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Discussion Starter #1
What is the minimum amout of clearance from the piston to valve? I checked mine the other day with my trw dome pistons and I had .083 clearance.
 

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That's marginal but liveable on an intake valve, pretty tight on an exhaust. What size cam, what spring, what valve, rpm range?, all need to be taken in to consideration.

dkp
 

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Discussion Starter #4 (Edited)
Solid flattappet cam .530 lift on both sides 222 dur at .050 on intake and 224 dur at .050 on exhaust and 110 LS. The springs are (I think) 120 lbs on seat and 300 lbs open or something close to that. If that will really matter I can get an exact when I get home. 6,000 rpm is max, but more like 5,000 rpm is where I shift it at. They are PBM 2.25 and 1.76 valves.

This clearance was measured at zero lash on the rocker arm and the lash is .012 on the cam at final setting.

I have the tool to cut the valve pockets bigger, how much clearance should I have?
 

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Piston - Valve

Is that on exhaust or Intake ? How big is the valve relief ? Is it for a stock 460 valves or opened up for your larger valves. You also need side or radial clearance. How big is your cutter diameter ?

On a blueprinted engine. Ford recommends .070 on Intake and .100 on exhaust.
Did you start 20 deg before TDC and go to 20 deg ATDC in 2 deg increments ? When I did mine thats how I did it and had to flycut pistons. After that it was still too close and had to retard the cam 2 degs. I then gained exhaust clearance. I think both of mine came out at around .070". My cam was quite a bit bigger overall.

FWIW Mark
 

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Discussion Starter #6
Is that on exhaust or Intake ? How big is the valve relief ? Is it for a stock 460 valves or opened up for your larger valves. You also need side or radial clearance. How big is your cutter diameter ?

On a blueprinted engine. Ford recommends .070 on Intake and .100 on exhaust.
Did you start 20 deg before TDC and go to 20 deg ATDC in 2 deg increments ? When I did mine thats how I did it and had to flycut pistons. After that it was still too close and had to advance the cam 2 degs. I then gained exhaust clearance. I think both of mine came out at around .070". My cam was quite a bit bigger overall.

FWIW Mark

The pistons are the L2443 pistons and I am not shure what size valve reliefs are in them, maybe someone can chime in and tell us but they are just the factory valve releifs. The intake was at .083 clearance and the exhaust was at .085 clearance.

My valve cutting tool is 2.3 diameter.

Tell me if I did this wrong or not, but I sprayed some pam cooking spray on the valves and then on the piston then put my kids playdo on the piston, put the head gasket on, set rocker arm at zero lash, and turned the engine over one time. Then took the playdo out and cut it into pieces and measured where it was smashed down the smallest.
 

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What is the minimum amout of clearance from the piston to valve? I checked mine the other day with my trw dome pistons and I had .083 clearance.This clearance was measured at zero lash on the rocker arm and the lash is .012 on the cam at final setting.Solid flat tappet cam .530 lift on both sides 222 dur at .050 on intake and 224 dur at .050 on exhaust and 110 LS.
I would say that with the addition of the 0.012" lash, you have plenty of clearance. That being said, I also would have expected you to have more P-to-V than 0.083", given your current camshaft and assuming typical installed centerline.


They (valves) are PBM 2.25 and 1.76 valves.
Ahhh, that explains it. The TRW L2443's have a 2.08" standard valve pocket, and so I'll bet that the 2.25" valve head is 0.083" from the highest point of the pocket (the uncut portion of the dome), not the deepest point of the pocket. Open the valve pockets up to accommodate the 2.25" valve (without going deeper) and you ought to gain P-to-V clearance. The 2.30" diameter cutter is the proper cutter for creating a pocket to accept a 2.25" valve.

Paul
 

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P-V

I edited my post, I had to retard cam to gain exhaust valve clearance at expence of intake valve clearance. If you do as Paul stated you will have tons of clearance given those cam specs.

Later Mark
 

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I edited my post, I had to retard cam to gain exhaust valve clearance at expence of intake valve clearance. If you do as Paul stated you will have tons of clearance given those cam specs.

Later Mark
Retarding the camshaft will TIGHTEN the exhaust valve clearance ... open the intake clearance.
 

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Discussion Starter #10
I would say that with the addition of the 0.012" lash, you have plenty of clearance. That being said, I also would have expected you to have more P-to-V than 0.083", given your current camshaft and assuming typical installed centerline.


Ahhh, that explains it. The TRW L2443's have a 2.08" standard valve pocket, and so I'll bet that the 2.25" valve head is 0.083" from the highest point of the pocket (the uncut portion of the dome), not the deepest point of the pocket. Open the valve pockets up to accommodate the 2.25" valve (without going deeper) and you ought to gain P-to-V clearance. The 2.30" diameter cutter is the proper cutter for creating a pocket to accept a 2.25" valve.

Paul
Yes that is correct the clearance problem is on the highest point of the pocket on the intake side. I will open those intakes up to the 2.30 size when it cools down some outside. Their is no exhaust valve pocket in the top of the piston, can I use the 2.30 cutter to cut a small pocket in the piston for the exhaust valve or do I need to buy the 1.80 cutter?
 

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Yes that is correct the clearance problem is on the highest point of the pocket on the intake side. I will open those intakes up to the 2.30 size when it cools down some outside. Their is no exhaust valve pocket in the top of the piston, can I use the 2.30 cutter to cut a small pocket in the piston for the exhaust valve or do I need to buy the 1.80 cutter?
1.80" cutter...different radius and all....and don't forget to debur the pockets for detonation......
Rob
 
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