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 Good shock for my GRiSO??

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Nobleswood
Grignapoco
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PostSubject: Re: Good shock for my GRiSO??   Fri Aug 25, 2017 4:38 pm

Cheers
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Baross
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PostSubject: Re: Good shock for my GRiSO??   Fri Aug 25, 2017 11:08 pm

Sidrat - I didn't measure the change in ride height but as I am tall (183 cm) it doesn't matter. I can still put my feet down flat very comfortably. Of course it might be an issue for a shorter person. I haven't changed front end settings - it's on the 5th preload mark and seems to like it there. No problems with stability over several thousand km of backroad riding and one track day.
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ghezzi
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PostSubject: Re: Good shock for my GRiSO??   Sat Aug 26, 2017 1:57 am

Baross, in round figures that increase in shock length would have increased rear ride height by 45mm.
Or enough to reduce your rake by 1.5 degrees, 23 degree rake ............ it should turn in sweetly now.
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Baross
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PostSubject: Re: Good shock for my GRiSO??   Sat Aug 26, 2017 4:44 am

Thanks Ghezzi - that sounds about right. Ah it now turns sweetly indeed! Very sharp but still very stable at any speed.
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waterbottle
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PostSubject: Re: Good shock for my GRiSO??   Sun Aug 27, 2017 6:44 am

Ok. I'll have a go at putting some pics of my Ohlins install here.

Top attachment, original bolt, but required is 2 spacer washers as the top eye is narrower than the one on the Sachs shock.

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The next 3 pics , Lower Clevis attachment. The Clevis is obviously wider than the Dog-bone it mates with. I measured and made 2 steel spacer washers to take up the excess clearance here too. The reason for using washers of such large outside diameter is to prevent the bolt/ clevis/ bearing bushing journal moving sideways. If you don't do this , it can and probably will move sideways and the bolt head or Nut will catch on the Fork. Resulting in damage to parts or if it locks it up, an accident.
Also on the inside of the 2 steel washers are Orings just big enough to fit around the bearing journal. This further helps centralize the fork on the dog- bone
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The bolt selected was long enough so the threaded end protrudes completely through the Clevis. This is so the loads imposed are on a solid section of the bolt and not on the threads. It also prevents the threads of the bolt getting hammered into the clevis and damaging it. Use a Thin nut or machine the back side of a standard Nyloc Nut down to achieve required clearance. Note here that this bolt is only in shear. There is minimal sideways or Tension loads on this bolt, so a Half Nut installed with light tension is more than sufficient. ( Use a dab of locktite for peace of mind if you prefer)
Just Recapping : The Bolt is a 10.8 grade, the parallel section goes through both sides of the Clevis. The thread end is then cut off so it is just Level with the outside of the Half Nut. Use THIN Washers. The inside of the Fork casting flashing was also dressed smooth with a smooth file and Wet or Dry sand paper. 600 grade. This achieved another 1 or 2 mm clearance. Dress length-ways only as cross-ways will leave Stress-Raisers.

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Last 2 pics are the springs I've tried.  My Riding Weight is around 92 Kg dressed to go.
Standard Tuono spring was 95 Nm. A Huge problem I've found pushing this GRiSO hard is that under hard braking the bike would Pogo bounce or skip from front to back until I let go of the brakes. Poo comes out when this happens. affraid  Laughing  I thought it was all to do with damping settings, but I finally worked out it was having too soft a spring.
I next went to a 105nm. Still too soft. A 115 Nm felt ok but still No Bike Sag and too much rider sag and still skipping under brakes when upset by a few bumps. I've settled on a 130Nm spring, and to date no sign of the pogo skipping.
It could also have been caused by having Zero Bike Sag. IE : nothing for the bike to work against when the the nose dives under brakes and the rear shock was Topping out. My present Sag Readings are Bike Sag = 7mm. Bike Plus Rider = 33mm.

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Last edited by waterbottle on Sun Aug 27, 2017 7:18 am; edited 2 times in total
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Nobleswood
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PostSubject: Re: Good shock for my GRiSO??   Sun Aug 27, 2017 7:05 am

Waterbottle,

Thanks for the details.

Questions; what do you mean by 'dress lengthwise ' & 'stress-raisers'

Did you use a 25mm clevis mount ? Do you know the part number ? Ohlins usa can only find it if it's referenced to a particular bike.
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waterbottle
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PostSubject: Re: Good shock for my GRiSO??   Sun Aug 27, 2017 7:28 am

If you are going to remove any casting marks by filing, File longways down the beam of the fork , not across the beam. Imagine it as filing a nick in a piece of Hi-Tensile fence wire. If you then bend it back and forth it will always break at the nick you filed.
Sorry I can't remember the Clevis Part Number, Ghezzi might remember or be able to find it for us ?
I will be removing the shock for other work i'm doing, so I could get measurements then, But this won't be happening for a couple of weeks yet.
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Brent S
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PostSubject: Re: Good shock for my GRiSO??   Sun Aug 27, 2017 11:14 am

Jesus Waterbottle. That's a whole lot of fucking around to get a shock to fit. You have greater patience than I. And a whole lot more mechanical aptitude I might add.

Interested in your impressions on the spring rate. You're not a heavy bloke by any means, and I'm wondering that if you need a 130nm spring, what does a bloke who weighs 110kgs stark naked use? Matters not to me, as I'm 75kgs dripping wet, but interested in different views.
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Sun Aug 27, 2017 11:19 am

Thanks for the clear explanation Ron!
I got a 25mm clevis from the Dutch Ohlins importer, so no problem with that. Nobleswood also contacted them.

Strange you need a 130N/mm spring @ 92kg Shocked
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waterbottle
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PostSubject: Re: Good shock for my GRiSO??   Sun Aug 27, 2017 8:31 pm

The 130Nm spring probably would be too much on the standard shock. But as the Eye to Eye length has increased the "Initial" rocker ratio has also increased due to the geometry of this suspension, IE makes a heavier spring Feel soft.
Another issue I had was when exiting a corner and getting back on the throttle, the rear was Squating down, unloading the front end, and the bike wouldn't hold a line. I mean it would go wide exiting the corner. The heavier spring helped this amazingly well.
This shock is on my track only bike, But as set up now it still feels very compliant.
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ghezzi
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PostSubject: Re: Good shock for my GRiSO??   Sun Aug 27, 2017 9:34 pm

I had the same pogoing front end problem on my race bike, but it was due to white knuckle fever and dinner plate eyes. Everytime I "blipped" the throttle to down change I wasn't fully closing it again.
Other novices with the same problem would pump the brake as they "blipped" the throttle, same result.
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