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Ford 9N, 2N & 8N Discussion Forum
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Help: New Style Lift Piston

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Dave_N_Ga

10-10-2004 19:28:58




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I finally needed to work on my 8N hydraulics. I wanted to replace the cam follower, adjust the linkage, replace the relief valve and install a new piston and ring.
The piston I took out was the three metal ring type and there was light scratching in the cylinder.
I'll hone the bore tomorrow but tonight I wanted to install the back-up ring and Oring. I soaked the backup ring in hot water and slipped it on, then oiled the oring and slid it on with out rolling it.
The question I have is is if the oring OD is larger that the OD of the pistion it isn't by one or two thousanths. How could this possibly seal better than the steel rings?
Or, is the oring I got defective? It came out of a TI$CO gasket set.
I feel like I should use the old piston and rings due to the fact the new oring I have isnt going to do anything.
Give me some advice guys! As always, thanks for the help!
Dave

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Dave_N_Ga

10-11-2004 10:26:03




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 Thanks to all! in reply to Dave_N_Ga, 10-10-2004 19:28:58  
Ok gents, here's the deal. I went to the dealer and got a FNH Oring. The ring that came in the TI$CO kit was in fact too small. The FNH ring is a larger diameter with a larger cross sectional diameter. It's also a harder composition and I can see it will be more difficult to stretch over the piston. I'll clean up the bore tonight and put the old girl back together.

Again, thanks to you all for taking the time to reply.

Dave

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souNdguy

10-11-2004 07:08:03




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 Re: Help: New Style Lift Piston in reply to Dave_N_Ga, 10-10-2004 19:28:58  
I just did mine a couple months ago. The oring sets ever so slightly higher than the od of the piston, and the backup washer sets virtually flush, if not a thou under.

I oiled my oring and the cyl with some 90wt tranny oil before I put it back in the bore. I started it by hand to make sure it was even.. and then tapped it in with a rubber mallet very gently. There was a decent amount of resistance. Lift is great now.
I honed the cyl to the limits of tolerance.

Soundguy

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Russ in SoCal

10-11-2004 08:09:01




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 Re: Help: New Style Lift Piston in reply to souNdguy, 10-11-2004 07:08:03  
Hey souNdguy,
What"s the "limits of tolerance?" Is that the cylinder or when YOU couldn"t tolerate any more honing?
Russ



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souNdguy

10-11-2004 08:47:42




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 Re: Help: New Style Lift Piston in reply to Russ in SoCal, 10-11-2004 08:09:01  
You got it.. Both actually.

I found that a good lubed brake hone.. even with an electric drill.. takes a bit of honing to get some metal down. I think My arm would fall off if i honed it out of spec.. unless it already had been out of spec.

After honing, I washed it down real good and inspected it.. decided it was good enough to put back in. So far it has been great.

Soundguy



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Russ in SoCal

10-11-2004 18:41:06




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 Re: Help: New Style Lift Piston in reply to souNdguy, 10-11-2004 08:47:42  
souNdguy,
Write the price of a new cylinder on a piece of paper. When your arm gets tired, look at the paper. ; ^ )
Russ



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souNdguy

10-12-2004 05:03:40




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 Re: Help: New Style Lift Piston in reply to Russ in SoCal, 10-11-2004 18:41:06  
Yep.. they like those cylinders.

A buddy of mine is a machinest. he says if they were just a tad more expensive that it would be cheaper to bore and sleave the old one, or simply machine a new cylinder out of aluminum billet.

I imagine a hobbyist with one of those compact cnc drillpress/mill/lathes could probably make one in a morning out of stock aluminum, if they had the lift cover and old cast iron body to measure off of.

Soundguy

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ZANE

10-11-2004 06:28:25




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 Re: Help: New Style Lift Piston in reply to Dave_N_Ga, 10-10-2004 19:28:58  
I can assure you that the O ring will do it's job and not leak. It does not have to be bigger than the bore. That is the beauty of the O ring seal. The oil actually presses the O ring against the sealing surface by the means of hydraulic principals. The oil gets under the leading edge of the O ring and pushes it up against the other part it is resting against. In this case the bore of the cylinder. The harder you push it the better it seals.

The back up washer is designed to prevent the lip of the ring land from cutting the O ring under extreme pressures.

Zane

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Rob

10-11-2004 02:30:56




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 Honed lift cylinders get too big. in reply to Dave_N_Ga, 10-10-2004 19:28:58  
Maybe your cylinder has been honed a time or three already. That oring should be a challenge to fit into the cylinder. I haven't measured the od of the ring to compare to the id of the cylinder. You have to shove pretty hard to get it in the cylinder. You may have the wrong ring but the od of the ring is not much larger than the OD of the piston. Consider that the FO-4 says the clearance of the piston in the ram should not exceed 0.0025". So the oring has to fit in that two and one-half thousands. Can't be much bigger than the piston. I would measure before I decide whether I need only rings, or ring and piston, or whether I should replace the cylinder. Two and a half thousands doesn't leave much for the hone especially if there is 1-1/2 or two thousands clearance between the parts when they are new.
Of course, the fix with the oring and piston is preferred by some because they save $60 or $70 on the rebuild but you might, probably will, be out of spec and have an oring holding a larger gap then it was designed to hold.
Contrary to board common wisdom I suggest the good rebuild is to reuse a serviceable piston and replace the iron rings and cylinder. $90 instead of $26 but you hold the spec and the cylinder is pristine without any scoring or scratches. In fact, if the old rings are not damaged and they gap ok in the new cylinder, which they probably will be because the problem is scoring and not wear, the old iron rings might go right back in, dunno. That saves $6 off that $90. Besides that, I like the idea of 3 iron rings better than the idea of one plastic ring because I'm pretty sure the iron rings will last a lot longer, especially in that rough cylinder. The other rams I own with orings have a polished surface.

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