Piston Stop/ignition Timing

[youngbloodhawk]

seems as though we used to use a stop with a

calibrated slide that telescoped out the center

to accurately set time on our Bulls and Pentons.

dont seem to be able to find what i remember now.

maybe i am dreaming

that said

what is the best/most accurate method of setting ignition timing

[pschrauber]

You need a piston gauge, beware off the cheap stick with a scale they don't show anything useful.

That's how mine looks like:

This is crap:

You need a multimeter too:

Here is one from the US:

http://www.hiperf.com/ATV/acatalog/Shop_Equipment___Tools.html

Maybe you find something likewise a little bit cheaper?

[feetupfun]

The tool that is labelled as crap is perfect for setting the motor to TDC, and this is useful because a timing mark can be applied to the flywheel rim using a measured distance from the TDC mark. Once you have the timing mark in place, the points can be set on future occasions without needing any tools in the sparkplug hole. The circumferential distance between the TDC mark and the timing mark can be derived from the geometry of the motor components, or by using a dial indicator.

The timing mark can be used to check the timing while the motor is running, using a timing light, which is the ideal way to test for correct timing.

[youngbloodhawk]

The tool that is labelled as crap is perfect for setting the motor to TDC, and this is useful because a timing mark can be applied to the flywheel rim using a measured distance from the TDC mark. Once you have the timing mark in place, the points can be set on future occasions without needing any tools in the sparkplug hole. The circumferential distance between the TDC mark and the timing mark can be derived from the geometry of the motor components, or by using a dial indicator.

The timing mark can be used to check the timing while the motor is running, using a timing light, which is the ideal way to test for correct timing.

thanks

you verified my old days way is still proper.was looking for old schoolslide stop,dial indicator nice but too new school for my need project

what i wanted to do was use an old school stop to mark tdc on flywheel then a Moon camshaft degree wheel to mark on the flywheel the desired timing range(cheating method for old guys) for non adjustable timing light. dial back lights can and usually do fluctuate unexceptably at the highest rpm's where timing is most critical.

have a shop full of vintage Sun Diagnostic and Distribuitor machines,various dwell meters ,mostly analog,a dozen or so timing lights going back to the 30's ,and even multimeters

why do i need a multimeter to time a Bultaco?

[pschrauber]

Anyway, You need to get the top dead center!

Just in own experience because I did tried out the stick with the embossed scale.

With that dipstick tool you might get an accurancy of around +/- 1mm, (beeing extremly fair).

The inaccuracies already in reading the scale, (which depends to the angle of view),

then the transfer to the rotor and the additional angle measurement will not lead to

good result maybe accidently this might happen ...

We don't have to forget it's an ultra short stroke with only 60mm.

But you will find out ...

The multimeter can detect electrical circuits and will then produce a beep, which is again much easier to hear when the points will close or open as with a light f. e. as you can then focus on other things and most household/riders do have a multimeter.

Btw. 01:

You will have to set the gap between the points first then the timimg. Sadly when setting the timing you can't measure when the points open or close, (this works only with the rotor mounted), so you will have to do the pocedure two to three times until you get the timing there where it belongs.

Have fun with the dipstick, you seem to have a lot of time ... and some resistent against a good tip

Btw. 02:

The red box is the original motoplat beeper for detecting when the point will open or close, for setting the timing correctly, but why do I explain anything here ???

[sherpa325]

The correct tool back in the day was a vernier gauge that screwed into the spark plug hole and gave a very accurate measurement of the timing. The one shown in the second post is a very poor copy and does not have a vernier scale on it, Bultaco owners manuals show a photo of it on page 46/47 under ignition timing. Not to sure if you would still be able to buy one these days.

Cheers Greg

[copemech]

The old dipstick tool does have its uses. somewhere I still have one with a vernier screw scale and a locking screw which is quite handy at finding true TDC.

One needs to lock it down at say 1mm BTDC till the piston stops, then rotate the crank counter till it stops. Split the difference and you have TDC.(avoids the null on top)

Once you have TDC marked, one can use a degree wheel to mark the preferred setting in degrees.

Using the dial indicator is simple and seems accurate enough. Not sure which is more accurate after taking in inherant errors.

One needs to decide if you want to measure in degrees or mm BTDC.

[pschrauber]

As said it's a ultra short stroke only 60mm!

With a dipstick and this short stroke you get 3° for 1mm of piston travel.

One of the reasons you have that much advance in ignition timing for

the Sherpa.

That sounds much but you have to measure them too which will be a real

task with that dipstick, the gauge in 1/100mm and adjustable 0 is much more

comfortable/easier to use, less time consuming and much more accurate and

you can use the gauge for measuring other things like roundniss, alignment, ...

too.

[sherpa325]

Bultaco timing is given as a measurement before TDC [2.5 - 2.7mm]. I have always set mine up using the vernier gauge and a battery powered light, the light goes out when the points open-you then check what the vernier is reading and adjust the point gap accordingly. I am not sure what the mm's before TDC translates to in degrees, it would be interesting to know. The distance the piston moves vertically changes as the crankshaft rotates and will be significantly different from say 90degrees[maximum vertical movement] to TDC[minimum or zero].

Cheers Greg

PS Reg May recommended 2.5 before TDC and points set at 15 - 18 thou and N12Y plug

Edited December 27, 2012 by sherpa325

[woody]

The thing to remember is that these are trials bikes, not Motogp bikes and having the timing absolutely to the degree isn't really necessary.

They'll run with the timing anywhere between 1mm to 4mm before TDC. Towards 1mm the engine pick up is slower, towards 4mm it's quicker, you just put it at the setting that gives the response you're happy with through experimenting. 4mm is a bit extreme I know, but I've run Ossa MARs at 3.5 in an attempt to liven them up. Works setting supposedly but it didn't make much difference.

On my TYZ Yam and SWM Jumbo I used to run both with the timing fully retarded on the backplate which made the TYZ throttle response smoother and the Jumbo, which is an animal, less aggressive - neither is anywhere near the manufacturer's recommended setting. No problems with performance, both still pulled as they should and both would rev out cleanly. You'd need a ship's anchor to hold the Jumbo back anyway...

I'd wager that if anyone rode my 340 Sherpa they couldn't tell me what the timing is set at from the way it peforms.

If you want to set it to recommended setting, then surely the best way is a dial guage and multimeter with beeper, as mentioned before

[sparks2]

well said woody

[colinf]

Just out of interest ( and for future reference ) what is the timing on your 340 set at Woody?

[woody]

Truthfully, I have no idea.

The ignition was fitted in Spain when I had some work done on the bike by Vasquez. I just had a fiddle with it to soften off the throttle response by retarding it a bit. I haven't a clue what it's set at.

[pschrauber]

Standard for the 199b with 340cc is 2,2mm in advance to TDC.

[john collins]

Set them to 2.5mm BTC

Use simple timing gauge down plughole

Disconnect all wires at junction box under tank

Connect meter or home made bulb/battery continuity tester to black wire one side - earth other so meter needle swings or bulb goes out when points open. You need this to happen at 2.5mm BTC

Almost always when you tighten the points screw something will move - so check again - and you can make slight adj by just slight twist on point adj screw

BUT as Woody states , these are not GP bikes and if your timing is even close to 2.5mm you will have no problems at all