getting bent (frame, that is)

[Anonymous]

Hi Everyone!
Jeb the Newguy here. I've owned my '81 GS850G for about two years now, and have enjoyed (nearly) every minute of it. Love the website. Tonight's big question: what is the procedure to determine whether my frame is bent? There is some crash damage by the previous owner (bent cyl. head fins), and the front downtubes have obviously been rattlecanned, hinting at AFL (abrupt fairing loss). However, they appear straight visually. There are some small handling problems (ie: headshake decelerating from about 40 mph).Thanks in advance for your input!

 

[argonsagas]

No professionalism involved with this opinion, and it won't directly address all of the frame, but it may make your bike track better.

First you must get a bit of enjoyment to set up your mood, before you visit a bank to get a loan for a terribly expensive bit of absolutely necessary equipment, so be sure to ride the bike there, circle the block where the bank is located a few times, have a coffee, then just go in and do it straight up.

You will need to borrow as much as $15., but be prepared for the bill to reach as high as $20.....depends on the stores near you.

You need a standard level and a piece of chalkline, or masonry cord. Looks like string, but, unlike household string, the chalk/masonry lines are resistant to stretching.


Basically, you will tie the line on something solid in front of the bike, and the tie-off point should allow the line to be brought back close to the bike, but not touching it.


The bike must be on its centrestand, and you must check that the bike is level, from side to side. Remove the seat and place the level on the frame. Use shims under the stand, if necessary, and take all effort required to make it exactly level.

Keeping it quite taut, pull the line STRAIGHT back until you are behind the bike.
Bring the cord in line with the tires, very close to them, but not touching. Sight along the cord, and you should see evenness in the cord spacing, meaning there should be exactly the same distance between the cord and the tire at both the front and the rear of each tire.

This will determine if your wheels are in alignment.

While the bike is in the same position, tie the cord well ahead of the bike, and above it. Draw the cord straight back, and over your steering head, taking great care that it passes EXACTLY over the centre, and draws straight back until it passes over the rear of the frame. Keeping the cord taut, and straight, bring it down until it touches the rear of the frame and mark that spot with a VERY sharp pencil point, or a knife edge. Measure the distances from each side of the frame to the mark. They should be identical.

You need to use a ruler that has is marked in fine increments, not a standard yardstick that has 1/8 inch markings.

The steering head itself is difficult, and should probably be checked by a shop, as you need to check it in fore-aft, and lateral directions. They should have instruments that will do it for you quickly.

For lateral directions, you remove the front wheel, then, using your cord and a plumb weight to ensure the line is vertical, you position the line close to the steering head, right at its centre. Use a bright light positioned close to the line. This is used to cast a shadow from the line against the steering head. Then do a visual check to ensure the shadow line is equal in spacing from top to bottom. Any variation means the head is bent sideways.

Note that the plumb line, once centred across the steering head, should not be allowed to touch the floor, or anything else. You should also find that it is exactly centred between the forks.





You could use the plumb line to check fore-aft bending as well, by having it just barely brushing the bottom of the steering head, and then accurately measuring the distance from the top of the head to the plumb line....but knowing what to do with the information requires that you know what that exact distance should be.



Headshake....check your tire pressures, and check wheel balance.

Also check for play in the wheel bearings and the steering head bearings.

 

[Anonymous]

getting bent (frame, that is)

WOW!! thanks for your considerable reply! I'll let you know what I come up with, after a few beers anyway. Does anyone know what a frame shop charges, and can they do work with the engine and forks installed, etc?

 

[terry]

Re: getting bent (frame, that is)

WOW!! thanks for your considerable reply! I'll let you know what I come up with, after a few beers anyway. Does anyone know what a frame shop charges, and can they do work with the engine and forks installed, etc?

I bought an '80 model GS1000ST a couple of years ago that the owner had crashed into the back of a car on his way home from having the bike serviced. Anyway, the forks were bent, and you could tell that the front downtubes were bowed as well.

I bought some used GS850G forks (they're the same as the GS1000) fitted them, then trailered it over to a frame straightener, the guy there told me that because of the special jigs they use, that it is actually preferable to leave everything on the bike, except the fuel tank.

Anyway, all up it cost about $400.00 (Aussie dollars, so about $250.00 US) and tracked and handled fine after the repairs. I rode it for a few months before I sold it and there were no irregularities that I could report, the guys at the shop said it wasn't a bad one, but steel frames are a lot more "repairable" than the new alloy frames, that are very brittle.

If your damage is not noticeable to the eye, the frame could still be slightly bent, but would certainly be repairable. Of course, there may be other reasons for that "head shake" that you mention, including worn or incorrectly adjusted steering head bearings, swing arm bearings, wheel bearings, worn shocks, tire pressure etc etc. The "rattle can" paint job on the front down tubes could be as innocent as touching up stone chips, as the front down tubes are the most common victims of this kind of trauma. :twisted:

 

[Anonymous]

Although I can ride it fine and no real handling problems:

My 82 GS750TZ obviously has the back tire out of VERTICAL alignment. The tire will actually touch the side of the fender if under heavy load or nice size bump in the road.

Does anyone know how to bring this tire back to vertical? Would it be the swing arm being bent? or the frame? or both?

How would I determine which?

What is the remedy for any of these situations?

Thanks for any assistance.

 

[SqDancerLynn1]

My GS850 had head shake if you let go of the bars it would shake violently Tightened the steering stem brg NO more problems. Just movve the adjuster like 1/4 in at a time while on the center stand after each adj check that the wheel will go from center to the stop using its own weight
Don't over tighten it IT will make low speed handeling very hard