Ohlins shock assembly question (Please Help))

[smadams68]

Currently assembling a pair of Piggyback Betor Shocks (factory for 82 125 WR). My question concerns the pressurized Nitrogen side. This part of the shock is nearly identical to the Ohlins piggyback so assembly principles are likely the same. My question is: Should the piston be pressed into the cylinder all the way until it hits the land in the cylinder or do you leave additional space above the top of the piston for oil. I would have thought that the piston should be pressed all the way down to the land, but reading the Ohlins teardown and assembly instructions buried somewhere here in a thread mentions something about pressing it in with a tool to a predetermined depth.

My thinking is: If the piston is pressed all the way down to the land and then later pressurized with 150psi Nitrogen the piston cant move therefore does not transfer the pressure over to the oil side. If the piston is not pressed all the way to the land, but rather to a predetermined depth, then when you pressurize the cylinder, the piston will tend to move thus transferring the pressure to the oil side. The second method described would also place this pressure on the shaft seals tending to cause leaks and oil oozing out the bottom of the shock past the shaft seals.

Please comment, should the piston be bottomed out during assembly so the pressure is not transferred over to the oil side or should the piston be installed to a predetermined depth thus leaving more space for oil, and less volume for Nitrogen.

Please help, or comment, this principle likely applies to remote reservoir shocks as well.

Scott

 

[2T_vs_4T]

Hi Scott,
Here are a few pages from an Ohlins Shock Manual, I can't remember where I found it.

 

[smadams68]

Thanks for your input. From these instructions step #11 the gas piston is pressed to the bottom and never pulled back to increase head space for oil. This is contradictory from what I read in another Ohlins instruction that I found in a thread at the same location I found the instructions you provided. Maybe I am misinterpreting something or reading to far into it. After talking to a suspension builder in town, he thought that you would leave a little extra room above the gas piston for oil by pulling the piston back slightly from bottom. Granted, modern suspensions are different, but possibly some basic principles are still shared. I assembled the shocks with the gas piston approximately 15mm from the bottoming. We will see how it works. Thanks again, Scott

 

[Chris Rowan]

Thanks for your input. From these instructions step #11 the gas piston is pressed to the bottom and never pulled back to increase head space for oil. This is contradictory from what I read in another Ohlins instruction that I found in a thread at the same location I found the instructions you provided. Maybe I am misinterpreting something or reading to far into it. After talking to a suspension builder in town, he thought that you would leave a little extra room above the gas piston for oil by pulling the piston back slightly from bottom. Granted, modern suspensions are different, but possibly some basic principles are still shared. I assembled the shocks with the gas piston approximately 15mm from the bottoming. We will see how it works. Thanks again, Scott

I am rebuilding the piggyback shocks on my ´82 WR 430, and am having trouble removing the reservoir/gas piston. I have tried penetrating around it with Liquid Wrench and forcefully pulling up on the piston with pliers, but to not avail. It seems I need to purchase the special tool shown in the image by 2T_vs_4T, some kind of screwdriver type tool that screws into the top of the piston? If there some method to avoid making this purchase?

 

[adam6402]

I am rebuilding the piggyback shocks on my ´82 WR 430, and am having trouble removing the reservoir/gas piston. I have tried penetrating around it with Liquid Wrench and forcefully pulling up on the piston with pliers, but to not avail. It seems I need to purchase the special tool shown in the image by 2T_vs_4T, some kind of screwdriver type tool that screws into the top of the piston? If there some method to avoid making this purchase?

Rather than buying or making a special tool, i went to my local hardware store and for less than $1 bought a long (4 or 5 inches) threaded machine screw ( I think M5). I scrwed it in tight and then was able to get a firm grip on the screw head with a pair of pliers to tug it out, as you would expect for something designed to contain 150+ psi nitrogen charge, it is in there very tight.

 

[Chris Rowan]

After some consideration, I have been thinking along the same lines, I just hope I don´t end up ripping all the threads out!

 

[dartyppyt]

I am rebuilding the piggyback shocks on my ´82 WR 430, and am having trouble removing the reservoir/gas piston. I have tried penetrating around it with Liquid Wrench and forcefully pulling up on the piston with pliers, but to not avail. It seems I need to purchase the special tool shown in the image by 2T_vs_4T, some kind of screwdriver type tool that screws into the top of the piston? If there some method to avoid making this purchase?

A trick I use to get the piston out: Take your allen out, put your hand over the main shock shaft tube, cover reservoir end with a rag and shoot air in the hole where allen is removed. Bingo, pops out in the rag real easy and doesn't go flying across the garage. I start at about 50 PSI and should pop it out.

 

[Chris Rowan]

Thanks dartyppt, I had been wondering about using compressed air, too.

I bought a long bolt to fit into the reservoir piston and have managed to pull it out and rebuild the shock, moving the piston up and down. I think it was a 6mm bolt.

 

[ct cr430]

This past Friday I finished rebuilding an ohlins piggyback single shock and followed this procedure . I measured the reservoir piston height at the bottom before installing the seal head . When the seal head is installed it will "trap" the oil inside the body and as it goes into the body the piston inside the reservoir will raise . The difference was between 9 to 10 mm . This is after the seal head is installed and the circlip that holds the seal head is in place . Then I pushed on the reservoir piston again so the seal head was against the circlip . So yes , following this procedure the piston in the reservoir does not end up all the way at the bottom .

 

[Picklito]

Yes, the reservoir piston should be "off the bottom" of the reservoir by a few mm. It should never touch either end of the reservoir during normal, full, compression or rebound strokes. The exact number is not critical, although it does affect the rising rate of the nitrogen as the shock compresses... a much smaller effect than the air chamber height on a fork.

If I'm rebuilding an old shock that I have no specs for, I cycle the shaft and make sure the piston is "one full stroke" away from the shock end of the reservoir when the shock is fully extended.

 

[silverstreakNZ]

Newer ohlins theory is bottom the piston . Fill the shock body with oil as you push the piston and seal head into tho body it displaces oil and sets the separator piston the right height from bottomed out .
It's really easy / clever tbph