Big Block Chevy Piston to Valve Clearance - Team Camaro Tech
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post #1 of 8 (permalink) Old May 18th, 12, 11:12 AM Thread Starter
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Keaton
 
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Big Block Chevy Piston to Valve Clearance

What dimension should I be looking for both the intake and exhaust valve to piston clearance? The cam is degreed in and I'm using a used head gasket. I measured about .093" clearance between the piston and intake valve the first time I checked. I'm going to do it all over again to be sure. I've read where .080 is good but I want to be sure. The motor has steel rods by the way.
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post #2 of 8 (permalink) Old May 19th, 12, 08:42 PM
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Paul
 
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Re: Big Block Chevy Piston to Valve Clearance

Comp Cams BBC

Piston to valve clearance must be verified –the minimum clearance is .080" on the intake side and .100" on the exhaust side. The easiest method of verifying piston-to–valve clearance is to check using modeling clay on top of one of the pistons.

See the COMP CamsŪ Master Reference Guide or www.compcams.com for detailed instructions on using this method.
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post #3 of 8 (permalink) Old May 20th, 12, 02:29 AM
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darrell
 
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Re: Big Block Chevy Piston to Valve Clearance

i always use .090 intake and .110 on exhaust- my opinion is 80 and is not enough on performance and high rev apps-when using larger valves, always chek intake valve to cylinder wall clearance
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post #4 of 8 (permalink) Old May 20th, 12, 03:46 PM
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Ron
 
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Re: Big Block Chevy Piston to Valve Clearance

Valve to Piston Clearance depends mostly on Size of Valve reliefs and Dia of Valves and Inversely Proportional to Duration of the Cam - That is the longer the duration the tighter the Valve to Piston Clearance. Basically do not worry about Valve to Piston Clearances with Cams under 300 Advertized Duration Degreed per Specks in STK OEM Specked Engines as Cam and Piston Manufactures take this into account. Ensure when Clay Modeling that you have enough Piston Valve Relieve Diameter when running Large Dia Valves.

Valve to Piston Clearances are closet when the Intake 1st Opens and the Exhaust Valve Closes - Advancing or Retarding the Cam by 2 Degrees generally changes the clearance by .010" respectively.

Head Gasket thickness, Milling either Deck or Heads change the Valve Seat Height and affect Valve to Piston Clearances - Generally Lobe lift has very little affect unless you running extreme (310+) durations.

Pending Cam, I've run .080"/.100" Int/Ext Clearances with 2.19/1.9" Dia Valves and TRW or Speed Pro Domed Pistons to over 7000rpm in SR BBC Mills without issues. Some will run clearances as tight as .060"/.080" (Not uncommon in SBC's).

As Darrel mentions Check Intake Valve to Cylinder Bore Clearance especially when running a 396 Bore and Large Dia Intake Valves in which case one may have to Fly Cut Clearance in the upper Edge of the Cylinder Bore around the Intake Valve above the Combustion Ring Stop Position.

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Last edited by Z15CAM; May 20th, 12 at 04:05 PM.
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post #5 of 8 (permalink) Old May 23rd, 12, 09:36 AM Thread Starter
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Keaton
 
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Re: Big Block Chevy Piston to Valve Clearance

Since I'm close at .093", are thicker head gaskets available to increase the clearance?
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post #6 of 8 (permalink) Old May 23rd, 12, 02:32 PM
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Casey
 
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Re: Big Block Chevy Piston to Valve Clearance

You didn't tell us what thickness your current head gasket is. Also are you using a solid lifter to check clearance as hydraulic will give you a false reading.
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post #7 of 8 (permalink) Old May 25th, 12, 08:30 AM Thread Starter
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Keaton
 
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Re: Big Block Chevy Piston to Valve Clearance

I did not use a solid lifter in my check. I ordered two solid lifters that will be here tomorrow so I can do this again. The head gasket is a Fel pro 1017-1, with a compressed thickness of .039". I do have two Fel pro 1017-2 head gaskets also, with a compressed thickness of .051".
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post #8 of 8 (permalink) Old May 25th, 12, 12:08 PM
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Don
 
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Re: Big Block Chevy Piston to Valve Clearance

Keep in mind while your are playing with head gasket thickness, you also change your piston to head quench. I look for about .040. I am 0 deck so the Felpro 1010 worked well for me on a sbc. Specs on a bbc may be a little differant.

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