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General Category => General Discussion => Topic started by: Stevex on June 07, 2018, 01:44:13 PM

Title: Fork internals transplant, how much oil?
Post by: Stevex on June 07, 2018, 01:44:13 PM
I'm now on the final stretch of completing what I hope will transform my original LM2 forks.
With a lot of advice from huub  :thumb: I've nearly finished fitting some 1997 Honda VFR750 Showa fork cartridges inside the original sliders and stanchions.
The hard part is deciding how much fork oil to put into the forks.
Does this make sense...The Honda sliders and stanchions when fully collapsed (ie, in the oil filling config) have a height of 63.5cm and require an air gap above the oil of 177mm. The Guzzi's height is 56cm, so has a comparable air gap of 156mm.
63.5cm divided by 17.7 = 3.6
56cm divided by 3.6 = 15.6cm
The Honda stanchions are 41mm in diameter and the Guzzi's are 35mm so I'm not sure this is a comparable oil level, but I can't think of any other way except the hit and miss method of adding oil until it feels right.
Recommendations / suggestions?
Title: Re: Fork internals transplant, how much oil?
Post by: Sheepdog on June 07, 2018, 03:26:24 PM
Unless the new internals take up a great deal of volume, I would put the oil at Guzzi's recommended level for the Lemans fork. At least as a starting point...
Title: Re: Fork internals transplant, how much oil?
Post by: TOMB on June 07, 2018, 03:45:06 PM
.5oz to start. That's ATF
If your adapting 72 Eldo fork then 5 oz fork oil..
 Of course it also depends on what manual you use as a source.
TOMB
Title: Re: Fork internals transplant, how much oil?
Post by: Stevex on June 07, 2018, 03:48:27 PM
Can't go by Guzzi recommendations for the original forks.
The forks original internals used sealed damper units with only enough ATF to provide lubrication.
Title: Re: Fork internals transplant, how much oil?
Post by: Rough Edge racing on June 08, 2018, 05:37:56 AM
 No need to get over technical in my opinion from experience...Just leave the same space above oil as the Honda recommendation...AT F is about 7.5 weight.. Showa most likely specs 5 or 10 weight fork oil...There is a difference....
Title: Re: Fork internals transplant, how much oil?
Post by: huub on June 08, 2018, 06:31:29 AM
No need to get over technical in my opinion from experience...Just leave the same space above oil as the Honda recommendation...AT F is about 7.5 weight.. Showa most likely specs 5 or 10 weight fork oil...There is a difference....

start with getting the ride height right ( use the ride height adjustment or spacers on top of  the springs)
using the honda air gap is probably a good start, if you experiance too much dive, add some oil.
( the air gap acts as a secundary - very progressive - spring)
oil grade is pretty much up to your personal preference , just mix until you have the feel you are looking for
I hate stiff suspension , and ended up with very thin oil.
 

Title: Re: Fork internals transplant, how much oil?
Post by: Stevex on June 08, 2018, 07:37:25 AM
start with getting the ride height right ( use the ride height adjustment or spacers on top of  the springs)
using the honda air gap is probably a good start, if you experiance too much dive, add some oil.
( the air gap acts as a secundary - very progressive - spring)
oil grade is pretty much up to your personal preference , just mix until you have the feel you are looking for
I hate stiff suspension , and ended up with very thin oil.

I measured the spring rate of the original longer spring and was surprised to find it came out at 1kg/mm; quite a stiff spring.
I have fitted a 25mm nylon spacer above the spring and have used 5w oil. Decided to start with 165mm air gap and if necessary add to suit.