Frame flex

Posted: Mon Nov 05, 2007 6:15 pm

How many of you ride your CB-Fs hard enough to feel frame flex?
For the past 8 months I have been riding my CBX only and the other day when I finally got to ride my red bike again, it was like riding a wet noodle the way she flexes.
It is amazing how much flex can be felt just getting up to freeway speeds on the CB-F but she accelerates so hard that I have to hold on for dear life and it feels like she wants to twist into a pretzel.
My CBX does not have any noticable flex compared to the CB-F and the CBX can handle more radical riding than I feel I can ride her at safely with my riding skills. A real race rider could probably make her scream around a track.
Anyways, do any of you feel your CB-Fs flex at all like I am trying to describe?

Posted: Mon Nov 05, 2007 6:22 pm

Only when I have the chassis loaded hard, I notice it the most on hard right handers, I'm guessing that is because of the removable frame rail

Posted: Mon Nov 05, 2007 6:41 pm

Yep, my 1100 is loose like a goose.
The 900 is tight...

Posted: Mon Nov 05, 2007 7:10 pm

I don't even think you have to load it up very hard to feel it. Heeled over I can feel it in the pegs over undulations in the road.

Posted: Mon Nov 05, 2007 9:04 pm

How much does the bracing of these frames take care of that? Where are the best places to brace them? Also does the 750 frame flex less because it is tied in to the engine w/o those rubber mounts? Just wondering if any of you have an opinion on this.

Jeremy

Posted: Mon Nov 05, 2007 9:39 pm

Ray,
Where do you feel the frame flexing? With my 1100 fairing install on my 750, I had to remove my steering stabilizer due to mounting issues. Without I definitely feel flex when I accelerate hard and into a turn.

Posted: Mon Nov 05, 2007 9:49 pm

BlueThunder wrote:

Ray,
Where do you feel the frame flexing? With my 1100 fairing install on my 750, I had to remove my steering stabilizer due to mounting issues. Without I definitely feel flex when I accelerate hard and into a turn.

The whole bike is a wobble in progress even with a steering damper, .95 kg Race Tech fork springs and Ohlins shocks.

Posted: Mon Nov 05, 2007 10:05 pm

I've had 5 1100F bikes and never noticed anything like what you call frame flex... Maybe I'm not paying attention, eh?

Posted: Mon Nov 05, 2007 10:10 pm

PapaLuker wrote:

I've had 5 1100F bikes and never noticed anything like what you call frame flex... Maybe I'm not paying attention, eh?

The way you ride a CB1100F and you never felt flex?
You are a mad man and earned my respect for your riding skills a long time ago. I wish I had the same skills you have. Rolling Eyes

Posted: Mon Nov 05, 2007 11:00 pm

My red bike has a new name, she is now called the Red Flexi-Flyer because as much as she flexes, she also flies super fast.

Posted: Mon Nov 05, 2007 11:21 pm

ive done the modern running gear swap on many old bikes besides my super F.

1100 katana,Z-1,gs1000,xs 650 etc etc.it made every one of exhibit pronounced flex.

they isntantly have geometry/traction they were never intended to have.

the 1500cc katana i built was a real handful.

Posted: Mon Nov 05, 2007 11:39 pm

burned wrote:

ive done the modern running gear swap on many old bikes besides my super F.

1100 katana,Z-1,gs1000,xs 650 etc etc.it made every one of exhibit pronounced flex.

they isntantly have geometry/traction they were never intended to have.

the 1500cc katana i built was a real handful.

I have been riding these bikes like this for a few years now and always noticed the flex but not like I notice it now that I have ridden my CBX that has the exact same mods as my CB1123 Super F does and there is no comparison. The CBX is a more firm bike frame wise and uses the engine as a stress member which really makes a hell of a difference so I am noticing for the 1st time.
I just got back from a ride on Mulholland Drive, not quite Mulholland Hwy but close enough for the middle of a city and the bike handles better now than she did when she was a fully stock CB1100F but, her flexing is more pronounced because I have been riding the CBX for so long and I am spoiled by a firm riding CBX compared to the flexible ride on my CB1123 Super F.
It is not that I can't control my CB-F, I can and quite nicely too. It is that I am just not used to riding the bike and it is going to take some getting used to all the new APE seals actually sealing the head on my semi new Wiseco 1123 piston kitted, FCR'd Dyna 2000 power along with the flex.
My CBX is slow compared to my CB-F. Rolling Eyes

Posted: Mon Nov 05, 2007 11:55 pm

My F bikes have always felt pretty solid to me for an old bike. The new radial tires will really load up the frame, but it never did anything funny. I do notice the engine moves a bunch under power.

One thing for sure is Da'Beast is more solid than the OMT bike. It has a welded R/H down rube and several braces, and feels pretty solid. Not a modern sport bike but not bad at all.

I think it is important to torque the engine bolts down in a certain sequence. First, make sure the bike has all the weight on its wheels, torque the frame tubes, torque the rear engine bolts, then torque the front engine bolts.

I doubt if you made this mistake Ray, but one time I bought a 900 that had the two front pivots arms switched. They are not the same. That bike had a bad wobble until I fixed it.

Other abvious stuff are swing arm pivots and steering head have to be nice and tight fitting. Also having all the engine spacers installed right.

My next project will have a braced 750 frame...

Posted: Mon Nov 05, 2007 11:57 pm

I took off my oil pan the other day and noticed a couple 12MM threaded holes I presume were for the original exhaust pipe mount.
I wonder if the stock exhaust plays a part in the overall rigidity of the frame?
As well I wonder if these same threaded holes could be used to somehow
strenthen and fix the flex problem.

Posted: Mon Nov 05, 2007 11:59 pm

That is a great picture of your bike Ray. It looks angry, and ready to go!

Posted: Tue Nov 06, 2007 12:02 am

Don't take this as black and white. Just what I think. It's really hard to actually feel frame flex. It has to be relative against another part of the frame. So, with your butt on a foam seat, hands on the moving handle bars and feet on rubber pegs, it would be very hard to notice at all. I can judge frame flex by handling and responsivness of a bike. But then again, there are factors like fork and shock settings, swingarm bushing and steering neck bearing wear, tire pressure, etc. I've had two superbikes with tubular trellis style frames which are famous for their flex and give. Both with very torquey L-Twin motors. I've never felt any flex on them even on the one with motor tweaked close to 130 HP. What I did notice, is that the bike was a lot more forgiving if you were sloppy in corners, or had to do mid turn corrections. I've pushed lateral grip more than few times past it's limits, and have gotten plenty of warning and been able to just drift it out sideways. I've even lost the front tire once and got it back without crashing. While really stiff bikes like GSX-R seem like they're on rails turning. And as soon as you jump the track just an inch, they will catapult you 10 feet in the air and self distruct.

Same thing on older bikes. I had a bunch of Suzuki GS bikes. All with solid frames. They were all a bit nasty tempered in corners. First thing I noticed when I got my 900F, is how forgiving the bike was if you were sloppy. I also noticed that the 750Fs are a bit more twitchy if you push them hard. Maybe what you're feeling is the rubber engine mounts. Honestly, who has bothered to replace the stock ones? And they are getting old.

Posted: Tue Nov 06, 2007 12:57 am

Ray,
If you feel the flex that much, I can't help but feel that something major is out of whack. I know you have the experience and knowledge for the obvious so I'm not even going to waste anyone's time stating them.

I had a slight wobble that got progressively worse at 60 and above to where I felt unsafe at 85. It turned out be tires. I replaced the Dunlops with Avons and the bike became rock solid. I have also found this on my car as well. Front end vibration disappeared when a new tire was fitted. In both cases, the tire still balanced fine. Other than that...

CB1100F Joined: Mar 03, 2004 Posts: 3278 Location: Seattle

Nope, sorry Ray.. I havent had any frame flex issues on my 1100F..... Shocked

Posted: Tue Nov 06, 2007 1:05 am

i get what ray is saying.its not that its not rideable or normal,just different than his cbx.

its something he would have never noticed had he not been flogging the cbx lately.

Posted: Tue Nov 06, 2007 1:29 am

burned wrote:

i get what ray is saying.its not that its not rideable or normal,just different than his cbx.

its something he would have never noticed had he not been flogging the cbx lately.

Yes, that is it, I have been flogging the hell out of the CBX and she is handling it better than I thought possible.
I am not saying that the flex is bad, just different and going to take some serious getting used to again. I used to be used to that bike but I have not really had a chance to ride her in the canyons but one time since I put the 41mm CBR F-2 forks on the bike and only twice with the Ohlins because she was not registered or insured and I had no license but, all that is changed now and I can flog her now too. {Her Cobra is un-corked and she has her velocity stacks on, whoa!!!}
I will take her up through Little Tujunga Canyon tomorrow and see how she feels after a run in each direction on that bitchin 18 mile twisty.

Bob, if you ever get down here to L.A. I will let you ride my CBX and you will see what a firm riding bike is like and then you will notice the flexability of your CB1100F.

Posted: Tue Nov 06, 2007 2:19 am

One of the big differences between the CBX and the CB-F bikes is how the steering head is braced. The CBX frame looks beautiful up there, very wide to handle the top engine mount hangers between cylinders 1-2 and 5-6. When you consider that on a CBX all three coils lay mount easily between the frame rails and you can barely stick two coils between the frame rails on an F that gives you some idea of how well (relatively speaking) the CBX steering head is triangulated against side loading and deflection.

Anyway, that's what I think that's the biggest difference between the two.

Solid mount the motor on any of the rubber mounted motors to make an F instantly better.

Posted: Tue Nov 06, 2007 2:36 am

DennisTheMenace wrote:

Solid mount the motor on any of the rubber mounted motors to make an F instantly better.

Yes, the CBX frame is a bit wider for sure.

My "R"eplica will have a solid mounted engine to go with the Pro-Link shock & F-3 forks. I have heard they handle pretty nice and am looking forward to finding out for myself.

Posted: Tue Nov 06, 2007 2:39 am

I ride a 1999 VFR as my alternate bike, and the 900f feels like a wet noodle in comparison. My 900 is stock but rebuilt with new steering bearings etc, so it is tight, but no comparison to the VFR. When you corner over bumps, the 900f has very complex motions whereas the VFR has simple suspension motions, no other degrees of freedom, in engineering speak. My 900 is stable at 70+ mph so I know there is nothing wrong--it's just the basic flexibility of the frame etc.

Posted: Tue Nov 06, 2007 3:19 am

The problem is part the rubber mounted motor. The 750 frame is really poor in that the drop out tube does not even attach to the rest of the frame,the gap is "hidden" by the motor mount.

The fix is a welded on tube for the drop out piece to enter similar to the 900/1100 frame.

The larger reason and the reason the CBX is better is the frame head as was stated. The 900/1100 frame has no engine connection except through rubber. This makes the entire frame head unsupported all the way from the gas tank rear mount around to the rear lower mount,this entire deal can move,and move a lot. On all the wrecked frames I have seen this entire deal is shoved some direction,but usually a sideways twisted look.

The CBX has the aluminum plates bolted to the top of the engine,so gives a wide support right next to the frame head.

CB1100F Joined: Mar 03, 2004 Posts: 3278 Location: Seattle

Only running 1100F I have is Da Beast, Ray... Cool

Posted: Tue Nov 06, 2007 1:15 pm

Blainethemono wrote:

Only running 1100F I have is Da Beast, Ray... Cool

I still want you to ride my CBX. Wink

CB1100F Joined: Mar 03, 2004 Posts: 3278 Location: Seattle

I definitely would like to give it a try Ray..... When I get Da Beast fixed, (you reading this Martin?), we will have to do another NW trip.... That should give Stout a chance to build his 1100F project too...

Posted: Tue Nov 06, 2007 6:57 pm

Blainethemono wrote:

I definitely would like to give it a try Ray..... When I get Da Beast fixed, (you reading this Martin?), we will have to do another NW trip.... That should give Stout a chance to build his 1100F project too...

I will bring the CBX next time I come up there to let you guys see for your selves how much of a beast she really is.
I told Jons I would let him ride it if I ever came back up there with her and I will let each of you that so desire to ride her try her out as long as you have the funds to back up any unforeseen circumstances. {That is a bike of equal value to replace mine if you wreck it.} Wink

Posted: Tue Nov 06, 2007 8:33 pm

DennisTheMenace wrote:

One of the big differences between the CBX and the CB-F bikes is how the steering head is braced. The CBX frame looks beautiful up there, very wide to handle the top engine mount hangers between cylinders 1-2 and 5-6. When you consider that on a CBX all three coils lay mount easily between the frame rails and you can barely stick two coils between the frame rails on an F that gives you some idea of how well (relatively speaking) the CBX steering head is triangulated against side loading and deflection.

Look at what Dennis was talking about in this picture of my undressed big girl.
I just did a valve adjustment and only found two valve that were not @ .005". They were @.004" so I changed the shim on one from a .292 to a 290 and the other was a 300 changed to a 295.
Now I need to wait for the tach drive seal and the 8 new valve cover bolt seals so I can close her up.

Posted: Thu Nov 08, 2007 3:48 am

I've always felt the X's were quite a handfull. They are stable bikes but you have to really work to get them to respond. Of course, I've never ridden one with good tires, suspension, and wheels. When I bought my new 750F back in 1980 it was known to beat the X (and almost any other bike of the time) in the handling department.

I think the real key is the frame. My R was rock solid but it never had modern rubber or wheels to really test it. Getting rid of the rubber mounts, and solid downtubes, must be the ticket on an F bike.