3 ring hydraulic cylinder

(quoted from post at 23:06:54 10/13/08) I am going to try the John Smith modification on the three ring piston for the hydraulic cylinder. If I use two steel rings and the third groove is for the backup washer and o-ring, how should I set the steel rings when I insert the piston into the cylinder? For example, should they line up, or should the gaps set to opposite sides?

Finally, does anyone have a measurement on how much I will have to machine the third ring groove to imitate the NAA piston?

Thanks.

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(quoted from post at 15:04:41 10/14/08)

(quoted from post at 23:06:54 10/13/08) I am going to try the John Smith modification on the three ring piston for the hydraulic cylinder. If I use two steel rings and the third groove is for the backup washer and o-ring, how should I set the steel rings when I insert the piston into the cylinder? For example, should they line up, or should the gaps set to opposite sides?

Finally, does anyone have a measurement on how much I will have to machine the third ring groove to imitate the NAA piston?

Thanks.

Click to expand...

The post from John that I reposted [color=red:24aef4cc84]here[/color:24aef4cc84] had his suggested dimensions in it. How much do you expect to pay a machine shop for this job?? I'm guessing 1/2 hour minimum charge. It's not a complicted operation - chuck the piston up on a lathe and use a grooving or parting tool to recut the groove. Probably 15 minutes actual labor start to finish including mounting the chuck if it's not already on the lathe. If your shop wants more than $9.30 x 2 flat rate it to me and I'll do it just for the heck of it.

TOH

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Well, it's pretty standard. O-rings are "nominal" sizes which means they vary a little and the design is for them to squish down and have the correct fit when installed. The o-ring for the NAA is a 3/16" nominal but it actually measures about .201" plus or minus. The cylinder bore is 2.500 so the o-ring groove depth would be 2.125" (2-1/8 + 3/16 + 3/16 = 2-1/2). Groove width is .3125". However, that's a lot of squish on the "nominal" o-ring size of .201" or so. Most factory NAA pistons have an o-ring groove depth of 2.118 to 2.120. Hard to install the piston in the cylinder otherwise. I cut the piston groove depth about 2.120" if the piston is going in a standard good bore cylinder and 2.125" if I've honed a few thousands out of the cylinder to make the bore slightly oversize (the usual case). It's been a while since I've cut one so this is from my feeble memory, but I think it's right.

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