Leaky Fork

[KRS1]

Noticed i had a leaky fork and everytime i stopped at a stoplight, i look down at it and dread having to leave my bike and pay mr.honda since im apartment bound.

But then i found this video on youtube, tried it and it worked ! Saved 1-2k baht, made it out of a plastic food lid container, and worked like a charm - no more leak !

Since my springs are sagging, i went ahead and ordered some Ninja 250 springs today (same part number as ninja 300 springs btw) ..going to lengthen the preload stalks and maybe go up to 350ml of 20w oil..unless there are better suggestions (im 167 lbs / 73kilos)

any suspension experts out there?

[yankee99]

Before i would change too much i would check my static sag. Setting the forks incorrectly is a major recipe for disaster.

[Overandout]

Wise words from Yankee.

You say that the forks are "saggy". But what do you mean exactly?

If the preload is too high the forks will not use any of their travel when you sit on the bike which means that there is no extension movement available under "neautral" conditions, this is not good. However you seem to suggest that the forks drop too much in the "neutral" condition, i.e. you sat on the bike.

Increasing the preload stalk length will solve this issue (be careful not to eliminat all static sag), but it will not increase the spring rate. In other words the springs will still be compressed by the same amount for any given load or force. If your meaning of too saggy is that the forks travel too much when absorbing a bump / cornering force then the only remedy is stiffer springs, which will then need their preload reset.

If the rate at which the forks compress and extend is too high (under-damped) then either you don't have enough fork oil or the oil has degraded or is too light.

Do not add oil to the forks beyond the capacity stated by the manufacturer, you will blow the seals. Fork oild weight is ver effective and can make a drastic change, if you go from 5 to 10 weight the difference will be very great, it may be worth mixing oils of different weights to achieve an intermediate weight oil to suit your damping needs.E

Edited to add: putting too heavy oil in the forks will prevent the oil from moving through the damping shims stacks, effectively causing an effect similar to hydraulic lock; the forks will not either not compress under bumps/ cornering/ braking, or worse, will compress on bumps but then not extend again before hitting the next bump, which will further compress the fork again. This is called "pump down" by some people and can even be dangerous (I have had to stop on a bumpy road in the past just to allow an over-damped - rebound - bike's forks to extend again before continuing, it was unrideable)

I can't see the video posted at work, but the ONLY way to fix a leaky fork is to fit a new seal that can cope with the pressure of the full level of fork oil.

[sup3r1or]

Speaking of forks, does anyone know how to check fork for damage? A month ago I went to Mae Salong, on the way back I drove into what I though was a puddle, which ended up being a huge pot hole. My bike went airborne and I almost flew off it. I was sure as I landed that front fork is probably busted. When I got off it looked normal straight, nothing unusual. Been riding for about a month and seems to be pretty okay.

bike is cbr500

[Overandout]

Speaking of forks, does anyone know how to check fork for damage? A month ago I went to Mae Salong, on the way back I drove into what I though was a puddle, which ended up being a huge pot hole. My bike went airborne and I almost flew off it. I was sure as I landed that front fork is probably busted. When I got off it looked normal straight, nothing unusual. Been riding for about a month and seems to be pretty okay.

bike is cbr500

As a preliminary check:

Hold the bike upright off the stand (get a mate to help).

Lift the front end by the bars so that the forks extend as much as possible.

Let the weight of the bike return the forks to their normal postion.

Measure the amount of visible fork tube between the top of the fork lower (where the top tube enters the lower outer tube) and the bottom yolk.

Now grab the front brake and compress the forks and allow then release and let the forks return to their natural position.

Measure the distance again, it should be the same.

If the distance is significantly less than before it is probable that the forks are bent and causing increased stiction.

To be even more sure:

Remove the forks from the bike.

Hold the edge of a metal ruler or any other perfecty straight rigid lenghth of hard material against the top tube.

Try to insert a feeler guage between the ruler and the fork leg at various points of "contact".

Repeat this around the fork leg top tube at the 12, 3 6 and 9 o'clock positions. If you can get a narrow guage (e.g. 0.5mm) in at any point, it's bent.

I rode an FZ 750 for 6 months with a slightly bent tube after running into a car before my mechanic did these tests and we discovered that the forks were indeed slightly bent.....

[yankee99]

^ remember when doing this do not bounce the forks just push down once firmly

[KRS1]

Thanks guys, the fork springs are shot, the bike has 37k on it. Thats what i meant by sagging.

Not going with 20w oil any more, after reading up on it, it seems people that suggested it weigh like 250lbs and dont have a clue.

just going with 10w and increase the preload stalk length by 1cm, then go from there.

[yankee99]

37k is nothing and very doubtful the spring would be worn out unless they are defective. I would measure them when removed to see if they are within spec.

37k is a lot on the fork oil if it hasnt been changed. Like i said previously check you sag this way if you do need to adjust preload you will know exactly how much. I assume your forks have no adjustment for preload?

It requires three people to do it. Then please post your results.

[yankee99]

looking a little deeper seems the oem are .440 kg/mm and for your weight you need a .671kg/mm What are the 300 springs rated at?

[denby45]

If your fork leaks then use a spoon.

Den

[KRS1]

37k is nothing and very doubtful the spring would be worn out unless they are defective. I would measure them when removed to see if they are within spec.

37k is a lot on the fork oil if it hasnt been changed. Like i said previously check you sag this way if you do need to adjust preload you will know exactly how much. I assume your forks have no adjustment for preload?

It requires three people to do it. Then please post your results.

not totally sure about the springs, i do a lot of riding downhill and in the mountains, so not sure if the springs are shot from repeatedly compressing them. They are also very soft since the beginning so would like to change them out. Fork oil has probably never been changed, got the bike used at 17k it now has 37k, i remember the forks riding much higher when i first got it. For the way i ride its probably the equivalent of a slow straight line rider going 70k kilos.

There is no adjustable preload, but the cbr250 uses metal tubes within the fork to adjust the preload, youd have to cut to length new tubing to set preload.

The Ninja 250/300 spring rate is .65

will try to get people together to measure sag.

Going to go with trial and error and testing and more testing on this one.

[Garry]

37k is nothing and very doubtful the spring would be worn out unless they are defective. I would measure them when removed to see if they are within spec.

37k is a lot on the fork oil if it hasnt been changed. Like i said previously check you sag this way if you do need to adjust preload you will know exactly how much. I assume your forks have no adjustment for preload?

It requires three people to do it. Then please post your results.

 

not totally sure about the springs, i do a lot of riding downhill and in the mountains, so not sure if the springs are shot from repeatedly compressing them. They are also very soft since the beginning so would like to change them out. Fork oil has probably never been changed, got the bike used at 17k it now has 37k, i remember the forks riding much higher when i first got it. For the way i ride its probably the equivalent of a slow straight line rider going 70k kilos.

 

There is no adjustable preload, but the cbr250 uses metal tubes within the fork to adjust the preload, youd have to cut to length new tubing to set preload.

 

The Ninja 250/300 spring rate is .65

 

will try to get people together to measure sag.

 

Going to go with trial and error and testing and more testing on this one.

Does it have 'rebound' adjustment? Make sure that is backed off as well before setting your sag.

[KRS1]

theres no rebound adjustment, just stock forks.

But ive been thinking about turning the forkcaps into adjustable preloads...i wonder if drilling a hole, tapping it and loading it with a bolt and putting something on the end of the bolt would work to compress the spring. I dont see any reason why i wouldnt work, same concept as a premanufactured preload adjuster.

[yankee99]

theres no rebound adjustment, just stock forks.

But ive been thinking about turning the forkcaps into adjustable preloads...i wonder if drilling a hole, tapping it and loading it with a bolt and putting something on the end of the bolt would work to compress the spring. I dont see any reason why i wouldnt work, same concept as a premanufactured preload adjuster.

Sure that will work but it will be just as easy or easier to add a piece of pvc or cut your spacer depending on your testing.

[William Osborne]

theres no rebound adjustment, just stock forks.

But ive been thinking about turning the forkcaps into adjustable preloads...i wonder if drilling a hole, tapping it and loading it with a bolt and putting something on the end of the bolt would work to compress the spring. I dont see any reason why i wouldnt work, same concept as a premanufactured preload adjuster.

Seriously.... i can't believe I just read that ... sounds like a good way to destroy your forks

[yankee99]

theres no rebound adjustment, just stock forks.

But ive been thinking about turning the forkcaps into adjustable preloads...i wonder if drilling a hole, tapping it and loading it with a bolt and putting something on the end of the bolt would work to compress the spring. I dont see any reason why i wouldnt work, same concept as a premanufactured preload adjuster.

Seriously.... i can't believe I just read that ... sounds like a good way to destroy your forks

I doubt he will destroy his forks its not rocket science what he wants to do.

[William Osborne]

i under the concept of pre-loading a spring... .but i'd hazard a guess if this abortion was carried out by a non-professional with a hand-drill it won't turn out too well.....not to mention what it would to do the re-sale value of the bike

[yankee99]

i under the concept of pre-loading a spring... .but i'd hazard a guess if this abortion was carried out by a non-professional with a hand-drill it won't turn out too well.....not to mention what it would to do the re-sale value of the bike

Plenty of machine shops to drill and tap the holes here in los. I would say about 300baht of machine work at the most. I doubt the oem caps cost much he could always buy a extra set to return the bike to stock.

[Garry]

This looks agricultural but seems functional

Honda Hornet kit

[KRS1]

Hey thats cool, pretty much what i had in mind.

[William Osborne]

to save you the bother of destroying your fork caps....

http://www.ebay.com/itm/2011-HONDA-CBR250R-CNC-ALUMINUM-FRONT-FORK-SUSPENSION-PRELOAD-ADJUSTERS-/231004121767?pt=Motorcycles_Parts_Accessories&hash=item35c8eb2aa7&vxp=mtr#ht_3953wt_1255

[KRS1]

good god $99 ?....destruction of fork caps will commence shortly.

have to take a look at how thick the caps are first, if its too thin aint gonna do it.

[thaicbr]

When I changed the fork oil on my cbr250 this difference was amazing. Just used a decent 10w. The standard stuff is dribbly piss.

Sent from my phone with the app thingy.

[KRS1]

How much do you weigh? You can PM me if youd like

[Garry]

http://www.sonicsprings.com/catalog/calculate_spring_rate.php

http://racetech.com

[KRS1]

thanks garry

[ll2]

Hey thats cool, pretty much what i had in mind.

you can get it cheap in Thailand krs. i had a set actually if you are interested, cal sell them to you. just pm me.

.

[KRS1]

thanks for the offer LL2, let me see how the bike rides after i get the springs and oil in first to see how it goes.

btw, dropped in a 13tooth front sprocket today, but dont think there was any gain down low, feels smoother though...you ever try this on your bike?

[BSJ]

The original fork caps are usually not suited to drilling and tapping. There isn't a lot of material where you need a lot of material for enough thread to engage the new adjusters thread.

[KRS1]

thats what i was thinking, still waiting for the springs so will be cracking them open soon.