Tips on installing external fork springs with preload

[jabcb]

Finally getting around to dealing with the really bad fork spring sag on my 69 T350.
My old topic on this is: viewtopic.php?f=2&t=10874

Am going to try springs that are longer than stock.
Any tips on how to easily install external fork springs with a good bit of preload?

[Vintageman]

acquire or fabricate a spring compressor tool? Either whole length or a multiple locations along the length.

How much force do you think you need to apply

[jabcb]

This will be my first time working with external fork springs.

The springs have around 1.3” of preload, which is about twice what new stock springs would have.
That works out to about 40lb of preload.

[rngdng]

I use cheap turnbuckles and "S" hooks from the hardware store to install shock springs. They would work for this as well....



Lane

[jabcb]

Have an possible solution.

Part #s for the 69 T350 & T500:
fork tube top bolt: 51351-11011
o-ring: 51181-11010 / ID 8.8mm & tk 2.4mm
fork assembly tool: 09940-30110

The Suzuki fork assembly tool screws into the tube instead of the top bolt & you just pull up to compress the fork spring.

If I can find a threaded rod that screws into the tube instead of the top bolt,
then the threaded rod + bearing seal driver + some nuts might allow me to easily compress the spring with a wrench.

[jabcb]

Finally getting around to dealing with this problem. This is for a 1969 T350 but it also applies to a T500.

The fork tube top bolt has M10 x 1.25mm threads.
So I got a M10x1.25 threaded rod that’s 150mm long. Used a fender washer + 3 nuts, and I had an easy to use tool.
Very easy to use. Just screw it in, hold the top two nuts, and use a wrench to turn the bottom nut.
(Use the lower triple tree pinch bolt to hold the fork tube before installing the tool & before removing the tool.)
SimpleTool_0702 by jabcb, on Flickr

I used a standard spring that I got from TheSpringStore.com, part # PC177-1875-12.000-MW-7.750-CG-GI-IN
Its a little longer than the stock spring:
AltSpring1_1 by jabcb, on Flickr

The TheSpringStore spring has a smidgen smaller ID than the stock Suzuki spring.
The fork dust boot sits on top of the fork seal. It easily drops in the stock Suzuki spring but rubs a bit when you push it in the TheSpringStore spring.
It pushes in on one end easier than the other, so I put the “easy end” down. Also used a little grease on the spring ID where it rubs against the dust boot.
AltSpring1_2 by jabcb, on Flickr

Will post more info in a few days after a test ride.

[jabcb]

T305/T350 fork spring spec:
T305_ForkSpringSpec by jabcb, on Flickr

T305/T350 spring calcs:
Suzuki_T305_spring by jabcb, on Flickr

T500 stock spring calcs:
Suzuki_T500_spring1 by jabcb, on Flickr

TheSpringStore spring calcs:
TheSpringStoreSpring2 by jabcb, on Flickr

And the resultant calcs for a T305/T350:
SpringComparisonCalc by jabcb, on Flickr

These springs are within 10mm of solid height when the forks are fully compressed.
Having exposed external springs might be cool, but they are a problematic design limitation.

The old Cycle World article recommended a 30# spring with an inch of preload for the GT500.
TheSpringStore spring is close to that, so hopefully it turns out well.
http://www.ozebook.com/compendium/suzi/ ... AtHome.pdf

[jabcb]

Went for a short ride & am definitely pleased with the result.

The gas tank on the bike when I got it was actually for a T250 — that tank is now on the GT250 cafe build.
Looking much better with the correct tank + some other improvements.
I got the rack from forum member, Johnakay a few years ago. But rats, the seat cover is not correct for 1969.
A little more sorting & the bike will be done. Pic from today:
T350-1969_0708 by jabcb, on Flickr

[sportston]

Went for a short ride & am definitely pleased with the result.

The gas tank on the bike when I got it was actually for a T250 — that tank is now on the GT250 cafe build.
Looking much better with the correct tank + some other improvements.
I got the rack from forum member, Johnakay a few years ago. But rats, the seat cover is not correct for 1969.
A little more sorting & the bike will be done. Pic from today:
T350-1969_0708 by jabcb, on Flickr

It looks great! You have a very lovely bike. I particularly like the colour. Don't fret too much about the seat. It looks nice, even if it is not the right cover.

[jabcb]

Was organizing stuff & just a bit curious about other options.

Stock T305/T350 & T500 springs are 7” long & have rates of 26 & 42 lb/in, respectively.
TheSpringStore spring is 7.75” long & has a rate of 29 #/in.

I found another option. Same as stock at 7” long. Rate of 35 lb/in, which is about the midpoint between the two stock springs.
Its Compression Spring Corp. spring 3148. http://www.centuryspring.com/compressio ... -3148.html

I haven’t run the spring stress calcs, so I don’t know how it compares. I would recommend do the calc before ordering the spring.