Timing.

[reb53]

Whilst winding a new cam chain in the other day I messed up the timing.
As it was screwed anyway I thought it would be a good time to pull the distributor and grease the advance weights.

To my surprise I see I've got a 40953A distributor in my Sprint.
All the books say this is wrong, and what the timing should be I can't imagine as all the books seem to be a minefield of conflicting information.
I got the car when it was 5 years old and unless someone changed it in that time it's the original fitting.......confused doesn't begin to cover it.

So I took my best guess as to timing and the car appears to run OK apart from getting hot a little easier than usual around town.
Have I got it too advanced, or too retarded, ( jokes about me and retardation will be ignored.. ).
And I have deliberately not told you what the timing is so as not to influence any replies.

Cheers
Ralph.

[UAB807F]

Hi Ralph,

I've always assumed that advanced timing gives pinking and retarded timing gives poor performance/overheating ? If there are no signs of pinking or uneven idling then my 2d's worth is for a retarded ignition setting.

It might be worth doing a search because I'm sure we've had a lot of posts this year regarding ignition timing and recall one where we seemed to have various distributors/workshop manual & Miles Wilkin's settings at odds with each other. FWIW I set mine to the manual and it seems fine, but I've never had it checked on a rolling road so I may well be missing a few bhp. But if it starts/goes/stops without overheating, then I'm happy. (or should that be "relieved" ?)

Brian

[gjz30075]

It's certainly not original, I"m sure. I retrofitted a 40953 to my Sprint, back when the car was about 8 years old, and found quicker acceleration. My timing is set at 12 degrees at roughly 900 rpm with no overheating issues.

Greg Z

[types26/36]

I would just advance the timing until pre-ign occurs than back it off slightly until it there is no pre-ign.
Then check the timing with a light to see what it is happy with.

[Orsom Weels]

I would just advance the timing until pre-ign occurs than back it off slightly until it there is no pre-ign.
Then check the timing with a light to see what it is happy with.

I would agree with Brian here, this is the rule of thumb I've used for years on anything I'm not sure what the timing should be. Also, remember the figures stated in the w/s manual are for 5 star or high octane leaded fuel, not the stuff we get nowadays, so they're probably only usefull as a starting point anyway. The ideal setting for most engines is as far advanced as poss without preignition so Brians advice is spot on. Do a few accelleration tests pulling up a slight hill in a high gear, if it doesn't pink, advance it till it does, then back it off a degree or two untill the pinking JUST goes away. You may find the sweet spot differs with different brands of fuel, so best to set it up with your usual prefered brand.

Regards, Tim

[mikealdren]

Setting timing to avoid pinking is an excellent starting point as it's easy to recognise and low speed detonation can soon destroy pistons etc.

However, detonation at higher speeds can't be heard so easily so a distributor with an aggressive advance curve will cause problems at higher revs as well as losing performance. Take care is you are using the wrong distributor.

I'm sure others (Grumpy John or Rohan?) can add a lot more here.


Mike

[69S4]

The ideal setting for most engines is as far advanced as poss without preignition so Brians advice is spot on. Do a few accelleration tests pulling up a slight hill in a high gear, if it doesn't pink, advance it till it does, then back it off a degree or two untill the pinking JUST goes away. You may find the sweet spot differs with different brands of fuel, so best to set it up with your usual prefered brand.

Regards, Tim

This is something I'll be playing with some time in the new year so let me see if I've got it right. I set the timing initially to something good enough to get the engine running - say 10 degrees before, and test it as per Tim's approach on a slight hill. If it pinks, I retard it a bit, if it doesn't I advance it a bit until it does and then retard it a bit. That should get me a usable setting for max advance. So what happens to the static/ idle setting? That could now be anywhere depending on what advance weights are in the distributor and what the max advance result using modern fuel has turned up. Should I next start modifying the weights to get the correct static setting? How do I work out what is the best static setting - the smoothest idle? My S4 is a Stromberg version so a smooth idle isn't easy to obtain.

[Orsom Weels]

Hello Stuart,
Yes, you?ve got the idea, that should give you a reasonable advance across the range assuming the distributor is somewhere near standard. Once you?ve done this, you can check the static figure by turning the engine until the points just open & then checking what degrees BTDC you have, you may have to use a degree disc or similar to get an exact figure, but you can usually get a ?near enough? from the scale on the timing cover. You can then hang the strobe on & do the same to check the advance at various rev patterns. If something is wildly out, then it?s time to have a look in the distributor. As springs weaken, full advance will happen at lower RPM & as wear sets in, this can affect things as well, you may get more or less advance, it may jump around all over the place, or it can stick in one place, I?ve experienced all of these on various dizzies over the years. You can play around with bob weights etc to get the best of all worlds if you need to, but it is, or at least can be, a lot of trial & error, a mapped electronic system is probably a better option if you want it perfect.
Know what you mean about smooth idle with Strombergs, I lived with them on my last +2, they can be a bugger to get right, & having done so, I could never get them to stay there for any length of time. I?ve found Webbers easier to live with, & they make that lovely noise!!! I am assuming you haven?t got the federal vacuum pod ? Obviously that has an affect on all the above.

As Mike says, I?m sure others will be able to add to this & give you some twin cam specific data.

HTH, Regards, Tim

[reb53]

Thanks for all the input so far.
I'm aware of the "get it pinking and then back off" process but am a little wary of cutting it a bit fine and not noticing the pinking at higher, ( and noisier...), revs.

Which is why I mentioned the new found tendency to get hotter than was usual around town.
I'm guessing that this is a real good indicator that the timing is out.
Do we all agree with Brian that retarded makes for over-heating ?

I do intend to experiment the next time I have a free moment so I'm not expecting the problem to be fixed on the forum without me laying a spanner on the car ! but the info I'm getting is pointing me in the right direction, so thanks.

Cheers
Ralph.

[twincamman]

PLINKING ??? PLUNKING???? twin cams are VERY sensitive to timing . set the cam timing accurately and make sure the ignition timing is set correctly 22 degrees advance at 2500 rpm then the car will perform as it should --------ed

[billwill]

Weights are not changed to change the curve! Springs are changed & the plate changed (or filed) to determine the start point where the springs start to have an effect.

There was a link in this forum to an excellent article, but I can't find it right now. All I can find is this:

http://www.distributordoctor.com/distri ... rings.html

[Sea Ranch]

Marcel Chichak, TDC Engineering, wrote this article, full of details on how to adjust Lucas advance timing, etc., including lots of pix (I believe I found it through the post/link you're referring to, Bill):
http://www.starchak.ca/tech/pdfs/lucastuning.pdf

I found this one handy when looking for a distributor cap:
http://www.starchak.ca/tech/pdfs/lucas.pdf

This one's great, too, for when it's time for re-wiring (or repair):
http://www.starchak.ca/tech/wirecode.html

The guy's got a lot of great stuff on his tech pages:
http://www.starchak.ca/tech/tech.htm

And . . . me think's he's a Canadian . . . Maybe he's related to Stu! Check out his other adventure: a custom made replacement distributor!
http://www.tdcperformance.ca/index.htm

Enough rambling . . . HTH . . .

Randy