Fork seals - Why do they leak?

Joined
Nov 8, 2003
Messages
200
Likes
0
#1
The fork seal has become the scourge of the modern motocrosser. Leaking at the most in-opertune time and creating the highest level of incovenience. But what causes them to leak. I have been reading many of the posts on this forum and it would appear that fork seals create the greatest amount of havoc for the greatest number of riders. Fork seals, contrary to popular opinion, rarely blow. Mostly they leak because they have a foriegn object lodged between the seal lip and the fork leg, holding the seal open and allowing oil to leak out. Usually this is dirt or mud, sometimes grass and so on. As modern forks grow in diameter to increase rigidity we also see an increase in seal drag due to the increased suface area. This additional drag creates unwanted harshness due to additional stiction or - static friction. In order to reduce the unwanted stiction the modern seals have less tension against the actual fork leg. Now when your wheel hits a bump we see the impact work in two directions. One tries to compress the fork and absorb the hit, the other tries to break the fork in half and push the front wheel back into the motor. This secondary force causes the forks to flex, usually at the lower triple clamp area. As the forks flex the seals are stressed and any dirt on the fork tube may get past the primary seal lip, lodging uderneath the seal and creating a path for oil to escape. Another from of stress to the fork tube is caused by the brake rotor. As you apply the brake there is a rotational toque applied to the wheel, opposing it's natural momentum. This force also creates stress to the fork leg which can affect the seals and create leaks. Hence the reason why most leaks occur on the brake side first. Obviously the dirt or foriegn matter needs to be removed from the seal to ensure correct performance. This is best done by removing the seal. Whilst the seal itself may not actually be damaged, I would still recommend replacing it with a new one. Only use genuine seals as aftermarket ones seem to leak shortly after installation. To the idiot that first come up with the suggestion that you dislodge the dirt by shoving something between the seal and the fork leg, I would like to see your balls in a vice and I will happily do the cranking. Ninety nine percent of the time you will simply shove that dirt further into the fork where it can do some real damage. Someone is making a tidy profit out of seal-savers. You can actually produce a more effective seal saver for almost nothing. Cut a small strip of foam appr. 10mm x 10mm x 160mm long. Apply a small amount of fork oil and massage in, similar to an air filter. Remove the dust seal and place the foam in the cavity between the dust seal and oil seal. Replace the dust seal and ride. Remove and clean the foam every time you do your air filter. Re-oil and replace. If any dirt gets past the dust seal it will be trapped in the foam before it gets to the oil seal. The oil on the foam lubricates the leg and further reduces stiction. Sometimes fork seals can leak because the seal lip burns due to excessive friction. If bikes are left for a long time or are washed with aggressive detergents the chrome tubes can dry out. When you next ride the seals are subjected to increased friction and a hardening of the seal lip occurs. This hardening reduces the seals flexibility and further promotes leaks. If you haven't ridden for a while or often use harsh detergents, apply a little lube to the fork leg to lubricate the seals before you ride. Good Luck!
Regards
Terry Hay
 

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#2
Terry, what a great post. I am heading out to my vise as we speak. Boy, this is going to hurt!

Honestly, I did this before I bought my seal driver and damper rod tool. Once a person see's the insides of the seal area, it is obvious that the "cleaning" of a seal would actuallly shove the dirt inside the fork bushing.
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#3
I too, have to go for the vise.
But it won't be the last time, as i will continue to shove dirt around(hopefully out) into the legs. Mine always start to leak just before a ride. The forklegs i mean.
 

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#4
I will just use my 3 inch vise. I too will do it if it means ride-no ride.
 

JTT

Subscriber
Joined
Aug 25, 2000
Messages
1,407
Likes
0
#5
Well said Terry!! Thanks for the insight....simple as it needs to be, no simpler ;)

I must admit to having to head for the shed too :( I've used the old "film" trick a few times too, but never really worried about it as I figured the dirt particle was pretty small and insignificant...but know deep down that any dirt is bad dirt....my bad :whiner:
 

bclapham

Lifetime Sponsor
Joined
Nov 5, 2001
Messages
4,340
Likes
0
#6
interesting points! as for the feeler guage- 35mm photo fim method for dislodging crap from the seals, i show the same contempt for those fix methods as i do for nitwits running their premix at 50:1 to stop the pipe spooge.

Terry: there is some debate on wether to pack grease behind the dust seal or not- care to comment??

also, when you say leave the aftermarket seals alone, does this include the Race tech ones also! ;)???

i think the other comment i have, is throw away that piece of PVC tube and get a proper seal driver- when they go in straight and firm they seem to work/last a lot better IMO!!!
 

JTT

Subscriber
Joined
Aug 25, 2000
Messages
1,407
Likes
0
#7
Originally posted by bclapham
nitwits running their premix at 50:1 to stop the pipe spooge.
You mean....that isn't "the fix"?? :eek: ;)

Actually the "ol' film" trick is still handy 10 mins before the start of a moto..beats fork oil on the brake rotor ;) ...of course, that too can be entertaining :laugh:
 

RM_guy

Moderator /
Damn Yankees
Joined
Nov 21, 2000
Messages
6,748
Likes
286
#8
I don't use film but a piece of card stock. I pray that the dirt will stick to the fibers of the card and get pulled out as I rotate it around. I never did like the idea of film. It just seemed like it could cut the seal and make the leak worse. And like JTT says, I only use it if I really want to ride right then :eek:
 

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#9
RM guy, I tried the business card thing a minute before changing my fork seals. I wanted to see how well it worked. I removed one large piece of grit, but found a surprising anount that looked fresh right against one of the bushings.
 
Joined
Dec 31, 2005
Messages
58
Likes
0
#11
I always thought seal savers were just some gimmick. If dirt or moisture got under those it would stay there and create more problems. The oiled foam between the seal and the wiper makes more sense.
 
Joined
Jan 12, 2004
Messages
21
Likes
0
#12
WOW, what a find. Terry Hay wrote this about 10 months after I started developing Synergy Seals. We did not know each other then. All his points are valid and precise. The hardening of the rubber and pivot points on the OEM seals are all real issues that we have fixed. Our rubber is exclusive and propritory and does not harden and our backup ring protects the seal and the DU bushing, it in essense is the pivot point during the forks deflection.
The past 4 years have been onging in development and has certainly paid off for Terry Hay noticed our quality and design and has become our main distributor for Synergy Seals in Australia.

Great write up Terry

Rob
 
Joined
Apr 5, 2006
Messages
33
Likes
0
#14
Old post worth coming up again for sure. :cool:

Now I'm gonna try out that foam trick, because I hate changing my fork seals :bang:

I know it's part of regular maintenance and all but it's one of those things I hate spending $$$ on, I'd rather be out riding than wrenching.
 
Joined
Nov 15, 2006
Messages
80
Likes
0
#15
Does anyone make these foam inserts? My foam cutting skills are probably not precise enough for the job. I am sure someone could make a nice profit on this great idea.