Twisting Frame

when i go around corners fast, my bike seems to twist and "hop" around the corners, it is a 1976 kz900. its like the back wheel goes out of line with the front wheel and then springs back really fast, but all of the bearings seem fine, to me it feels like the frame or swingarm severely twisting, is this possible? if so can it be remedied? also, my speedo doesnt work and i was wondering what mph 8500 rpms would be, i believe i have stock chain and sprockets. thanks, ryan

your frame could be twisting, and yes there are ways to stiffen up the chassis, but I'll let some of the more knowledgeble ppl answer more on adding braces in certain locations. speedo question, what gear are you in? Mph at 8500 will be different in each gear

The 900 frame werent know for their strength. They were more known for their flex.
Heres a link to the archive showing a frame bracing kit for the Z-1

kzrider.com/forum/viewthread.php?tid=6818

Daniel

sounds like your suspension is not set correctly, you might have an old tire that needs replaced, wheel alignment needs adjusted, or bad bearings in your wheel or steering stem.

well i was going down the highway in 5th gear at 8500 rpms. i was definately going fast but i was wondering if anybody ever looked at the tach when they were going fast in 5th and would be able to approximate how fast i was going. and the swingarm bearings seem find and i just put on a new wheel with seemingly good wheel bearings. maybe the bike wasnt designed to be cornered like that i dont know, i have scraped the crash bars several times on corners like that so its defenately about as far over as it can lean. so maybe you could tell me some things to do for the bike for racing. thanks, ryan

You need to check a number of things.

Swingarm bushes - make sure there is no play on the swingarm.
Wheel bearings - you should not feel any movement of the wheel when rocked side-to-side
Chain alignment - do not rely on the chain adjuster marks - either get down on the ground behind the bike and visually line up the wheel, or run a straight edge or string alongside the tires to check alignment.

Pretty much everything flexes on the 900 frames (Z1 and KZ). The older Z1 frames had smaller diameter frame tubes and less bracing at the head, but it's worth checking both frames for cracks at the head from wheelies/crashes. The KZ frame actually flexes a lot less than the older Z1. In addition to the frame, the forks flex, the swing arm, and, if you have spoke rims, your wheels will be flexing as well. BUT, the flexing inherent in all of these components should not cause any kind of sudden "hop" in corners (unless you're totally off the throttle in which case pretty much anything could happen). So, as has been mentioned, you can brace the frame, and you can brace or replace the swingarm, and buy a brace for the forks. Of course, you should make sure that you don't have any other issues, and it sounds like something is not right - all the flex and proper technique should result in predicatble "wallowing" - no "hops", so check your drive chain, fork action, rear shocks, front and rear wheel alignments, wheel rim runouts (and maybe even balance), and by the way, if you're grinding some kind of crash bar/case savers in the corner then this will produce some "hops", that is, until you're catapulted off the road - take the bars off and get a low profile timing cover.

Post edited by: jenshhj, at: 2005/10/18 11:25

bangshift440rt wrote:

well i was going down the highway in 5th gear at 8500 rpms. i was definately going fast but i was wondering if anybody ever looked at the tach when they were going fast in 5th and would be able to approximate how fast i was going.

See how fast you're going at 4250 RPM in 5th and double it. That's assuming your tach and speedo are accurate at normal highway speeds.

my speedo doesnt work at all though, i just know i was in the passing lane flying past some cars with incredible haste.

My vote is for something worn as Jeff suggested you check. I have a 76 900 and it exhibits none of the problems you're experiencing. Have you taken a really close look at the frame welds, is something broken?


When I had about 10K on the meter I started to have a problem with the front end going everywhere if I hit a bump while in a turn. I went so far as to fit a steering stabliizer. Two years later I decided to tear down the back end for maintence. Lo and behold the swing arm bushings were all ovaled out, that was the problem all along.
KZCSI

Post edited by: kzcsi, at: 2005/10/18 15:04

The most likely problem is old and uneven fork fluid.
Real old trouble shooting guides would tell you to look at the fork if you have a problem with the rear wheel tracking and a loss of fork oil is common for these old bikes.

Replace your fork oil an see if it makes a difference.

Spock

You can also weld gussets on the frame and that will help. There is a company that sells a kit but it's a bit spendy. I think it's around $160.