which of 2 gasket types for lower fork screw plug?

[jjwithers]

I am starting to put my forks together and while going through my parts, i realized that the new gaskets that I purchased for the large lower screw cap that goes on the bottom of the fork slider... are copper rings.
The old gaskets are a thick ring made of a traditional gasket material.

Is one better then the other? Any idea why BMW changed the style?

I have a hard time believing that the copper is better... for the other ring seems like it would do a better job at sealing that area snugly vs a large copper style crush ring.




Thanks in advance.

-josh

[esman100]

I've had no problems with copper on my airhead forks.

[Motorhead]

In Maintence I use thread tape on the fork plug and a aluminum and rubber on the nut and rubber "O" ring on the top plug

I use what ever comes in a full rebuild kit

[jjwithers]

I used the copper ring on my last rebuild because that is what came with the kit.
I think my R100S has the other gasket though.

I'll probably end up using the copper again because that is what is 'new'. But the other gasket seems like it would make a better seal. If i had a new one, i would use it in place of the copper.

Motorhead, what are each of the plugs you are referring to?
I never thought of using thread tape...

-Josh

[Motorhead]

Bottom plug threads teflon tape where the big copper gasket goes

the 8mm nut on the bottom aluminum washer with rubber gasket

top plug with 2 pin wrench hole rubber "0" ring

[jjwithers]

Just an update to this 2 year old post. I assembled my forks a few months ago and added fluid. I keep noticing the left side was leaking slowly from the copper gasket (due to investigating a small puddle beneath the fork leg).

I didn't use teflon tape around the large screw plug. I probably should have taken your advice.

There is really no spec on how tight to crank on that large lower fork cap though. Should i really crank on it with a breaker bar to crush that copper gasket a bit more? I tightened both sides pretty good but i'm always afraid to use too much strength on aluminum parts. At this point in the game, if i ruined a fork slider, it would be a costly mistake.

I have since drained all the fluid on that side and plan on cleaning and re-assembling that lower section.

And this time I will use teflon. And re-do/repeat on the other side.

I'm also confused with where you put a rubber gasket on the 8mm nut. I usually cinch the threaded hex and 8mm nut and washer pretty tight. with a rubber gasket between all that stuff, i can see the rubber wearing down and creating a big leak in the future.

[Ken in Oklahoma]

And this time I will use teflon. And re-do/repeat on the other side.

Hmmmmm,

Teflon tape is wonderful stuff, but I wouldn't use it for straight threads. I understand that teflon tape is intended for tapered threads, that is pipe threads or certain air or hydraulic fittings. Tapered threads will jam against each other as they are tightened, compressing the teflon between them, creating the seal.

With straight threads, however, compressing happens between two flat surfaces as the threads are tightened. And when a gasket is between the two flat surfaces, sealing happens. Teflon tape might work with straight threads, but you would really need to get the number of wraps just right so that the void is just filled. (Theoretically there is a spiral of air between the male and female straight threads.)

But before I resorted to teflon tape I would re-examine the gasket and metal surfaces again to make sure that there are no nicks, voids, or whatever might inhibit the seal. If I still couldn't get a good seal then I might wipe a very thin layer of grease or silicone on the surfaces and try again. With copper gaskets, you could try re-annealing them. Copper crush washers are intended for one use only, but I would try re-annealing one and see if it worked.

Either that or I don't understand how teflon tape is supposed to seal. And if teflon tape does fix the problem with straight threads, good deal! Never mind what I said.


Ken

[Major Softie]

Ken, your theory is completely correct on the Teflon tape and what it is best at, but that's not why I would avoid the Teflon tape. Little bits of it can get dropped down into the fork when you remove the plug and cause problems. That's why I would avoid it.

[jjwithers]

Ken, your theory is completely correct on the Teflon tape and what it is best at, but that's not why I would avoid the Teflon tape. Little bits of it can get dropped down into the fork when you remove the plug and cause problems. That's why I would avoid it.

The teflon is for the large lower fork end cap that screws into the fork slider's bottom end and has a large copper 'gasket'.
I can't see how teflon would fall into the fork from the bottom.

[robert]

A thin coat of gasket sealer on either type has worked for me.