fork work, tutorial needed. please

John390

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Hey all, I want to change my fork springs and fork oil on my bike.

I'd pay someone locally to do it, but they are all either scared to do it, or I don't actually think they know how and are just going to wing it. I don't want to pay someone to wing it, thanks.

I just need a step by step so I don't screw anything up.

I have good tools and am a liscenced auto tech so i can do most things.

thanks!!
 

Andy

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If you download the repair manual it has it step by step. The RC manual is hard to find but the Duke 390 manual is readily available on line.


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SnotRkt

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Its not really a job for a novice. My suspension guy at Solid Performance a WP suspension shop said these are a bear! Too many opportunities to mess them up and then if you trash them you are out a ton more than what you would pay a reputable shop...
 

ReidMcT

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I agree it is not a novice job, but it certainly is not a 'bear.' In fact, I think it is easier than most upside down forks. No spring compressor needed.

There are some writeups to be found on this forum, but here is an abbreviated list of the main steps.

'Special' tools needed are soft vise, pin spanner with 6mm pins, a heat gun or torch, and maybe a fork oil height syringe (useful but not essential)

Remove fork from bike and clamp upright in vise
Remove cap
Pour out oil (there will be even more coming out later)
Remove lock nut under cap and remove cap from rod
Carefully/slowly separate upper and lower parts of the fork leg over a drain pan. There is a hole in the side of the lower part that when exposed will gush oil.
Apply heat to the bushing retainer cap (the one that the pin spanner will be use on). The manual specifies 120 degrees F, but most people say go much higher. This is to soften the excessive threadlock goo. Softer goo equals less stressful wrenching.
Remove cap along with rod. Remove spring and spacers.
Dump any remaining oil.
Install new springs and spacers.
Reassemble fork without oil or thread sealant.
Do the same to the other fork leg.
Reinstall both forks and check sag with rider and gear.
Remove and disassemble forks and increase/decrease spacers as needed to get closer to desired sag.
Repeat above two steps until sag is right.
Remove forks,
and clamp upright in vise,
remove caps.
Add oil as recommended by spring mfgr (by volume or by measurement from top of tube).
Reinstall caps.
Reinstall forks, wheel, brakes, per manual.
Test ride.

Ta da.
 

hvlmike

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separating the upper from the lower is the hard part...but get it hot enough and it comes apart pretty easy with the right tools... I made my own.
 

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John390

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great stuff guys!!

Yes, I get that its not a novice thing, but I am not a "novice" per se :) I am a liscenced tech and have been wrenching at least 10 years before I became an apprentice.

However, the point about effing it up is what my main concern is.

thanks CDN Duke, thats a great idea. I am assuming I could get one of the "clamp" parts and one cheap clip on? Then use this as a wrench? Alternately, I was going to use a strap wrench.

big thanks to Reid Mc T! this is what I was after.

I'd love some clear pictures of some of the trickier parts.

I'd also really love to know the volume of oil to put back in, and the procedure to remove all the air when I'm done. I saw that video from the guys in Thailand and they had to move the shock lots to bleed it I am assuming?
 

ReidMcT

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Fork oil: 460ml per leg.

You do not have to remove the air. You may need to pump the damper rod a few times to get the oil level to drop as you are filling it. Otherwise, it all sorts itself out as you ride the first few miles.

This is one of those jobs that reads more complicated than it really is. Of course you have to be reasonably careful and methodical, but it would be hard to mess it up if you are just doing springs and oil, and not completely disasembling everything.

You need a pin wrench - preferably a proper pin spanner, though home made will do. I would not even consider trying to make a strap wrench work... or any kind of gripping device. The 6mm pin holes are there to be used. Use them. As a licensed tech, don't you have a pin spanner? If not, this is a great excuse to buy another tool. I have one that includes many different pin sizes. Very handy:
https://www.amazon.com/OTC-6613-Variable-Spanner-Wrench/dp/B000F5JMEA


 
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ReidMcT

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<p>
Oh, and regarding fork oil, though the manual specifies SAE 4, when I installed Racetech springs I went to a heavier oil (on advice from Matt at Formula 390): https://www.amazon.com/gp/product/B000WJYNP2</p>
 
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hvlmike

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You need a pin wrench - preferably a proper pin spanner, though home made will do. I would not even consider trying to make a strap wrench work... or any kind of gripping device. The 6mm pin holes are there to be used. Use them. As a licensed tech, don't you have a pin spanner? If not, this is a great excuse to buy another tool. I have one that includes many different pin sizes. Very handy:
https://www.amazon.com/OTC-6613-Variable-Spanner-Wrench/dp/B000F5JMEA



Good point. The handle on the tool I made actually fits into the 6mm pin hole. I didn't want to risk deforming the upper by clamping too tight.
 

John390

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great stuff!

Yea, no need for a pin wrench, not one time, so no, I don't have one, but I always have no problem getting a tool that will make life better.

thanks for the oil level. And yea, I am going to put heavier oil in for sure. Not sure if I am going to 7w, as I may just add preload to the stock springs with a spacer. I am pretty happy with the suspension on the bike now, it just has too much static and dynamic sag in the front. I don't want to overdo the oil viscosity. That said I don't want to do it twice either. thoughts on that?
 

ReidMcT

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great stuff!

I am going to put heavier oil in for sure. Not sure if I am going to 7w, as I may just add preload to the stock springs with a spacer. I am pretty happy with the suspension on the bike now, it just has too much static and dynamic sag in the front. I don't want to overdo the oil viscosity. That said I don't want to do it twice either. thoughts on that?

Well, if it's working well for you as is, then maybe no reason to change. I ride my RC390 exclusively on a pretty bumpy track, and I am very satisfied with the suspension now. to me, if I'm not thinking about the suspension when I ride, then it must be working well.

One thing I want to call out about fork oils that is a source of great bother and irritation for me, is that the 'weight' ratings the manufacturers use, bear only the slightest of relationships to the viscosity performance of the oil, which is pretty much the most important thing in a fork oil. The better measure is cSt (Centistokes) at a standard temperature (usually 40C or 100C).
For instance the Maxima '7wt' oil I use measures 26.7 cSt. Other '7wt' oils range from 16.1 to 29 cSt.

And PJ1 Fork Tuner (2.5 wt) comes in at 26.1 cSt.

The more common '5wt' fork oils range from 10.75 cSt for Torco all the way to 33 cSt for Shell Advance Fork 5. That is crazy.

Going by 'weight' is useless. You might as well just randomly pick an oil.
 
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ReidMcT

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Oh, and you might ask, 'What is the cSt rating in the stock 'SAE 4' fork oil?' I don't know for sure, but I think it is WP '4wt' which I think is about 18 cSt.
 
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John390

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awesome! is there a list somewhere so I can make an informed descision?

It does work well, but there is way to much static sag. Like 35mm or more.
 

ReidMcT

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Yes, there's a nice list with many oils listed. A web search will turn it up for you. IIRC, it's an Australian site or fellow. Great resource because it takes a lot of reading to find the numbers for an oil.
 

mattv

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p.s. - if anybody knows a shop in SE Michigan that they trust to work on these bikes, let me know. I'd like to upgrade the springs, but don't want to do it myself.
 

ReidMcT

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I think this is NOT a good video for someone wanting to understand how to change the springs and oil of the stock fork. This video is about completely changing the cartridge and spring from stock to Andreani. If I hadn't already done the simple spring and oil swap myself, I'd have been thoroughly confused and misled by this video.

The parts of the operation that would be relevant to a simple spring/oil change are left out, except where the presenter talks after the fact about his home-made pin spanner.
 
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