Author Topic: Replaced fork seals on my 750k2. Strange noise. (Read 9372 times)

dylboss · « **on:** May 27, 2012, 11:19:27 AM »

i just replaced the fork seals on my k2 with honda OEM seals. Put everything back together. Have 10W fork oil in them. I noticed now that when it is on its center stand and I pump the forks and they fully retract, I hear a bang almost like the fork pipe guide is hitting the top of the chamber. I don't remember hearing that before. Is that normal? It doesn't happen when on the bike, I'm guessing because the forks are compressed to begin with and don't ever really fully retract.

I'm just concerned I didn't reassemble properly or maybe even the wrong seals? I used honda part # 91255-KBH-003.

Thanks!

Tews19 · « **Reply #1 on:** May 27, 2012, 08:40:02 PM »

I have the same sound on my K1. Not sure why, I had to much fluid in there and it was like driving with square tires everytime I hit a bump. No noise though. I let some fluid out and now I hear the thud noise. Tomorrow if I have time I am going to drain the forks completely and refill..

How much fluid did you put in? I went with facotry amount and it seems like way to much

HondaMan · « **Reply #2 on:** May 27, 2012, 09:29:56 PM »

Some things that can go wrong when replacing K0-K2 fork seals:
1. The bushing in the top of the fork does not get set all the way down before the seal and snapring are installed. This lets it rattle up and down.
2. If you also removed the damper guide rod from between the axle bolts (unnecessary on these forks), it may not be seated all the way back down. This will promote leaks at the axle and a too-long fork, which will hit the bottom of the afore-mentioned bushing.
3. Too-thin fork seals. Some of the 'generic' seals today (including those dealt out by young, green Honda parts techs) are only 7 or 8mm tall (or, "thick") top-to-bottom. If the seal can move up and down when the bushing is pressed down into place, that seal needs a backup washer above it, below the snapring. Aftermarket seals usually come with these, if they are the correct part. It should be a washer of about 0.5mm, to 0.8mm thickness for a 7-8mm thick seal. The original K0-K2 seals were 9mm tall, had 2 wiping seal surfaces in them.
4. Too little oil or too much oil. The former will not dampen the rebound, while the latter will compress the air so much that the forks cannot circulate the oil into the inner pipe area, so the forks hydraulically lock. The proper amount of oil after an on-the-bike draining from the bottom bolt is 7.0 ounces: if the forks were dry then it is 7.3 to 7.5 ounces. They can tolerate up to 9.0 ounces from dry, or 8.0 ounces wet drain.

dylboss · « **Reply #3 on:** May 28, 2012, 05:46:45 AM »

Thanks. This is very helpful info. I used OEM seals that have the 2 wiping seal surfaces with 2 springs, one on each side. I put the fork oil in when the forks were OFF the bike, and I used exactly 7oz. I completely dismantled the forks and cleaned them, so yes everything was apart. I used a wooden broom handle to keep the piston guide rod in place while I tightend the bottom hex bolt, and everything tightened up good. I do have a washer in place that is on top of the seal and under the circlip. There wasn't a bushing at the top under the seal. The only thing that was there and movable was the large piston guide, which is cylidrical about 2-3 inches long with a lip on the top that appears to come in direct contact with the seal. That was free and removable from the seal side of the fork tube.

Should I drain the oil and fill while it is on the bike? The forks in general feel very soft with not much damping in either direction, like I have water in there or something (maybe a slight exaggeration).

Johnie · « **Reply #4 on:** May 28, 2012, 06:08:40 AM »

Yah, hoodleyhoo and I were trying to chase that same noise down. My K4 was fine when I got it. Put in new OEM seals and have the same noise. So I just live with it. Then I got this K3...was fine when I brought it home. Put in new OEM seals and have the same issue? I thought maybe both bikes had to little fork oil, but I put in what the manual calls for 7.3 after a rebuild. I was thinking of adding a bit more to see if it goes away. The sound seems to come from the left fork only. Let us know if you figure it out.

dylboss · « **Reply #5 on:** May 28, 2012, 08:18:09 AM »

Quote from: Johnie on May 28, 2012, 06:08:40 AM

Yah, hoodleyhoo and I were trying to chase that same noise down. My K4 was fine when I got it. Put in new OEM seals and have the same noise. So I just live with it. Then I got this K3...was fine when I brought it home. Put in new OEM seals and have the same issue? I thought maybe both bikes had to little fork oil, but I put in what the manual calls for 7.3 after a rebuild. I was thinking of adding a bit more to see if it goes away. The sound seems to come from the left fork only. Let us know if you figure it out.

Yeah. Very strange. I just don't get it. I'm afraid something is going to break in the fork if it fully retracts over time. It can't be good for that metal on metal to slam against itself. Did you fill the forks on or off the bike? I'm also wondering if you are supposed to put in 7.3 oz after draining via the plug while on the bike, and NOT pumping the forks to remove all the oil. That would explain not having enough oil if 7.3 oz went in after a completely dry fork, which is what i did.

HondaMan · « **Reply #6 on:** May 28, 2012, 10:35:38 AM »

The "new" seals you are describing are not correct in design, so I suspect they are not correct in thickness, either. The "2 wiping surfaces" I am clumsily attempting to describe here are both lips on the inside of the seal, and there should be one garter spring on the inside (oil side) of the seal. If you have the dual-spring version (which I have also seen), they are for the DOHC CB75/900 bikes, so someone has goofed, somewhere. The design of those post-SOHC4 forks is considerably different, and do not use the seal as an integral part of the stack-up of the parts.

Dylboss: the moving part you're describing near the seal is the "bushing" for the fork leg lower, which is the bearing surface that guides the lower up and down on the fork leg itself. If this gizmo is not settled tightly to the bottom of its groove, it thunks up and down, and the fork never reaches full bottom inside to let the oil circulate fully up inside the (removable) damper tube guide at the bottom. This removes almost all damping in the fork, as the oil is trapped on the fork-leg side and can't get inside to work thru the valve rings. So, the forks "boink" to their full travel after every bump, like pogo sticks, for lack of any damping.

So...first thing I'd recommend is the proper seals, of the proper thickness. This thickness is between 9-11mm (11mm seals don't use the top backup washer, often have 3 lips inside -very stiff). If you can't locate some, PM me: I keep a bunch of them around, but not from Honda - for the same reasons you are now suffering.

dylboss · « **Reply #7 on:** May 28, 2012, 11:17:24 AM »

Quote from: HondaMan on May 28, 2012, 10:35:38 AM

The "new" seals you are describing are not correct in design, so I suspect they are not correct in thickness, either. The "2 wiping surfaces" I am clumsily attempting to describe here are both lips on the inside of the seal, and there should be one garter spring on the inside (oil side) of the seal. If you have the dual-spring version (which I have also seen), they are for the DOHC CB75/900 bikes, so someone has goofed, somewhere. The design of those post-SOHC4 forks is considerably different, and do not use the seal as an integral part of the stack-up of the parts.

Dylboss: the moving part you're describing near the seal is the "bushing" for the fork leg lower, which is the bearing surface that guides the lower up and down on the fork leg itself. If this gizmo is not settled tightly to the bottom of its groove, it thunks up and down, and the fork never reaches full bottom inside to let the oil circulate fully up inside the (removable) damper tube guide at the bottom. This removes almost all damping in the fork, as the oil is trapped on the fork-leg side and can't get inside to work thru the valve rings. So, the forks "boink" to their full travel after every bump, like pogo sticks, for lack of any damping.

So...first thing I'd recommend is the proper seals, of the proper thickness. This thickness is between 9-11mm (11mm seals don't use the top backup washer, often have 3 lips inside -very stiff). If you can't locate some, PM me: I keep a bunch of them around, but not from Honda - for the same reasons you are now suffering.

Hondaman, thanks a lot for the great info. I'm guessing this is the problem. Are you suggesting that when the "bushing" is positioned correctly, it shouldn't move up and down freely on the pipe? When I put everything back together it was moving freely up and down. Should it sort of "snap" into place at the bottom toward the piston?

Johnie · « **Reply #8 on:** May 28, 2012, 01:12:34 PM »

dylboss...I did completely removed all the fork oil until dry. Cleaned out the lowers until they were spotless. Put in the new OEM seals and filled 7.3 from the top down. Then pumped them up and down by hand before I put the forks back on the bike. I do not have the clunk everytime, but only with a small pothole.

dylboss · « **Reply #9 on:** May 28, 2012, 01:17:55 PM »

Quote from: Johnie on May 28, 2012, 01:12:34 PM

dylboss...I did completely removed all the fork oil until dry. Cleaned out the lowers until they were spotless. Put in the new OEM seals and filled 7.3 from the top down. Then pumped them up and down by hand before I put the forks back on the bike. I do not have the clunk everytime, but only with a small pothole.

Thanks. I think Hondaman has some interesting info here. I'm curious to hear his response to my last comment. Really wondering if that bushing needs to be snapped into place or not and if that is in fact causing the noise and lack of damping.

dylboss · « **Reply #10 on:** May 28, 2012, 06:29:11 PM »

Interesting. I'm seeing some inconsistencies between my fork internals and the '72 and '71 part fiches on bikebandit.com. It would appear that my fork internals match a '71. The manufacture date of my bike is 11/71, but is registered as a '72. The orientation of the "bushing/fork guide" is opposite on the two fiches. I'm confused at this point? There is also no lower rod showing in the '71 fiche, but mine has one with a 6mm hex bolt that screws into the bottom, and looks similar to the '75/'76 version without the small spring.

Any ideas?

Tews19 · « **Reply #11 on:** May 28, 2012, 06:46:14 PM »

I was thinking I may have the same difference as you just mentioned Dylboss...... I have a 12/70 build. FIche forks are different then mine as well. I am picking up a bunch of 750 parts this week and will check the forks out on them as well.

HondaMan · « **Reply #12 on:** May 28, 2012, 09:27:16 PM »

Here's the correct picture for the 1969-1973 forks. Honda started using the "other" forks in the New Factory, circa approx. 9/71, on some of the bikes, but not all. Thus, they were pretty mixed, starting in the 1972 model year (aka K2).

All these details are covered in my book in the "Suspension" section.

dylboss · « **Reply #13 on:** May 29, 2012, 09:03:28 AM »

Why is the rod not showing that gets inserted at the bottom of the piston? That rod gets screwed into the bottom of the fork housing. I noticed that on the fiche on bikebandit.com as well.

HondaMan · « **Reply #14 on:** May 29, 2012, 05:09:14 PM »

Quote from: dylboss on May 29, 2012, 09:03:28 AM

Why is the rod not showing that gets inserted at the bottom of the piston? That rod gets screwed into the bottom of the fork housing. I noticed that on the fiche on bikebandit.com as well.

That 'rod' was press-fitted into the bottoms before the K1 came out, becoming removable somewhere during the New Factory K1 forks. The original K0 bikes often had no screw between the axle studs, and this tube was not removable. So, their parts fiche often don't show the right things, because today's parts Techs don't have a clue to the history of these great bikes.

Also, on the pre-"damper-rod" versions of the forks, there is no need to remove this bottom bolt to remove the fork leg(s). In fact, if you do, it is likely that you will have the problems cited above once you do remove it, as it is tough to get it properly realigned. If it is tilted even 2 degrees, the fork tube will not settle all the way to the bottom, which makes it difficult to get the oil to commute between the inside and outside of the tube. This removes all damping, trapping the oil inside the fork tube.

On the later forks, you cannot remove the fork seal unless you also release the bolt and the "damper rod", as it then became called. This later "rod" captured the fork tube, as it was crimped into the bottom of the fork tube on assembly at the factory.

dylboss · « **Reply #15 on:** May 29, 2012, 06:25:56 PM »

First off, Hondaman is the bomb as most of you already know! Thanks for the great info. Here's an update to my debacle....

Took the forks off tonight and completely disassebled AGAIN. Confused, because these parts are not rocket science, I put everything back together and obsessively inspected all parts. The only thing i did differently was that I left the fork tube fully seated and not compressed with the spring slightly exposed at the top by about 4 inches when I put the 7 oz. of oil in. Then I put the cap on and tightened it down. I pumped each fork off the bike to circulate the oil and all felt like it was good. Put the forks on the bike, and same FRIGGIN thing!

After multiple swears, I thought I would try to put in an extra ounce of oil after they were mounted and see what happens. Did that and all is normal now!! No thunk bang any more when fully retracted, and the damping is back to normal.

I don't understand how 1oz of oil can make that much of a difference. Nevertheless, this is the outcome.

Thanks to all who participated.

Tews19 · « **Reply #16 on:** May 29, 2012, 08:00:10 PM »

Great news but now I am curious as to how she feels when driving.

Johnie · « **Reply #17 on:** May 29, 2012, 08:44:40 PM »

Well, if that is all it took I will try it in my K3 & K4. Let us know how it drives and if it is indeed gone. If so, I will add the 1oz and report back.

dylboss · « **Reply #18 on:** May 30, 2012, 01:06:33 PM »

Taking her out tomorrow. I'll report back. I'm also wondering if there was some air trapped in the fork causing the issue, and it was released when I pulled the caps off after they were back on the bike.

dylboss · « **Reply #19 on:** May 31, 2012, 10:46:49 AM »

So, took her out this morning. All seems to be back to normal now. I do notice that there is a lot of head bounce when the road is less than perfect, but that seems the same as it was before I did anything anyway. I'm not sure if that is normal out of these 750's, as I've only been riding them for a season now. I'm used to sport/superbike suspensions.

Tews19 · « **Reply #20 on:** May 31, 2012, 05:10:18 PM »

HAHA I am curious about the head bounce. I had that really bad as well on the 750 when I didn't have the clunking in the front end. This was after the rebuild but before the removal of some fluid. It is much more then my 550 I have. Insight will be much appreciated.

dylboss · « **Reply #21 on:** May 31, 2012, 07:13:22 PM »

well, after a lot of searching. I'm going to fill the forks with 15w oil to see the difference. Plus I'm going to fill them while on the bike this time, rather than off the bilke. Not sure if that will make a difference, but I'm out of ideas.

I took a weight off the front wheel thinking the balance was off, and that actually made a difference. Plus I rebalanced the wheel, and I think the dealership that did it added too much weight.

I'll report back after I change the oil to 15k.

dylboss · « **Reply #22 on:** June 13, 2012, 07:14:36 PM »

Well, I replaced the fork oil with 15w with the forks on the bike. Pumped the forks to get all the oil out, and then refilled with 7.5 oz of 15w fork oil. Checked the damping, and NO difference. I just don't get it. Fork seals are perfect, no leaks. I have about 150 miles on the new seals. It just seems like there is little damping with not much pressure. I'm at a loss!

Tews19 · « **Reply #23 on:** June 13, 2012, 07:19:26 PM »

SO the thumping is back? or the really bad head bounce?

dylboss · « **Reply #24 on:** June 13, 2012, 07:23:10 PM »

Quote from: Tews19 on June 13, 2012, 07:19:26 PM

SO the thumping is back? or the really bad head bounce?

Thumping isn't there, but it just seems like it is very squishy. Like there is water in the forks. I would assume 15W fork oil would be a bit different. SO.....yes, head bounce, but more of my concern is the lack of damping. I can literally push the forks down with little effort with one hand while on the center stand. Can't be right.

Tews19 · « **Reply #25 on:** June 13, 2012, 07:43:59 PM »

Oh thats what you meant. My bad. When I had mine full, I couldn't budge them.

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Author Topic: Replaced fork seals on my 750k2. Strange noise. (Read 9372 times)