Topic: Fork Flex

[BrickWoll]

Hey all,

Is it by design that 550 forks flex forward and rearward a bit under normal road chattering?  This movement is a little disconcerting when I'm looking down at it.  Forks and triple are stock '77 CB550 K3.  Forks are lowered about 1.5". 


Thanks!

[Don R]

 Those are probably the same #341 lowers the 750's use but with a shorter chrome tube. I wouldn't expect to notice flex. Check the top tree clamps for broken loops where they clamp onto the tubes. 
 (The reason I mention it is, my 750 had modified 550 triples and both sides were broken)

[bryanj]

What front fender is fitted?

[ofreen]

Some fore and aft flexing is visible even with forks with thicker tubes than the spindly ones on our old bikes. Sight along the tubes when you apply some front brake. You will see some deflection. Disconcerting? Just another one of those things that’s best not to think about when riding down the road with any of a myriad of mechanical failures that could happen at any moment resulting in you wearing your bike as a hat.

It wouldn’t hurt to check steering head bearing adjustment, though.

[PeWe]

I had a badly worn front tire that caused fork tube flexing in higher speeds.

[newday777]

What front fender is fitted?

+1
Without the front fender you loose stability built into the fender brace.

[Tracksnblades1]

I’d check for fork spring spacers…not sure if it was a 550 thing or not..

Ran across a 4 inch set in a 75k.  Forks wouldn’t compress unless you used the front brake…

[BrickWoll]

Those are probably the same #341 lowers the 750's use but with a shorter chrome tube. I wouldn't expect to notice flex. Check the top tree clamps for broken loops where they clamp onto the tubes. 
 (The reason I mention it is, my 750 had modified 550 triples and both sides were broken)

Thanks, Don. Not exactly sure what I'm looking for.  I don't see any obvious cracks in the top tree.

[BrickWoll]

What front fender is fitted?

Stock fender (bobbed).

[BrickWoll]

I had a badly worn front tire that caused fork tube flexing in higher speeds.

Thanks PeWe, but just got new rubber at the end of the last riding season.

[spotty]

my first 750 ( K2 ) had longer forks ( about 5 inches or so ) and would flex around 3-4 inches at the wheel. i cured this by not looking down there 

[seanbarney41]

You ever notice that the only modern motorcycle that still has 35mm fork tubes is a hell of a lot smaller and lighter than a cb550?  hmmm?...

[spotty]

You ever notice that the only modern motorcycle that still has 35mm fork tubes is a hell of a lot smaller and lighter than a cb550?  hmmm?...

whats worse is they kept using them right up into CB900s

[Don R]

 This, Except I didn't notice any flex.

[TwoTired]

This, Except I didn't notice any flex.

Isn’t that what happens when those clamp limiter washers aren’t installed and the bolts over tightened?

[MauiK3]

Ouch, scary!

[Don R]

This, Except I didn't notice any flex.

Isn’t that what happens when those clamp limiter washers aren’t installed and the bolts over tightened?

   In this case, both sides had the D washers, but the bolts were extremely tight. This was a set of 550 trees on a 750 frame, the neck had been welded to make it long enough. Apparently, he wanted the smaller 550/500 offset. It's a road race thing I guess.

[Ichiban 4]

When I bought my '77 550K years ago..it had that 'fork flex' thing going on that Brickwoll was talking about earlier..same thing..high speed wobble..seemed to be above 50 mph..if memory serves me.

My solution was to install a fork brace from Spec II in So. Cal.  Not sure if they're still in business but URL to their website is: http://www.spec2.com/clips.html#apps 

Since that time (over 20 years ago)..I never noticed the high speed wobble anymore..so seems to have fixed it.

I also think that there are other brands of fork braces available..or that were made..that would probably do the same thing as the Spec II brace that I got.

Ichi

[Shtonecb500]

I had lots of fork flex when my springs went bad.

[calj737]

I had lots of fork flex when my springs went bad.

fork flex is a reaction of deflection of the tube and has nothing to do with the compression of the slider/tube as it relates to the stiffness of the spring.

These 40+ year old tubes are too long, too thin-walled for the weight of these bikes. Fork braces help a bit, but they reside on the sliders, not the tubes so as to not interfere with the travel, thus not really eliminating the flex.

It’s as Sean said, old tech for too heavy bikes. That’s why modern forks are bike are better-rated for their weight.

[BrickWoll]

This, Except I didn't notice any flex.

Yeah - that's all bad.  If the bolts on the bottom triple loosen, the riding position gets real aggressive real fast.

[HondaMan]

When I bought my '77 550K years ago..it had that 'fork flex' thing going on that Brickwoll was talking about earlier..same thing..high speed wobble..seemed to be above 50 mph..if memory serves me.

My solution was to install a fork brace from Spec II in So. Cal.  Not sure if they're still in business but URL to their website is: http://www.spec2.com/clips.html#apps 

Since that time (over 20 years ago)..I never noticed the high speed wobble anymore..so seems to have fixed it.

I also think that there are other brands of fork braces available..or that were made..that would probably do the same thing as the Spec II brace that I got.

Ichi

Back 'in the day' we used several things to reduce the wobble of the 500/550 at hiway speeds when the tires were a little 'flat' in the center from wear/lack-of-care issues.

The $5 'fix' was to install cut pieces of [electrical conduit] pipe into the forks, against their springs, to raise the front end, as it was sprung too soft for all but the lightest of riders. Essentially, this restored the lost trail, which was marginal when new, in the front: this improves stability naturally.

The $50 'fix' was the fancy  stainless-steel 'hoops' that were the over-the-fender fork brace (I've forgotten the maker) that was a show-stopper. It worked REAL well, but they never made one for the 750. (Dang...) I also added spring shims (usually 3 thick washers on each side) when installing these, and it gave the bikes a little more aggressive-looking stance, if it did make them lean over further on the sidestand.

[PeWe]

Tricky with a fork brace for the 341 lowers CB750 K2-K6. Probably the earlier too.

It has been a variant before with stock fender in place
http://forums.sohc4.net/index.php?topic=103654.0

Another thing is a clamped one as this.
https://carpyscaferacers.com/shop/shop-our-store/motorcycle-parts-accessories/honda-cb500-cb550-cb750-parts-upgrades/alloy-fork-brace/

I doubt it can sit that close to the lowers. A deep road bump need some dampening. Not a hard sudden bottom out.

But it must improve  even if sitting a little higher.

[spotty]

having the front guard/clamps/over the top hoop in place aren't going to do much for back /front flex, as said above its the cr4ppy long thin tubes that are flexing backwards and forwards.

all the above will stop or reduce lateral twisting which basically occurs between the axle and the lower triple clamp so having a stiffening method between those points will eliminate ( or at least reduce ) twisting

and like i said above, if you don't look at it then all is good.....