HOW TO "flycut pistons"
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so you used a newhead, and a cuter that actually fit in place of a valve in the seat? then had to go back and grind the diam. larger to provide the side clearance needed right? thats different, but a good way to do it w/o haveing to buy a junk head to destroy and make the tool. the only problem I see with this is some people will have a hard time making close to the same size notch for each piston and there's more room for error.
the only problem I see with this is some people will have a hard time making close to the same size notch for each piston and there's more room for error.
The way I did it uses a cutter designed for the valve head diameter which means the diameter is slightly larger.
The cutter actually has a cut on it like a valve so you don't ruin your valve seat in the head.
then had to go back and grind the diam. larger to provide the side clearance needed right?
I've done this before on a different big block, used the same procedure as described by you, on that engine I had to go deeper, I used the same head for cutting that was going to be used.
the only problem I see with this is some people will have a hard time making close to the same size notch for each piston and there's more room for error.
One other thing that will probably blow your mind, you don't need to get the piston to TDC with a dial indicator. Get it close and when your cutter rests on the stop rotate the crank to move the piston up to tdc and back down.
Think about how the engine operates and how you're cutting. the valve doesn't pop open and close with the piston at TDC. As a precautionary measure I would make the cut at TDC then move the piston up and down with the cutter moving.
You want to talk about inaccurate cuts, you're using a head that hasn't been milled to do your cut then running a head thats been milled.
Last edited by PREDATOR-Z; May 16, 2007 at 01:46 AM.
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From: waterford MI.
Originally Posted by 8a8mfh
I had to increase the diameter of the cut not the depth.
also, you didnt read my directions, DID you? I said that I DID make up for the difference of my milled heads, and the non milled "tool" head. reread step 3. it clearly says I DID make up for the difference. thats why there's no head gasket between the "tool" and the block in my case.
Last edited by PREDATOR-Z; May 16, 2007 at 01:44 AM.
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also, question for you. how does that tool adjust? it looks interesting. would like to see it in person, but it looks like a better design then the standard type I used.
Originally Posted by Irocss85
also, question for you. how does that tool adjust? it looks interesting. would like to see it in person, but it looks like a better design then the standard type I used.
I don't see what the big deal is, the tool I used is custom made for what ever you call in for, in my case a big block with 2.30 valve head diameter and a 11/32" stem. It has an adjustable collar on it, it has a cut on the back that looks like a valve seat. If you use the head you plan on running you take one measurement and thats piston to valve. Then swap the valve for the tool and adjust the collar up the amout you need to cut down.
First time I used one of these tools I was cutting .080 deeper so it was straight forward. Piston to TDC and cut.
Second time I used one I was cutting diameter, I couldn't even install the head with the cutter in it and the piston at tdc. Had to move the piston down, istall the head, turn the cutter with it resting on the stop, and move the piston up by turning the crank.
My whole point was that you need to use the head that you're going to run. It may not be as common on LS1's but a lot of engines use aftermarket heads with different valve angles, heads can be angle milled, etc.
Why risk ruining a set of pistons.
Last edited by PREDATOR-Z; May 16, 2007 at 01:41 AM.
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Okay I have a big question, how the heck do you flycut and not have to balance your pistons again? I guess on a blue printed, machined, and precisely balanced motor this wouldn't be done anyway. Just curious though, if you are spinning a motor to 6500 or so wouldn't it be nuts to cut on the pistons and not balance them again, thanks.
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to an extent, this is true. it would be better to balance them, but it is such a SMALL amount of material to remove, and its just about the same exact amount of weight from each piston if you do this accuratly. its proven to work effieciently enough. NEVER seen a post like "notched pistons and my motors dead" right? or motor vibrates. or whatever. atleast thats the way I look at it.
yeah you are right about there not being any specific post about that but plenty stranger things have happened. The thing about balancing is that you aren't going to "feel" it in the motor at all. Spinning a accurately balanced motor at high rpms rattles your teeth out regardless. It would be interesting to see what they would weigh after flycutting. Whatever happens, I think that i would flycut to get me by while I built another motor on the side perhaps, like you said it is done by alot of people
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hmm, thats an interesting thought, someone here has to have flycut, then gone on to build the motor with aftermarket pistons. I would be very curious to see how much flycutting affected the weight of the piston, and hence, how far off balance it could make it. hmmm
In response the the piston weight question, most machinests will tell you that lightening all of the pistons the same amount will not hurt anything, infact it would create an "overballance" situation in which the counterballance weights are slightly more than what is needed to ballance the new lower piston weight. An overballance situation can actually be benificial in high RPM applications, but it is often difficult to validate weather or not an overballance is an improvement or not without special equipment.
...the point is that reducing the piston weights an equal amount on all 8 will not hurt a ballanced motor.
...the point is that reducing the piston weights an equal amount on all 8 will not hurt a ballanced motor.
how much can you safely flycut on an ls1 street car. Is .110 too much? I'm at .080 right now and only have .035 clearance. I don't wanna have my car fall apart on the dyno or somthin crazy like that!
-Chris
Question answered, .110 is about the limit. Stock pistons are around .250 thick
-Chris
Question answered, .110 is about the limit. Stock pistons are around .250 thick
Last edited by jimmypop13; Jun 19, 2007 at 06:01 PM.
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I cut mine (or dads I should say) .120" on the intake side. I read where someone else cut like .140" and ran nitrous no problems. not sure where the max is, but I felt totally comfortable at .120" depth cut.
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How far from TDC would a psiton be in an actual P/V contact? 1/8"? 1/4"?When flycutting, the valve would be more toward the center of the piston if it wasnt at TDC when it touched. The TDC cuts would be ok since the valves wouldnt be contacting an uncut area but less depth would be available on the part of the cut toward the center where actual valve contact would occur. In other words actual valve contact could be part way down the flycut. If the piston was too low, the valve could touch the top of the flycut since the cuts would be lower and lower on the piston toward the exhaust side.
So during the closest part of the P/V travel how far from the top would a piston be? The valves are actually closed at TDC. As you lower the piston down the cylinder, the cuts would be further from the intake side of the piston. At TDC the measurement of all these variables such as gasket thickness and head milling wouldnt matter. The cut is still above the place where the valve would touch although some part of the cut would affect P/V clearance just not as efficiently.
Is my thinking off here?
So during the closest part of the P/V travel how far from the top would a piston be? The valves are actually closed at TDC. As you lower the piston down the cylinder, the cuts would be further from the intake side of the piston. At TDC the measurement of all these variables such as gasket thickness and head milling wouldnt matter. The cut is still above the place where the valve would touch although some part of the cut would affect P/V clearance just not as efficiently.
Is my thinking off here?
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no you got it right, thats why you gotta measure clearance before, during, and after. cause as youve stated, no measuring will get you exactly in the right spot, or depth for a one time deal. I cut mine .080" first time through, then clayed it (with the solid lifter, so no preload ofcourse) and figured out pretty quick that I needed to cut deeper. and since the contact would occur now more towards the center of the piston, you'll be away from the edge of your cut with the edge of the valve face. I liked the other guys idea of turning the motor, making the cut, turning the motor, cut again, turn motor, cut again. so that the piston would start maybe 1/4" down first pass, 1/8" down second pass, TDC final pass. that would get you all the room you need. basically makes the deepest part of the cut wider as measured from the center of the valve to the edge of the cut.
you could just measure for the closest point if you used a degreewheel, and a checking spring with a dial indicator on the top of the valve spring to locate the point on the degree wheel where the closest point between the valve and the piston really is. then you'd know for sure.
all that is why the timing of the CAM decides how much clearance you have or dont have, and where-in crankshaft degrees- the contact would be.
you could just measure for the closest point if you used a degreewheel, and a checking spring with a dial indicator on the top of the valve spring to locate the point on the degree wheel where the closest point between the valve and the piston really is. then you'd know for sure.
all that is why the timing of the CAM decides how much clearance you have or dont have, and where-in crankshaft degrees- the contact would be.
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like you thougth, just inside the deepest part of th eyebrow. Id say less the 1/8" in though. still very close to it. but, you want that extra room on the SIDE of the valves too. now what I mean? Im doin a head/cam swap right now, and when I get to that stage, Im goin to measure the distance with a dial ind. and checking spring. I'll report here if Im gointo flycut. dont think I'll have to with this setup. we'll see.