Piston to Valve clearance

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Piston to Valve clearance

Post  pigs521bbf on April 22nd 2018, 8:11 pm

I have a 523 bbf and I am doing a head swap. I had one some PI heads with mild port work and CJ valves. I ran across some iron CJ head with some port work done. I am using head gasket Fel-Pro #1018. I have Icon Piston #IC859-040 Forged Flat Top Pistons 4.400 Bore.

I did put some clay on my piston to check the valve clearance. The clay measured at 0.100in on intake and 0.070in exhaust. Any recommendations? Thicker gasket?

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Re: Piston to Valve clearance

Post  rmcomprandy on April 22nd 2018, 8:19 pm

pigs521bbf wrote:I have a 523 bbf and I am doing a head swap. I had one some PI heads with mild port work and CJ valves. I ran across some iron CJ head with some port work done. I am using head gasket Fel-Pro #1018. I have Icon Piston #IC859-040 Forged Flat Top Pistons 4.400 Bore.

I did put some clay on my piston to check the valve clearance. The clay measured at 0.100in on intake and 0.070in exhaust. Any recommendations? Thicker gasket?

If those were the minimum clearances through the entire cycle then that is usually enough ... advance the camshaft 1 or 2 degrees to reverse those numbers if you like.

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Re: Piston to Valve clearance

Post  pigs521bbf on April 22nd 2018, 10:06 pm

What is recommendations for the correct number of exhaust and intake?

Is there another head gasket (thicker) that I could get away with?

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Re: Piston to Valve clearance

Post  Colt Macara on April 22nd 2018, 11:22 pm

pigs521bbf wrote:What is recommendations for the correct number of exhaust and intake?

Is there another head gasket (thicker) that I could get away with?

RHS™️ strongly urges you to check the piston to valve clearance on the larger street cams and all race cams. The easiest and most accurate way to check this is to place strips of modeling clay on top of one piston, and then rotate the engine over by hand with the cylinder head bolted in place and all of the valve train components adjusted. If there is any resistance during rotation of the crankshaft, STOP! The piston has probably hit the valve. Then you must decide whether to fly cut the piston, or exchange the cam for a profile that will fit into your engine. Note: Minimum piston to valve clearance is .080” on the intake and .100” on the exhaust valves. If aluminum connecting rods are being used, add a minimum of .030” to these suggested clearance figures. Aluminum rods will stretch and expand more than steel rods. wrote:
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Re: Piston to Valve clearance

Post  Colt Macara on April 22nd 2018, 11:27 pm

Colt Macara wrote:
pigs521bbf wrote:What is recommendations for the correct number of exhaust and intake?

Is there another head gasket (thicker) that I could get away with?


http://www.racingheadservice.com/docs/rhs/16000IS.pdf
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Re: Piston to Valve clearance

Post  pigs521bbf on April 23rd 2018, 8:08 am

Thanks for the response. Any issues with fly cutting the piston?

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Re: Piston to Valve clearance

Post  68galaxie on April 23rd 2018, 9:29 am

One can fly cut the pistons (if needed). Take your pistons out and have a shop cut them with the correct tooling (piston vise).

However, in your case I would simply advance the cam 1 or 2 degrees - like Randy M already mentioned.
This should put you near 0.070" intake and 0.130" exhaust clearance - just fine.

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Re: Piston to Valve clearance

Post  gt350hr on April 23rd 2018, 11:06 am

I would follow Randy's suggestion and advance the cam 2*s The engine will run better and you will be safe on piston to valve clearance.

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