Author Topic: Is this frame bent? (Read 1133 times)

Stoli · « **on:** March 14, 2015, 06:42:08 PM »

This is a CB750 '77 Super Sport.

Is this normal for this year/model? All my other bikes are Ks and the back doesn't slope down like this.

goldarrow · « **Reply #1 on:** March 14, 2015, 06:44:19 PM »

I don't have a 77 but that looks way off

754 · « **Reply #2 on:** March 14, 2015, 06:46:17 PM »

Bent..

Stoli · « **Reply #3 on:** March 14, 2015, 06:48:29 PM »

That's what I thought but both sides are perfectly symmetrical. How does something like that happen?

Maybe the passenger weighed 500 lbs?

disco · « **Reply #4 on:** March 14, 2015, 06:58:14 PM »

Ouch! Likely been rear ended. Definitely bent.

754 · « **Reply #5 on:** March 14, 2015, 07:16:20 PM »

Or an endo, check the front.
When you eyeball the front downtubes from the side, do they look parallel.

Stoli · « **Reply #6 on:** March 14, 2015, 07:30:31 PM »

If it was in an accident, it has been rebuilt since. The rest of the frame looks staight. It rides fine. Little shimmy at around 45 mph but smooth on both sides of that.

Don R · « **Reply #7 on:** March 14, 2015, 08:25:34 PM »

I had a 75, it was similar but it was bent on one side. I put straight edges on it from side to side and had 3 different angles. If you could jig it up somehow that could be straightened, the question is what else is bent. It may have done an endo.

Retro Rocket · « **Reply #8 on:** March 15, 2015, 01:16:37 AM »

Quote from: 754 on March 14, 2015, 07:16:20 PM

Or an endo, check the front.
When you eyeball the front downtubes from the side, do they look parallel.

I'm with you on the endo, I certainly wouldn't ride using that frame until it was put on a frame jig and straightened or replaced...

MoMo · « **Reply #9 on:** March 15, 2015, 04:06:50 AM »

If there was an endo most likely there would be damage around the steering neck too. No signs of stress marks around the neck?...Larry

calj737 · « **Reply #10 on:** March 15, 2015, 04:55:35 AM »

I tend to disagree about being rear-ended. Because the seat rails are open on the end, any direct impact from the rear sufficient to bend those two tubes symmetrically downward would have dislodged the seat and spared the tubes. And if rear-ended to that degree, the swingarm and axle stays would be rather damaged.

I suspect the force came from above the seat, toward the rear of the bike, perhaps even intentionally? It is bent, no doubt.

You can bend them back, carefully! Use 2 steel square tubes laid above the bent tubes as guides. Weld cross braces in, and then use some heat on the points where the tube is bent. Draw the tubes up with straps/clamps by running another square tube under the open end. Heat, patience, and do each side individually. This is a DIY method, but a frame shop/jig is a sure fire way to fix it too.

Retro Rocket · « **Reply #11 on:** March 15, 2015, 05:08:23 AM »

It would be a bit harder than that to straighten Cal, there is a bend in the rear down tube, the top bend is actually after the shock mount, in front of the rear down tube, so its not quite that simple mate...

calj737 · « **Reply #12 on:** March 15, 2015, 05:29:14 AM »

What I did not say, cuz I thought it was obvious, is the shock gusset needs to be relieved to allow the tubes to move freely. Nothing is too hard with some fabrication, but this approach will work. I just didn't document all the steps/attachments... Gotta leave something to the imagination

Garage_guy_chris · « **Reply #13 on:** March 15, 2015, 08:55:49 PM »

Id say bent too but were forgetting one thing:

Just plain too much weight on the rear extension part of the frame.....

As for fixing it I see the bend in the two rear down tubes too. I think it would require a tear down and some big heat and force to bend back. In the end it may be easier to find a virgin unbent frame, paint it and transfer everything to the new frame

Retro Rocket · « **Reply #14 on:** March 15, 2015, 11:14:18 PM »

Seeings though these frames have a weak spot at the swingarm pivot I would be worried about alignment there, racers put an X brace above the pivot for strength and to restrict movement, I also wouldn't be surprised if the back engine mount bolts are tight as well, that would have taken a pretty large amount of force to have done that much damage...

Stoli · « **Reply #15 on:** March 16, 2015, 08:13:36 AM »

Thanks to all for the insight.

I just found a replacement frame on eBay. I'm rebuilding this bike for my son, so I'm not going to take any senseless chances. We can't prevent all accidents but it seems to me that riding around on a questionable frame is a risk that can be easily avoided for relatively short money.

MoMo · « **Reply #16 on:** March 16, 2015, 08:30:39 AM »

Don't let this guy ride as a passenger on the new frame or you will wind up with the same problem

SOHC4 Cafe Racer Fan · « **Reply #17 on:** March 16, 2015, 08:48:54 AM »

Quote from: Stoli on March 16, 2015, 08:13:36 AM

Thanks to all for the insight.

I just found a replacement frame on eBay. I'm rebuilding this bike for my son, so I'm not going to take any senseless chances. We can't prevent all accidents but it seems to me that riding around on a questionable frame is a risk that can be easily avoided for relatively short money.

Good call.

Retro Rocket · « **Reply #18 on:** March 16, 2015, 02:43:56 PM »

Quote from: CB750 Cafe Racer Fan on March 16, 2015, 08:48:54 AM

Quote from: Stoli on March 16, 2015, 08:13:36 AM
Thanks to all for the insight.

I just found a replacement frame on eBay. I'm rebuilding this bike for my son, so I'm not going to take any senseless chances. We can't prevent all accidents but it seems to me that riding around on a questionable frame is a risk that can be easily avoided for relatively short money.

Good call.

+1

News:

Author Topic: Is this frame bent? (Read 1133 times)