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Message started by engineer on 05/02/13 at 13:34:58

Title: fork oil change, Honda
Post by engineer on 05/02/13 at 13:34:58

Well it's not my Savage but I need some help. I thought I was well informed before I tore down my Honda CB125s forks. All the manuals are for an earlier version, usually mid to early 70s. The available manuals indicate that there was a drain plug at the bottom and that 130cc of 10w40 oil was needed in each tube.

My CB was made in late '79 and has no drain plug so I removed the shocks and dumped the oil out. Then I measured out 130cc of oil and tried to pour it in, that amount overflows the shock tube even when extended.

So how much to put in. I thought about compressing the shock and filling it to the top but several inches of the springs stick out that way. I extended them again and poured in about 100cc which put the oil level about an inch from the top and put the cap bolts on. After assembling them I can compress each shock by leaning on it. I can compress one about 3 1/4 inches and the other only about 2 1/2 inches so they don't match. Not good. I need to some how determine the right amount of oil to put in. Honda forums have no information about this.

So I am hoping for a little guidance from this group. Thanks

Title: Re: fork oil change, Honda
Post by Dave on 05/03/13 at 05:39:14

When you turned the forks upside down, did you pump them in/out several times to get the oil out of the damping rods? There is oil in those that does not come out if you don't cycle them in and out, and this may be the cause of you having too much oil.....you didn't get it all out.

If that is not the issue.....then I suggest you start over. First dump the oil out and cycle the forks to get everything out. Then with the fork upright, add about 80cc......and pump. You should hear the air coming in and out of the damping rods as the oil enters. After a few strokes you should not hear anymore air, and the forks should have a consistent damping from top to bottom....if you still hear air and the forks don't dampen smoothly, add more oil and measure it as you add. Try adding 20cc more, and pump again. When you find the place where the dampening is smooth and the air sounds are gone.....add a bit more oil for a reserve amount. You should be down in the fork leg a considerable distance before you add the springs. With the forks compressed - the oil should still be far below the top as there needs to be space for the air to compress as the forks move to the short position. Then put the forks together and ride. If they feel too mushy you can add a little bit more oil later on to cut down on the air space and make them less apt to bottom out.

Title: Re: fork oil change, Honda
Post by bill67 on 05/03/13 at 05:58:39

With the forks fully extended about 2 inches down with out the springs in is were the oil was on my suzuki s40 and 1500 so i think that would be a good starting point.

Title: Re: fork oil change, Honda
Post by engineer on 05/03/13 at 08:00:17

Thanks Dave and bill67 for the advice. I dumped the oil and worked the tubes and drained everything again, it wasn't a waste since more dirt got flushed out. I had been getting two fairly distinct pahses as I would test them, one that felt like oil flowing through the damper and the last phase felt like air compressing, very hard but springy and far short of the specified travel. Too much oil.

I finally worked my way down to 85cc of oil per leg and they feel smooth and consistent the whole way. It's not much oil but the tube diameter is small and it looks like the oil will cover all the damper plus lubricate the working parts eventhough the level is down there quite a ways.

This time I used ATF as I did learn that Honda changed the spec from motor oil to ATF in 1976 when they changed from external to internal springs on this model. I'll give it a ride and add oil if it needs it. Lesson learned is there is no easy way to determine oil level if you don't know the manufacturer's recommended oil capacity.