Distributer Advance

[PYU940F]

Hi all.

Any dizzy experts out there? I have just stripped, cleaned and lubed my distributer and installed new advance springs. Moss said install the two strongest springs first. I guess this will delay the advance with increasing RPM. I know on performance engines this would increase power but do you think it will affect the old 4 pot lump? My engine is in good condition but is unmodified so softer springs maybe better? What do you think?

Also what static advance is best. The manual says TDC and then advance one division on the vernier adjuster. This was written for the days of good old 5 star with tons of lead. I run on super unleaded with no additive. I only do a couple of 1000 miles a year so I do not think the head is going to give up on me..

 

Cheers

 

Simon

TR4A

 

[Peter Cobbold]

Simon,

Standard curves here:

http://s258.photobucket.com/user/TR3driver/media/Manual%20pages/Electrical/Lucas%20Distributor%20Advance%20curves.gif.html

NB double the numbers to get crank degrees ( we normally use ) and rpm.

 

I dont run a 4A so am guessing **, but looking at that curve I'd set the static to 10BTDC, giving a total of 30BTDC at 3000 rpm (crank).

The manual static of BTDC is odd, because a total of 20 BTDC is very retarded for a 9; or 9.5:1 compression.

 

Fuel octane doesn't affect best spark timing, except when the engine starts to knock and yours is long way off that point.

 

The other way to set the static is to warm up the engine and at tickover slowly turn the disy a few mm to and fro until the rpm are best, then reclamp it. You can check the centrifugal advance with strobe light, keeping hands well away from the fan.

 

Peter

 

** useful expertise here:

http://www.tr-register.co.uk/forums/index.php?/topic/28937-ignition-timing-on-my-tr4a/

(also note comment about timng marks going off)

Edited April 19, 2017 by Peter Cobbold

[iain]

Hi Simon

 

personally i think you're best off getting Martin Jay to service the unit and build it to your current engine specification.

 

http://www.distributordoctor.com

 

He really is the expert and comes highly recommended by many

 

 

Iain

[PYU940F]

Hi Ian

You are probably right but I like fiddling and learning about the theory and then putting it into practice. I would get a superb dizzy from Martin but not learn very much. Stripping my unit was easy and I am sure most dizzies underperform because they are simple crudded up. I stripped it, cleaned it with solvent and reassembled using small amounts of lithium grease. It certainly feels smooth when I spin it. I put the 2 strongest springs in. I will let you know if I detect any improved performance when I go for a thrash today. I am still a bit confused about spring weights. In the packet from Moss there were 5 springs; two heavy ones and 3 various strength ones. Does that mean I can mix and match spring weights? Sounds a bit odd.

 

Cheers

 

Simon

[barkerwilliams]

Simon,

 

Have you an adjustable timing light such as https://www.ebay.co.uk/p/?iid=360513112288&&&adgroupid=43333907642&rlsatarget=pla-301332972158&abcId=1088846&adtype=pla&merchantid=7449114&poi=&googleloc=1006790&device=c&campaignid=805983114&crdt=0&chn=ps ?

 

When you have re-installed attach the strobe light get the car running and set up to your base setting (10 to 11' possibly) and have an assistant steadily and slowly increase the revs and you will see the timing mark "move" in the strobe as the weights and spring combinations actuate, Ask the assistant to hold the revs and adjust the dial on the strobe to re-zero the timing mark under the strobe light and read off the degrees of advance.

 

This then gives you readings of the distributer advance at various revs so you can ensue the distributer advance is performing as expected / required.

 

Easy and quick to do.

 

 

Alan

Edited April 20, 2017 by barkerwilliams

[PYU940F]

Hi Alan

Yes, doing a strobe check quite easy. I will do it if not happy with performance. Peter, thanks for the link to the advance curves. Question. why does the 4A curve stop at 10 degrees whilst all other marques go on to 14? Do they have a much more retarded static setting?

 

Simon

[peejay4A]

Static advance from the book is 4 deg btdc. My personal view is that now you've discovered how to put the distributor together it might be wise to abandon the poke and hope approach. If you get it wrong and don't notice the engine knocking then damage will result. Give Martin Jay a call and if your engine is standard ask him which springs are appropriate. Another thought is that it's possible that a previous owner has been in the distributor and modified the maximum advance stop which is a good reason to get it to Martin and remove any doubts as to its suitability.

 

PS The differences in distributor degrees is probably due to different cylinder head design.

Edited April 20, 2017 by peejay4A

[PYU940F]

Thanks Pete

The max advance stop does not look tampered with and is marked 10 degrees (20 crank) so that is correct. Will call Martin and check on correct springs.

 

Cheers

 

Simon

[Peter Cobbold]

Hi Ian

You are probably right but I like fiddling and learning about the theory and then putting it into practice. I would get a superb dizzy from Martin but not learn very much. Stripping my unit was easy and I am sure most dizzies underperform because they are simple crudded up. I stripped it, cleaned it with solvent and reassembled using small amounts of lithium grease. It certainly feels smooth when I spin it. I put the 2 strongest springs in. I will let you know if I detect any improved performance when I go for a thrash today. I am still a bit confused about spring weights. In the packet from Moss there were 5 springs; two heavy ones and 3 various strength ones. Does that mean I can mix and match spring weights? Sounds a bit odd.

 

Cheers

 

Simon

Simon,

I'm all for leaning how to do it too. Theory too !! - great.

You have the standard curve, and if the head has not had a dramatic increase in compression that will be what you want.

The curve has a fast rise followed by a slower rise- the weaker sping does the fast, the stronger spring the later rise. Fit them and use a strobe to see what you get.

Set static to 4BTDC as per book. See how it pulls.

 

The curve differences. The head design did not change much, both bathtubs with similar squish. I dont take heed to small degree differences, and it varies with the tune of the carburettor and mixture. And the vac adv capsule operation- often they dont work and cannot be tested in the home garage. If the va adv has seized than the spark will be too retarded by maybe 10-15 crank degrees at cruise.

 

Theory here. There are graphs in here showing how timing can typically vary with load and mixture. And slide 60 shows that even 5 deg out in either adv or ret direction has bugger all effect ( because of cyclic variability..slides 43 on)

https://supertrarged.wordpress.com/2016/07/21/iwe-2016-technical-seminar

 

Peter

Edited April 20, 2017 by Peter Cobbold

[BlueTR3A-5EKT]

Print_Area.pdf

 

This any help?

 

It is test done with a standard distributor as it was fitted and details of fitting other springs. Nearest outcome to one suggested and ultimately bought from DD used springs of 0.025" and 0.030" wire diameter that came off a NOS USA spec TR6 distributor. I have no idea what DD fitted in the distributor he supplied me. I was doing a set of tests on an old distributor before having it rebuilt.

Strangely it exhibits 16 degrees as max advance on the standard as found distributor so I guess some interpolation of the curve is required to shift it up to 18 Max advance. Unless of course I cleaned some junk off the mechanical stop of the original distributor when fitting the replacement test springs.... Sorry these are not lab conditions.

Cheers

Peter W

 

PS I had read this for guidance Distributor Tuning.pdf

Edited April 20, 2017 by BlueTR3A-5EKT

[Steve Priest]

 

Have you an adjustable timing light such as https://www.ebay.co.uk/p/?iid=360513112288&&&adgroupid=43333907642&rlsatarget=pla-301332972158&abcId=1088846&adtype=pla&merchantid=7449114&poi=&googleloc=1006790&device=c&campaignid=805983114&crdt=0&chn=ps ?

 

 

Just a word of caution regarding these adjustable advance timing lights...

 

Before using it to check the timing, first make sure that the RPM figure it reports is plausible and stable. It uses this to calculate the advance offset, so if the RPM is wrong, the timing position will also be wrong for any non-zero advance you've programmed in. Strangely enough I had this issue last night. Suspect it was picking up multiple triggers, possibly due to my EMC unfriendly copper leads. I eventually managed to get it working by changing the clip position on the lead but it was still hit and miss.

 

Steve

Edited April 20, 2017 by Steve Priest

[Lebro]

I do have one of these, but generally prefer to set the advance to zero, & use marks on the crank pulley to determine the timing.

 

Bob.

[PYU940F]

Thanks all you have been all a great help with my "learning curve" on the "timing curve". Pete mentions the light spring does the early advance whilst the stronger spring does the advance at higher RPM. Does it matter onto which posts these two springs are fitted or should they be fitted in a particular way/sequence? When I took mine apart I felt both springs were equal strength and quite weak so guess this would cause maximum advance at too low an RPM causing poor response from the standing start. Just what I was experiencing. I have a dwell/tach gauge but will invest in a strobe.

Determined to get it right.

FYO I did what other posts admitted to and got the assembly 180 degrees out. Also managed at one stage to get the assembly nicely fitted but 90 degrees out!!! Refitting the weights correctly and the right way up and not back to front is quite a challenge, I should have taken a photo before they all fell out onto my workshop floor. Oh well, as I said I like to learn.

Also used a circuit light attached to coil and earth to find out when the points were opening and then used the dwell meter to get the points gap correct.

 

Cheers

 

Simon

[Peter Cobbold]

 

Peter W

 

PS I had read this for guidance Distributor Tuning.pdf

Peter

Thanks for the Lucas pdf.

It reminds me that factory curves are usually set very conservative ( ie retarded) to allow for indifferent sevicing ( points wear etc),carbon build up, carbs madjusted, fuel quality, etc The last thing a factory wanted was thousands of complaints about 'the engine's knocking/pinking'.

So TRers should with immaculate motors should be able to depart from the stock curve and gain a percent or two of extra sparkle and oomph. I'd suggest a tad more advance from stock.

The old trick is to advance the spark until at wot it just started to knock and then back off about 3 crank degrees. Tin ears help hear knock:

http://www.dynotechresearch.com/blog/archives.asp?chosenMonth=4&chosenYear=2013

Peter

Edited April 20, 2017 by Peter Cobbold

[PYU940F]

Pete,

Surely you have explained your last post backwards. I always thought retarding the timing a few degrees gave you a bit more power but with the risk of detonation. If the factory settings were conservative then they would have put the curves on the slightly too advanced side. Excuse me if I am talking a load of bollocks.

Off to buy a timing strobe today. I think the easiest way to do it is to mark up the crank pulley with degree markings. Does any one have to hand either the circumference or diameter of a standard crank pulley?

[Lebro]

Other way round - advancing will often improve performance, but at the risk of pinking

 

Bob.

[iain]

If you buy a Strobe with advance and retard function all you need is the TDC mark. The gauge on the Strobe then tells you what degree of advance or retard you have at the that particular engine RPM (as recorded by the Strobe). Much more accurate than relying on a Rev-counter that will in all probability be inaccurate due to age.

 

Iain

 

PS I am not sure that Pinking and Detonation are the same. As I understand it, Pinking is spark induced, detonation is caused by heat/pressure and often a hot spot somewhere in the combustion area.Detonation being an engine destroyer.......

[peejay4A]

Also check that your TDC mark really is at TDC by using a piston stop.

[RogerH]

Hi Iain,

a few months back I put a new meaning to 'advance and retard'.

Retard became the person operating the knob.

 

I took a measurement and found that the flashing white reflection on the pulley wheel was miles out at tickover.

So I started to adjust the dizzy. I sort of got it set up, but it didn't look right.

When I took another measurement with the strobe I then found that the knob actually moved and this had an effect on the reflecting white dot.

 

How many times have I used this bl**dy instrument and I still got it wrong.

When operated properly they are very good tools.

 

Roger

[peejay4A]

I've got an old Snap-On strobe which is the dogs whatsits. It's digital but I've still not found its fingers.

[PYU940F]

Found a lot on the web about the 25D4 dizzy. I just googled Lucas 25D4 distributor and opened a web page by simon lacey. On the first page there is a link to a pdf called "tuning the lucas distributor". Brilliant. Explained all about primary and secondary advance springs. Spoke to Distributor Doctor and getting the correct springs for the stock TR4A engine. Also getting springs that are 5 thou shorter to compensate for wear in the spring posts (if there is any). Will try both and with my soon to be acquired strobe I will get the results I want.

Will report back.

 

Simon

[Peter Cobbold]

My strobe is out of the ark - it flashes when the spark is made. Simple...just read the timing off the pulley.

 

The correct setting of advance/retard is when peak cylinder pressure occurs at 15-18 degrees after tdc. That's where peak torque happens. If the spark is too retarded from optimum the peak pressure occurs too late - the gas 'chases the piston down the bore' so to speak. If the peak pressure is too early (over-advanced spark) the conrod angle is too near vertical and pressure does not have as good a mechanical advantage - leverage to turn the crank. And too much advance means more pressur occurs when the piston is still before TDC ! Other influences are in slides 14-18.

 

Pinking is detonation. Preignition from a hotspot is different and much more damaging. Slides 72 onwards summarise.

https://supertrarged.wordpress.com/2016/07/21/iwe-2016-technical-seminar/

 

Slide 80 shows the torque loss from running a factory curve that avoids customer complaints from low-rpm pinking. This may be the reason why it is often said advancing the spark improves power. In reality there is only one best spark timing for each operating point.

 

Peter

Edited April 21, 2017 by Peter Cobbold

[PYU940F]

Waiting for the springs from the DD. However, fitted springs from the bag from Moss and matched as best I could from pictures I found on line. Wow, she is running so sweet, the best since the dizzy was overhauled in 1986. I suspect wrong springs all that time and sluggish weights from dirt and lack of lube. A delight to drive now.

 

Simon