Ignition timing - swing method

[88V8]

Still getting a bit of run-on, so having airily recommended to another member that they set the timing by swinging it, something I haven't done for 30+ years, I thought I'd try it myself.

 

Initial setting- according to the crank pulley - 11 BTDC.

Normal idle 750 rpm with the bleed valve fully shut.

No vac advance.

Engine has SAH medium cam, and high compression, don't know how high.

Using 97 RON unleaded.

 

The recommended method, I believe, is to swing until you get the fastest idle, then back off about 100 rpm, and check for pinking, then back off more if required.

 

But as I advance the ignition, the idle goes up to 1,100 rpm and rising. And above 800 rpm (?) the centrifugal advance starts, so the basic setting vanishes.

 

Am I missing something ?

 

Thanks

 

Ivor

Edited May 12, 2008 by 88V8

[TIMS]

Ivor

 

No real expert, but have you not answered your own question. "Normal idle 750RPM with bleed valve fully shut". So where is the engine getting the air to continue to run? On mine, shut the bleed valve and it stalls.

 

I can only suggest that the butterfies need closing down first (Richard Crawley and fag papers comes to mind) and then proceed as you have discussed.

 

Regards

 

Tim

[Richard Crawley]

My thoughts are also too much air getting through; either butterflies incorrectly set, worn spindles or some other air leak; you should be able to stall the engine by screwing the air bleed screw in.

[88V8]

Good thoughts.

When the head was polished/ported in the 70s, the polisher decided to 'improve' the throttle bodies, with the result that the (new) butterflies and the bodies are slightly different shapes. As the bodies were port-matched, I elected to keep them, and when Malcolm at Prestige rebuilt them he said they will reseal in due course.

In the meantime, the only way to get a reasonable idle is by shutting the air valve.

 

This morning, I tried setting the static timing by turning the engine forwards until 11 BTDC is aligned, then turning the dizzy slowly backwards until no 1 plug sparks.

The timing light at 850rpm now shows that according to the marks on the crank pulley, it's so retarded it's off the scale.

 

Road test this evening, I think.

 

Ivor

[Richard Crawley]

This morning, I tried setting the static timing by turning the engine forwards until 11 BTDC is aligned, then turning the dizzy slowly backwards until no 1 plug sparks.

Ivor

Ivor

I wouldn’t trust that! Set the timing with the motor running on the strobe & see what you get; as long as you’re below around 900 RPM, the centrifugal advance won’t affect it. Do you run electronic or do you still have points?

 

Perfect evening for a road test here though; in fact I think I might just do one for the hell of it!

[88V8]

Ivor

I wouldn’t trust that! Set the timing with the motor running on the strobe & see what you get; as long as you’re below around 900 RPM, the centrifugal advance won’t affect it. Do you run electronic or do you still have points?

 

I've bought a Lumenition, but not fitted yet, so still points. I checked the gap, which is OK.

 

Unfortunately, can't keep the speed below 900 because even if I just swing the dizzy on the micro-adjuster, the speed soon rises above 900, 1,000, 1,100 but I did notice that at 1,200 the crank pulley still says it's miles retarded. Very odd. If I had a transparent dizzy cover I could see if the advance/retard is working, there's a marketing opportunity for someone.

 

Anyway, off for road test now. I'll mark the setting on the dizzy before I start, and then advance it until it pinks a little, hope I hear it.

[Tom Fremont]

The timing light at 850rpm now shows that according to the marks on the crank pulley, it's so retarded it's off the scale.

 

Wouldn't think it capable of running at all like that

 

Maybe a TCD check is in order, and marking the pulley once found. Others have reported spun pulleys ( hence the odd reading, maybe? ) but I've not had this myself.

[88V8]

Wouldn't think it capable of running at all like that

 

Maybe a TCD check is in order, and marking the pulley once found. Others have reported spun pulleys ( hence the odd reading, maybe? ) but I've not had this myself.

 

Yes, Agrimech have a TDC tester, it whistles as the piston rises. Think I'll order one.

 

Well, last night spent an hour back & forth on a nearby service road, first gave it 20 twizzles of Advance on the microadjuster, then found I could easily make it pink by pulling away with not much throttle but insufficient clutch slip at 1500 rpm in first, it pinked as it launched.

Then gradually retarded it on the micro-adjuster, nearly used up all the adjustment, I wonder how many degrees that is?

 

So, having manually set it at 11 BTDC to the pulley, then had the strobe tell me it's perhaps 30 degrees retarded, it's now even more retarded. Put not your faith in pulleys.

 

Seems happy now, no pinking, but Lord knows what the actual setting is.

 

Ivor

[bat10man]

Yes, Agrimech have a TDC tester, it whistles as the piston rises. Think I'll order one.

 

Well, last night spent an hour back & forth on a nearby service road, first gave it 20 twizzles of Advance on the microadjuster, then found I could easily make it pink by pulling away with not much throttle but insufficient clutch slip at 1500 rpm in first, it pinked as it launched.

Then gradually retarded it on the micro-adjuster, nearly used up all the adjustment, I wonder how many degrees that is?

 

So, having manually set it at 11 BTDC to the pulley, then had the strobe tell me it's perhaps 30 degrees retarded, it's now even more retarded. Put not your faith in pulleys.

 

Seems happy now, no pinking, but Lord knows what the actual setting is.

 

Ivor

 

Ivor,

 

The TDC mark on my pulley is about 8degs out. I remarked the pulley when I rebuilt the engine.

It would definatlely be worth checking the actual TDC position of the piston and comparing it to the

pulley position.

 

regards

Andy

[JohnC]

If you don't mind a bit of fiddling around you can check TDC by looking through the spark plug opening of No 1 cylinder. The key is to find a blemish on the part cylinder wall that you can see which is passed by the piston crown well before/after TDC, i.e., when vertical movement is high relative to crank rotation. Note the indicated crank angle as the piston passes the mark on the way up, and then again on the way down. Half way between is true TDC.

 

EDIT: At a pinch you could use the shadow created by torch light instead of a blemish. And FWIW I had to get my pulley reconditioned when I rebuilt the engine. The guy who did it mentioned that as the rubber (?) deteriorates with age the outer can rotate relative to the inner part. He got the alignment spot-on based on my check afterwards. Reconditioning the pulley cost so little that I can't even remember the amount (less than £20 I guess).

 

Cheers,

John

Edited May 14, 2008 by JohnC