh valve/pston clear -- inlet valve/pston clear
0 deg -- 0.136" -- 0.049"
-2 deg -- 0.126" -- 0.058"
-4 deg -- 0.120" -- 0.073"
so is 0.073" enough on inlet or do I need to try -6 deg.
I'm thinking -4 will be ok, and any lose of bottom end power due to retarding cam should be more than made up for by added compression and better flowing heads.
Thoughts anyone ?
Last edited by Johnv; Jan 26, 2006 at 05:24 AM.
-4 is retarded enough I would say -6 would definitely bring you well into the .080's though. I don't know that you will have lost too much low end really, but there probably is some...What gears are you currently running? Plus I was waiting for the opportunity to say that something was retarded. 
I wouldn't be afraid to retard it 4* as far as power goes on the 112 lsa. My 230/232 cam is on a 113 lsa and I retarded it to a 112 icl due to piston-valve clearance. Just makes a bit more power up top and you'll never notice a loss of low end with a M6.
IMO, .073" is fine on a 6500rpm motor. There are several 'off the shelf' LS1 cams out there that are tighter than that.
BTW, I ran my 496" 7200 rpm solid roller motor for a minimum of 20 and maybe as much as 100 passes with .010" p-v clearance on the intake valve. The timing chain skipped a tooth sometime mid season. No bent valves, reuined parts, nothing. Go figure.
IMO, .073" is fine on a 6500rpm motor. There are several 'off the shelf' LS1 cams out there that are tighter than that.
BTW, I ran my 496" 7200 rpm solid roller motor for a minimum of 20 and maybe as much as 100 passes with .010" p-v clearance on the intake valve. The timing chain skipped a tooth sometime mid season. No bent valves, reuined parts, nothing. Go figure.
