Hi Guys,
I'm in the process of flycutting my pistons, I checked piston to valve clearance with a .040 Cometic gasket and my Dart 225's milled .018, and came up with .022 before the flycutting, to be on the safe side I set the feeler guage to .080 and cut my first piston, before i cut the rest of them I put my cometic back on with the Dart head and meaured again and I only have .067. By looking at the relief and holding a Nickel to it which I have been told is about .075 the relief is not as deep as the nickel on the upper side. I am measuring with the cutter on the piston and .080 between the collar and the seal and then locking down the collar.Can anyone with experience with this tell me what I might be doing wrong..

By the way free drop was .122 milled .018, Dart 225. if anyone needs this info.

John

 

ttttt

 

Corrected the problem, for whatever reason setting the feeler guage at .080 only cut out about .055. I cut another .030 out and everything is fine, holding a nickel to it now looks alot more on the money...ha-ha and also gave me .080 without taking into consideration valvetrain deflection, becuause i measured with the light springs.

John

 

New problem, collar has stripped keyway so I can't adjust it for the remaining cylinders, another thing i found was that the head i recieved had valve stem seals on it and thats why I was getting the false reading with the feeler gauge it wasn't all the way onto the seal.

 

Honestly, I think it's rediculous to flycut with the pistons still in the motor...

You still have to take the pistons out to be rebalanced... that means you could've cut the pistons the correct way in a vise with the proper equipment, or taken them to a machine shop to have them done correctly.

Good luck. ~Joshua

 

When you flycut .080, youre flycutting from the edge of the cutting tool, which is likely wide than the actual valve is, and since the valves are on an angle, youre not going to hit the deepest part of the cut. Furthermore, when you flycut, youre at TDC. When you measure p to v clearance, youre not at TDC, the piston is partially down the bore. This means that the valve is moving laterally as it moves downward. Again this will mean you wont be hitting the deepest part of the flycut.

With a ~.075 flycut, your probably only removing a gram or two out of the piston. Youre lucky if your engine was balanced that close to begin with.

Ive been running fine with my flycuts for a while now. No problems.

 

throw the collar out. It will only cause you trouble. Cut each pocket by cutting, then measuring. You are counting on the valve guide being in the same place on all 8 cuts, and counting on the fact that the collar doesnt move.

How are you measuring your PTV? If you are speculating that the coin is 75 thou thick, you might want to use another form of measurement that is just a tad bit more accurate.

 

new collars can be found at mcmaster.com for about 2 bucks each... That what I used on my home brew tool.

Theres a local shop that flycuts without a collar and they just go by counting a couple seconds each cut. Not very accurate. Id prefer to use a collar. Since you have to take the collar off every time you move the tool, if you set it each time it should be pretty accurate regardless of the height of each guide. you set the collar referenced to each guide anyway.

 

I had only cut one piston before realizing that the collar was stripped, when I measured for the first cut I put the feeler guage between the seal and the collar and it measured .080 but after the first cut I then realized that it didn't go deep enough ,meaning the collar did not come close enough to the seal, thats why it was off,not because I measured incorrectly. I reinstalled the head and closely watched as the collar came very close to the seal before stopping, I then got my .080 This is my first experience with cutting, so I thought the collar had contacted the seal initially in which it didn't. When I went to measure the second cut it was off by maybe .020-.030 thats when i went to adjust the collar and found it was stripped so I didn't cut it. I have built many BBC engines in the past and I don't want to eyeball something as critical as this. As far as using the nickel,I only used it as a reference not a measuring tool, I have feeler guages,dial indicators,adjustable pushrods at my disposal for measuring, I just knew that by looking at the depth of the cut that it wasn't near .080.

Louis how are you, glad you chimed in, I have a question, I'm running a G5X3 on 114,stock shortblock,Dart 225's 2.05 Intake /1.60 exhaust,I was told I only need to cut the Intakes and not the exhaust, I haven't measured the exhaust yet but your tech dept. told me I'd have plenty of room, Intake is only problem.

Another quick question do you think that I'm going to be able to use the stock length pushrods 7.4, cutting .018 off the head and using a .040 Cometic gasket, zero lashing the adjustable pushrod of course is shorter than 7.4, and I haven't had the rockers on to see where they sit on the stem,what type of preload is acceptable on the lifter?

Guitboy where you from in L.I.,I grew up in Queens, and then lived in Hicksville.
Thanks for the Help guys
John

 

John, Im personally not familair yet with the Darts, so I cant speak on the valvetrain setup. You would like to see 1-2 turns of preload, depending on the lifter/valvetrain setup. Some cases I need 10-20 thou, others I need 80 thou.

Use a dial caliper, the end of it, to measure the pocket depth. I also measure the width of the pocket just to make sure they are all the same, or as close as humanly possible to it. It is just another reference point, but certainly dont use that as a basis.

When I flycut, I take the collar off, measure from the top of the guide (Not the seal, make sure the seals are gone) to the top of the cutting stem. This way, you can see where you start, and where you end up when you think you are close. It takes a little more time, but you know you didnt go too far. I have cut .125 out of my personal stuff that made 480+ rwhp and saw 7500 rpms of fun with no issues. The motor is still running strong.

Let me know if I can help or discuss it with you over the phone. Sometimes it is easier that way if this doesnt help Im working on a flycutting FAQ, but I do not think it will go live till august sometime.

Louis

 

I like louis' idea of using the dial indicator to measure the depth of the flycut, however, how can you get the drill on top of it with the indicator in the way, and if you move the indicator, what says its gonna go back to the same spot, as the valve angle is not the same as anywhere you could reference the indicator's base.

And Im from medford, which is in the middle of suffolk county. I work out in uniondale so im pretty familliar with hicksville. Anyone reading this who's not from LI is thinking WTF is with hicksville! Bunch of rednecks. lol

 

I'm going to have at it again tonight, I just want to feel comfortable knowing that as I'm cutting that I have a solid reference point. Your idea about using a caliper sounds good, I have many engine building tools so I'm sure that I will come up with something that I will feel comfortable with. I measured the lower portion of the cut meaning the straight part at the bottom with my small steel ruler and have 1.625 from end to end, and the upper part of the cut is def, at .080 again I can use these as reference to get close, so i can continue cutting the rest of the pistons.
Louis I'll give you a call probably later in the day to talk about it,Thanks much for the help.

Guitsboy I'm familiar with Medford and Uniondale, Back in the day I was a Sales Manager at Dobler Chevrolet in Hempstead,Yea Hicksville does sound kinda redneck but it def. isn't, I miss it up there as i live in Florida now for the past 6 -7 yrs.