Author Topic: XS650 Fork Damper Valves in RD400c 34mm Stanchions  (Read 451 times)

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Offline Doland

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XS650 Fork Damper Valves in RD400c 34mm Stanchions
« on: January 13, 2021, 06:53:54 AM »
Hi Everyone,

Does anyone know if the Mikes.xs damper valves at https://www.mikesxs.net/blog/how-to-install-the-xs650-fork-damper-valves/ fit in a rd400c's stanchions? Someone I spoke with swears they do... I mentioned maybe he was thinking about the rd400f Daytona as it has 35mm forks, but he confirmed he was referring to the rd400c.

If they fit, it would be considerably more cost effective than the Race Tech gold valves, however I suspect he is mistaken.

Offline 5port

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #1 on: January 13, 2021, 09:02:45 AM »
Well, I have not tried these yet but.. Race Tech list different emulators with different diameters for these forks with different diameters and different damper rods. I think someone posted about machining the larger mikesxs ones down to fit a while back.
My own opinion with the 73-77 34mm forks if you find them soft is that just some extra preload using about a 20mm alloy spacer and a fresh oil change with 10W-30 can help.  Worth checking the spring length is stock at the same time, they might have been swopped out or sagged, mind you I haven't seen sagged springs on my RD's.  Cheers

5port   
« Last Edit: January 13, 2021, 09:48:19 AM by 5port »
5port

Offline paul n

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #2 on: January 13, 2021, 10:26:41 AM »
I have YSS valves in my 250e which are alot cheaper than the racetec equivalent, however these are for 35mm fork legs.

I have read on here that you need to modify the yamaha damping tubes to fit 34mm emulators as the design is different but I have no experiance of this.
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Offline 5port

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #3 on: January 13, 2021, 10:39:31 AM »
I have YSS valves in my 250e which are alot cheaper than the racetec equivalent, however these are for 35mm fork legs.

I have read on here that you need to modify the yamaha damping tubes to fit 34mm emulators as the design is different but I have no experiance of this.

Yes, the later Yam 35mm forks (with top-out springs) have an open top rod, but the 34mm earlier rod has a solid top that has to be modified to fit the Race Tech emulators.

5port
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Offline D Peacock

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #4 on: January 13, 2021, 02:45:32 PM »
On the emulators I have for the 34mm forks the instructions tell you to drill extra holes in the damper rod (basically to render it ineffective) so all damping is handled by the valve in the emulator. There should also be a bush that sits on top of the emulator and stops oil bypassing between the inside of the stanction and the emulator body.
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Offline Tailchaser

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #5 on: January 13, 2021, 07:36:08 PM »
Hi Paul,

Where did you get the YSS valves for your 250E from as I can't find any 35mm ones only 33.5 and 36 ?

cheers,

Jeff
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Offline paul n

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #6 on: January 13, 2021, 08:44:44 PM »
Hi I got them from brook suspension. Its the 26.5mm size which is slightly smaller than the internal diameter.

Here is a link as well as my write up when fitting and trying them out.

https://www.brooksuspension.co.uk/fork-internals/yss/yss-fork-emulators/

https://www.aircooledrdclub.com/smf/index.php?topic=57599.0

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Offline 5port

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #7 on: January 13, 2021, 10:06:33 PM »
Hi Paul,  Thanks for highlighting your findings again.  :)
One thing I note having looked more closely is that the dedicated fork oil specs are listed and rated at temperatures that RD forks do not operate at in normal UK weather.  If you take 20*C as a likely UK day, the RD forks may warm to 26/27*C.  That is a big factor.  I do not know how real cartridge forks respond with their small separate oil filled damper units, maybe they run at higher oil temp like rear units?
I suspect VI's or oil temp related viscosity stability judged between 40 and 100*C is of little relevance to early RD forks because the viscosity usually increases rapidly below 40*C and this is still above our old RD forks in the 20 to 30*C range, except in a heatwave with molten tar!  :D
The available oils with dedicated viscosity ranges are the high quality multigrades.  The best of these are truly alot more visco-static, and specified between minus 18 and plus 100 degrees C.   Yamaha specified 10W-30 50 years ago for that reason on the simple damper rod forks, and the improvements I can find are; that the best ones that match the old RD forks now are even more visco-static at 0W-30 spec and, the best are full Synthetics with superb lubricity, anti foam etc.  :)
Even with emulators, I suspect the old RD forks will work well with high quality multigrade.  I think the VI aspect at the working temp is probably better covered in the old forks by an appropriate high spec multigrade like fully synth 0W-30.
The list of speciality fork oils and their specifications is quite amazing, especially how many of the specifications don't match what you might expect!  :-\
Cheers

5port 
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Offline paul n

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #8 on: January 13, 2021, 11:58:01 PM »
Hi 5port
Yes I was suprised at the oil specifications having a none to accurate labelling.

As for the type of oil, multigrade or specific fork oil, the only way to find out which is best for a persons specific application is to test by trial and error.

It would be an interesting comparison if someone trys it out.


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Offline 5port

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #9 on: January 14, 2021, 07:50:47 AM »
Hi 5port
Yes I was suprised at the oil specifications having a none to accurate labelling.

As for the type of oil, multigrade or specific fork oil, the only way to find out which is best for a persons specific application is to test by trial and error.

It would be an interesting comparison if someone trys it out.

Yes, the personal preference for handling can only be done by trying it out but, that can be a lot of work.
Cheers

5port
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Offline 5port

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #10 on: January 15, 2021, 11:48:22 AM »
A very rough guide to damping that I read includes checking the rebound rate.  Rebound is quite important and, is easier to check than compression.  You test by compressing the forks as far as you can, then releasing the load and timing the stroke back to rest.  It should take "about a second" supposedly.  That seems a bit slow to me, I would say more like half a second.  But, the main thing is that there should be damping, not shooting straight back up in no time or, overshooting up and down.  Also, overdamping with real slow coming up is bad too.  I would also say, you should be doing this with the forks about 27*C.  Stone cold winter in the garage might be way off.    A good comparison is when you drain the forks, do both together and compare with no oil in!  ;) Cheers

5port   
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Offline Doland

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #11 on: January 16, 2021, 08:48:48 AM »
Hi 5Port and Paul N,

Thanks for all the information. I think for now I'll just put some race tech shocks in and see how it does. Maybe I'll re-visit modifying the damping tubes and spending some more money next winter. I had put damping valves on my other bike a few years back and really appreciated the improvements to the fork damping it provided.

I appreciate the link to a possible alternative to the expensive race tech gold valves Paul. I'll need to measure up the internal bits of the suspension to better understand what could possibly fit in the 34mm RD400c forks.

FYI, I had originally considered trying to turn a set of oversize damping valves down on a lathe, however I don't think it would be wise. The damping valves appear to have some fairly large cavities inside them to accommodate the valving. I think reducing their outer diameter a mm could significantly weaken them and lead to failure.

Offline Doland

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #12 on: January 16, 2021, 08:50:59 AM »
On the emulators I have for the 34mm forks the instructions tell you to drill extra holes in the damper rod (basically to render it ineffective) so all damping is handled by the valve in the emulator. There should also be a bush that sits on top of the emulator and stops oil bypassing between the inside of the stanction and the emulator body.

Hi D Peacock. Can you let me know if you are using Race Tech Gold Valves, or something else? What bike did you install them on?

thanks,

Don

Offline 5port

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #13 on: January 16, 2021, 12:09:59 PM »
When you say Race tech, do you mean $1,000 Race Tech?  ???

5port
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Offline Doland

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Re: XS650 Fork Damper Valves in RD400c 34mm Stanchions
« Reply #14 on: January 16, 2021, 06:24:21 PM »
When you say Race tech, do you mean $1,000 Race Tech?  ???

5port

Hi 5Port,

I should clarify, I'm referring to the springs below in USD. I'm going to stick with just the springs this year, and may think about cartridges again next winter. I'm not familiar with the $1000 Race Tech option.

Fork Spring Series (pair) - FRSP S2341  - $129.99
Gold Valve Cartridge Emulator Kit  - FEGV S3002 - $209.99

source: https://racetech.com/ProductSearch/12/Yamaha/RD400/1976