675.cc • Triumph 675 Forum

Daytona and street triple outer forks – are they interchange

Discussion in 'Other' started by Deleted member 2280, Oct 2, 2013.

  1. Deleted member 2280

    Deleted member 2280

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    I'm currently searching for outer fork tubes for my 675 that I pranged recently.

    I've been offered a set of street triple tubes but it seems that the ST ones are a few mm shorter, does anyone know if they are interchangeable as new ones cost a fortune?

    There are also a set or two on ebay but it would be good to get some solid advice before I buy

    Cheers
     
  2. motorinmatt

    motorinmatt

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    They'll be fine mate, I have used all manner of different combos of st and Daytona inner and outer tubes, and I've never been able to tell the difference between any of them on the road, the fork feet can be a bitch to change though if your using st inner tubes
     
  3. Matt, can you elaborate on what your experiences have been please?

    I have a pair of (non-R) 2008 Daytona forks ready to swap into my (non-R) 2012 Street Triple, but unfortunately one of the Daytona forks arrived slightly bent while my ST forks are straight.

    Matt, are you suggesting that I can use my Street Triple inner and outer tubes with the Daytona internals and feet (I have Daytona calipers also)?

    I've measured both forks and although the overall length (from top of outer tube to centre of axle) is identical between forks and inner and outer tubes are the same diameter, the outer tube length by itself is 5mm longer on the ST than the Daytona. This might just mean that the ST has 5mm less suspension travel than the Daytona (which is the opposite of what I'd expect), but it might also indicate other differences.

    Also, do you think the springs be interchangeable? I haven't had the ST forks apart yet to look at the spring.

    Sorry for the thread hijack OS2, but hopefully these questions (and the comparison/measurements I took) will be of interest to you too.
    I'd never heard of any parts being interchangeable between these forks until now.
     
  4. motorinmatt

    motorinmatt

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    Right here goes :)

    First combination i had was ST outer tubes with Daytona inner tubes, feet & internals
    Second was ST outer tubes, ST inner tubes and Daytona feet & internals
    Third set was Daytona outer tubes, ST inner tubes and Daytona feet & internals

    All using Daytona Springs, i think the ST springs are softer if i recall correctly, all combinations bolted together as they should and once the sag had been set and damping & rebound set up seems to all function the same, no issues with bottoming out or similar, although i never used them on track just on the road.

    I usually run my forks with around 5mm showing through the top of the yoke, all were set at 90mm air gap when rebuilt and using 5w oil.

    Hope this helps, Matt
     
  5. Deleted member 2280

    Deleted member 2280

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    Cheers Matt,

    Helped a lot and Im going to press ahead and use the ST outer tubes with the 675 inners along with the K Tech internal workings :)
     
  6. Thanks for the response Matt.
    It's good to know it behaves as it should when riding normally.

    My only remaining concern though is what happens when the forks bottom out?
    With a mix of Daytona and ST tubes and internals, what bits *should* be making contact when the forks bottom out versus what bits *actually* make contact?

    Here are some scenarios as I see them (feel free to correct me):

    My understanding is that when Daytona forks bottom out the inner tubes are supposed to make contact with the underside of the cap. The damping rod shouldn't be bottoming out and neither should the outer tube. There is a "hydraulic bottom out" feature of the Daytona internals which provides extra damping just before this happens, but it doesn't actually prevent a physical bottom out, just slows it down.

    Now what happens if you take a Daytona fork but put a ST outer tube on there (which is 5mm longer)? Well it rides fine 99.9% of the time, but that 0.1% when you bottom out the forks, now it will probably be the outer tube hitting the fork feet instead of the inner tube hitting the cap! Ouch. Best case scenario it will shorten the life of your fork seals, worst case scenario it will damage the bottom of your outer tube.

    Ok, so lets say we use both inner and outer tubes from the ST and just use Daytona internals and feet (which is what both OS2 and I would like to do). This time it should bottom out correctly (inner tube hitting cap), but we likely have 5mm less travel due to the longer outer tube. This means that the Daytona's "hydraulic bottom out" feature will be less effective because it will cut in 5mm closer to the end of suspension travel. Is this a problem? Probably not, but it's not ideal.

    But lets go the other way and say we use ST internals and feet with Daytona inner and outer tubes. This time the tubes will allow for 5mm *more* travel than the internals were designed for, and this time when they bottom out it's likely that the damping rod will take the full force of the bottom out. And with the ST's already soft suspension this is quite a likely scenario (I bottom my forks out fairly regularly). This is not good.

    Here's an interesting read related to bottoming out the Daytona forks: http://www.triumph675.net/forum/archive ... 54662.html

    And here's an interesting vid on how the Hydraulic Bottom out feature works: http://www.youtube.com/watch?v=VQn36sMT ... e=youtu.be

    I don't pretend to be an expert on any of this so please feel free to call me out if you think this is bullshit.
    But I'd be super pissed off to hit a pothole and bend my fork internals so I'm trying to look for potential problems before trying anything.
     
  7. motorinmatt

    motorinmatt

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    First thing i would check if you have both outer tubes side by side would be the distance internally between the top face where the fork cap sits, and the face where the inner oil seal sits, from memory the ST outer tube is in total approx 3mm longer overall measuring on the outside of the tube, but there is a slightly longer machined lip on the dust seal end when you compare the two side by side? It may be the case that the important part ie between fork cap and seal is the same length so the rest shouldnt really matter, the dust seal is never going to get near enough to the bottom casting to worry about 3mm extra length.

    I will openly admit that what i know about suspension is very limited, i'm confident enough to rebuild forks and set them up myself, in my experience the forks i have put together have all worked exactly as they should with no issues, pushing them pretty hard on the road everything has been ok, i ran a magura front master cylinder with mine which put extreme amounts of braking force through the front and never moved the tie wrap marker any nearer than around 15mm from the foot casting.

    I'm sure with the small differences the average rider would be hard pushed to tell, if they were 10mm + difference in length i could see it being an issue. Dont forget the Daytona internals are naturally a lot stiffer to start with so i cant imagine them getting anywhere near to bottoming out with a correct set up.
     
  8. You're right Matt. The internal measurements are very important in this case. Hopefully I'll get my Daytona fork back from the machine shop today and will tear down one of my ST forks to take some internal measurements over the weekend. A few tests bottoming out the forks with different combos of tubes/internals (but no springs or oil) might also provide some answers.

    That's reassuring to know that in the real-world testing you've done the forks have been fine, even under high load. I'm 100kg without gear however (and often ride my ST with luggage), and bottom out my stock ST forks regularly, so I'm a little paranoid.

    How much of a PITA are the feet to get off the inner tubes? I've never done it before but read that heating the foot helps relieve the loctite they use at the factory when unscrewing the foot.
    Is there anything special to know about the grub screw? Just looking at it, it seems to have a little cross on it. Does it just unscrew like a normal hex grub screw or do I need a special tool?

    Sorry for dragging this out, and thanks for your answers so far.

    OS2 I'm hoping to run the same combination as you (Daytona internals in ST tubes) so hopefully all this stuff will help you out as well. Are you looking at the R or non-R ST forks? (black or pale gold outer tubes?)
     
  9. motorinmatt

    motorinmatt

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    Bit of heat on the grub screw also as these are fitted with loctite, as for the feet two pairs I worked on came off fine but the last set were really difficult, to the point were I had to carefully cut slots in the casting with a dremel to get them off, I guess it's the luck of the draw
     
  10. Cool. Thanks for the info.
     
  11. Alright guys, I did the swap over the weekend and took loads of measurements. You were right Matt, but it's good to have some numbers to back it up.

    I ended up using the Daytona forks and only swapped to the Street Triple Outer Tubes (not Inner Tubes).

    The bottom line is that YES, it's fine to use ST Outer Tubes with Daytona Forks (suspension travel remains the same and although the ST tube is slightly longer it does not cause bottoming-out problems). Also the Inner Tubes appear to be identical and interchangeable (assuming you swap feet). And the Spacers are interchangeable as well (although the Street Triple doesn't use the metal Spacer Cap that the Daytona has). Pretty much everything else is different between models however.

    But there is a caveat if you intend to use ST Outer Tubes with Daytona internals. The 8mm longer ST Outer Tube made it basically impossible for me to compress the Fork spring (using my home-made tool) enough to reassemble the Forks. I ended up drilling a second pair of holes in the Spacer so I could mount my Spring Compressor tool higher up to compress it properly. Apart from this minor setback it works great.

    If you are using a "proper" purpose-built (ie RaceTech) Fork Spring Compressor then you might not have this problem, but it will be tight compressing the spring.

    Below is a diagram with the measurements I took along with a photo of my modified Spacer.
    I might turn this into a little guide or something if there's a need for it.

    agalleries.broughtonphoto.com.au_photos_i_7CW6zS2_1_X3_i_7CW6zS2_X3.jpg

    agalleries.broughtonphoto.com.au_photos_i_PNG6Z9b_1_X3_i_PNG6Z9b_X3.jpg
     
  12. Deleted member 2280

    Deleted member 2280

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    Cracking post Kombisaurus and very useful for me as I'm fitting ST outer tubes to my Daytona (Well, K-Tech are)
     
  13. motorinmatt

    motorinmatt

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    Wow, that's pretty comprehensive there mate, good diagrams :)
    I'm guessing my fork compressor must have different mounting points as although it was a tight squeeze it was ok.
    Good to have things confirmed though
     

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