Lykins Motorsports 427FE Build, Alan Carter

[blykins]

I run the cam timing pretty advanced on a lot of my engines. This cam was ordered with a 110 LSA, on a 104 ICL. It degreed in at 103.25. When we run that advanced, you can really see how piston to valve clearance is affected. The trend is that when you advance cam timing, intake valve clearance decreases and exhaust valve clearance increases. As you can see in the next two pictures, it's very apparent: intake valve clearance was .100" + head gasket thickness, exhaust valve clearance was a whopping .300" + head gasket.





Valve springs are set up at a nominal 1.900" install height. Valve spring pressures are tested based on install height, full lift, and coil bind.





And if you've never seen a factory MR intake port that approaches 320 cfm, then here's your chance....

[olddog]

Strange, I never actually used clay to check valve clearance, and I new it was the best way. I have measure the valve stem movement with the valve spring off. In my defense, that was back in my puppy days.

I was surprised how close the intake valve comes to the notch in the piston. Especially surprising to me after seeing the exhaust is a mile away, in comparison. I never gave clearance radially from the valve to the piston cut any thought. Measuring the valve stem travel, only measures one dimension. The edge of the valve may only have 0.002" clearance from the cut in the piston, and that method of measure wouldn't tell you that. That would get ugly when things heated up.

I learned something today. I'll never miss this step again.

Thanks

[Gaz64]

Originally Posted by olddog

Strange, I never actually used clay to check valve clearance, and I new it was the best way. I have measure the valve stem movement with the valve spring off. In my defense, that was back in my puppy days.

I was surprised how close the intake valve comes to the notch in the piston. Especially surprising to me after seeing the exhaust is a mile away, in comparison. I never gave clearance radially from the valve to the piston cut any thought. Measuring the valve stem travel, only measures one dimension. The edge of the valve may only have 0.002" clearance from the cut in the piston, and that method of measure wouldn't tell you that. That would get ugly when things heated up.

I learned something today. I'll never miss this step again.

Thanks

Yes, it certainly is the best way.

I have had one engine where the valves were increased to almost total bore diameter, 52% and 43% and the block needed to be notched for clearance for the exhaust valve.

Same for making custom valve reliefs in the piston.

Observe how blykins has about the same radially as it does vertically.

[olddog]

Originally Posted by Gaz64

Observe how blykins has about the same radially as it does vertically.

Yes that is what caught my eye. A picture is worth a thousand words.

Then when you think of all the head and piston manufactures (especially twisted wedge and Cleveland types SB), the valve reliefs and heads are not always going to match.

Just one of those light bulb moments for me. I'm not afraid to admit I learned something or didn't truly understand it in the first place.

Even though I was aware the other dimension (radial) existed, I always thought one dimensional in valve clearance. I was fully aware of valve shrouding by the cylinder wall, and that some applications people notched the top of the cylinder wall. It just never clicked that the radial clearance needs to be checked until I saw that picture.