Is the steering stem/bottom clamp square?

[Royboy]

A little advice please.

Here's something I have been pondering for a couple weeks now. After the 77'D took it's spill this spring, and during the subsequent rebuild, I've been fretting over the front end alignment. The bike doesn't handle as well as it did prior to the accident. New parts, (fender, headlight stays) don't fit as well as they should.

The bike went down on the left side, the bars hooked the pavement and slammed hard left, breaking off the steering stop and allowing the fork to punch in the tank on the left side.

We removed the lower clamp, made repairs, replaced the bearings, tried to check for square and reassembled. When I check front to rear alignment now I'm getting several (maybe three) degrees of bias to the left. Yet the stem is 90 degrees vertical to the clamp and the clamp seems to sit square when placed on my sheet of 1/2" glass which is kept around to check such things. The fork tubes roll smoothly when placed on a flat surface.

So here is the question, how do I determine whether the lower clamp and the stem are square? And if not, how do I correct?

As always your wisdom is appreciated.

roy

 

[gggGary]

Both fork tubes should slide up into the top clamp with little or no pushing and shoving to align them with the holes. If that's good then; well you (don't really want to) know.

It wouldn't be the first tweaked frame.

If it comes to that give me a yell.

 

[TwoManyXS1Bs]

I can think of 2 things.

First would be to chuck up the steering stem in a large and/or gap bed lathe, then take indicator readings of various parts of the clamps.

Second, since you have a 1st class floor, use a pair of machinist or carpenter squares, placed a couple of feet behind the bike. Get behind them by a few feet, and eyeball the rear wheel. Move them so that they visually appear to sandwich the rear tire. Shim the centerstand as necessary to get the rear wheel perfectly vertical.

Then relocate the squares to the front of the bike, a couple of feet ahead of the front wheel. Again, from a few feet away, nudge them to visually sandwich the front wheel.

Use yer eyecrometers to see if the front wheel and/or front forks look crooked...

 

[Royboy]

Gary, Bent frame?.........it wouldn't dare. Don't even want to think about it.
I really don't think the hit was big enough to do that kind of damage.

Two Many, I like your lathe idea. (Mainly because it's easier than Gary's)

I've always used two 8' florescent tubes to align front to rear since they really don't bend and were born straight. Maybe that thinking is flawed? IDK I just bungee them to each side of the rear tire and check for equal gaps at the front. That's how I'm coming up with the slight deflection noted.

roy

 

[TwoManyXS1Bs]

...I've always used two 8' florescent tubes to align front to rear since they really don't bend and were born straight. Maybe that thinking is flawed? IDK I just bungee them to each side of the rear tire and check for equal gaps at the front. That's how I'm coming up with the slight deflection noted...

Sure, that's a good way to get the front and rear wheels to align on the same track. But, it can't account for differences in camber, like from a bent neck or twisted swingarm.

Camber induces a very slight turning moment, due to the nature of the differential rubber deflection at the tire contact patch. If your tires are in alignment using your fluorescent tube test, but the bike requires a little handlebar force to ride straight, or a tailgating friend notes that the wheels seem offset while you're riding, suspect differences in camber...

 

[fredintoon]

Gary, Bent frame?.........it wouldn't dare. Don't even want to think about it.
I really don't think the hit was big enough to do that kind of damage. - - -

Hi Roy,
just because you are in denial don't mean it ain't so.
I reckon you have three options.
1) Lower your expectations and ride the bike "as is"
2) Give Gary that yell and see if he's got a tweaked frame fix that'll work for you.
3) Hang a chair on it.
Sidecar rigs don't care if the bike's frame is tweaked because they steer funny anyway.

 

[Royboy]

Thanks guys, I'm off to find a dead level piece of flooring to analyze the relative verticality of each wheel. Considering the local indoor hockey rink. It would be a good test of the rink management's sense of humor and a great way to drop the bike the other way, thereby equalizing the damage!

roy

 

[Royboy]

Just to bring this thread up to date: This spring we had time to get to the bottom of the misalignment woes that the 77'D has been experiencing since last June. We totally disassembled the front end and began a judicious examination of each individual part.

We discovered that in the accident both the upper and lower triple tree clamps had been tweaked, left bent down and right bent up. Very little bend at each point compounded to be a fairly significant misalignment in total. Much measuring and rebending in tiny increments eventually resulted in a front end that tracks true. There was also a miniscule bend in the handlebar which added to the problem.

During the repair process I was amazed to discover just how soft these parts are. Just a bit too much pressure applied in attempting to straighten one side of a clamp would result in going too far. I also hadn't realized how much the front fender does in strengthening the entire structure. I'm thinking fork braces could be important on my bikes in the future.

roy

 

[angus67]

Glad you figured it out. A misaligned bike will eat tires, and on long rides, puts unnesseary stress on your shoulders..
Funny thing about bending steel....tough to get it to start bending, but once the bending starts, it goes quick.

 

[TwoManyXS1Bs]

Roy! Glad you're back. Thanx for the followup.
Bent triples, but straight forks? That's some strange *bonk*...