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Checking ignition timing w/o marks
https://www.ausmini.com/forums/viewtopic.php?f=2&t=76948		 Page 1 of 1
Author:  Anto [ Mon May 28, 2012 2:41 pm ]
Post subject:  Checking ignition timing w/o marks
So I spent some time yesterday fine-tuning my ignition timing with the aid of a quiet stretch of road with a decent incline.

Advanced it a fair bit and got it running better.

Problem is my lightened flywheel had no timing marks on it. I marked TDC and 10* when I built the engine - reasonably unscientifically I might add - and when I checked it with a strobe light it showed something like 30* advance at 1000rpm. Clearly I got the markings wrong because I don't think it would run very well if that was the case. :P

So what's a good way to double-check my timing is set reasonably well with no timing marks? I'm thinking check that full advance is being reached at around 4000rpm is a good start, followed by a check on the dyno some time.

Other suggestions?

Dizzy is a modified Pulsar BTW
Author:  Timbo [ Mon May 28, 2012 3:45 pm ]
Post subject: 
Some models had the timing mark on the front pulley with a toothed indicator mounted on the timing cover. It might be possible to replicate that, after working out where TDC is.

Tim
Author:  drmini in aust [ Mon May 28, 2012 3:49 pm ]
Post subject: 
1. Stick a pushrod into #1 plug hole (as vertical as possible) with a dial gauge, find TDC, mark the flywheel accurately.

2. Borrow or buy a `dialback' timing light, you can then rev the engine to ~4000 rpm (beyond the max advance point) and set the timing to 28-30° BTDC, with vacuum disconnected.
Works for me (I have 2 motors with Pulsars) and it's far more useful that setting it static, then hoping... :lol:

Doing it this way you only need the TDC mark, & no others.

Convertible mini sells these timing lights pretty cheap, or you can one get off eBay.
Author:  sgc [ Mon May 28, 2012 3:58 pm ]
Post subject: 
You can work out TDC on #1 pretty easily even with no reference marks.

Make a pointer up out of stiff wire and attach it securely to the engine so it points at the harmonic balancer. This will be your reference for TDC in the future, so make it permanent and make it strong ;)

Take out #1 spark plug and wind the motor over by hand until you can see the piston in the bore, but before it comes to the top of the stroke. Take a bit of your stiff wire and poke it down the near side of the bore - make sure it's touching the side - until it touches the piston, and take close note of the depth - make a reference mark on it with a knife or something sharp.

At this point, mark the harmonic balancer where the pointer is pointing.

Now, continue to wind the motor beyond TDC and keep measuring the depth of the piston with your wire in the plug hole. Once it goes back down to your reference mark, stop and make another mark on the harmonic balancer.

Now measure the distance between the two marks on the balancer, and exactly half way between is top dead centre, spot on.

Make sure you do this with the dizzy rotor pointing towards plug #1 and not #4, otherwise you've found TDC on the exhaust stroke, not the compression stroke.

[edit] Doc beat me, even if we have slightly different methods - his is probably easier :lol:
Author:  Anto [ Mon May 28, 2012 4:27 pm ]
Post subject: 
Dialback timing light definitely sounds the go. Time to add one to my collection :wink:

And double checking my TDC mark. I will be interested to see how far out it actually is - even being a complete gumby I can't see that I could have got it as wrong as it 'apparently' is :lol:
Author:  drmini in aust [ Mon May 28, 2012 4:33 pm ]
Post subject: 
I weld a pointer lug onto the (early) timing cover, it's easier than peering through the damn clutch cover hole with a torch and mirror... WTF was Issy smoking when he designed that! :lol: :shock:
Author:  Anto [ Mon May 28, 2012 4:40 pm ]
Post subject: 
Kinda wishing I'd fitted a timing cover with the timing marks already on it, rather than the shiny chrome one lol

Unfortunately I don't have enough hands to hold a mirror, and a timing light, and rev the engine...
Author:  Anto [ Mon May 28, 2012 4:50 pm ]
Post subject: 
BTW, is it possible to get a dialback timing light that works on wasted spark ignition systems?

Unfortunately my motorbike also doesn't have timing marks either... it's just the way I roll...
Author:  drmini in aust [ Mon May 28, 2012 4:53 pm ]
Post subject: 
Anto wrote:
BTW, is it possible to get a dialback timing light that works on wasted spark ignition systems?

Unfortunately my motorbike also doesn't have timing marks either... it's just the way I roll...

Yep pretty sure it'll still work, as the wasted spark is at the same timing point, just on the exhaust stroke not the compression one.
Author:  Anto [ Mon May 28, 2012 5:00 pm ]
Post subject: 
drmini in aust wrote:
Yep pretty sure it'll still work, as the wasted spark is at the same timing point, just on the exhaust stroke not the compression one.


My google searching suggested it would read incorrectly (roughly double the actual advance) because the timing light gets confused about the engine rpm. :?:

Worth checking as I need to mess round with the bike's timing once I'm finished practising on the Mini :)
Author:  simon k [ Mon May 28, 2012 5:45 pm ]
Post subject: 
Anto wrote:
Unfortunately I don't have enough hands to hold a mirror, and a timing light, and rev the engine...


get a little bit of angle/aluminium/whatever, bend it, drill a hole in it, glue/velcro your mirror to it and use the inspection hole screws to hold it in place

frees up your third hand for other tasks

and yes, timing lights work the same way no matter what sort of ignition you're using - a spark is a spark - doesn't matter how fast they're going or if you have twice as many....
Author:  drmini in aust [ Mon May 28, 2012 5:56 pm ]
Post subject: 
Anto it will just spark twice as often (and tacho speed indication on the timing light will read 2x high) but the advance point will still be right.
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