Hi guys.
What's the correct method for measuring advance?
I've been attaching the induction thingie (techical name) to the offside lead, nearest the plug - is that correct?
I'm seeing 28 degrees at idle, and 32-33 with some revs, does that sound ok?
Don't forget wasted spark so most timing lights read double
Chris your figures sound ok ....if by "a few revs" you mean >3,500rpm ;D
Pickups "thingies" can be polarity sensitive and as a 2cv fires one plug backwards and it varies on which way the LT is wired up it may be a case of flipping the sensor over if the light is stuttering or scattering. It therefore makes little difference which HT lead you choose. ( the pickup on the SnapOn gear has a (-) marked on one side). The lost spark and 2 missing cylinders plays havock with built in tachometers or dial in advance - much simpler to mark the flywheel and keep things simple. Negates any arithmetical error in the heat of the pits.
The peg is 8* or you can mark up TDC - and then you can mark up the flywheel to the max advance using the starter ring as a guide - each tooth is 3.36*( 360*/107 teeth) count round clockwise when looking from the front. Once marked ( and double checked) watch as the max advance mark comes round and stops at the datum, the max advance is reached at 3,500rpm and should stay there while the revs increase.
32-33 is pretty good, 28 at idle suggests a fast idle- but idles not really that important on a racer.
Sean
Chris,
marking the flywheel, as already recommended by Sean.
(https://farm5.staticflickr.com/4030/4313805292_7c537cbacc.jpg) (https://flic.kr/p/7zco2j)timing marks on flywheel (https://flic.kr/p/7zco2j) by slcchassis (https://www.flickr.com/photos/30132857@N06/), on Flickr
Checking the ignition timing with a strobe.
(https://farm5.staticflickr.com/4154/5449076261_81e77f4c72.jpg) (https://flic.kr/p/9ivWwH)Timing with a strobe (https://flic.kr/p/9ivWwH) by slcchassis (https://www.flickr.com/photos/30132857@N06/), on Flickr
The amount of centrifugal advance you've given does seem low, unless someone's altered things with that intent, which makes sense for a race engine... ;)
Thanks people - The flywheel doesn't have the 6mm (8 deg BTDC) timing hole because it's been lightened, and I was using a strobe with the advance knob, so my figures might not be entirely accurate. I probably need to go over it again, marking the flywheel properly.
The procedure I have been told for marking TDC is to stick a screwdriver in a spark plug hole, turn the engine by hand until the piston hits the end of the driver, mark the flywheel, then turn the engine the other way until it hits again, then mark the flywheel again, and TDC is the midpoint between the two flywheel marks.
You could put a balloon on your compression tester tube chris.
something a bit more fixed than a screwdriver ...a long reach plug for instance. but yep thats the principle.