Rebuilding koni motorcycle shocks

Hello,

I put some old steel-bodied winged logo Koni shocks that I got at a
swap meet on my Norton Commando. They were a big improvement on my
worn out NJB's, but they're still a bit mushy I'm thinking they could
use a change in oil. Good news is that they don't appear to leak at
all.

I asked someone at IKON about getting parts for them, they said that
the design of Koni shock they were reproducing were a bit later, so
they couldn't supply seals, etc. They recommended using 5 wt oil, but
didn't say how much. It looks like I could probably just take the
springs off the shocks unscrew the top of the shock body and change
out the oil by turning the shock upside down and pumping it out.

Has anyone done this before? Not sure how much to add. I was
thinking that I could measure the amount of oil that comes out of each
shock and put in whichever has more in it, if they have different
amounts, due to slight leakage over the years.

Thanks,
Eric

 

It's quite commonly done. You really need a shock compressing tool, to
compress the spring so that you can remove the split collets that hold
it to the body. It is *exactly* like compressing a valve spring to
remove the collets on that. Only bigger.

Measuring the oil will be difficult, because you always get some left
in the shock. Better to mark the oil level with a small scratch mark
on the inside and refill to that level.

 

But how do I know how much oil to add? You mean look at where the oil
level is , before I dump out the old oil?

-Eric

 

Er, yes, duh.

 

Yes, just like with forks. There's a motion-pro tool to do this, which
is a long metal tube that clips to the side. You set the clip to the oil
distance from the top and the tool sucks out oil until it's down to the
proper level.

It's overkill unless you're doing a couple dozen bikes, but it does
illustrate the idea.

I use a wood dowel and stick it in and mark the wet line and the line
where the wood sticks out the top of the fork/shock.

-gc

 

But he doesn't *know* what the correct level or volume of oil
should be, so your suggestions are useless, as is TOG's idea
that he should scratch a line on the inside of the shock body,
because the OP doesn't know how much oil has wept out of the
the shock over years of the rod stroking in and out of the seal.

This shock may be a dual cylinder unpressurized air-over-oil
type, with a piston on the end of the rod stroking up and down in the
center cylinder, pushing oil oil of that cylinder through a hole
connecting the center cylinder with the outer cylinder.

The piston might have a rebound control valve on it, restricting oil
flow as the shock extends and a foot valve attached to the bottom of
the
inner cylinder that blows off excess pressure on compression.

How much oil would a shock like that need? I would think that filling
the
shock until the oil was up to the top of the inner cylinder would be
work just fine.

When the piston is inserted and pushed slowly to the bottom
of the center tube, oil shouldn't overflow the outer tube, there
should still be an airspace above the oil...

 

Except he says they aren't leaking, duh.

The amount of oil lost by the rod going in and out of the seal will be
so small as to be immeasurable.

In other words, guess. Not a good call.

 

There has to be a significant air space over the fluid, or the air
spring effect builds up too rapidly.

There is .pdf file that has a cutaway drawing of an air over oil twin
cylinder shock at the Koni distributor's site, I think it's www.konia-na.com