OZO Pro Vintage Twinshock Rear Shocks, A Look Inside

Discussion in 'Trials' started by PMK, Dec 6, 2018.

  1. PMK

    PMK Been here awhile

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    Had the need to open a set of these up. Not sure if others have posted photos or not of them. Monotube design with an IFP seperating piston. Very basic gas shock.

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  2. lineaway

    lineaway Long timer

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    So, yes it comes apart easy enough. Is it a quantity of oil? Nitrogen at? I never know when I just might need to know.
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  3. PMK

    PMK Been here awhile

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    I think you are asking if the oil is a specified quantity, and what was the Nitrogen at.?

    Using a zero loss gauge setup, I checked both shocks for gas pressure before releasing it. One indicated 80, the other a touch over 60. No gas was lost so there was certainly a split in pressures. The gas pressure was low enough the rod would not extend completely in the one.

    As for oil quantity, checking each shock for IFP height dimension offered up a one being at just under 33mm while the second was at 22.7mm.

    I accomplished some internal modifications to build two identical performing shocks.

    The reason these were taken apart after only 10 minutes use since brand new, they were overdamped and had a lot of seal drag.

    If you want to get them back together without mods, the seal is an odd fit, so inserting the sealhead will see the oil seal not installed and excess fluid can purge out past the rod bushing, then the seal installs.
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  4. lineaway

    lineaway Long timer

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    Thanks!
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  5. Brewtus

    Brewtus Buffoonery, Inc.

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    Hmmm. Brand new "modern" shocks for your TS bike, only needing some modifications to work properly? :eek7

    Not thinking of OZO shocks for the 348 anymore... :nah
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  6. PMK

    PMK Been here awhile

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    Actually, these are my friends shocks for his MAR getting the footpegs relocated. Since that chassis is not finished yet, he fitted them onto his pretty much stock MAR.

    For the money, these are not bad shocks. Maybe with time they would have freed up a bit more. Because we have an event tomorrow, I suggested we open them up and dial them in for now and if needed make changes again later.

    Again, for the money, not bad. As a suspension tuner / suspension geek / shock guy, my suggestion is to buy decent quality shocks with parts that are readily available. Not every part, but common wear items. These being made by Betor, pretty sure they are anyway, we need to find a place to buy the shaft seal and O rings.

    Crazy thing on my own personal MAR, I am running period correct Curnutt shocks. Those too were not so good being designed for desert and mx racing. After a tiny bit of sorting out the damping, I find they work good for me. Best part, seals are common O rings, and a common dust seal. all available at Grainger or on the internet for short money. Other parts, such as a shaft or springs are tougher to find, but could be made if needed.

    If you avoided the OZO Pro shocks, and realize these are the Pro version, not the least expensive or the elites, which other shocks are you considering?
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  7. Brewtus

    Brewtus Buffoonery, Inc.

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    For the 348 I had been considering Rock Shocks, they're fairly popular with the TY175 crowd in MWVTA. I've heard good things about Magicials as well, but don't know anyone running them. Of course I had also heard good things about Betors when we were shopping for shocks for the Team TY80, the seller said they "would take a lot of abuse". I guess his idea of abuse and our idea of abuse differed greatly, the Betors blew their guts out on the first Trial they were in, and one bent in the second. Vintage RM80 shocks have been used ever since.

    All of this may be academic. Motobene was looking at the vintage Marzocchi shocks currently gracing the back of the 348 (Lineaway had installed them a few years ago), and was saying he could make them work pretty well. I may take him up on that. :thumb
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  8. PMK

    PMK Been here awhile

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    Got a photo of those Marzocchi you can share. Something to see them a bit up close. Curious which they might be.

    These OZO shocks, not bad. The seal design and parts availability would be my number one concern. Bending a shaft, anything is possible.

    If you do go with OZO, I have these sorted out regarding repeatable assembly, vs however they did it before.
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  9. Brewtus

    Brewtus Buffoonery, Inc.

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    I'll snap a pic of them when I get out to the shop later. :D
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  10. Boom Boom

    Boom Boom Been here awhile

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    Have had good luck with the Rock Shocks from England. Have a local guy that is up on them and does a bulk buy every year. I ran them on my 199b Bull and now they make a mono replacement for the TY so I had to try one..working well. They sell all the rebuild / service stuff. Worth looking into. Very popular at MAVT events.
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  11. Brewtus

    Brewtus Buffoonery, Inc.

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    For your viewing pleasure -

    20181207_110431.jpg 20181207_110452.jpg 20181207_110508.jpg
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  12. lineaway

    lineaway Long timer

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    Those shocks were only used to push the bike around the shop. The time I rode that at the Nationals, I had a borrowed set of Betors. Those shocks were brand new in the box left with me by a customer two decades ago. I believe he passed away. The springs were on the shocks that were on the 348.
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  13. Brewtus

    Brewtus Buffoonery, Inc.

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    They could use a bit of reworking for Trials, that's for sure. They're slightly less supple than the rear suspension on my Dodge dually. :umph
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  14. Nodabs

    Nodabs Been here awhile

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    I like how you said supple.
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  15. PMK

    PMK Been here awhile

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    Even better was slightly less...
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  16. motobene

    motobene Motoing for 46 years

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    The OZOs look like Curnutt shocks inside, but do they use balls too?

    Most of the older shocks are over damped by a bunch. Like Brewtus' Marzocchis... OMG! A wood stick might be more compliant.
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  17. PMK

    PMK Been here awhile

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    The OZO vs the Curnutts are not similar at all. The OZO uses a single shim for compression damping and also acts as arebound checkvalve, forcing fluid through very small drilled ports.

    Considering the low cost of the OZO when new. If someone took the time to design or adapt a new main piston that offered a wider range of tuning, AND redesigned the sealhead for a common style low friction seal, these could be some very nice low cost twinshocks. As is, they are not bad, especially at the price point they hit.
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  18. motobene

    motobene Motoing for 46 years

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    Interesting! Just one shim, then small holes for the rebound. Charles Curnutt I believe only used orifices and balls acting as checks. but it's been SO long since I saw inside one of those.

    I have one remaining Works Performance shock, on the Fantic. Gas emulsion type and only uses 4 orifices, three of which have check balls.

    Goes to show there are many ways to provide damping. Kinetic to heat energy, that's it.
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  19. PMK

    PMK Been here awhile

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    Essentially, yes, Curnutts are as you described. Works Performance is one step more evolved with spring loaded check balls.

    After the OZO shocks competed Saturday and were deemed as much better, if we go forward with them to the next level, it will require more work, but nothing difficult or expensive.
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  20. motobene

    motobene Motoing for 46 years

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    Yes, true!

    No matter what the design, I count on dampers from the past being over damped. What is considered 'critically damped' (similar to the amount of suspension travel that is considered minimal) has changed over time as understanding and techniques have evolved.



    Of course it's far more complicated in our case, but the knowing the concept of critical damping helps. And the there is the rider's type of riding (loading) to consider too.

    I've ridden a Pat Smage set up bike with an Ohlins. It felt very tight, short, and stiff on the butt end. My hips hurt riding that bike after a while! Then again Pat is younger and bull strong and slams into stuff WAY harder than I do.

    The majority of us, especially those of us with bikes early 2000s and older, benefit from some 'relief' in damping. Thise bikes are often set to zero clicks on the rebound/bypass and yet are still on the slow-to-react side, even well worn in.

    When I first put the Works Performance on the Fantic, for example, gosh it was slow! Damping assumptions on that shock as delivered came from a fast-bike mentality, and an older one at that.

    In my notes I find about a 3-year progression in tweaks toward faster. I overshot the mark one time and had to plug the open bypass hole and make a smaller one.

    I eventually ended up a little slower overall than what I consider more ideal for me on a modern bike, but still quick enough for useful rear-ended hops and smaller unweights. I thought about one more revalve before the 2017 nationals, but left it alone.

    One interesting thing about the setup on the Fantic was it just turned out, via re machining, to be a long-travel setup like Randy and I do with Ohlins shocks. Quite a bit of sag and negative travel from the static sag angle.

    One particular competition had some quite large rocks. I could point and shoot and just slam them controllably! Given the engine is 'retro high' in the frame, longer travel plus lots of skid plate clearance produced an interesting capability. I was riding GasGas at that time and used to hitting the footpegs frequently....

    But I diverge.... The point is that every bike is an individual to ride and test for the feel of the suspension, which is complicated thing that defies encapsulation into easy rules. I've done quite a few revalves this way with great results. Most of the time on the old stuff I mover or add rocker shims closer in the stacks toward the piston to gain low-speed compliance. Usually works great for the 90% of us who are not hard-slamming Supermen.
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