Fork oil - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

 
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post #1 of 9 Old 04-18-2015, 06:12 PM Thread Starter
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Fork oil

Hey guys I'm replacing my fork seals and was wondering what the easiest way to measure my oil levels when I replace it. I read something about 180mm from the top and I was wondering if that was with the fork fully extended and upright and the springs in or out. Any help would be great.
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post #2 of 9 Old 04-18-2015, 07:04 PM
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Fully compressed and vertical.

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post #3 of 9 Old 04-18-2015, 07:23 PM
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Quote:
Originally Posted by Tom Schmitz View Post
Fully compressed and vertical.

Tom
With or without the springs (or does it make much difference)?

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post #4 of 9 Old 04-18-2015, 10:03 PM
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Springs out!

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post #5 of 9 Old 04-19-2015, 01:38 PM
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It makes a great difference in oil level. If the springs are left in the oil level will be far too low in effect since the oil level is predicated on the amount of oil displaced by the springs.

Some of us have discussed this subject because it should be obvious that different springs must result in different oil levels once the springs are installed. If that is the case, it might be better to measure the level with springs in place since this should reduce the variation of oil level when different springs are installed.

FWIW, the oil level affects the compression ratio of the air void above the oil. The higher the oil level, the greater will be the compression ratio and so the greater the spring effect of the air.

If one were to specify the oil level with spring installed (I have not measured this but have just face palmed), then one might reduce the compression ratio variation between various springs.

The empiricists are flying to the keyboard at this moment to point out a number of facts:

1) The KLR forks are very crude so it would need to be demonstrated that this effect actually makes a significant difference. I don't know.

2) Every rider is different as is every type of riding so one needs determine the best spring, oil viscosity, and oil level by experiment under actual conditions so any recommended oil level must be speculative.

I think this holds the prospect of becoming an oil thread but there may be some useful discussion. Thoughts?
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post #6 of 9 Old 04-19-2015, 01:56 PM
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Forgot to post: some of us have found it quite satisfactory to check oil level with fork tubes on the bike. The level is checked at the 3 o'clock or 9 o'clock positions because this should be the average level = same as with forks vertical.
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post #7 of 9 Old 04-19-2015, 01:56 PM Thread Starter
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I think this is a great discussion as there seams to be a great variation in the info I've been finding. The common theme seems to be that it varies on the rider and the riding style. I'm going to go with 15 wt. oil as I am a fairly big guy. Any thoughts on putting air in?
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post #8 of 9 Old 04-20-2015, 12:00 AM
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I'd start with setting static sag and race sag. Once the sag is correct, you will have a good starting point for fine tuning. Adding air can be helpful for a temporary remedy but usually best to rely on less variable effects, IMO. Too much air pressure from pre-pressurization or suspension compression is likely to blow the fork seals.

If you are wondering about using a higher oil level than standard, that will increase the compression ratio of the air in the shock and act like a stiffer progressive spring. Too high oil level will result in hydraulic lock which will make the suspension bottom out too early.

Adding spacers is the usual way to set sag but one needs keep in mind that the ultimate spring rate does not change so the spring will coil bind under too much load as before.

IME, the best way is to take an educated guess as to oil viscosity so 15 wt sounds like a good try for a heavier guy. You will be able to work that to a finer setting later. First is sag, then find a section of typical riding you do. Ride the section many, many times until you have it down pat and it's becoming boring. Then make a change to see whether your timed ride of the section is better or worse, then make a change and evaluate.

At 5' 7" and 170 pounds, you aren't going to receive ridicule from this quarter. ;-)
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post #9 of 9 Old 04-20-2015, 06:03 AM Thread Starter
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Thanks for the advice. I think I'm really going to enjoy wrenching on my old bike. Forks are off the bike, can't wait to get started breaking them down.
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