well that didn't work(Forks)

Went for a test run, but as soon as I got the bike off the lift it felt weird! I have way too much rebound, so much so that when I bounce on the forks, they stay down and slowly retract to ride height, but visibly slow all the same. On the other hand there ain't much compression dampening going on, the forks bottomed out a couple of times.
So I will go back to standard damper pistons, but I might make up some modified compression dampening washers, to try and get a bit more and bump up the preload a tad?
On a brighter note the engine is freeing up nicely with 120 miles down now, the JS pistons and rod package are very smooth, I think the Altair ignition is helping too, she idles rock steady at 1K revs and is really smooth on the transition from idle until the ISO's take over. Drained the running in oil, same to throw it out, but in goes some more non friction modified for another 100 miles.

Cheers Richard

Hi Stockie2 , I would like a really good detailed update on your JS running gear, now that I have two '730 850's , I would like to build one with lots of good bits inside one of them.
Will probably be up for a set of carbs from Jim, so may end up getting extra bits to travel with them to keep them company all the way from the States to NZ.
If you already hava a thread on the build just point me to it via a link.
THanks Mike

Mike,

I only have experience of my 850 and a mates 750, with the Norton pistons I noticed the 850 a lot more vibey than the mates 750, not as sweet. Fast forward the forged JS pistons with Carillo rods and, mate she is nicer than the 750 in my opinion. The pistons and rods make up for a 1/3 less reciprocating weight than a standard set up. So either you can rev the bejessus out of it, that is not my bag, or simply marvel in a smooth ride. It is hard to be subjective, but I think the engine is more punchy too. I fitted the Total Seal rings, that Jim offers, these make the kicking a little firmer, but gee, she draws up the fuel real good now, hardly need to tickle the carbs and the oil stays clean too. So yes I recommend Jim's setup, if you had an Atlas or rigid mount motor, it would be the first thing to modify!

Cheers Richard

Ok Richard, sounds like the go then, a nice project for me next year building a mill with nice goodies, but not to severe, still want it to idle and be able to kick start it!!!
Keep us all posted please.
Did you take any pics during the build?
Regards Mike

stockie2 said:

Went for a test run, but as soon as I got the bike off the lift it felt weird! I have way too much rebound, so much so that when I bounce on the forks, they stay down and slowly retract to ride height, but visibly slow all the same. On the other hand there ain't much compression dampening going on, the forks bottomed out a couple of times.
So I will go back to standard damper pistons, but I might make up some modified compression dampening washers, to try and get a bit more and bump up the preload a tad?
Cheers Richard

Click to expand...

Sounds like the wrong grade of fork oil used :?:

Sounds like the enemy of good is better just doing the kit per directions and adjust it from there must just find the right oil and stop.

20 wt. fork oil and stock valving works for me.

I"ve had same symptoms on old forks so suspect the insides of the stanchions are rusted up grabbing the springs action. 20 wt is fairly thin for Roadholders so not likey the issue. If not then a real mystery we all can learn from.

hobot said:

I"ve had same symptoms on old forks so suspect the insides of the stanchions are rusted up grabbing the springs action. 20 wt is fairly thin for Roadholders so not likey the issue. If not then a real mystery we all can learn from.

Click to expand...

On another thread he states he is using 10 weight oil :!:

OK 10 wt is pretty thin to function in regular Roadholders and ya can't trust the manufacturer's oil grading scale either. I thought the complaint was forks sticking then releasing causing upsetting handling over lumps. He mentions making clearances tighter in damper valve and non stock -ugh- regular off the shelf progressive springs, so still possible the spring sticking in the stanchions or the valve binding d/t some damper rod flexture. That combo can cause stiff and over reaction of forks that seem to reverse your inputs and steering compensations. Must roll stanchion against each other to check them for restriction straightness as can't assume online or at home anything at this point of frustration.

Might try forks w/o the damper valve in there to see how much its doing or not doing. Don't over fill as I've done to find horrific handling after 1/4 mile pleasure of extra bump resistance on rough driveway, whoowhooie. Had to slow to under 10 mph to make it back w/o hitting fence or bluff rocks. 175 ml is most I put in now.

Okay, now I am on to something. The forks now have some nice compression dampening and don't bottom out on drive way transitions etc. I checked the forks action without loading from springs and dampers and they slide up and down nicely, with the wheel and guard installed. So my new bushes are good and the sliders are not bent or misaligned.
I have changed my damper pistons, made them out of bronze to tighter clearances than my originals. I have 7 thou clearance on the piston to dampers and made the end float clearance on the piston 25 thou, this is about half the original. So the theory is the end float clearance determines oil flow on compression, oh I also halved the original clearance between the damper piston and the damper rod, I can report back that on 10 weight Motul Expert oil I have strong rebound still and now some decent compression dampening. I did also add a 1/2 space to further preload the progressive springs, so now I have the std thick washer, plus 1 inch of alloy preload. I am rapt with the fork action now, did a test through the Royal National Park just south of Sydney, with my son on the back and now the back end feels, ho hum? But the forks are great not mush, but not over firm. And no top or bottom outs even on the nasty bumps. I may even try a lighter grade, just for fun. Before the ride I was dissapointed that the rebound seemed still to strong with a slow response to returning to ride height after bouncing on the front, but in practice this does not seem to be an issue.

Cheers Richard :wink: