Rapid Robert
Well-Known Member
360 flat top cast pistons. how do I go about adding valve reliefs. it will be a wild circle track cam so I'm assuming there'll be interference. thank you for your time. RR
piston valve reliefs, how to
- Thread starter Rapid Robert
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Go to brand racing engine on you tube, I believe I saw a video on it there.
In-Head Piston Cutters Might be cheaper to make a tool. Or the sleazy way, mark it and use a die grinder. What is this wild circle track cam? I don't think I would take those cast pistons much past 6000 rpm. If the cam likes lotsa rpm, you may be better off with something smaller.
mygasser
Well-Known Member
i don't want to put you off but...... surely if you'll be using a 'wild circle track cam' you should use decent performance capable pistons? i know from past experience cast pistons don't like repeated high revs, they break. now if the plan is for a car to pose in that won't see the high revving potential of that cam then most machine shops will be able to machine valve reliefs for you. have you checked the pistons will even get close enough to the deck at tdc to even worry? you may not need the valve reliefs at all if the pistons are down in the hole a bunch.
neil.
neil.
Normally, assemble engine with head gasket, heads and cam. With clay on top of piston, rotate piston 180*. Remove head and measure thickness of clay.
Locomotion
Well-Known Member
It would help to know what the minimum amount of material is safe to leave under the deepest part of the relief. Flattops may not have a lot of thickness to accommodate deep valve reliefs and it can vary with the piston material. Lift, cam timing & piston-to-valve clearance are all factors. Exhaust reliefs often need to be deeper.
Rapid Robert
Well-Known Member
good comprehensive info guys & very much appreciated. A 6K rev limiter is required
You are not required to run a 6k rev limiter. It's 7k.
2025-Hobby-Stock-Rules.pdf https://share.google/atadii4vAjXBPSXlI
Rapid Robert
Well-Known Member
You're right they changed it, it IS 7K now
Rapid Robert
Well-Known Member
yes one time way back I did glue sandpaper to a valve & used it as a grinder, not sure what grit I used. worked good. what grit would you recommend?
The rule has been 7k for about 20 years.
What are your wild cam specs? What brand of piston do you have? How far is the piston in the hole? You will need to mock it up with a degree wheel, checking springs and a dial indicator to see where your at. Then you need to measure the piston deck thickness to find out how far you can cut before you start cutting. Sand paper will just plug up. Unless your piston is way down in the hole and it shouldn't be for a race engine, It's not likely to have a thick enough deck. Also if these pistons are cast and not at least a hyperutectic performance piston (which would most likely already have valve pockets in it) there is little chance they will hold up to racing at 7000 rpm. for any length of time. Give us more information about your build please.
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I welded a piece of high speed steel to a valve and spun it with a drill to cut reliefs. First I filled the edges of the chamber with a thick layer of vasoline to make cleaning the chips a lot easier. I was real careful to cut them the same depth to keep the balance.
Woody500
Well-Known Member
Nice method, like an old school hot rodder, figure it out yourself!
I would have a machine shop do it according to the MP race manuals once you determine what is needed. Make sure they know what they are doing. I had a machine shop in Hampton VA who had not done this before but said he could do it. He did it but none of the pistons afterward would fit into the block bores as he mashed them when mounting for the machining operation. Great day for me...not!
@Rapid Robert the first thing to do is mic the piston heads and SEE how thick they are. Lots of cast pistons are not thick enough to have valve reliefs cut in them, so do that FIRST. You might be sorry if you don't and that would suck.
65TerrorCuda
Well-Known Member
What did you do then?
He offered to "make them fit" if I would bring him the block and pistons. No way was I going to do that and so I walked.
Bobzilla
Well-Known Member
Doing it this way will not give the required radial clearance. You will still have to manually grind the radial clearance.
I have the Lindy tool mentioned in post 3 for 2.08" valve diameters. It worked well and it has the radial clearance built into the cutter head. If I remember correctly, they even have a rental option if you only want to do this procedure one time. They were excellent to deal with and answered my questions pretty quickly before my purchase and also after purchase.
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Sorry Myron. I missed that you treed me.
Dirt track stuff usually has options where you can buy a competitor's engine dirt cheap, so they don't build 20K engines. lol
Claim is unlikely. Lots of hurdles and hoops for a claim to happen in this scenario.
Call this guy: In-Head Piston Cutters
middleagecrisis
Well-Known Member
I highly encourage you to read Post number five and do that before you randomly start trying to cut piston reliefs. My zero decked 360 with flat top forged pistons (no valve reliefs) has plenty of piston valve clearance for the hefty solid lifter cam that I am using. I checked it using the clay method and using checker springs and a dial indicator.
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