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ignition timing?

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burgundyben

Jedi Hopeful
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well now she's pretty much running ok, I'd like to spend some time getting the ignition spot on.

Before the engine rebuild the car ran as if timing and carbs were spot on, I took the distributor out by unbolting the plate from the block rather than slackening the clamp off, so when I came to refitting, provided I got the gear drive into the right groove I knew I would be close. I have acheived this and the cars runs.

I'd like to use a strobe light to check its spot on. (My XKE has a pointer and a notch in the crank pulley, two spots of white paint and the strobe and its dead easy).

The BN1 has no timing marks to spot the white paint on.

I propose to stick a dial guage down a plug hole, find tdc, place a paint mark on the front cover and a corresponding mark on the pulley, then measure the right number of degress of advance at idle (need to check this in the book, about 6 or 7 for 95 octane fuel?) around the pulley and place a second mark for the strobe light.

Any comments? Better ideas? Possible reasons why my idea is rubbish?

Cheers.

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Hi there should be a very small notch in the vibration damper that liines up with a pointer attached to the timing chain cover and a Strobe light can be used to set the timing in the usual manner.---Keoke
 
Your idea will work, but you'll need to pick a point, say .050 thou down from TDC on each side of the top of the stroke, then mark each and split the difference, since the piston sits at TDC for a couple of degrees. Then you'll know your timing mark is dead on.
 
Hi Burgundyben, this subject can probably be found in the archives of this forum, but for general purposes the timing should be set at about 15degrees BTDC. That equates to about 3/4 of an inch around the pulley from the notch. I can't take credit for these facts because they came from this forum, but this is what I recorded here some time ago:
5 degrees = 17/64"
10 degrees= 17/32"
12 degrees= 21/32"
15 degrees= 51/64" or about 3/4"
It was John Loftus who post this back in july 2002.

Then you can play with this setting a degree or two either way to fine tune according to fuel or altitude or whatever.
Generally if I want a smooth ping free acceration from a very low RPM you can retard it alittle,or keep it right on the 15 degrees. If you are looking for quicker acceleration from a higher rpm starting point and a higher top end especially when you want to wring out 3rd gear for all its worth or pull 4th as high as you can get it just before hitting Oveerdrive, then you can advance it a degree or two. But too much advance will give you pinging everytime you accerate.
Good Luck & Enjoy.
 
Ben,
Some BN1's had no front timing mark. The flywheels had a 1 & 4 TDC mark but this is hard to use. Later BN1 & BN2's had an embossed arrow on the timing chain cover that was supposed to line up with a tiny round dimple near the outer edge of the rear pulley flange at TDC. The arrow point is quite broad & too far from the dimple to be very precise. The shop manual also suggests to set #1 cylinder at TDC & rotate the distributor body until the points are "widest open". Again, not very accurate.

I would bend a short piece of wire to about 90 degrees & epoxy it to the timing cover to rest near the pulley outer circumference & align with the dot/dimple when the engine is at TDC.

You will need to accurately find TDC first with one of the methods described above, & if no mark is present on the pulley, make one.

If you wish to add other marks, measure around the circumference of the pulley & place other marks. For the BN1, BN2 pulley, each 5 degrees advance is .232" clockwise viewed from the front. ie- 35 degrees would be 1.62 inches cw from the tdc mark. If you are patient, once you mark TDC & align the pointer, you can turn the crankshaft 180 degrees & notch the edge of the pulley at 5 degree intervals from the bottom of the car with a small triangular file. Mark the edge of a piece of paper at the desired intervals, place this paper around the pulley & transfer the marks.

In any event, I would set the timing to 35 degrees at 4000 rpm, & let the intermediate & idle timing fall where they may. Vacuum advance disconnected of course. It is this maximum timing that is critical to engine life. If there is not enough advance at lower rpm, the centrifugal advance curve can be recalibrated. Or, the centrifugal advance mechanism may be sticking. The DM2 distributor, as found in the Healey Fours, Is not noted for having a precision centrifugal advance mechanism nor is it very reliable. Jeff converted my DM2 distributor body to the much better 25D advance mechanism.

It is important that this 35 degree timing not be exceeded by more than about three degrees, or 38 degrees maximum. Exceeding this maximum timing carries the very real possibility of getting into unheard detonation at higher rpm. It will do just as much damage as the more commonly heard pinging.

Aside: I suggest marking the pulley for the desired advance readings & using a conventional timing light. Some of the modern "dial back" timing lights are not very reliable or accurate, & a few suggest temporarily using a resistor type plug wire while doing the timing. Supposed to make the timing light more stable.

Vette,
The Fours had a different pulley diameter than the Sixes. Thus different measurments.
D
 
Dave, I conceed your point about the 4-cyl. I described what I needed to know to do my 3000. For me it's close enough for **** good driving. Boy, this forum is great. What a wealth. don't anybody go away.
Dave C.
 
[ QUOTE ]

Hi there should be a very small notch in the vibration damper that liines up with a pointer attached to the timing chain cover and a Strobe light can be used to set the timing in the usual manner.---Keoke

[/ QUOTE ]


Ah ha!

Very careful inspection has shown a small hole in the rear flange of the pulley which is the timing mark! And the tip of the arrow on the timing cover!

Not the most obvious marks in the world!

Thanks

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Oh! I guess I should have told you they be a 'Bugger' to find! /ubbthreads/images/graemlins/cheers.gif---Keoke-- /ubbthreads/images/graemlins/laugh.gif
 
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