Brand new fork seals leaking.

[K_grendell]

I gave my front end a service last week and redid the front seals with fresh fluid. It's an early 87 k75s with the non snap ring forks. I used oem seals from max BMW (p/n 31421451478) and Honda 10 weight fork oil at a 275cc per leg (precisely measured) Both sides leak an equal amount and the stanchions aren't bent or pitted and in good shape. Any clue as to what I may have buggered up?

[Martin]

You need to reduce your font size we're not deaf. Check to see if the forks tubes are round and not oval. You could try using Johnny's home made Seal Mate just in case you have picked up some gunk under the lips. Were the seals soft and not old stock that had gone hard. You might have inadvertently damaged the seals when fitting.
Regards Martin.

[Laitch]

I gave my front end a service last week. Any clue as to what I may have buggered up?

You probably added too much fluid and/or assembled the parts incorrectly. You'll need drain the all the fluid into a container and measure it then you'll need to disassemble the components and show us the sequence of their installation or it will all remain a mystery.

[K_grendell]

Laitch, the seals seemed to be in good shape, and I even put a film of oil on them to make sure they didn't tear going on. This is probably the 30'th something set of seals I've put on a bike out of all the years I've been wrenching. I made sure to seat them correctly without damage. I think I'm going to order another set of seals and redo it in case it was a hardened set of nos. That didn't even occur to me.


I'll toss another set of seals at it before I pull the legs and Chuck them in a lathe with a dial indicator to check for ovalizing.


Martin, I only slid off the lower legs. I left the upper tubes in the triples, and didn't remove the spring/absorber components. I let drain for 30 mins and compressed the absorber to get out all the fluid. I measured the cc's with a ratio right @ 275. I guess I could have a few cc's more in there then required but I would estimate only 5 or so at most.

[Laitch]

This is probably the 30'th something set of seals I've put on a bike out of all the years I've been wrenching.

I see one or more a few conditions operating here, K gendell.

The seals were installed incorrectly.
The seals were of poor quality. Many of us only use OEM seals.
Lastly, you're the victim of an ancestral curse. You wouldn't be the first here in that category.

[Scott_]

I've not been able to install a fork seal into the lower, then install the upper through it, without deforming it and eventually causing a leak.
Which in the end means I had to remove the whole fork from the tree, with the seal removed from the lower, install the upper into the lower, then slide the seal down the entire length of the upper and seat it into the lower.  Guaranteed no chance of deforming the lips this way.

Like Johnny said, check your bushings. Also suggest you get some gaiters to put on it at the same time as well, keeps the bugs rocks off the uppers. Rancho 1952's are a popular option.

[K_grendell]

Thanks, I've never had a seal deform on me before. I'm going to do new bushes and another set of seals. These leaked immediately after install before even getting 20 miles in. I'll measure the fluid that comes out of each leg as well.

[Laitch]

These leaked immediately after install before even getting 20 miles in.

If that is a result of the seal marketing strategy by BMW to which johnny's friend was alluding, that's just plain over-reaching. :giggles

[Martin]

I've had to replace one set of seals about 16 years ago. I don't run gaiters, but I do place heavy silicone grease under the dust covers, and change the grease when I change the fork oil. Try using Johnny's  home made Seal Mate it's worth a go.
Regards Martin.

[Glacial]

I had one seal leaking, the other OK. I bought new seals off the local BMW dealer and started taking things apart. Mine is a 1990 K75S, so the sliders come off without taking the stanchions out of the headstock. Turned out the dealer had sold me the wrong parts so I had to put the old seal back on. Fortunately I had taken it out carefully. I put the seal on the stanchion and then used a feeler gauge to ease the lip, which had bean bent under, into proper alignment by pushing up from below. Refitted the slider up from the bottom and then used a jury-rigged slide hammer to mostly seat the seal. Final seating required a little tapping in using a C-spanner and a tack hammer. This rather crude and makeshift approach has cured the problem.