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Author Topic: Fork Spring Question  (Read 1334 times)

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Offline Kustomizer

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Fork Spring Question
« on: January 13, 2015, 08:23:52 PM »
I'm in the process of tearing my front forks on my cb750 apart and the springs are 18 5/8th" long and I was wondering if these were within tolerance to keep using?
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Offline scunny

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Re: Fork Spring Question
« Reply #1 on: January 13, 2015, 11:40:36 PM »
there are manuals available on here, just down load yours. sorry I can't give you specs, I ride a 650
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Wobbly

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Re: Fork Spring Question
« Reply #2 on: January 14, 2015, 01:02:28 AM »
If it is a K7/K8, they need to be replaced (service limit 19 1/2 in or 495.0 mm). I don't know about the earlier models.
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Offline oldhatt45

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Re: Fork Spring Question
« Reply #3 on: January 14, 2015, 06:42:07 PM »
Kustomizer,

I recently replaced my fork springs (1976 CB750 K6).
I put in the Progressive fork springs (progressive rate) that came with a PVC spacer.
If I recall correctly, the springs were around that 18 5/8 length dimension.
Once you add the PVC spacer you're right around the 19 1/2 inch dimension that Wobbly quoted.
I'd have to go dig out the paperwork, but I'm pretty sure I'm right.

What I would check is are your current springs "progressive rate"?  If so they are not in all likelihood original, and probably should have spacers.  If they are not "progressive rate" springs, then it may be more difficult to figure out if they were replacement springs that should have had a spacer or springs that have collapsed over time.

I know this is not much help, but a few things to check.

Charlie
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Offline bjbuchanan

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Re: Fork Spring Question
« Reply #4 on: January 14, 2015, 07:07:34 PM »
They are probably saggy originals

You can't compare aftermarket sizes even with preload spacers because preload spacer is dependent upon the actual spring rates and free lengths. The length being near stock can be totally coincidental
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The dirty girl-1976 cb750k, Ebay 836, Tracy bodykit
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Offline evanphi

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Re: Fork Spring Question
« Reply #5 on: January 15, 2015, 05:58:52 AM »
Serviceable limit is 18.11" for up to K6, yours are 18.625". Getting sloppy! Time to upgrade!

« Last Edit: January 15, 2015, 09:08:57 AM by evanphi »
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--Evan

1975 CB750K "Rhonda"
Delkevic Stainless 4-1 Header, Cone Engineering 18" Quiet Core Reverse Cone, K&N Filter in Drilled Airbox
K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

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CB750 Shop Manual (all years), searchable text PDF
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Wobbly

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Re: Fork Spring Question
« Reply #6 on: January 15, 2015, 08:35:41 AM »
Quote
Serviceable limit is 18.11",
Definitely not for the K7/K8
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Offline evanphi

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Re: Fork Spring Question
« Reply #7 on: January 15, 2015, 09:09:14 AM »
Quote from: Wobbly on January 15, 2015, 08:35:41 AM
Quote
Serviceable limit is 18.11",
Definitely not for the K7/K8


edited mine. :D
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--Evan

1975 CB750K "Rhonda"
Delkevic Stainless 4-1 Header, Cone Engineering 18" Quiet Core Reverse Cone, K&N Filter in Drilled Airbox
K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
Calculating the correct input circumference for digital speedometers connected to the original speedometer drive

Offline Kustomizer

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Re: Fork Spring Question
« Reply #8 on: January 15, 2015, 09:53:00 AM »
Quote from: evanphi on January 15, 2015, 05:58:52 AM
Serviceable limit is 18.11" for up to K6, yours are 18.625". Getting sloppy! Time to upgrade!


Thanks for the info!
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Offline PeWe

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Re: Fork Spring Question
« Reply #9 on: January 15, 2015, 12:00:17 PM »
Progressive springs and correct amount of oil, see attachment in this thread.
http://forums.sohc4.net/index.php?topic=144208.msg1641369#msg1641369
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http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
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http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
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http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967
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