Tuesday, July 24, 2007

Opensource Primer on How To Set Ignition Points

iknewit wouldcometothis.

for points,
'First Find Top Dead Centre'.
That is when the piston is highest. Do this by holding a long (!) bolt into the spark plug hole, after removing plug.


You can also remove a bent pipe and observe the piston from there. Draw markings on the piston with a marker pen if you need to. This method will require a new bent pipe copper ring gasket, so it can be costly.

To turn piston, use ring spanner on centre cam bolt. Its usually better to turn the piston clockwise, but that could just be a superstition.

Second step is to look up reccomended point Before Top Dead Centre (BTDC). BTDC is when the piston is coming up towards the sparkplug and is compressing the mixture in the cylinder.

(The mixture is transfered from the ports in the cylinder walls on either side in case of our bikes - yz, jw, cz. you can see the transfer ports bulging on the side of the cylinder base from the outside. Just look at the middle part where the fins end on either side of the cylinder. anyway, back to things that spark in the dark...)

Now do your research, find the correct setting for your bike from the various documents, manuals available at jawaclub.com; yezdiclub.com, yahoo yezdi group.
I can tell you, but in my experience these are all old bikes and each one is slightly different from the other. So exact factory settings would go out of the window if, for example, there is (free) play in your camshaft! - can be detecting by putting an o-ring spanner on bolt and rocking up and down/sideways and observing if it causes the points to move, when it is not rotating - obviously)
I have had friends not talk to me and vice versa because we differed on how to set points exactly.

In any case, this setting is to be made before TDC. If it is said as 23 degrees, then i use a compass and the spanner as my pointer, measuring backwards (anticlockwise turn on spanner) from TDC. Watchout, the piston tends to stay at TDC slightly, so that lag would have to be built into your roatation.

You could also mark the piston as it goes downwards with the marker pen through the exhaust opening . Or you could measure the long bolt you are placing through your spark plug hole. Again, be careful here.

I suggest get the gap at the spark plug to the standard 0.5, keep the points to open a the specified point Before TDC, and let it close whenever the bloody thing closes. Watch it running and you will understand that the flat side of the cam is for the points to open.

Just ensure that the gap does not open too far wide. Look at the setings specified in the jawa/model b manual at
www.jawaclub.com. try that gap setting.

1 comment:

Abhijith said...

Hi, Arunesh,
I have followed these steps & it worked & no probs.
Thanks man.