fork compression question

[Anonymous]

Despite having had a license for years, I am still pretty much a newbie when it comes to bikes. Over the last year or so I have got my '82 GS650G running to the point where it seems to run pretty well. (It had sat in someone's garage for 7 years before that.)

However it seems to me that the forks compress an awful lot upon braking. Is there a way of determining the appropriate amount of compression and if they are compressing too much what do I do about it?

Dan

[wizard]

The amount of compression of the forks isn't as important as how FAST the forks compress. This is governed by the amount of oil in the forks. Do the seals show sign of leakage? If they do, you may need to change them. When this is done, you will add the correct amount of new oil to the forks.
Are the forks air assisted? If there are little chrome caps with a hex on them at the top of the forks, you should check the air pressure. Do you have an appropriate amount of pressure in them?

[Anonymous]

If you haven't done it yet, I would take the forks off the bike (they slide out of the triple tree), open the tops to get the springs out, then drain, flush and refill with fresh oil.

[Anonymous]

Thanks to both of you. The forks do compress too fast as well as too much - it's basically just too easy to compress them. Will draining and refilling the forks fix this?

How hard is it to do this? I am a pretty average mechanic but I do have access to tools so I would like to have a go in order not to spend extra money on the bike. Also, what do I fill the forks with? Is it just regular motor oil or some special oil?

Dan

[wizard]

If you have air forks, they can be relatively easily drained and refilled in place. If the seals leak, they should be removed, and the seals replaced.
If they are aire forks, remove the trim caps and depress the valve center to release any air pressure. There should be a small screw on the side of the fork, down by the axle. Remove it with a pan under it to drain fork oil. Put a wrench on the flats of the cap(not the air fitting, the whole cap) and break it loose. As you turn it off, keep in mind that there is a really big spring behind it, so press down as you remove the cap. Once the cap is off, the oil should really run right out. Push on the forks once or twice to assist the evacuation. When empty, replace the screw and refill the fork from the top with the correct amount of oil. The right amount should be listed in the service manual. You DO have a service manual, don't you? If you don't have air assisted forks, you must remove them from the bike and take the top cap off to drain them(they have to be turned upside down). At that point, you might as well disassemble and clean them, replacing the seals before refilling and reassembling.
Keep us posted.

[Anonymous]

Fork Compression

What is the proper amount of air to put in the fork?

[earlfor]

Re: Fork Compression

I believe most people that put air in their forks use between 3 and 7 or 8 lbs.
I dont use any air pressure in my forks. You can modify the dampening rate with the oil viscosity. I use 20 weight non detergent motor oil in my forks. that gives a fairly stiff front suspension Some people use ATF (automatic transmission fluid) and some mix it with oil to modify the viscosity which changes the dampening rate. Most bikes require between 7 and 10 ounces of fluid in each fork, but it varies with each model of bike, so you will need to look up the spec for your bike. It is important to measure precisely and put the same amount of oil in each fork. If the fork oil levels are very unbalanced, compression and dampening on each tube/leg will be different and can cause weaving.

Earl

What is the proper amount of air to put in the fork?

[Anonymous]

I use 15W fork oil in my forks. For both my bikes, I have removed the forks from the triple tree clamps and drained/flushed them off the bike before refilling them with fresh oil. Easy to do.

[snowbeard]

I had a similar problem when I got my six fitty, but just adding air seems to have done it quite well. I should probably change the oil as well, but for now I'll take it!

just a note, you can add air with just a bicycle pump, but it takes almost nothing to add too much, at which point you blow your seals... the best was is with a gauged pump. or you can dink around with the tire pressure gauge, but it lets out something like 0.4 lbs of pressure each time you use it... with such a small volume of air it takes very little volume to make a huge change in pressure.

good luck!!

[Anonymous]

Make sure you have the weight off the front end before removing the cap bolts on top of the forks.