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TOPIC: Front Suspension

Front Suspension 04 Oct 2019 07:06 #811766

  • martin_csr
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Guess I shall make a spacer based on these test fail and trie serval times ?

That's what I'd do. The fork springs are probably 25mm O.D. In the USA 3/4" pvc pipe has an O.D. of about 1" >> 1 inch = 25mm
Others have reported using pvc. but if you don't like the idea of pvc in there, you could then make a spacer from steel or aluminum after determining the correct length.


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Last edit: by martin_csr.

Front Suspension 04 Oct 2019 08:24 #811778

  • TexasKZ
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The spacer is explained in the link to the springs at Z1E in the original post. However, since Gordone is heavier than the mythical average Japanese rider, he may need to use slightly longer spacers, or even stronger springs.
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Last edit: by TexasKZ.

Front Suspension 04 Oct 2019 08:32 #811781

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Racetech has a calculator. I plugged in 1980 KZ650, commuting, and rider weight of 240lb. As you can see, they recommend a much stronger than stock spring.

racetech.com/ProductSearch/12/Kawasaki/KZ650/1977-80
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
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Last edit: by TexasKZ.

Front Suspension 04 Oct 2019 09:06 #811785

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Before you insert the spacer you need to measure the "Sag" of the forks. then adjust preload from there.

www.motorcyclenews.com/advice/maintenanc...rebound-compression/
-Vic
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'78 kz1000 LTD long term project

'80 kz750G project

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Front Suspension 07 Oct 2019 03:15 #811958

  • gordone
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Thank you all...

Since it looks like I should have a stronger spring I have started to think about…. install emulator valve + new spring...

If I install a new spring now and then install emulator later I need to by another new spring... ???
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Front Suspension 07 Oct 2019 05:21 #811971

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No. The emulator only adjusts fluid movement.

As far as springs go, when you preload a spring by adjustment or adding "spacers" you are only changing the ride height /preload of the spring. The spring rate is still the same. You can calculate and shorten the spring, then add spacers to what you removed. To calculate you can put a broomstick in a vice, place the spring over it, add weight and calculate the amount it compresses.
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Front Suspension 08 Oct 2019 01:56 #812050

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Kidkawie wrote: No. The emulator only adjusts fluid movement.

As far as springs go, when you preload a spring by adjustment or adding "spacers" you are only changing the ride height /preload of the spring. The spring rate is still the same. You can calculate and shorten the spring, then add spacers to what you removed. To calculate you can put a broomstick in a vice, place the spring over it, add weight and calculate the amount it compresses.


ahh okey, but the emulator will also make a preload since it "building", so I need to go down in spacer when I install the emulator, but hopefully the emulator is not "building" more than the spacer?
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Front Suspension 08 Oct 2019 12:57 #812068

  • slayer61
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Shortening forks is a fairly common modification in vintage flattrack racing.

Removing coils from the upper & adding a spacer of similar length to the lower (topping) spring pulls the ride height down.

Ride safe.
Don't be ridiculous! It's only a flesh wound!

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Wife's BIG bike...... 1981 GPZ 1100 Kerker and factory FI
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Front Suspension 08 Oct 2019 14:44 #812076

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Come on guy, you really are putting us on - right? You say you are "heavy" at 140 pounds! So an average weight rider is what - maybe 85 pounds? Did you notice the seat on the bike is built to carry 2 people? So if 140 pounds is heavy then carrying 2 folks who each weighed 70 pounds would be stressing the stock front forks? The bottom line is that Kawasaki was not building bikes for little children who were feather weights, so the stock forks are far more than enough to carry anyone weighing 140 pounds. In fact, the front forks can very easily carry 2 folks who weigh that much with no problems at all. The rear shocks are a different story; the stock shocks were only ok when new and they quickly worsened to a point where they were awful.

The bigger question is how do you plan to use the bike? If you plan to use it on the street the stock forks in good condition work perfectly fine. I know because I've owned my KZ650 for more than 42 years (62,000 miles) and the stock forks still work fine even though I now weigh 200 pounds - of course I do change the fork oil on a regular schedule. If you plan to seriously race the bike on the track you may want to invest in some very expensive suspension parts, but that still won't make a 42 year old bike competitive with many of the newer machines. However, if you install racing suspension pieces on the bike and use the bike on the street you may quickly learn that public roads with bumps, potholes, etc. have totally different qualities than race tracks that are meticulously maintained and that racing suspensions may not work particularly well on many public streets . Ed
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Front Suspension 08 Oct 2019 17:04 #812083

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650ed wrote: Come on guy, you really are putting us on - right? You say you are "heavy" at 140 pounds! d


It was a typo for 240 lbs. I installed race-tech emulators and springs on my 750 twin. It completely transformed the front end. Brake dive is gone, road holding is improved. the bike handles incredibly well for its age. Well worth the expense IMHO.
-Vic
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'80 kz750G project

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Last edit: by DoctoRot.

Front Suspension 08 Oct 2019 23:19 #812104

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So there shall not be any conflict, get correct springs and preload and then install emulators on a later stage?

I have heard I shall not use progressive spring with emulator ?
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Front Suspension 09 Oct 2019 00:13 #812105

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do not use progressive spring with emulators.. I would check your sag and adjust that first, then play with the oil viscosity and level. if your still not happy get new springs and then emulators.
-Vic
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'78 kz1000 LTD long term project

'80 kz750G project
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