Dial Indicator Clearance For Timing

[mcman56]

I'm trying to verify and adjust timing on my 2.9. However, the spark plug thread mounted dial indicator I have will not fit. It looks like I need to remove the radiator fan and radiator to get clearance. Is there a way to get this done without pulling these pieces? The RYP site shows the process but does it use a smaller than standard indicator?

[copemech]

What year is it?

[mcman56]

It is a 2002, 2.9. The indicator will almost fit but the fan motor pushes it a little to far forward to thread in.

[copemech]

Well, if it simply will not fit I don't know what to tell you unless you disassemble the fan.

That year should have the factory alignment mark on the stator plate that alighns with the top casting web. That is all I normally use as a reference point and adjust from there to taste. Putting a specific number in mmBTDC seems less important than how it actually performs in my mind.

[paulthistle]

Copey,

So let me get this straight, you don't use a resistor plug because it is going to affect spark dwell. But when it fires......awww heck it'll fire close enough!

Mitutoyo made a kit with a small diameter dial indicator. I also have a timing tool that screws into spark plug hole that looks like a micrometer. I will look for the brand tomorrow. Central tools made a fixture that allowed the indicator to be off to one side for clearance.

[copemech]

Copey,

So let me get this straight, you don't use a resistor plug because it is going to affect spark dwell. But when it fires......awww heck it'll fire close enough!

Mitutoyo made a kit with a small diameter dial indicator. I also have a timing tool that screws into spark plug hole that looks like a micrometer. I will look for the brand tomorrow. Central tools made a fixture that allowed the indicator to be off to one side for clearance.

Paul, you have to keep things relative dude! Even a factory setting is usually a tradeoff! Fact is you can move the stator a mm or two in either direction and not tell any difference from the base setting. Do you want maximum performance, or smoother operation less prone to kickback and stalling? And this has nothing to do with ease of starting or better low end response and durability of a high end plug.

Within the adjustable range of the ignition timing, you must set it for what you desire and how you want it to perform, and yes, there are limits. A look back to even the factory specs of that time they were all over the board from 2.7 to 3.8 mm BTDC.

Any idea what this translates into DEGREES of angle? You can find TDC then use a strobe to measure it, but you would have to use the strobe only to transfer the particular setting to a different bike due to variences in the individual flywheels and their trigger points.

And yes, my TDC indicator is accurate to within .01 mm, not that means anything with the plug hole at an angle! Go figure!

[paulthistle]

If the 290 has a 60mm stroke with about a 95mm long rod 2.7mm would be about 21.5 degrees and 3.8mm would be 25.5 degrees. You could tell the difference. Although you couldn't tell if you were using a resistor plug or not.

See you at the WR?

All things being relative, I hope to be there most of the week.

[michaelmoore]

On a bike where the plug hole is not parallel to the cylinder centerline I'd do one of two things.

Preferably, I'd hook up a degree wheel and use a piston stop to determine TDC and then set the timing with the degree wheel.

Otherwise, I'd pull the head, set up the dial indicator to run parallel to the cylinder bore, and then set the timing AND make a mark on the flywheel so that I could duplicate that setting in the future.

Most pistons have several degrees of "dwell" at TDC that are very difficult to distinguish with a dial indicator. I'd much rather use a piston stop and a degree wheel to find TDC. Even if I was doing the second method I'd use a piston stop and degree wheel to find TDC first, and then set up the dial indicator.

But if you know the stroke and rod center-center length you can ditch the dial indicator and use the degree wheel (and mark the flywheel afterwards).

cheers,

Michael

[jse]

Preferably, I'd hook up a degree wheel and use a piston stop to determine TDC and then set the timing with the degree wheel.

Michael

What Michael refers to is the "positive-stop method" of determining TDC, developed by ole Ed Iskenderian of "Isky Cams" fame in the 1950's, and still probably the most accurate method using "low-tech" tools. It involves using a device (solid, but with a rounded tip to not damage the piston crown) that threads into the sparkplug hole far enough to stop the piston a little before it hits TDC. An accurate degree wheel is attached and the crank is rotated till the piston softly is stopped by the device and the degree wheel is then marked, then rotated back the other way till stopped and the wheel is marked again. TDC (and BTC) is exactly halfway between those marks. I often use that method to check the accuracy of factory timing marks.

As Michael also mentioned, depending on rod center length, piston dwell at TDC can make using a dial indicator a little "iffy" if you're not very careful. We use "long rods" in engines (say, using a 105mm connecting rod in place of a stock 100mm one in a YZ250 and installing a 5mm spacer under the cylinder) to get two things: a more advantageous mechanical leverage in the crankpin center to piston pin center angle and also to establish longer "dwell" at TDC (it helps the combustion process) and it's that "dwell" at TDC that you have to watch out for when using a dial indicator.

Then again, in Trials engines, we probably don't need to be as accurate in most cases in timing adjustments as, say, setting up a top class roadracing engine, but a lot of us like messing with the machinery and that's part of the fun.

Jon

[michaelmoore]

Here are a couple of piston stops I made from old spark plugs. Getting the ceramic out of the plug body can take a bit of doing, and when you are hammering on the ceramic to break it be sure to wrap a rag around it as if you don't you'll have bits of ceramic shooting all over the place. Eye protection is recommended even with the rag.

cheers,

Michael

[jse]

Here are a couple of piston stops I made from old spark plugs. Getting the ceramic out of the plug body can take a bit of doing, and when you are hammering on the ceramic to break it be sure to wrap a rag around it as if you don't you'll have bits of ceramic shooting all over the place. Eye protection is recommended even with the rag.

cheers,

Michael

Those will work perfect. I've used sparkplug shells for various things like a fitting to use low pressure air to pressure test a two-stroke and stuff like that. I've got a lathe so it's easy to machine off the swaged area at the top of the shell that holds the ceramic center in (the whole ceramic center can just be tapped out). I wonder if one could use a grinder to cut the swage off enough to tap the center ceramic portion out? One of my stops is threaded through the center of the shell so I can use a threaded rod and locknut in it to adjust it's length depending on the engine size I use it in. A very useful tool to keep handy for both 2 and 4 strokes.

Jon

[michaelmoore]

I wish I'd known about that swaged section being what held it together. Removing that sounds like far less aggro than mauling it with a big hammer. I'll have to give that a try and make some more with different sizes of plugs.

The one on the left is threaded while the one on the right is brazed in place. I can't recall why I made the brazed one so long, but there must have been a reason. I'd think that stopping the piston more towards midstroke when it is moving farther per degree of rotation might be a little more accurate, but the difference is probably splitting fractions of a degree.

cheers,

Michael

[jse]

I wish I'd known about that swaged section being what held it together. Removing that sounds like far less aggro than mauling it with a big hammer. I'll have to give that a try and make some more with different sizes of plugs.

The one on the left is threaded while the one on the right is brazed in place. I can't recall why I made the brazed one so long, but there must have been a reason. I'd think that stopping the piston more towards midstroke when it is moving farther per degree of rotation might be a little more accurate, but the difference is probably splitting fractions of a degree.

cheers,

Michael

The longer one would probably not make any difference in accuracy as the measurement is based on static position, not differential rotational degrees.

Don't carry the porcelain centers around in your pocket, in California they are classified as burglary tools under the Penal Code. Car burglers use them to quietly shatter car sidewindows (non-laminated and tempered, unlike the front windshield). Burglers already know this technique, so I'm not revealing any secrets.

Jon

[copemech]

This is why I love Jon, he is a bucket load of (bs) knowledge.

Yet, I digress. You can do the same (dead stop) method with the dial guage either by setting it to where it just moves OR just starts to slow, and splitting the difference, and you don't need an old modifir=eckup plug to do it!

Now just to screw you up even more, I estimate that a 1mm move on the stator plate of your average modern trials bike is roughly equivelant to 1 degree ov timing change.

To quantify this a bit more, my simple mind (only caring where they run as I like) said 1mm would have to equal 1 degree of angle for that to be true. And my simple math then told me that for this to be true, you would need a radius of the stator plate of 57.3mm or so! Huuummmm!

Sounds pretty close to the basic theory so lets proceed. If not, then there is also a ratio of arc angle that can be calculated using the actual stator plate diameter vs the 57.3mm radii to achieve 1degree timing change per x mm of rotation.

So exactly what is the radii or diameter of the inner screw hole pattern or the outer diameter of the plate?

As mine is not apart, (which I am not going to do because I really do not know where it is at to begin with) can anyone tell us those basic circle diameters so I can calculate a basic number based upon the spanish preset dimensions and post a simple number to Jon that can say what I am running and he will then be happy enough with the Spanish equivelant of an answer?

[jse]

This is why I love Jon, he is a bucket load of (bs) knowledge.

Darn, Mark.

I thought I had you fooled.

One of the cool things about my age is, when people ask me

questions and I don't have the answer, I can just make up a

bunch of obtuse stuff and people think I know what I'm talking

about and those who know I'm fulla bs put up with me because

I remind them of their old, beloved, senile Grandfather.......

I think it's time for me to go into politics.

Jon

ps.The bit about the sparkplug centers is actually true.