Setting ignition timing with a strobe

Posted by Jon June 15, 2012

Following on from our static timing guide, this article shows you how to do it with a timing strobe, which is a whole lot more accurate.

Ignition timing is somewhat of a tricky subject, not because the act of checking ignition is difficult, but rather because there are just so many variables. To start with, VW and Bosch produced more than 100 distributors for the Beetle engine over the years, so the chances of having the correct one in your engine aren’t great. Also, there are many different bottom pulley markings and most are interchangeable.Fear not though, because armed with this feature you will be one step closer to unravelling the mystery.

First though, what actually is ignition timing? Put simply, it’s the point at which the spark plug fires in relation to the piston’s position in the bore. You may have seen the abbreviations BTDC and ATDC and wonder what on earth they mean. BTDC means Before Top Dead Centre and ATDC means After Top Dead Centre. So 10 degrees BTDC refers to the spark plug firing 10 degrees before the piston reaches the top of its stroke and 10 ATDC would mean the sparking plug would fire 10 degrees after the piston had passed TDC (Top Dead Centre). Got it? Good.

This feature is designed to get you thinking about the correct timing figures for your engine and finding the correct markings on your pulley. I make no bones about the fact that you will have to do some work to find out exactly what engine you have, but this will give you a good starting point.

Before checking the ignition timing on any engine with contact breaker points you must check the points gap is correct (see page 24 for how to do this). The reason for this is that the points gap directly affects the ignition timing, which is one reason why electronic ignition modules make good sense as the relationship between electronic ignition and ignition timing remains constant, whereas with points gaps it changes with time and wear.

Bottom pulley markings are there to signify TDC and ignition timing points. If your engine is completely stock and original to the car then they’re probably correct, provided the distributor is as well of course. If not, you need to check exactly what you’ve got, but no longer will there be an excuse for your engine timing to be out.

Feel free to download this article as a .pdf file so you can print it out and use it in your garage. However we do recommend reading the entire article first, so you can familiarise yourself with the procedure and know what your getting in to.
(To save the file to your computer right click the link below and select ‘Save file as’ or ‘Save linked file as’. If you click the link normally it will open in your browser.)

COST: From £30 for a stroposcopic timing light
TIME TAKEN: 30 mins
DIFFICULTY:
TOOLS NEEDED: Screwdriver, 10mm socket and extension, feeler gauge, strobe light with advance and retard ability and reads revs

To check ignition timing thoroughly you will first need to check your points, tappets and plugs. Get all this right before you start on the timing.

The guides you need before you complete this one are: Adjusting Points – Adjusting Tappets – Spark Plugs

This is a snazzy stroboscopic timing light, but they’re available from as little as £30. Just make sure it has advance and retard and reads revs though, okay?

Ok, have you got all that? Good – lets proceed! Continue through the steps by clicking on ‘Next page’ or the page numbers below.

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