OzVMX Forum
Clubroom => Tech Talk => Topic started by: Jumbo J on January 20, 2016, 09:01:45 pm
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Any suggestions out there on what might be causing this severe fork gouging problem. (TM250L forks)
I had PD valves fitted and after the first race deep gouges started to appear on the stanchions. Got RAD to re-chrome them, same problem. Tried a different set of sliders, re-chromed again-same problem. There was also fair bit of fine alloy particles floating in the oil when i drained them, possibly came from the emulators by the look of the marks on them.
- quality 10-15wt Motorex oil used. 120mm air gap.
- damper rods modified (but shortened :() to take the emulators.
Suspect the material being stripped off the emulators may be getting lodged between the stanchion and slider which could be causing the deep gauges - but why?
ideas anyone?
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_150917_zpsulktdgtn.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_150917_zpsulktdgtn.jpg.html)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_153801_zpsupcsb54o.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_153801_zpsupcsb54o.jpg.html)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_140553_zpseujgrgkr.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_140553_zpseujgrgkr.jpg.html)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_142920_zpspemry6id.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_142920_zpspemry6id.jpg.html)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_151519_zpsqo5xmvyo.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_151519_zpsqo5xmvyo.jpg.html)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_170634_zps37s41wo8.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_170634_zps37s41wo8.jpg.html)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_160338_zps0hc9zdo7.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_160338_zps0hc9zdo7.jpg.html)
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Dislodged seal gaiter spring?
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I'm no expert but am thinking the emulators are too tight a fit in the fork leg.
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Dislodged seal gaiter spring?
meaning? - you got a bit more detail Momus
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Im trying to visulise this in my head and Umm. why shorten the rods? Wouldnt you have to shorten an internal spacer or spring as thats the part that the valve is going to replace the space as far as My head sees it or your spring is preloaded a lot more.. if thats the case try it with new rods unshortened. I wouldnt rechrome again untill you sorted this
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Looks to me like the emulators are not " located" on top off the damper rod
which would allow the spring to push it to the side of the staunchion which probably has a fairly course surface finish
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what is the surface finish like inside the fork tubes where the damper rod pistons and emulators run?
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Doesn't the damper rod go inside the stanchion? Looks to me like the stanchion is rubbing on the slider, so maybe a slider bush?
Having said that, the chrome is bloody hard stuff. Is it maybe a deposit of slider material on the stanchion instead of gouging?
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when you re assembled these, was there two brass bushes included in that assembly ?
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Bingo David, thats what i think..
the emulators are suppose to be inside the staunchions then the spring sits on that.
if the em is inside the leg on a shortened rod. I guess it will still dampen but the spring preload will be out so its loose and not holding the valve and rod tight. Then it rattles around and rubs on the inside of the leg..
have i got it arse up? id ask myself this question like i just did.
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Looks to me like the emulators are not " located" on top off the damper rod
which would allow the spring to push it to the side of the staunchion which probably has a fairly course surface finish
Yes Noel, the emulator can float on top of the damper rod, there is nothing retaining it in place. furthermore the OD of the Emulator is .6mm larger that the OD od the original springs - i don't have a relscopic vernier to get an accurate measurement of the ID inside the fork tubes
what is the surface finish like inside the fork tubes where the damper rod pistons and emulators run?
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there are scuff marks on the swept area inside the fork tubes David
Doesn't the damper rod go inside the stanchion? Looks to me like the stanchion is rubbing on the slider, so maybe a slider bush?
Having said that, the chrome is bloody hard stuff. Is it maybe a deposit of slider material on the stanchion instead of gouging?
No bushes in this old sliders fred, alloy ID of the slider runs up against the OD of the staunchion.
and on top of all that the original oil gallery the holes in the damper rod have not been enlarged or drilled out, nor are there any additional holes drilled in there.
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My forks are not happy also, tried to tidy them up with the bench grinder- polisher >:( The knives were pretty pissed off too and the spoons ................... :-[
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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
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when you re assembled these, was there two brass bushes included in that assembly ?
Well i didn't assemble these, at the time i didn't know enough about it so i paid someone "who did"
if you mean were there two brass bushes included in the emulator kit , then no. the photos show all there is re: the damper and emulator assy. if you mean where there brass bushes in the slider - also no just alloy agains hard chrome.
Pokey they are assembled in the correct place, inside the fork tubes on top of the damper rod with the spring on top of that with pre-load. the standard variable rate springs with replaced with linear one as part of the conversion job.
There were also no top out springs in there, but i'm not sure if that is standard or not on 74/75 TM250 forks. there was a holed spacer and washer set up located inside the tube at the bottom which could be for a hydraulic top out mechanism instead of a spring - if anyone knows?
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(http://3.bp.blogspot.com/-klgvNodcsSM/VDv6BxAbXFI/AAAAAAAAAQs/e4VaCtMkE6w/s1600/pd_fork_assembly.jpg)
If they are assembled like above then chopping the rod just reduced your travel and as said alows the fork to run on a different part of the staunchion
the spring and internal preload spacer needs to be reduced to allow for the valve dimension. this will hold things correctly with the correct spring preload. i would remeasure everything
if not assembled as above then ther's the problem.
if the spring isnt correctly loaded its going to allow things to move around.
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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)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160117_164525_resized_1_zpspc3crvg3.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160117_164525_resized_1_zpspc3crvg3.jpg.html)
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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.
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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.
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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.
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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.
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Hmmm very interesting ....
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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.
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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?
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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.
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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.
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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
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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.
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Do the emulators fit snugly into the top of the damper rod? They shouldn't be rocking in any way, shape or form.
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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?
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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!
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There's a top-out spring visible in your second and third photos?
Yes, drilling out the damper rods is the preferred option!
The damper rods should be square and centred, but after 40+ years and some questionable machining, anything is possible. Old Yammie forks had fibre sealing rings on the head of the damper rods, which would help to keep them centred and minimise wear if they ran into the inside of the fork tube (along with the obvious task of improving sealing).
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There's a top-out spring visible in your second and third photos? actually nathan those springs did not come out of the forks after i got them back. i was experimenting with them, and besides with them installed the travel is further reduced than it already is after the damper rods have been shortened :(
Yes, drilling out the damper rods is the preferred option!
The damper rods should be square and centred, but after 40+ years and some questionable machining, anything is possible. Old Yammie forks had fibre sealing rings on the head of the damper rods, which would help to keep them centred and minimise wear if they ran into the inside of the fork tube (along with the obvious task of improving sealing).
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I’m not a suspension guru (my disclaimer) but I have fitted some emulators.
They are a tight fit so a bit fiddly to fit in small diameter fork tubes, while yours may be scraping I don’t believe the damage to the fork sliders could be caused by some alloy ‘paste’
That is some serious damage to the sliders and it looks to me that the forks are missing the bushes from the top of the lower sections resulting in the forks being metal on metal during their travel.
Also for that amount of shrapnel I would expect the emulators to be quite damaged as well but it looks like minor damage.
Look up a parts diagram and do a roll call for all parts.
As already mentioned the damper rods should have been drilled out as the original damper holes are still controlling the oil flow before the oil reaches the emulators, therefore making a lot more compression damping. Whoever fitted them didn’t follow the instructions making fitting of the emulators a wasted effort.
The damper rods should not have been shortened as this reduces travel, the springs should have been shortened to make room for the length of the emulators
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Most of the old forks didn't have bushes. But I otherwise agree.
Jumbo, In case it isn't perfectly clear by now: don't go back to whoever fitted the emulators.
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When I fitted emulators to my TM125 forks I removed the cap on the damper rod and the floating piston. I made new damper rod tops to suit the emulators directly and fixed these to the damper rods.
The new damper rod tops had an “O” ring to seal against the inner fork tube and stop metal to metal contact.
When I striped the forks I found wear marks on one side of the damper rod top which indicates the damper rods are not sitting central.
I machined the bottom of the damper rods so they were square and made sure the damper rods sat in the centre of the fork tube. Now there are no more wear marks and no dirty oil.
I believe most of your problem is the damper rods not sitting central and the original floating piston is allowing this. The offset damper rod is allowing the emulator or the mounting bush to rub on the inner fork tube.
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no mate they rock around anything but snug!
On some emulators I have seen small rings which allow a snug fit into the top of the damper rod.
As Nathan said, dont go back to the bloke who did this.
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As stated that emulator fit job is a good stufff up in several respects..but easy enough to fix
Re the chrome damage which is probably unrelated, how straight or not are those stanchions?
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As stated that emulator fit job is a good stufff up in several respects..but easy enough to fix
Re the chrome damage which is probably unrelated, how straight or not are those stanchions?
I also paid for the stanchions to be straightened by the same guy.
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As stated that emulator fit job is a good stufff up in several respects..but easy enough to fix
Re the chrome damage which is probably unrelated, how straight or not are those stanchions?
I also paid for the stanchions to be straightened by the same guy.
Well, that's something to worry about...
Put a straight edge on the tubes, and then again after rotating them 90*. Report back.
I must admit that Momus' point was embarrassingly obvious after he'd made it.
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Please tell me that this bloke is not a member here. or anywhere?
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Chrome hardness? If you have been teamed by a pro the stations may have been decoratively plated; so the chrome is very thin.
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I think in earlier post that they were re-chromed properly. Makes me still think that the chrome is not damaged but picking up alloy for another reason. Like someone else mentioned , are the stanchions straight?
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If the tubes have been rechromed they would have to be straight as they are ground between centres as part of the process.
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Most of the old forks didn't have bushes. But I otherwise agree.
Jumbo, In case it isn't perfectly clear by now: don't go back to whoever fitted the emulators.
So what did they use instead of bushes ? I would have thought they needed some type of bushing.
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If the tubes have been rechromed they would have to be straight as they are ground between centres as part of the process.
Bent axle or triple clamp?
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If the tubes have been rechromed they would have to be straight as they are ground between centres as part of the process.
Bent axle or triple clamp?
No. The front wheel spins true, tubes slide up between upper and lower triples no hesitation or misalignment. There was no issues with the front end before the forks were sent off for the conversion. no gouges no weird noises. there have been no frontal impacts or crashes since the job was done.
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Hey Jumbo I have sent you a pm
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Please tell me that this bloke is not a member here. or anywhere?
...Sadly Fred, he is in fact member here ...!
After taking into account all the feedback, i'm still uncertain as to what the root cause might be, so I will revert to the stock setup prior to the conversion. Remove the YSS PD valves, springs and my original shortened damper rods. Then re-chrome the inner tubes again (the fourth time !) use the correct length damper rods, original compression springs, plus the "missing" top out springs. Then see if the problem still occurs, and whether there is any foreign matter in the oil.
Will probably have to sleeve the top of the alloy sliders now too :(. So if anyone knows who could do that i'd appreciate a name - thx
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Jumbo might be far cheaper to just get another pair of forks, than try and repair those.
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Jumbo might be far cheaper to just get another pair of forks, than try and repair those.
True not that easy to find tho - 74/75 model TM250. You got a set, 35mm ??? :) :) :)
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Theory No 565 :), I have been studying the pics of the std damper rods v the modded ones, they have been shortened to have the same overall length with the valves fitted so as to have the same spring preload,I think this is wrong, the spring needed to be swapped out for a shorter one or if there is a preload spacer pipe it should have been shortened to suit,I don't think this is the cause of the damage though but will affect travel,The other thing I noticed is the piece removed from the original damper rod top to allow the valve to be fitted is quite a bit smaller diameter than the valve,could that be causing a problem at full bottom/top out :)
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If this is the photo you are referring to:
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/20160116_160338_zps0hc9zdo7.jpg)
I cant see a lot of sense in what was done. Can anyone explain why it may have been modified like this? Rebound damping would be impacted as well I guess.
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Yep, thats the one, my guess is to have the same spring preload as before :)
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Hmmm. Shortened damper rod with no top-out spring is longer than stock damper rod with top-out spring, meaning there's probably insufficent overlap (depending on how heavily preloaded the main springs are, but I'm pretty confident in saying they're nowhere near that heavily preloaded).
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Theory No 565 :), I have been studying the pics of the std damper rods v the modded ones, they have been shortened to have the same overall length with the valves fitted so as to have the same spring preload,I think this is wrong, the spring needed to be swapped out for a shorter one or if there is a preload spacer pipe it should have been shortened to suit,I don't think this is the cause of the damage though but will affect travel,The other thing I noticed is the piece removed from the original damper rod top to allow the valve to be fitted is quite a bit smaller diameter than the valve,could that be causing a problem at full bottom/top out :)
Actually you are right the head piece is a different diameter on the modified/shortened damper rod to the std one. Compare a close up of the modified rod to the std one which has two upper oil holes, the modified one has three holes, the ctr one is filled with a rivet and blocked off- maybe he miscalculated when he was doing the drilling. Then have a look at the piece of rivet material in the ctr hole in the rod on top, the same piece is missing from the rod underneath it, and compare that to the round piece of material the that came out with the fluid on the gauze in the bottom pic
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160124_162816_zpslhme1vax.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160124_162816_zpslhme1vax.jpg.html)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_160338_zps0hc9zdo7.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_160338_zps0hc9zdo7.jpg.html)
(http://i1274.photobucket.com/albums/y432/jrhx/TM%20Forks/th_20160116_153801_zpsupcsb54o.jpg) (http://s1274.photobucket.com/user/jrhx/media/TM%20Forks/20160116_153801_zpsupcsb54o.jpg.html)
Re the springs: Remember there were no top out springs when they came back to me. The new main springs that were supplied fitted up approx 15mm shorter than the std ones from the top of the inner tube - Fitting the correct top out springs brought them back to the same level as the std spring but reduced the travel by the same amount :(.
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So i removed the shortened damper rods / PD valves / compression springs that were supplied with the emulator conversion job. Had the fork tubes re-chromed again (for the 4th time since this saga began!) as well as fitting bushes into the top of the fork legs that were now badly scored by this time. Fitted standard damper rods (no emulators) rode the bike at a couple of meetings one club round and Broadford GP track, and the problem of gouged fork tubes has miraculously disappeared :) . Front end feels much better now in standard trim than it did after the emulator conversion job!
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That is a good outcome to return everything to stock and have it work as intended, but I am still intrigued as to what the issue was after the conversion, if only to avoid making the same mistake in future.
I did a MikesXS 35mm cartridge emulator conversion to my IT175G front end and had to make adapters because the valves didnt fit in the top of the damper rods. Worked a treat and fitted in well.