Dial indicator to measure timing ?

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Kthomas

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Does anyone know how many (if any ) degrees one should add to compensate for the angle when using a dial indicator to measure piston position ? I guess I should just use a disc.
Also, we’re there differences in primary covers as far as the timing scale piece. I’m trying to figure out what is wrong either with my rotor of the gauge. When I find tdc with the gauge the mark on the rotor is straight up so I don’t think the rotor has come apart. I’m using a tri Spark. When I first set the timing using the scale and rotor mark the bike just backfired so I put the dial gauge in and set it. The marks on the scale looked to be about 10 degrees off. After setting it with dial gauge at 29 degrees ( which is what my manual said / not 28 ? ) the bike fired up first kick and ran good although after a hard rum for a couple miles the pipes were bluish. Aaarrrrgggghhhh ! Maybe carbs but plugs looked ok. Premiers 19 pilot 260 main 3.5 slides.
 
www.accessnorton.com

linear piston travel and advance degrees

I was not able to edit my previous list of figures that were generated using an incorrect metric con-rod length for the Commando. Here is the new list using an 89mm stroke, 5.875 inch (149.225mm) rod length. 31°= 0.320" (8.127mm) BTDC (Before Top Dead Center), 30°= .300" (7.63mm) BTDC, 29°=...
www.accessnorton.com www.accessnorton.com
 
Several reports of timing scales being off anywhere from half a degree to 3 or 4 degrees. If any doubt, you should check your via a degree wheel and a piston stop to determine true TDC (rotate one way til contacting stop, noting wheel number, then rotating other way til stopped and taking that wheel number, dividing the two reading difference to be true TDC; place wheel zero at that pointer location), then set to your desired advanced position, remove wheel, fit primary cover without disturbing crank, and see what scale indicates. Mine was out reading is about half a degree further advanced than reality.
 
Rgm Norton Pipes. I wish I had coated the inside but I really don’t mind.

I suppose I’ll pull the primary cover and verify whether or not my dial indicator procedure was correct. I really don’t think it will be any different but ?
However I don’t understand why the marks on the rotor are so far off unless the rotor has come apart internally and moved.
 
Kthomas said:
Rgm Norton Pipes. I wish I had coated the inside but I really don’t mind.

I suppose I’ll pull the primary cover and verify whether or not my dial indicator procedure was correct. I really don’t think it will be any different but ?
However I don’t understand why the marks on the rotor are so far off unless the rotor has come apart internally and moved.
Click to expand...
What makes you think the rotor is off? I'm not sure where the marks end up when at TDC....but most certainly not in line with anything on the primary cover scale as that only shows a limited range around 30 deg BTDC.
 
When my dial indicates 29 degrees the TDC mark on the rotor is to the left of the scale with the leading edge of the hump ( that the mark is on ) at about 18 degrees on the scale.
 
Maybe my rotor was originally from a triumph or BSA or ? Wouldn't that kinda make sense if it’s about 10 degrees off ?
 
The angle of the indicator "feeler" matters not whan determining TDC.

It only needs to be carefully set by turning the crank forward and marking the position, then cross-checked by turning the crank backwards and verifying the same exact position (as nearly as possible). OR, if they differ slightly, carefully determining the half-way position between the two readings, and re-verifying they are repeatable.

The rest is up to your careful mounting of a good degree wheel to the crank nose.
 
Kthomas said:
I suppose I’ll pull the primary cover and verify whether or not my dial indicator procedure was correct. I really don’t think it will be any different but ?
However I don’t understand why the marks on the rotor are so far off unless the rotor has come apart internally and moved.
Click to expand...
Yes do that and correct the degree scale.

If the rotor center is slipping, I would think the numbers would be reversed and the timing marks showing retarded. However, I might be thinking more about what would happen with a harmonic balancer on a V8. Check and compare where the keyway is on your rotor in relationship to a new Norton rotor image. Must be an image of one here or on one of the vendor websites.

Yes you'll have to remove the nut. Comes off real easy though with an air impact wrench.
 
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I do not use a dial micrometer when setting my timing. I use a spark plug with the electrode removed and soap bubble to find TDC, and set the degree disc pointer. Then I rotate the crank backwards from TDC to the required timing. I never use timing marks for anything on any motorcycle. If the timing error is one degree off, it can be compensated for, by jetting. But more error than that might be a problem.
The combustion conditions in your motor are a balance between fuel octane rating, compression ratio, ignition timing and jetting. It is important that once your ignition timing is set, it should not move. Each time I work on my ignition timing, I always check my jetting afterwards. I get best acceleration by jetting as lean as possible on the needles and needle jets, so it is important the ignition timing does not move.
 
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Kthomas said:
Maybe my rotor was originally from a triumph or BSA or ? Wouldn't that kinda make sense if it’s about 10 degrees off ?
Click to expand...
No they are the same except for the Trident or Energy Transfer rotors. Trident rotors are thicker and ET rotors have three holes in the back to set the rotor timing.
 
For those who miss the obvious (like me), how does one make a soap bubble and how does one transfer it onto the hollow spark plug? The principle sounds to me like the most accurate and simplest way to find TDC.
 
BERT said:
For those who miss the obvious (like me), how does one make a soap bubble and how does one transfer it onto the hollow spark plug? The principle sounds to me like the most accurate and simplest way to find TDC.
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The most accurate method is the degree wheel/piston stop. ALL other methods are less accurate because they do not account for the "dead spot" at the top of the piston movement where the crankshaft moves but the piston does not.

That being said, other methods are "accurate enough" depending on what level of accuracy you need. Heck, putting your thumb over the spark plug hole is all you need (to feel the compression) in some cases. ;)
 
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Bert writes: "For those who miss the obvious (like me), how does one make a soap bubble....?"
Perhaps it's not true that all we really need to know we learned in kindergarten. :)
 
MexicoMike said:
The most accurate method is the degree wheel/piston stop. ALL other methods are less accurate because they do not account for the "dead spot" at the top of the piston movement where the crankshaft moves but the piston does not.

That being said, other methods are "accurate enough" depending on what level of accuracy you need. Heck, putting your thumb over the spark plug hole is all you need (to feel the compression) in some cases. ;)
Click to expand...
I simply extracted the electrode from an old spark plug and broke the exterior porcelain off fairly level. I add a bit of washing-up detergent to water to make a bubble over the hole with my finger. As you wind the piston up towards TDC, the bubble gets bigger, and past TDC it gets smaller. It only takes an extremely small movement of the crank to find TDC when the piston moves. I rotate the crank backwards and forwards a bit and stop where the bubble is at it's largest. If the bubble is inside the hole, I stop where it is closest to the top of the hole.
You usually only have two variables to contend with - the ignition timing and the jetting. If you advance the timing, it has the effect of leaning-off the jetting. But if you are jetting really close to the optimum, it is extremely important that the ignition timing does not move. That applies even if you use an advance curve - the curve always needs to be in the same place ( static advance).
One degree error in the ignition timing is probably too much
 
MexicoMike said:
The most accurate method is the degree wheel/piston stop. ALL other methods are less accurate because they do not account for the "dead spot" at the top of the piston movement where the crankshaft moves but the piston does not.

That being said, other methods are "accurate enough" depending on what level of accuracy you need. Heck, putting your thumb over the spark plug hole is all you need (to feel the compression) in some cases. ;)
Click to expand...
I totally agree
The positive stop method is the only method that is absolutely precise
But it's not necessary on an old pushrod twin
Just stick a screwdriver in the plug hole
Find tdc , find the amount of "rock" you have at tdc
Then halve it
That'll get you accurate enough to zero your timing disc
 
The piston stop method is the only method if you have the head off the bike, otherwise the bubble, or a TDC tool that screws into the spark plug hole is the go.
 
I recall reading on another thread that it is best to take your degree measures a fair bit away from true TDC as the angle of the plug hole means greater error as you near zero degrees. Hence why a piston stop is best.
 
"The piston stop method is the only method if you have the head off the bike,"

Not sure why you'd say that. The piston stop method is equally "easy" (or not) with the head on or off. But as Baz pointed out, on these old machines, for most operations, that level of accuracy is overkill.

Frankly, if you are intent on getting a precise reading for your timing scale, even with the piston stop method there is enough slop in the assembly of the chain case cover to produce at least one or maybe two degrees of variation every time you remove/replace the cover. ;)

IOW, if you were to "correct" the scale based on the piston stop (or any other) method, if you removed/reinstalled the cover and checked it again, there's an excellent chance it would not agree.
 
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