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Post by gcrank1 on Aug 5, 2023 9:56:17 GMT -5
On my '81 SR500. Ive had it a number of years, bike came out of California and has many of the old school mods that used to be in the bike mags from the intro of the SR here in The States. The tubes have individual air caps, spring sag with -0-psi is 38mm with me on. Guess I better pull 'em down to find out if progressive wound springs were installed and what pre-load spacers may have been used. Of course no idea what type and quantity of 'fork oil' may have been used, or last done. Then there is the question of the 'Minton Mods' popular back then. Lots of info on those, and 'discrepancies' of same now clarified, on the XS650 forum. Thinking if no Minton Mods to do them (c/w the updated changes) and choose the oil 'wt' based on that. Disassemble, Identify innards, Note mods if any, Drain/Clean/Flush, etc. Should be a nice easy morning's work  LOL |
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Post by stevep on Aug 6, 2023 9:36:13 GMT -5
Be interested to know what weight oil you settle on. My forks are standard, but have factory air assist valves, which I do not use as such. I've settled on 17.5w which I mix from 20 and 15w. I've also added 6mm as a stack of washers on top of the standard fork spacers. I'm around 10.5st in weight.
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Post by gcrank1 on Aug 6, 2023 12:54:15 GMT -5
Good info, thanx!
Btw, do you know your weight in pounds and what the front sag when on it.
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Post by gcrank1 on Aug 6, 2023 17:01:23 GMT -5
Decided on a 'quick & dirty' fork job today. Jacked the front up and pulled the drain plugs; drat, one is almost stripped out. While draining I go through my small screws bin and find a bit oversize, wrong thread but self tapper. Turned the head to fit the recess in the fork leg, moved the seal washer and its good to go. Popped the aftermarket air caps (I use no air but they look trick, I use them like an 'air bleed screw')The spring length, pressure and preload was all soft enough that the caps could start catching threads with just a little persuasion. Measured the cap depth, spacer and spring washer at 4 1/4". Springs are progressively wound (as I suspected, that was what most everybody was doing back in '80's), 17 7/16" long, no idea of the 'weight' but I know a bit soft for my 215ish # (in gear) as the sag was 38mm (which is about 25% of the total 150mm/5.9" of travel). I wonder if these 17 7/16" springs are oem or aftermarket? I 'flushed' the tubes in-situ with a pour through 2x of about 6oz K1 kerosene I have on hand and left to drain well. Buttoned up, poured in 7oz of ATF Mercon II since I had it, on the cSt chart it rates a 37.5, about the same a many specific fork 10w oils. Btw, cSt ratings are a very good way to compare fork oils from different makers 'so-called' weights/viscosity lables. This makes for a baseline fluid this time as I have no idea what was in there. The 7oz is a bit more than the manual, no worries. I suspect more preload would be good for me so I went digging in the spacer bin, found a nice pair of 7/16" of the right dia. and discovered those with the originals I took out is the limit to what I can get to start the caps in! I had to use a big socket and a 'T' handle wrench to get the straight down pressure and turn at the same time. Sag with me on bike now is about 28mm/1"+, a change of +10ish mm from before adding the extra preload spacer. Sitting and pumping the forks it is quite supple. Road test (The Beast starts on the 1st kick, wha hoo).....down the bumpy country paved lane at about 40mph....the front is decently compliant on compression, no nasty rebound, no bottoming, tracks nicely. Brake test: hard progressive squeeze from about 40mph and it does a controllable dive,though not squishy, and doesnt bottom. I suppose a harder rider than me may find it too much but its riding nice as a road bike. I think I could try adding another 1/2oz of fluid to each side to reduce the air space and stiffen up the lower end of the dive a bit. My goal is to use about 80-85% of the travel but the easy cable tie trick on the fork leg wont work for me as I have gaiters. I also do suspect from the compliance that the Minton Mods have been done, it really aint bad for an old fork. More road tests are required  |
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Post by gcrank1 on Aug 8, 2023 13:38:30 GMT -5
Had a nice 20ish mile run today on my fav backroad loop, it has some nasty patching, potholes, and a serious subsidence in need of repair (its a small slamming whoop as is and getting worse).
The front end is working well, little transmitted through the rubber mounted clubmans until the patching is at its worst, of course slowish speed is the best; ie, 40ish mph, but faster is not bad. NO bottoming and Im getting used to the brake dive (not as bad as it was before the fluid and preload changes).
It showed a deficiency in my Gazi HyperX rear shock settings, it was too harsh, so I went back to the comp & rebo default (left the preload as is because the sag is right), ran a short test, loosened the comp all the way, another run, comp good, backed off the rebound some and the ride is pretty close. I will concentrate on the rebo setting from here.
Btw, Im no track guy so Im sure my settings front and rear are street firmish/sporting with a lean toward comfort.
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Post by stevep on Aug 8, 2023 15:38:32 GMT -5
I'm 155 pounds all in with boots and helmet and cause 30mm of sag when I climb aboard. Your roads sound like ours and we don't get any repairs in the good weather so the mental map of potholes just turns into a library of road issues to remember on any given circuit.
I found the move to increased weight of fork oil helped especially with rebound since there's no rebound damping (that I can tell.)
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Post by gcrank1 on Aug 8, 2023 17:25:24 GMT -5
Lol, I havent been 155 since maybe a junior in HS
Regarding oils, I cant help but think 'heavier than what'? Did you change to a certain brand oil, baseline it with which 'wt' and change to a heavier of theirs? Gotta keep it within a brand to be meaningful.
Thing is, Fork Oils have no standardization and the old SAE motor oil 'wt' thing is very nominal. That means that one company's 10wt fork oil can be another's 5wt or a 12.5.
The 'cSt@ 40C and/or cSt@ 100C' rating is how the oils flows through a 1mm hole at those temps; waayy better than a nominal 'wt'.
Online charts of various fork oils are easy to find using the 'cSt' as a keyword; I have found it Very Enlightening.
It allows you to go to an up/down cSt number (higher numbers are more resistant to flow) within a brand or choosing another.
Note that it also applies to atf's and hydraulic oils which are quite similar and have been used by some for 'damper forks' with success (and far cheaper).
For instance, my heavy duty Mercon II atf has a cSt@ 40C (being specific about the temp IS important) is 37.5, well up in number from many fork specific oils. If I want to go 'heavier' I can choose an incremental increase; ie, maybe something around 45, and I know what the increment is to judge it by.
Now to be sure these damper forks are just past primitive so the cSt may be overkill, but it sure tickles my OC tendencies. Before finding out about cSt it was pretty much by guess and by golly.
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Post by stevep on Aug 9, 2023 15:58:26 GMT -5
Reading your post I realise I'm at the gosh and golly phase of my fork oil journey! I currently mix two different brands to arrive at my "17.5w" so what it is technically, I have no idea how but I know it works! Previous stabs at 15w (too soft) and 20w (too hard) and I arrived at baby bears porridge. That and the extra 6mm in fork spacer. They're actually a 20 and a 10 I mix in varying proportions. The 20 is Motull expert range. (Ha! Little did they know!) The 10 is Castrol synthetic grand Prix.
My rear shocks are very softly sprung, Hagons road shock, very light springs I have to use on the highest of 3 preloads. Couldn't take a pilllion but then I have no pillion pegs fitted. Looks cleaner minus those bulky ugly jobs. The front works well with the soft set up in the back and that's what counts for me and I got there by luck not much judgement. I had no idea the Hagons would be so soft but I like them.
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Post by gcrank1 on Aug 9, 2023 16:37:09 GMT -5
Steve, your Motul Expert 20 is a cSt @40c of '81', the Castol Syn GP 10 is maybe a '10'; at 50/50 that may make a '45'ish? Not too far from 'my' fluid at '37.5' and possibly the next incremental step up I may make. I like a softer road ride as well; have my Gazi Hyper X's set to 31ishmm sag, full soft on compression setting and still messing about with the rebound, it still hops a bit after a good bump though is has to be a pretty stout bump. They say the rebound setting is the most important after getting your sag set. The front and rear should, in an ideal world (lol), feel about the same when in your seated position and bouncing on it (still or down the road). Im using the dreaded clubmans so a good long lay-over; may go back to the V-N 'flats'...... I just today went to the next tuning step after thinkin on my overall trial results. I dropped the preload spacers I had added and put in 1 more oz per leg of my fluid (for a total of 8oz per). Also pulled the top tree to inspect the tapered Timkin's condition and reset the tension. I tighten then lightly bounce the fork side to side twice on the stops, tighten a smidge, repeat that 3 times until I still have a little 'fall over' when I turn the fork to a side but it is slowish. They always seem to loosen a bit from that in a few miles to (as Goldielocks said,"Just Right"). Front to rear is is nicely 'balanced' now over my test run, still no bottoming and the brake dive is 'tighter'; I think that 8oz of fluid (likely a max amount!) helps when the fork goes deep. The compliance over the rough, slow or at speed is really very good, plenty good for the condition many of our roadways are in. On the smooth it is touring bike pleasant Btw, I should add that Im running a tall 120/90-18 rear tire on the oem cast mag, 12 7/8" tall shocks and have an 18" front wheel (maybe an RD400 cast mag) c/w a 110/90-18 tire, the fork tubes are above the top triple clamp by 10mm. This gives a bit of a forward drop aggressive stance that handles better than I do anymore. |
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Post by gcrank1 on Aug 11, 2023 18:00:58 GMT -5
Before the crash my Gazi rebound tweak (+a few clicks) it was not hopping out of the holes as much. The trouble with external adjustments is I feel compelled to tweak  Oh well, now that reality is post-crash any tweaking and test riding is temporarily suspended until further notice. |
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Post by gcrank1 on Aug 28, 2023 14:42:33 GMT -5
Post crash refurb has gone well, all mechanical bits are back in place and the fire-up and test to the end of the driveway and back to the garage pad in 1st went fine.
The last nagging question has been if the forks (that were tweaked well out of line betwixt bars and wheel) are bent now that the rest has been eyeball and to hand aligned? I know Id like the tubes to be within .002" runout though to be sure of that requires complete disassembly, and for now Id like to make a slow speed test ride, so how to get better than the 8' standoff eyeball down the angled legs?
I have thought about using my 2' carpenters laser level to project the dot but that dot isnt going to be very precise from the top to bottom of the length of a fork leg. And it is an hour away at our off-grid cabin property (another ongoing, long term project!).
So I went with a thin-ish length of a yellow cordage I have, looped at the top cap and down the whole leg to the center of the axle. With it eye'd center top and bottom I could stand back and eye it all the way down. Not precise enough, you say?, Well, the human eye can be remarkable if the light and setup are good AND one is used to doing such work. Keep in mind that any bend from a front on hit is likely to be at the point of fulcrum just below the bottom triple tree clamps. If bent, the slider bottom where the axle sits will deviate quite a bit from a few thou' at the tree.
Glad to report that the line looked great top to bottom!
I can feel much more confident that the bike is ready for a test ride now. Now? Yes, maybe yet today!
UPDATE:
I did it, after doing a couple miles on my Suz TU250X to 'get me wheels under me'. The town road across the state highway from my driveway is similar to the one I hit the deer on; ie, overgrown shoulders, 2 cars wide but barely, no escape routes.....all I could muster was pushing my comfort zone at 30mph.....ATG this time too! Kept waiting for something to jump out of the long grass or treeline. I cant imagine how those guys do the IoM at ludicrous speed.
Got back and took the SR down the highway with better visibility, felt it out in each gear and did get up to 55mph. Bike was good but I was uncomfortable.
This is gonna take a while
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Post by stevep on Sept 1, 2023 7:57:31 GMT -5
Body remembers the shock, but it will fade. Glad the SR looks to be in usable shape, that's a real result.  |
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LOL
