M750 Showa forks.....rebuildable ?

[utopia]

I have a yr2000 M750 fitted with non-adjustable forks as std.
These are not the usual Marzocchii units ...the fork lowers clearly bear the Showa logo.
They are a little choppy over rough surfaces at lower speeds, but seem fine on smoother surfaces and at higher speeds.
I've been thinking for some time that I might try and tweek them rather than fit some replacement forks with adjustability, possibly starting with a pair of progressive springs.
Trouble is I may then decide that the damping also needs a tweek and although I know that the cartridges in the Marzocchi forks which are usually fitted are pressed together and are not rebuildable, I'm not sure that the same applies to these Showa units.
I'm a little wary of changing springs only to find that they need further improvement to the damping which is not possible (beyond changing oil grade, air gap etc) without massive expense (in which case the better option would have been to start off with replacement forks in the first place).

So my question is, does anyone know what the internals of these non-adjustable Showa forks are like.

[Darren69]

I fitted Hyperpro springs in my adjustable Showas and found I had to back off the rebound damping a bit as it was set too high, it had been fine with the standard springs. I think the oil you get with the spring kits is a higher viscosity than the standard oil. I seem to recall it went from 7w to 10w.

[utopia]

Yes, my thinking is that its far more important to get the springs right (both spring rate and linear/prog) after which I may find that the damping is near enough for my needs and any minor tweeks can be made via different viscosity oil......hence I may not need adjustable forks anyway.
I'm very tempted to fit Hyperpro progressive springs....however I'm not even certain that the std springs in my forks are linear.
The reassembly instructions for these forks (according to Haynes) say to make sure that the TAPERED end of the spring is fitted uppermost, but although that might suggest that they are progressive, it may just be a short reduction in dia at the end to suit whatever the spring fits to, ie spring seat, top cap or whatever.
The forks do feel like they are too stiff at the top, so I suspect that they are linear, but I'm loathe to buy progressive replacements until I'm sure.
The bike specs that I have do not give any details other than oil weight, spring length and airgap.....no mention of spring rate or type.
I'm not even certain that they don't have a hidden damping adjustment in the bottom of the fork lowers to be honest, but I suspect that they don't (which is a shame because that would be enough for my needs really).
Anyway, this winter the front end is up for a full overhaul, so its time to gather as much advance info as I can.

[jerry]

I have a M750 ,, standard springs are linear ,,, i have 8.5nm Ohlins springs in and 5w oil and its OK

not as good as my S4 with 996 forks and ktech valves and ohlins 7.5nm springs and also fully adjustable but its good enough

[Mr Gazza]

A good indicator of any adjuster being present at the fork bottoms, would be a hollow spindle with two cut outs in the end of the spindle wall at the offside end.

The cut outs should align with the split below the axle hole, up and down on the fork center line.

This makes sure that holes in the spindle line up with the adjusters buried in the fork bottoms, and allows access right through the spindle and into the fork with a screwdriver.

[utopia]

Ah, thanks Jerry, I thought you might have some info.
What year is your 750 though, and do you know whether your forks are Marzocchi or Showa ? ....mine say Showa on the inside of the fork bottoms.
Also, do you know what rate your std springs were ?
And, if I may be so bold as to ask, what sort of body weight are you (I'm a medium/skinny six-footer, probably no more than 12 stone max).

Actually, if they are Showa like mine, do you know if there is a hidden damping adjuster underneath ?

I do quite like the simplicity, both of design and of appearance, of these non-adjustable forks and they don't seem to be a million miles away from decent, so I'm inclined to keep them if they can be made to work just that little bit better.

[utopia]

Yep, my forks do have the bigger dia spindle, hollow all the way through, and with the cut-outs and the hole.
I can't quite see whether there is anything beyond the hole in the spindle or not, though.
I've tried squinting from underneath to no avail and my dentist's mirror is too big to get inside the hollow spindle.
I have prodded around with a selection of allen keys and a Philips screwdriver but nothing seems to engage.
And even if it did, I wouldn't be sure whether it was an adjuster or merely a fixing for the fork internals.
The cut-outs and hole aren't perfectly aligned though, so that might be muddying the water.

[pompone]

There's a bolt on the underneath, behind the spindle recess to fix the internals. Also an Allen grab screw on the inside of the leg to hold the stanchion in (this is threaded on the fork bottoms) on your one you'll have a bit on the bottoms that on adjustable has a needle adjuster.

[Mr Gazza]

I think on mine that the adjuster is a quite small slotted screw, and quite a good way into the fork too.

Alignment of the slots is essential to get the holes in the right place for access...:D

[utopia]

Had a poke with a thin, flat screwdriver, but although it passes beyond the spindle by about 15mm, it doesn't engage with anything.
The misalignment of the holes is only very slight......though maybe enough to prevent a large allen key from engaging.
At the moment, my best guess is that mine have no damping adjustment, as Max suggests, and that the hole is access to a fixing for the internals.
This is not a big issue for me just now though as, like I said, I'm more interested in getting the springing right and reckon I may not need the luxury of damping adjustment to get the forks good enough for my needs......or at least I can't really detect such minor issues at the moment because more major issues (ie springs) are masking them.

Then again, if the internals are pressed together and not rebuildable (ie like the Marzocchi ones), I might be inclined to fit some different forks anyway.

[Zimbo]

The Showa non adjustable forks are of the cartridge type, and the damping characteristics can be fine tuned with replacement cartridges being available. Maxton for instance will rebuild the forks with a custom cartridge and springs, no doubt K-Tech will as well!

[Nickj]

Don't forget that the air gap is as important as the oil viscosity especiall towards the last third of the forks stroke range,
Air as we might remember from school physics is compressible and it will compress progressively. So from a 'normal' setting, that is adding the prescribed volume per fork leg and then making sure the oil levels match.

If the last third of the suspension travel is a bit hard over rough road surfaces (most roads it seems these days) then you want to remove a little oil to increase the gaps. Try 20mls initially, ride and then incrementally remove 10, then 5 OR add back to the level in 5's untill you are happy with the end travel.

If the last third of the travel is a bit soft the add a little oil to reduce the air gap. As before test and see how it feels then fine tune.

As long as the damping cartridge is covered with oil the level then the damping will still work, its independent of the air gap and is there to control the compression/rebound of the spring.

If you have schrader valves on the fork tops then you can add a little pressure to a fixed air gap. More pressure gives a similar effect to a HIGHER (smaller volume) oil level.
Dropping pressure gives a similar effect to a LOWER (smaller volume) oil level.
In both cases the effect is less than a real change in the air gap volume so is really only a fine tuning aid.

I spent quite a time on dirt bike forks which you want to work well over their range of travel in fair extreme conditions. Same works on road bikes

[utopia]

Yes, I've been pondering the airgap, but my gripe with the forks at present is their compliance at the upper end of their travel.
In dirt bike terms I guess I would describe it as choppy over the whoops (is that what you call those multiple humps in the track ?).
My thinking is that the airgap doesn't become significant until the forks are compressed beyond my area of interest.
Might be worth a bit of experimentation though since, as you say, the effect of the "air spring" will be progressive.

To be honest, these forks are a far better design than any I've had before as most of my experience is with older, "right way up" forks with relatively spindly stanchions.

One other area of pondering is that I don't want to make the ride more plush over the bumps at the expense of introducing too much fork dive under braking.
So I'm probably only looking for a small tweek to their existing performance.

[gary tompkins]

Adjustable forks have damping adjusters top and bottom. So if yours hasn't got anything visible at the top, then it won't be externally adjustable for damping or preload. Best option with non-adjustables is usually to get them rebuild and set up for your weight/riding style by a specialist like Maxton