Thread: enlarging the intake valve reliefs

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I came across an issue that is new to me. Building a sbc engine and the cam which I'm using with the intake valves, I having a piston to valve contact. My question is how do you enlarge the intake valve reliefs for clearance?

Isky has tools to rent, but they have always been out of them whenever I tried to use them.
http://www.iskycams.com/onlinecatalog.html
If this link does not show the tool, go to page 17 Isky catalog, valve notching tool.

I have made my own cutters in the past from an old valve and a lathe tool bit. Sharpen the edge of the bit and silver solder/braze it to the valve face. Use a bushing collar with a set screw on the valve stem to limit the depth of cut. Grind the end of the bit for a 0.125" radius to prevent a sharp corner on the piston crown.

McMaster Carr has the collars and tool bits. Go to their site and type in Shaft Collars for the collar. Type in Square Tool Bit Blanks for the bit. 1/4" x 2 1/2" M2 high-speed steel is what you'll need.

Like this....

i have welded a pice of tool steel 1/4by1/4 a cross the hole face of the valve then ditch out the center two cutter faces work better for me keeps it from hopping when using a hand drill grind down past the keeper in a hex to drive the valve this helps to if the chuck slips and cut in the valve stem it will still let you get the valve out of the head and on screwing up the guides i have done this a time or two last time i use this was on a Zo6 ls engine in the car it works ok but makes me abit nervous. use the mill and my piston vice what works very good to is the brown rollock 3m dics on a die grinder or air drill they will cut and help smooth out the piston noch here is how i do the valve not as nice as tech drawing but you get the idea

If the intake and exhaust valves are very different diameters, you may want to make two tools. The flat part of the cutting tool needs to be at least 0.050" longer from the centerline of the valve to the tip of the cutting tool so that when you make your cut, the valve relief will be at least 0.100" bigger in diameter than the valve head you will use in the motor.

Valves dance around in the valve guide bores more than you might think and you need to allow this clearance in the valve reliefs.

yes 050 min abit more is better piston rock loose valves but if you had to do the intake and EX thats alot of work i would be pulling them pistons out and cutting them on the mill i did the intake side and the ex on the ls in the car that was a big pain in the back you have to watch on some engines like the bbc you do not open up the 1st ring land ..now thats a bad day...

I know your next thought will be "what if I cut too deep and see the wrist pin?"

Engineering practices dictate that the piston crown thickness will be anywhere from 7% to 10% of the bore diameter. So, on a 305 for instance, with a 3.736" bore, if we multiply 3.736 times .07, we find that the piston crown is probably at least 0.261" thick.

well that about right or Nos would be thicker i have cut down for lower ch and recut pistons from big chief to 24 angle low buck job for a friend and have a punch that is made out of a old valve to find center to fly cut on the hi 700 to 800 lifts i have cut some set for the bbc the old trw you had to cut them all the time cutting thru the ring land on the intak side is the deal on a bbc alot of the fly cut is over the pin boss so you will see the ring land first be for you see a rod that a why i like to do them out of the engine i can check how thick the piston is were i am going to fly cut .i knew a guy that used a 4 1/2 angle grinder to trim the ex side of a 427 bbc the hands of a surgeon he did not have

Originally Posted by pat mccarthy

i knew a guy that used a 4 1/2 angle grinder to trim the ex side of a 427 bbc the hands of a surgeon he did not have

Geez Pat, I thought using an angle grinder on pistons was just one of those urban legend stories!!!!!!! Too actually know someone who did it is certainly one of those stories to relate to the guys at one of the bench racing coffee shop sessions!!!!!!!!

Been a couple decades since I worked in an automotive machine shop, but I do remember that from time to time we did see some very strange engineering approaches----------

The reason we use aluminum for pistons is because its softer than cast iron to grind ---sometimes when racing karts I have rubbed pistons on the pavement to change there shape!!!!!

I have also used body/belt/disc sanders to shape pistons for my pro stock engines---but valve notches have always been done on a mill with a vise--the best way to control depth of the notch---if you have any extra clearance its too much and too little is too little

Thanks Tech and Pat. I'm glad I asked before I went ahead. A friend of mine who's a pretty good mechanic is going to work with me so I'll do it right and not go to deep. Tech, he has the tool your talking about.

Originally Posted by Dave Severson

Been a couple decades since I worked in an automotive machine shop, but I do remember that from time to time we did see some very strange engineering approaches----------

well hell yes but i lock the door and practice all my black magic in the cloak of night it helps me to get tune in with the metal gods then they take over