1981 GS450L Fork Oil Level

[Northish]

Hey fellow GS'ers,
Does anyone out there have a 1891 Suzuki GS450L Factory Service Manual handy? I'd like to know what it lists for the fork oil level.

In all my searching I've found a few folks say that it will require 145 mL in each leg, but I'm swapping in Progressive springs and would like to maintain the correct oil level for a starting point to tune from if needed.

My '81 GS450L shocks don't have the air valve caps on their tops. Does this mean it is specifically a '81 GS450LT?

Clymer lists the following volumes which is a bit confusing and conflicting with the volumes others have mentioned in posts:
GS450N, C = 145 mL
GS450LZ = 189 mL
GS450LD, LF, LG, LH = 277 mL

Clymer also lists the following oil levels for "L" variants:
GS450LZ = 117 mm
GS450LD, LF, LG, LH = 118.5 mm

So if anyone has a hard number from an actual Suzuki Factory Manual I'd love to hear what it calls out.

 

[RichDesmond]

I would just set the level to 125mm. Measured according to step 10 here:

http://sonicsprings.com/catalog/damper_rod_forks_tech_article.php

I would also cut the spacer like the Note A section of those instructions. You don't want the total spring/spacer length to be the same as stock, that will be too much preload with the new springs.
Holler if you have questions.

 

[Gorminrider]

Closest I have per SHOP Manual (not Clymer or Haynes) is from my gsX400 manual...yes my engine is slightly different than yours-still, I've attached a picture so you can see how similar the 1981 GSX L is to your 1981 GS450L.. I pasted a picture from the manual to the page.PS this shows LEVELS in the tube in mm and (inches)

.View attachment 49839

Added: the Haynes manual agrees with this for the GS450 LX (="1981 450L") Haynes does not give volume of oil added for your 81 specifically except as "other" 145cc/4.9 fl oz. of 15w fork oil

Yes there are differences in other years..LZ is 189cc,LD,LF are 277cc. Their oil levels are therefore higher.
It maybe that thes differences are about whether which has air adjustment type or anti-dive or just a new design of fork. And you have made your own changes. so read up on it all...

add-added...I guess simplistically,see it as: you are adjusting the compressible air versus the non-compressible oil

 

[Northish]

RichDesmond - Thank you for the link. That'll be a useful guide for tinkering with things. Much appreciated!

Gorminrider - Thanks for digging up your GSX400 shop manual. Our bikes look very very close to each other.

What I may do as a third check is:
1) Drain the forks
2) Add the 145 mL volume that several sources corroborate on with stock springs in place
3) Measure the height of the oil on the stock springs from the bottom of the spring (like reading a dip stick)
4) Make a Sharpie mark on the new springs from that distance measurement
5) Add 100 mL or so and cycle dampers to fill passages
6) Pull springs, check level, add additional oil until the level reaches the mark

A bit of a process but I don't think it'll be that bad.

 

[Nessism]

I think you are making this too hard. Just pull the top caps, remove the springs, drain the old oil, and replace the drain plug.

Add 100 ml or so of oil, the exact amount is not important. Extend and compress the forks several times to remove air in the damper rods, then fully compress the forks.

Measure how far from the top of the fork tube the oil is using a dipstick of some sort. Then add more oil until you get up to within 125mm of the top as Rich says.

Then extend the forks, install the springs back in and install the caps and call it done.

 

[Guest]

I think you are making this too hard. Just pull the top caps, remove the springs, drain the old oil, and replace the drain plug.

Add 100 ml or so of oil, the exact amount is not important. Extend and compress the forks several times to remove air in the damper rods, then fully compress the forks.

Measure how far from the top of the fork tube the oil is using a dipstick of some sort. Then add more oil until you get up to within 125mm of the top as Rich says.

Then extend the forks, install the springs back in and install the caps and call it done.

Northish says to check the level using the spring, which would read higher than if you used a dipstick. Which is correct, or does the level not change that much - springs in, springs out?

 

[bwringer]

Always measure oil levels with springs out, forks fully compressed. Yes, the springs make quite a difference in fork oil height, not to mention measuring the fork oil and removing excess would be very awkward with the springs in the way and sticking out the top.

 

[RichDesmond]

Also, pay no attention to the factory numbers. Remember, they are from the same geniuses that spec'd the crazy soft stock spring rate.

 

[Northish]

Also, pay no attention to the factory numbers. Remember, they are from the same geniuses that spec'd the crazy soft stock spring rate.

This is a good point. Thanks all for the input. I ended up pulling the forks out yesterday and putting in the new springs and 10W oil. The springs I pulled out also had a progressive wind to them, though the wire diameter was smaller. Perhaps they were also an aftermarket spring? They seemed pretty soft though and I was able to bottom them out and I only weigh 160 lbs.

I've filled them up to 140 mm ( with springs out and compressed) from the tops to start with. I can always add a bit more after a test ride.

 

[herostar]

What are the issues/benefits of being over/under the recommended oil level?

 

[Nessism]

What are the issues/benefits of being over/under the recommended oil level?

More oil = less trapped air inside forks = greater pressure increase inside the forks when the forks are compressed. And visa versa for less oil.