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Author Topic: Fork oil question  (Read 867 times)

WillW

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Fork oil question
« on: April 09, 2011, 12:35:35 PM »
It's 7,500 mile service time for my G5, and I'm wanting to change the fork oil.
I've read through some of the fork oil threads here and find various opinions about viscosity  -  10w, 15w 20w etc, but my manual recommends 10w-30 for the forks. What, if any, is the advantage of 10w-30 against, say, 20w for the forks?
I generally just go along with manufacturer's recommendations for this sort of thing, but am intrigued that many folk here seem to favour the single rather than multi-grade.
Then again, Pete Snidal recommends ATF.
Any thoughts?
2010 Royal Enfield Electra (G5) DL

2004 Kawasaki W650
~ the best british bike they never made ~

Bill Harris

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Re: Fork oil question
« Reply #1 on: April 09, 2011, 01:28:43 PM »
WillW,

I like ATF Type F for the Royal Enfield forks.  But It's not what I like, it's what you like and how you ride and the way you like the bike to feel that matters.  Basically, the thinner the fluid the faster the rebound of your wheel will be after a bump.  Too thin and the wheel keeps bouncing.  Too thick and the wheel will not follow the terrain.  And this has to do with how hard you rid and on what terrain you ride on.

Cheers,
Bill   

WillW

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Re: Fork oil question
« Reply #2 on: April 09, 2011, 01:55:00 PM »
Thanks Bill.
Just road riding for me, although I do like hammering it a bit round the curves. Usual variety of UK road surface. I was really wanting to understand the advantage, if any, of the recommended multi-grade 10w-30 against single - 20w, 15w etc. Persumably it'll be "average all-purpose"
The bike as it is, with the original fork oil (inch or so showing on wire dipstick and still clean) handles fine, but of course it's the only bike I know...

edit -  I went with Silkolene 10w.
« Last Edit: April 09, 2011, 06:41:44 PM by WillW »
2010 Royal Enfield Electra (G5) DL

2004 Kawasaki W650
~ the best british bike they never made ~

clubman

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Re: Fork oil question
« Reply #3 on: April 09, 2011, 09:45:19 PM »
Hi Will,

On a slight change of subject I put mine in for it's 7,500m service a few weeks ago and said I wanted the fork oil and air filter changed as per handbook instructions at 7.5k. My dealer said that fork oil should be changed every three years but they are assuming annual mileage of 2.5k. We agreed to change it anyway and of course I don't notice any difference but at least I know it's done. They also said they'd left the air filter in as there was nothing wrong with it. We did change the fuel hose as instructed - for 80p why not? - but not the inlet manifold rubber.

WillW

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Re: Fork oil question
« Reply #4 on: April 10, 2011, 07:45:38 AM »
Thanks Clubman.  Yes I doubt the fork oil actually needs changing - I'm just going by the book as I do my own servicing. I tick off the items in the book each time, just to keep things straight in case of warranty issues - hopefully all that was dealt with in year one.....
The rubber hoses they suggest changing look fine too, but, yeah, for 80p why not!
Of course I wont mention the 18 tooth sprocket - when I get around to it - too much good riding weather just now for that kind of tinkering.... ;)
Do I remember you had a second sprag clutch issue? Was that resolved?
2010 Royal Enfield Electra (G5) DL

2004 Kawasaki W650
~ the best british bike they never made ~

clubman

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Re: Fork oil question
« Reply #5 on: April 10, 2011, 07:46:06 PM »
Yes, the weather's been great recently hasn't it? I've put 800 miles on the bike in the the last three weeks!  :)

I assume you mean the 19 tooth sprocket? I was talking with my dealer about it yesterday and I'm sure I will go that route sometime soon. Just slightly peeved that I already bought a new 101 link chain last summer, (which I haven't fitted yet - the original is still usable at 8.5k  :o ), when a 102 link would probably be better with the extra tooth. Yep, my sprag clutch was replaced twice. At 4,700m and then 5,700m. Second one was dodgy more or less from day one. The third, (current), one is the upgraded part and so far, so good. (Don't say anything more!)

Btw, it wouldn't start last night until I jiggled the wiring for the sidestand cut out switch. Same again this morning. So glad that it's a known issue thanks to this forum or I could have spent hours tracking it down to that. I don't even use the sidestand so I thought if the switch is never operated it wouldn't play silly buggers. Wrong! It's coming off tomorrow!

Ducati Scotty

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Re: Fork oil question
« Reply #6 on: April 10, 2011, 09:47:29 PM »
Pretty much any oil type fluid will 'work' in your forks, that is to say it will provide some damping.  As already mentioned weight is a matter of personal preference to some degree.  Too thin, the fork will act like a pogo stick and keep bouncing.  Too thick, the fork will be over damped and bumps will feel harsh through the handlebars, the tire may not stay in contact with the road.

I prefer my bikes to be more heavily sprung in the front with light damping.  This makes them resistant to diving on hard braking but lets the fork react quickly over stutter bumps and the like.

Overall, fork oil is more suited to forks than motor oil.  I doubt we are working these machines hard enough to really exceed the limits but engine oil is made for lubricating hot engines., fork oil is made for getting repeatedly squeezed back and forth through little holes.  Go with fork oil for forks.  I suspect that India being India and Bullets being Bullets they just spec'd something that anyone can get in any auto shop rather than some fancy oil.  Remember, these bikes are the Model T of India.

It's good to replace the oil every year or two.  It breaks down but it also tends to get sediment and gook in it from seals breaking down and metal rubbing on metal.  While it's not undergoing the punishment of engine oil it does get worked.  Replace it and keep your fork working.  

Also, it seems from every fork thread on every website on every bike I've ever read, whenever someone takes their stock fork apart their are different volumes of oil in each leg (neither of which ever seems to the the recommended volume) and sometimes different colors and obviously different viscosities.  It seems that getting the right amount of the right weight good quality oil in fork legs is not something any manufacturer takes too seriously.  Change yours out just to be safe.

I think your 10W Silkolene is a good place to start.  If it's too harsh, go with a lighter weight.  Too bouncy, go heavier.

The other thing I'd recommend is to fill to a height rather than a volume.  Tip each leg over and pump it until it's dry and all oil is out.  Then fill with the recommended volume of oil and pump several times to get all the air bubbles out.  Fully compress the leg and measure from the top of the tube to the oil.  That's the oil level.  Do the same for the second leg.  No doubt, they'll be a little different.  Average the two or pick on and fill both legs to that level, once again, make sure to pump several times to get rid of all the air bubbles.

A final word on overfilling, heavy oil, and excessive.  Many bike come with soft front forks, especially Japanese bikes designed for 150# riders.  They're just too soft for us heavier Americans.  There are three cheap and easy ways to make the forks stop diving, and all three are usually the wrong thing to do.  

Overfilling or sdding more oil:  The air space you leave in the fork acts as a progressive, rising rate spring.  If you fill the fork higher it gets stiffer faster during compression.  A little of this can be good as it can stop the bike from bottoming out but too much is bad, it can raise the pressure in the forks to high levels and blow your seals.  This is quite common in dirt bikes that have large air spaces.  In road bikes more than 10-20mm means this is not your optimal solution.

Heavier oil: Many people with diving forks swap out the oil for a heavier than spec's weight oil  This kinda stops the dive, or at least it dives slower so it's not so jarring, but as mentioned above the fork now reacts more harshly to bumps.  This can result in a harsh ride, the tire leaving the road, and loss of control.  Again, it's personal preference to some degree but if you stopped your fron end dive but your hands rattle loose over every bump you've gone too far and this is not your solution.

Preload:  Another common remedy is adding preload.  By using a longer spacer there is more pressure on the spring to start with.  This makes the spring feel stiffer to a certain degree.  Once more, a little can be good, too much can be bad.  If you over load the spring you don't get full travel out of the fork and the spring is stiffer through it's more limited range.  Once again, harsh ride and potential loss of control.  It's better to have a stiffer spring to start with so that you get more travel and a better reacting fork.

The better solution to all of these issues is the right spring for your weight.  If you go to any decent suspension shop they should be able to measure the rate of your current springs, take your weight, bike, and riding habits into account, and round up a more suitable spring for you.  The difference is night and day AND allows you to get the right oil and oil height so the damping can work as designed rather than compensating for a weak spring.

This is the best concise description I've seen on the web about how to set up suspension right.  
http://www.ohlins.com/Checkpoint-Ohlins/Setting-Up-Your-Bike/Underrubrik_1/
Now with mild bikes like our humble Bullets our options may be more limited but even doing a few of the right things can make a huge difference in both comfort and performance.

I hope this doesn't come across as a rant, it's not.  I just think suspension is something we all should understand more.  Setting a bike up right makes it handle better in all circumstances and that keeps us all safer.

Hope this all helps.

Scott


GreenMachine

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Re: Fork oil question
« Reply #7 on: April 10, 2011, 10:23:13 PM »
ducati scotty: replaced mine two years ago with 15 wt fork oil and haven't had a bit of problems...wasn't haven't problems before i changed it...did it for the hell of it...the irons are easy to do..open the top, cracked the bottom bolt and pump the forks a couple of time...let it drain out slowly for 15 min or so a leg...i measured per snidal the amount he recommends..i was talking to yamaha dealer tech and since my other bike had never been changed (03), he stated, its best to leave it alone as I might as well wait till the seals act up...from his experience, changing out oil on a older machine that was never done after a certain amount of time is waste of money and it would probably speed up seal deterioration....one could probably say, just do a fork seal rebuild and add new fluid....like anything else, what is one comfortable with especially if u not having any issues whatsoever....enjoyed your analysis on fork oil..
Oh Magoo you done it again

Ducati Scotty

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Re: Fork oil question
« Reply #8 on: April 10, 2011, 10:33:06 PM »
Yeah. the older bikes (and  I think the G5s) can be done with the forks on the bike.  The C5 has to be totally taken apart which is part of why I've been stalling.

I could see what your tech says about old bikes, kinda like changing the tranny fluid in your car when it hasn't ever been done.  It's the sure road to problems starting.

These bikes don't have bushings in the fork legs, the lower leg rides right on the upper.  With that in mind I think it's good to change the fork oil every year or two.

Scott

GreenMachine

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Re: Fork oil question
« Reply #9 on: April 10, 2011, 10:37:14 PM »
yeah that what i was thinking...every 3 years or sooner is a good bet...so the c5 is more of a PIA to change....well they said its a completely different machine...
Oh Magoo you done it again

Ducati Scotty

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Re: Fork oil question
« Reply #10 on: April 10, 2011, 11:02:43 PM »
Yup, different fork internals and slightly less travel.  I think it's also shorter overall than the G5 fork.

Scott

WillW

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Re: Fork oil question
« Reply #11 on: April 11, 2011, 07:29:33 AM »
Many thanks Scotty.
I think you've written the definitive Fork Oil thread - perhaps it ought to go in the Tech Tips section as a sticky?
2010 Royal Enfield Electra (G5) DL

2004 Kawasaki W650
~ the best british bike they never made ~