Wobbling points cam? 1973 CB750

[Gas]

Do you guys know if it is possible to true out a wobbling points cam? it has an unknown history so unsure about how it happened. Although busted lower points cover screw threads and aftermarket points cover suggests it may have been laid over. It runs fine. Because the cam is shaped oblong it's hard to tell if it is wobbling, but the nut at the end of the crankshaft/points cam sure does wobble. Is it fixable? Any ideas before I take it apart? I do have a machinists dial indicator and stand  if that helps.

[Lucky 1]

The nut may be wobbling because bolts are never perfectly centered. That IS normal.
That is true of all engines.

QUOTE
"Although busted lower points cover screw threads and aftermarket points cover suggests it may have been laid over. It runs fine. Because the cam is shaped oblong it's hard to tell if it is wobbling, but the nut at ."

You may be wasting your time chasing ghosts.

Many bikes get laid over. More than once. Happens all the time. It does not mean the crankshaft is bent.
You are worrying too much.


IF you have nothing to do.....

Take the points cam OFF. Inspect for damage. Check for damage
to the points cam, and check for damage to the crankshaft.

Use a bright light and really look.
Now measure from each side of the engine case to the center of the shaft.

USe a pair of vernier calipers. Or use your dial indicator.
Do not expect it to read Zero.

[TOOLS1]

The points cam sort of butts up against the end of the crank, and is held on by the 6mm bolt (10mm head.) It has a little nub sticking out of it that aligns it on the end of the crank to time it. I have never seen one wobble, and the engine still be able to run, but I suppose it could happen.
TOOLS

[Black 750K8]

Yes you can without a doubt.

The points cam sort of butts up against the end of the crank, and is held on by the 6mm bolt (10mm head.) It has a little nub sticking out of it that aligns it on the end of the crank to time it. I have never seen one wobble, and the engine still be able to run, but I suppose it could happen.
TOOLS

The 6mm bolt that tools refers to is what gets bent usually from someone turning over the motor with a socket on that big nut with the plugs still in.

You said " It runs fine" so wait till your next 3K tuneup to look at it. If the 6mm bolt is bent it is easy to fix you all ready have the tool and I can walk you through it.  

[Gas]

After a second look, it certainly wobbles at the center of the bolt. Looks to be about .5mm deviation No callipers needed. It'll run better after I replace the 2 bad condensors (never seen that before..) and sync the carbs. But I can't do that until I sort this out.

The bike is worth the time. Whoever had it made it a beautiful bike but never bothered with the technical stuff.

My brain tells me tightening the 10mm nut back to spec would butt the 2 machined surfaces on the crank and cam together and make the cam true, but the bolt/nut might still visibly wobble. That may be the case now I suppose.

[Lucky 1]

.5mm is only .019 thousandths!

How can you see that.?
Look at .019 on a pair of calipers. It is very very small. Silly

[Gas]

When a shaft is rotating at high speed, it's pretty clear when it is out of true. .5mm is a big deal. I don't go by inches. THey are obsolete

[Black 750K8]

When a shaft is rotating at high speed, it's pretty clear when it is out of true. .5mm is a big deal. I don't go by inches. THey are obsolete

Very true the easy way to tell if it is bent when you put your timing light on it will be real jettery you will see the flash in one spot then another it wil bounce around. to fix it just take off the advancer then put the bolt back in by itsself put your dial indicator on it then turn the engine over by hand I use the kicker and take the slack out then bump it with my fist move it 180 when you see how far off it is then with a small tack hammer gently tap the head off the bolt the way it needs to go and get it as true as you can maybe .001 if you take some time.

[Lucky 1]

"I don't go by inches. THey are obsolete"

Not in this country!

Use metrics it still comes out the same.
What is the next smaller icrement below mm's?   Huh?

[Black 750K8]

You have that right.

[TOOLS1]

I'm with you there Lucky. Ever tried to divide 10 by 3, or 4? It just does not work. That is why country's that use the metric system still use foot inches in construction.
TOOLS

[Gas]

LOL. you guys lost me here...

That's 3.33, and 2.50.

Metric is superior in every possible way. In construction, there's no need for mm precision. Also, it's easier to communicate it in a loud shop or across a job site and there's no subtracting or adding of fractions to do in your head. Please reference info that shows where metric countries use inches in construction. I've made mistakes on 50 foot steel beams because of god forsaken fractional inches.

[Black 750K8]

Sounds like someone did not do well in math class. I can ad or subtract fractions in my head and all ways be perfect well within a mm or two

[TOOLS1]

I also have no problem working with fractions. However a lot of carpenters will just holler to the cut man a number like "3 feet 4 inches, and 10. The 10 being the number of 16th of an inch needed. As for precision metric is not any more precise then feet inches.
As for other countries building with standard measurement, just ask any one from another country. I have friends from Mexico, Guatemala, Honduras, Dominican Republic, Brazil, Ireland, Denmark, and Canada. They all know, and use the Standard system when building. The reason for this is because building materials are still made to industry standards, Dimensional lumber is always cut to standard measurements ( 1X?, 2X?, 4X?, then there is plywood. It's always 4'X8'. A foot can be divided by 1, 2, 3, 4, and 6 evenly. Can't do that with metric.
TOOLS

[Gas]

Europe industrial went metric in 1968. The sizes are still the same because lumber is an international commodity. I just got done reading a few pages in a forum where several Europeans from different countries were explaining to an American architect how they design their buildings in metric (a requirement) and how they cut and order their lumber. Then a Canadian chimed in. They construct in metric also. Not just the architects in their CAD programs, but the carpenters, too. Some old guys still use imperial measurements when calling out cuts, but they admit to creating confusion among workers when the floor plan is drawn out in meters.  A 4x8 sheet of plywood is known as 1.2 by 2.4 m

Metric doors are a slightly different in size, for instance. That can create some real confusion.

How quickly you can divide a foot by different numbers is irrelevant, and rarely happens in construction. And if you're fabricating or drawing out a part, a calculator or cad application is usually in front of you already. Not that you'd need it, because the only uneven divisions are (3)3.33 and (6) 6.66. That's 33.3 centimeters. Easy to remember. The .3 is irrelevant, unless you're cutting that piece of wood or metal to a third of a mm, which is nanometer precision.

If you yell 3 foot 4 and 10 you're gonna confuse someone. That's 5/8ths

I looked this information up to satisfy my own curiosity, not to argue points. There are cases where some carpenters/drawings in nearby countries still use inches. But they, like US, are the minority. The only reason lumber sizes are matched to the original imperial equivalent, is because when the industrial powerhouses of the word started going metric, it made sense to not throw out or recalibrate the cutting machines.

[Gas]

I fixed the wobbling points cam and went through all the wiring in the bike and used dielectric grease. There were a few other issues that popped up with the bike but for the most part it went smoothly and the bike ran great except for a bland spot in the mid range which I blame the pods for. Plug chops showed fine for idle and main. Clip adjustments made no improvement, and air screw either. It was my customer's first bike and I recommended he go back to the stock air box so the bike runs like it was designed. A bike with pods is impractical anyway. You get stuck in the rain and you're screwed. I should have taken a picture of it. It was beautiful. Thanks guys. I have another nice looking cb750 a friend owns that has sat in a shed for about 5 years. He wont finish it because he doesn't have the technical know-how and never owned a bike before. We are talking about "stealing it" and fixing it up behind the scenes with his girlfriend for their wedding.