My forks are not happy

[Jumbo J]

When I fitted emulators to some forks of mine that are very similar to the TM250 forks inside (1976 TY250 forks), I realised that my emulators were going to operate further up the inside of the fork tubes than the damper rod pistons do. Because of this, I smoothed out above the original swept area to avoid damaging the sealing rings on the emulators (Gold Valve) when the forks get close to bottoming. I figure your setup also puts the emulators above the old swept area

Not really, he shortened the damper rod and so the piston actually sits lower in the swept area, the pic of the two damper rods above (old and new) show that. luckily i had some spare damper rods from another set of forks i bought whilst trying to sort this problem out. as my original ones were machined down for the emulators.

here is a pic of the holed spacer and washer that fits into the bottom of the fork tube which i suspect might be the hydraulic top out mechanism (because they did not come back with any top springs in them and i never took them apart before i sent them away to see if they were in there or not)
 

[Tomas]

Sure you have enough oil in your fork legs. That looks like a lot of wear for well oiled metal parts. There must be something that is too tight, something is missing or something is not getting enough lubrication.

[David Lahey]

I wouldn't be impressed if someone shortened the damper rods on my 1970s bike, unless it was being done to lower the bike for dirt track or road race use.

[pokey]

So the valve is just rubbing up against the inside of the staunchion  chewing itself to pieces as it
 A) hasnt enough clearance or missing bushing
B) its loose on the top of the stem because of insufficient spring preload.


hmmm. what a headache.

[Nathan S]

At full extension, how much slop is there between the upper tube and the lower leg?
If the lower legs are worn, then wear will be greatly accelerated - maybe the wear on the emulators is collateral damage, rather than the cause. 

The fact that you've tried different lowers doesn't mean much when we're talking about dirt bike bits that are over 40 years old.

[Oldfart]

Hmmm very interesting ....

[Jumbo J]

At full extension, how much slop is there between the upper tube and the lower leg?
If the lower legs are worn, then wear will be greatly accelerated - maybe the wear on the emulators is collateral damage, rather than the cause. 

The fact that you've tried different lowers doesn't mean much when we're talking about dirt bike bits that are over 40 years old.

there is some slop at full extension with no oil, but if it was there prior to the conversion it would have been picked up otherwise why go ahead without bushing the slider or identifying that it was not serviceable, i would have expected?

There are also scuff marks on the swept area of the inner tube surface where the emulators are located
There was no issue with gouges, slop, or weird noises prior to sending them away to be converted.

[Nathan S]

I don't think there's much question that the emulators scraping inside the upper tubes is the source of the swarf and wear. But why...

Is it too obvious to suggest that maybe the emulators are simply too large in OD?
What happens if you slide the emulator up and down inside the upper leg? Does is slide freely for the entire range of travel?

[Jumbo J]

I don't think there's much question that the emulators scraping inside the upper tubes is the source of the swarf and wear. But why...

Is it too obvious to suggest that maybe the emulators are simply too large in OD?
What happens if you slide the emulator up and down inside the upper leg? Does is slide freely for the entire range of travel?

yeah it seems too Nathan, but as noel mentioned previously there is no method of retaining the valve in "a correct" position on top of the damper rod, which even though there is preload on it from the spring there may be a situation where it sits unevenly in the inner tube and causes the aluminium to sheer off it. on the flip side the valve is a pretty neat fit inside the inner tube so probably less likely to sit unevenly i would imagine. I don't have a telescopic gauge but as mentioned above i did put the vernier on the OD of the valve
 and compared it to the original compression spring OD and the valve was .6mm larger. so I'm tending to think the valve doesn't have enough clearance at this point. 

when riding it, on the big hits, it feels like they are locking up -ie just not soaking up the bumps, and BIG jarring on the bars. the damper rod holes have not been drilled out- they are the same as on the std rod with no additional ones added either. Would that be the reason it is "locking"  (for want of a better word) slow bumps are fine hard hit are NOT! Don't want to confuse or over complicate the topic but there are a few things that are causing me grief, just not sure if they might be interrelated or not.

[fred99999au]

So you are effectively running stock compression damping on top of a cartridge emulator. I cant see that working well.

The idea with the cartridge emulator is to remove the stock compression damping and just use the emulator. There is no going back (unless you call welding the holes up and then redrilling them) once you install them.

Find the manufacturer and follow their instructions for fitting the emulators and you might have a better chance of having them work.

I think I would be using your spare full length damper rods and drill them as per the instructions and fit them.

[brent j]

The fork internals look similar to my TM125L

The piston floats on the shaft under the head of the damper rod and it is held in place by a circlip underneath.
If there is any mis-alignment in the damper rod when fitted the float in the piston allows for this and still gives the same degree of sealing as if it was straight.
The cartridge emulator appears to sit in a sleeve above the head of the damper rod and is a close fit inside the stanchion.

If your damper rod does not sit straight when tightened the float in the piston will take up the difference but the head of the damper rod, and the emulator, will be off to one side.
This may be causing the problem.

I’d suggest putting the forks together completely but with just enough oil to lubricate everything but leave the holding bolt in the bottom finger tight.
Compress the forks and see how it feels’
Now tighten the holding bolt and repeat. If they are tight or noisy I’d guess your damper rods are not in the centre of the tubes.
The other way is to install the damper rods into the sliders and look down the inside to see if they are concentric

[Nathan S]

The top-out spring doesn't have to travel up inside the upper fork leg - it will generally sit in the bottom of the tube as the fork compresses.

Everything Fred9999 said is spot-on. The main point of having emulators is to avoid that "spike" on bigger hits - but if the stock dampening is still in play, then the emulator can't help - removing the emulator is likely to improve your fork action.

I think Brent is onto something. If the head of the damper rod isn't square, the act of compressing the main spring will tend to force the top of the damper rod sideways into the inner of the fork tube.

[fred99999au]

Do the emulators fit snugly into the top of the damper rod? They shouldn't be rocking in any way, shape or form.

[Jumbo J]

The top-out spring doesn't have to travel up inside the upper fork leg - it will generally sit in the bottom of the tube as the fork compresses. - There is no top out spring in these forks anyway, see the pic at the top of this page, supposedly a hydraulic top mechanism?

Everything Fred9999 said is spot-on. The main point of having emulators is to avoid that "spike" on bigger hits - but if the stock dampening is still in play, then the emulator can't help - removing the emulator is likely to improve your fork action.or drilling out the damper tube oil galleries according to manufacture spec?

I think Brent is onto something. If the head of the damper rod isn't square, the act of compressing the main spring will tend to force the top of the damper rod sideways into the inner of the fork tube.fair point, wonder why that process wouldn't have been followed then during assembly, post conversion. So a similar principle to aligning brake shoes in the hub before tightening up the axle then - is this normal practice when assembling forks?

[Jumbo J]

Do the emulators fit snugly into the top of the damper rod? They shouldn't be rocking in any way, shape or form.

no mate they rock around anything but snug!