play in shock seals

[Juddy]

I have found that my shocks are gaining rebound after a couple of runs after bleeding. I've heard about this issue and apparently shimming the play out between the o-ring and plastic spacers is the solution? has any one tried this and did it work?
If so what did you use? I was thinking of trying to get some of the old nylon shims we used to use to shim the old brushless motors? Does anyone know if these are available, or have a better solution?

Thanks

[janus_77]

from RCtech:

Janus
Ok, I'm going to restart the shocks discussion a bit.

Like most of you know, the shocks have a fair bit of sideways movement between the shaft and the shock housing.

Problem is that in testing it was found (mainly by Nik Weyers) that air gets in this way no matter which caps (alu/plastic) you run. We tested a number of different o-ring types ( original, low friction, aftermarket 801's 70sh ), but the problem remains.

I have some custom shaft guides in mine ( the guide ring between the o-rings made to much closer tolerances), which helps a lot (!). But not everyone has access to a lathe.

Not sure if it's a batch issue or more widespread, since the cars that were tested were all bought around the same time. So there probably all from the same batch.

Do any of you have, or had this issue ? and more importantly is there an actual solution ?

Janus
Not sure if we have a solution, but its a "work-around" anyway http://www.rctech.net/forum/classic_images/smilies/sneaky.gif

Just add thin shims (I used 0,3mm) to the o-ring cartridge to put more pressure on the o-rings. This enables the O-rings to support the shaft better. Just add untill you notice the shaft has added friction when moving.
Its not really a job they're meant to do, so rebuilds will become more common I guess. But it does help. Now after 2 runs the shock has added a little rebound but nothing as silly we saw at the MIO track

Hope this info helps....

Sitting Duck
I have found a solution for the shocks that build rebound.

At first i thought it was the bleeding screw, so i put some o-rings on the bleeding screw but the problem stayed.

Then i thought is was the side play of the shock shaft. I replaced the big flat collar with another one from TLR. It is 3x7x1 mm and i think it is used as a ballstud spacer.
Replacing the collar was better but didn't solve the problem.

Then i tried some robitronic P3 o-rings and now my shocks are ok. I think the robitronics are the same as the kyosho p3 o-rings but i am not sure. Next i am going to try kyosho grooved o-rings because the robitronics seem to have a lot of friction.

Skrichter
Shocks - I'm not sure if the clear orings have been updated, but I COULD NOT BELIEVE the amount of friction/sticktion. My AE (and TLR) vehicles don't have anything close to this amount of friction. I replaced the stockers with AE orings (since they both use a 3mm shaft). To combat the air suction that everyone is reporting, I added a .3mm shim (which was suggested somewhere in this thread). Shocks are good now (almost too free) -- I can bleed my shocks with ZERO rebound with no problems now.

[neallewis]

I rebuilt my shocks last week and they have had one indoor meeting run. I replaced all the seals completely with fresh ones. I've just removed them and both were pressurised, one a bit more than the other. I'm running yok blue o-rings. I've re-bled and have placed a two 4x6x0.15mm shims in each of the bottoms to press the plastics into the orings.

I'm running friday night and will check them afterwards to see how they go.

[OneKiwi]

Mine are similar with building pressure. I also bleed/air them after a couple of runs. I do notice that if I have a little less oil in the shock from leaking they don't be as pressurised
Where did you get the shims?

[janus_77]

Where did you get the shims?

KYO96642
TDR709010

[MiCk B.]

I've had similar running the AE bigbores.

(Product Plug)

This is what I've been using in mine to 'pack' the o-rings.
Teflon shims.

http://p-dubracing.co.uk/images/DUB007.jpg

I have them in 0.010 (http://p-dubracing.co.uk/index.php?main_page=product_info&cPath=5&products_id=41) and 0.015 (http://p-dubracing.co.uk/index.php?main_page=product_info&cPath=5&products_id=42).

MiCk B. :-)

[janus_77]

Ok, Did a bit of playing around with some parts to get a good shock cartridge without needing hard to make custom parts. You just need to drill out the cartridge cover a bit. Now it doesn't build up rebound anymore and the shaft support is much more accurate.

Note 1: Yes you need to use the smaller yokomo shim (6,4mm) twice, your not using the larger ring (7mm)

Note 2: The AE o-ring will fit, but of course I'm using the Janus "801" O-rings ;)

[OneKiwi]

I've had similar running the AE bigbores.

(Product Plug)

This is what I've been using in mine to 'pack' the o-rings.
Teflon shims.

http://p-dubracing.co.uk/images/DUB007.jpg

I have them in 0.010 (http://p-dubracing.co.uk/index.php?main_page=product_info&cPath=5&products_id=41) and 0.015 (http://p-dubracing.co.uk/index.php?main_page=product_info&cPath=5&products_id=42).

MiCk B. :-)

YOu have them in stock?

[smokes]

Is anyone running x rings? could you let me know what part no's they are?

Please note:From a engineering perspective o-rings are not that great at reciprocating sealing at high speeds as they roll x-rings are better. Also because the o-rings roll they need a toleranced groove that stop the rings distorting. The Plastic spacers are not stiff enoungh for this role.
For good vacuum sealing the suface finish must be between 0.8 and 3.2 ra or the gas will find a way in. It is achieveable on plastic but the shaft spacers yokomo provide are closer to about 32 ra. The nitride coating is dependant on the surface it is coating if the shock shafts are cold drawn the polished before coating you should get a good finish of about 1.6 ra. but I suspect it not as it quite expensive to achieve these surface finishes on such small parts.

I guess what I am trying to say is unless you are willing to design the parts to meet surface finishes and groove tolerances required for vacuum sealing applications. You won't stop gas leaking back into the shock. And the solutions above will only slow the rate of vacuum leakage.

[janus_77]

With the AE small bores I tried using an o-ring for the lower seal and an x-ring for the upper seal. This because an x-ring hates dirt, so I used the o-ring a bit more as a scraper for the dirt and the x-ring could do the actual seal. But since switching to industrial quality o-rings I've never had any real issues with the AE small bores which I've used on my X-6 until switching to Yokomo.

But, yes I'll get a set of these once there released. Only if it's just to try. http://www.teamassociated.com/parts/details/91495/ ;)

[MiCk B.]

YOu have them in stock?

Yes,the teflon shims are in stock:

1/8 scale (8mm x 4.2) (http://p-dubracing.co.uk/index.php?main_page=product_info&cPath=25&products_id=315)

1/10 (0.010) (http://p-dubracing.co.uk/index.php?main_page=product_info&cPath=5&products_id=41)

1/10 (0.015) http://p-dubracing.co.uk/index.php?main_page=product_info&cPath=5&products_id=42

I use the 1/10 for suspension shimming and for the shocks.

MiCk B. :-)