timing light use

grumpyvette

Administrator
Staff member
IM only too aware that most guys have a timing light or at least know what they are used for and its just not that glamorous, but its a very necessary tool..
There's no question that timing lights are a rather basic tool,and are reasonably easy to use, but theres a great difference in accuracy between different models.
the basic concept is deceptively simple, get the ignition to light off the compressed cylinder full of that fuel/air mix at the exactly correct instant that will produce the best torque and least wasted pressure working against the piston to drive the rod and spin the crank.
naturally its nearly useless to try and time the ignition until you've carefully verified TDC marks on the damper are correct
To do that you need to know the exact piston location in its repetitive 720 degree cycle. by watching the TDC indicator mark on the damper in relation to a timing tab on the timing chain cover.

but accuracy is critical to success, get that ignition to fire a bit early and detonation can cause major problems, if its delayed in relation to the pistons location it will result in less effective pressure and a hotter exhaust header.

http://www.corvette-restoration.com/res ... ing101.pdf

Many timing lights are less than consistent or accurate, nor can they give exactly consistent results.
MANY are cheaply constructed and not all that accurate. some won,t work well with solid core wire, some are heat sensitive. the type that allows you to set the timing advance or retard for the flashing strobe light,with a dial are usually not nearly as consistent.
if you own a couple timing lights check them all at the same engine at at least 3000 rpm, and you'll commonly see variations in the results and THAT'S BAD, if its off a couple degrees at 3000rpm, at 6000-7000rpm it can and probably will cause problems, when your engine timing is not even close to what you expect it to be.
The older model Sears Craftsman Timing Light (P/N A-2134) is usually consistent, MSD, makes their own, timing light (P/N 8990). that is also one of the better ones.
When your using a timing light you'll need to verify the battery connections are correct as to polarity, and the wires cant contact moving components like fans, fan belts and pulleys, you'll need to verify that only the wire from the #1 cylinder contacts the timing lights inductor clip, and that NOTHING contacts the hot headers, and you should NEVER wear a TIE or LOOSE clothing around a running engine!




obviously getting the ignition timing correct in relation to the compression stroke and piston location in the engine will result in far less chance of detonation and piston damage or loss of potential hp, and getting the ignition advance curve correct is also critical, IVE generally found having full advance all in by about 2900-3100rpm is a good compromise and while the components used in the engine can change the results, full advance at about 36-38 degrees at 3100rpm is a good basic starting point

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SBC cylinder numbering;
-2-4-6-8
1-3-5-7


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ITS not complicated, pull the #1 plug and put you thumb over the hole tightly, turn the engine in the normal dirrection of rotation, with a breaker bar and scocket untill you get compression in the #1 cylinder, as the damper TDC line approches the TDC timing tab, drop the distributor in with the rotor facing the #1 cylinder,compensate for the way the distrib gear causes the rotor to rotate as in seats,so its seated pointing where you intended, if it won,t fully seat turn the oil pump drive with a very large flat blade screw driver untill it will,with the distrib removed and try again, once it seats,facing the correct dirrection, install and tighten the distrib clamp so its difficult to spin the distrib easily by hand but still possiable to spin the distrib by hand, re-install the #1 plug and wire, install the cap and all ignition related wires, use your timing light and set the ignition timing,per the shop manuals instructions, tighten the distibutor hold clamp so it can,t move, IF it takes more than 10 minutes your in need of more practice or nearly hopeless as a mechanic.


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how come its 180 degs out of phase?
I get this question all the time, well here’s something I see lots of guys don’t understand, ONCE YOUVE INSTALLED A CAM WITH THE TIMEING MARKS YOU MUST ROTATE THE CRANK 360 DEGRESS BEFORE DROPPING IN THE DISTRIBUTOR, while its true that if the, timing marks are positioned so the crank is at 12 o,clock and the cam gear is at 6 o,clock that the cam lobes will be in the position that fires #6 cylinder that HAS NO EFFECT AT ALL (on finding TDC,) for aligning the degree wheel with TDC,or THE timing tab pointer, for degreeing in the cam, the piston passes thru TDC TWICE in every firing cycle once on the firing/power stroke and once on the exhaust stroke, the cam rotates at exactly 1/2 the speed of the crank so to make it easy to line up the marks they install it with the marks at the closest point 6/12 for easy indexing, rotate the engine 360 degrees to the #1 TDC power stroke and the crank gear will still be at 12 oclock 12/12 but the cam will be at 12 o,clock also, rotate another 360 degrees and your back where you started. its simply easier to index the cam at the point where the index marks align closely. look at how the cam lobes themselves open the valves when the cam is just installed the #1 cylinder valves are slightly open and the #6 are closed per "Lunati" ‘’YES YOU ARE RIGHT - WHEN CRANK IS AT TWELVE AND CAM IS AT SIX THEN #6 CYL IS FIRING AFTER YOU LINE UP YOUR MARKS AND INSTALL GEAR THEN ROTATE YOUR CRANK ONE REVOLUTION AND THEN DROP THE DIST. IN - AT THAT POINT
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http://boxwrench.net/specs/chevy_sb.htm
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AS a general starting point for tuning your SBC or BBC engine your HEI MSD,or similar distributor timing should be at about 8-12 btdc at idle, and all in by about 3100rpm at about 36 degrees total advance, naturally youll want to make some adjustments in the timing or fuel/air ratio as needed, and reading plugs and verifying your TDC, and timing tab and use of timing tape on the damper , use of a vacuum gauge and timing light are a good place to start.
you can normally change the total advance and rate of advance by changes in the distributors weights, springs, etc.

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installing a damper with degree marks or at least a degree cover helps
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