Front forks air gap

[KiwiBiker]

I managed to bluff my way through replacing both my front forks oil seals today on my GK76a.
I see in the specs that I was to pour in 390ml of 5wt fork oil (which I did) but whats this 97mm air gap all about?
Ive screwed them back together and they feel fine testing them in the workshop but not back on bike yet.
Thought I would sort out this air gap business first before re-fitting them.
Thanks for any help proffered.
Al.

[wullie3xv9]

The air gap is (usually) checked with the springs removed & the forks compressed before you finish rebuilding them & refitting them to bike. You'll need a dip stick of some kind, ( I use a six inch / 15 cm ruler ), to check the gap.
I put a piece of of masking tape across the ruler 10 mm above the spec. level which I line up with the top of the fork,
( in this case at 107 mm's ), so you can see when you're getting close to the correct level. You'll have the correct air gap when the oil is up to the 10 mm mark on the ruler. ( Remeber to hold the forks vertical ).
Hope this makes sense. Unless you're the pedantic type I wouldn't worry about it tho'.
If your forks were fairly well drained of the old oil then the air gap won't be a million miles away.


If you'ed like to firm up the the forks a bit you can reduce the air gap 10 mm's at a time. ( i.e. 87 mm's) .... or
.... to soften them a bit you can increase the air gap by 10 mm's. ( i.e. 107 mm's ). Hope this also makes sense.
( Less air in the forks means the air will build up pressure quicker when compressed so the forks shouldn't compress as much under braking. Too much oil will blow the seals early tho' ).

FYI, KB, I have SILKOLENE 5 weight fork oil & stock springs in my GK76's forks at the stock 97 mm air gap & I'm more than happy with how they feel/work , & some of the roads in my neck o' the woods are far from smooth!
(Mine is a road bike with one track day under its belt).

[KiwiBiker]

Thanks for the reply wullie, yep I understand all of that. What I dont understand is how you adjust the air gap? It would have to be by reducing or increasing the amount of oil you put in the forks wouldnt it as there's pretty much only one position you can screw the top cap back on to the forks in.
So is this just a more accurate way of checking you have both forks even encase you still have some old oil sitting in the bottom of the forks when you poured the fresh stuff in? Mine were flushed out fully with brake clean and blowen out with compressed air.
I work in an engineering workshop which is why I'm surprised that I dont get this whole air gap thing. Lol.

[wullie3xv9]

Quote Kiwi Biker :- "What I dont understand is how you adjust the air gap? It would have to be by reducing or increasing the amount of oil you put in the forks wouldnt it as there's pretty much only one position you can screw the top cap back on to the forks in".

Wullie. Sorry for slow response, K.B. Yes, you can reduce or increase the air gap by increasing or decreasing the amount of oil into the fork. i.e., More oil = smaller air gap. Less oil = bigger air gap. I should 'ave put it that way in the first place!

Quote K.B. "So is this just a more accurate way of checking you have both forks even in case you still have some old oil sitting in the bottom of the forks when you poured the fresh stuff in? Mine were flushed out fully with brake clean and blowen out with compressed air".

Wullie :- Aye, so your air gaps shouldn't be a million miles away then.