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qim

Spark plugs

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If you set the gun to zero advance, Camilo, you should see the hole in the pulley "frozen" a few cm away from the pointer on the engine cover. As you dial in advance the hole will "move" back toward the pointer. When it's lined up with the pointer, read the advance directly from the gun.

 

Where the gun starts doesn't matter at all. You want to know the advance when the hole and pointer are aligned.

 

Definitely disconnect the vacuum advance. It's likely to add ten degrees or more to your timing advance, and you don't want to consider this in your initial measurement.

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Well... I tried again, after diconnecting the pipe that goes to the carbs and as I could not find anything to block it I used some tape around the entrance. I don't know if it blocked totally but I got the same result: around 24º

 

I guess that could mean that the vaccum pipe is not good... but the car runs well and accelerates well

 

Anyway, if the timing is 24º what are the consequences? What is the maximum that you have heard of and suits the car?

Edited by qim

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I run about 14° BTDC on my car and slightly rich mixture, based on my cam and the advice of Jeff at Advanced Distributors (our equivalent of the Distributor Doctor over here). Works for me.

 

24° BTDC advance at idle with no vacuum sounds like a lot, Camilo. How does it run if you take the advance down ten degrees?

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How does it run if you take the advance down ten degrees?

 

 

Do you mean rotating the distributor? Never done that, and as you probably noticed I am very nervous about new adventures... But of course if it needs doing, it will be done. However... I read the following that recommends the old-fashioned way of setting the timing. I am going to wait until my electrician comes back from holiday on Monday and get him to make me a bulb tester.

 

EDIT

 

All these posts are assuming that the white mark on the pulley represents the hole. I wonder if it could be instead a mark to allow the 3/8" (or something similar) as in the attached article.

Setting-the-Ignition-Timing-on-a-TR.pdf

Edited by qim

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Do you mean rotating the distributor? Never done that, and as you probably noticed I am very nervous about new adventures... But of course if it needs doing, it will be done. However... I read the following that recommends the old-fashioned way of setting the timing. I am going to wait until my electrician comes back from holiday on Monday and get him to make me a bulb tester,

 

 

Ken's method works for me as a basic set up as detailed in the pdf.

Peter W

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The instructions you attached are to set static timing, which is consistent with original factory recommendations and still done by many folks (including Mark Macy, whom you referred to earlier). If you're going to do it this way you don't need your timing light at all. And a child could make a test light -- you certainly don't need an electrician. Do you know how to solder a couple of wires? That's all it takes to make a test light to be honest. Alligator clips are a useful upgrade but aren't required for it to work.

 

I'm not a big fan of static timing, although it does give an adequate result. You can also rotate the distributor as the car's running by loosening (just enough) the baseplate clamp to adjust timing and check with the strobe gun. That's what I do.

 

But tell me, why do you spend hours and hours fooling with the car and asking countless questions here if in the end you're afraid to do anything? :) It's only a TR -- it'll take a lot of abuse!

Edited by Don H.

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If removing the vacuum pipe made no difference then you do have a problem with that which needs fixing. Perhaps your basic advance has been set much too high to compensate for the vacuum advance not working ?

 

The advance capsule is connected to the distributor base-plate by a spring which is looped over a pillar. A visual inspection will show whether it is in place and connected.

You can check whether the vacuum advance capsule is working without the engine running, by connecting a pipe to the distributor and sucking on it. (You might get a nasty taste of petrol doing that). With the top off the distributor you should see the base plate rotate a bit clockwise as you suck. If it doesn't move, its stuck. If you can't get a vacuum there is a hole in the operating diaphragm. If that checks out OK then the pipe to the carb might have an air-leak.

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Hi Rob

 

Thank you. That will be my next job

 

But tell me, why do you spend hours and hours fooling with the car and asking countless questions here if in the end you're afraid to do anything?

 

Hi Don

 

In the end, when I feel I understand the theory and feel I asked all the questions I needed to get confidence I go ahead and do it, just like the carbs which have turned out quite well.

 

But, yes, I do realize that I ask too many questions and some people may be getting a bit fed up with me . I'll keep that in mind.

 

Thanks

Edited by qim

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Dig in, Camilo. Not much you can do that can't be undone.

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If removing the vacuum pipe made no difference then you do have a problem with that which needs fixing. Perhaps your basic advance has been set much too high to compensate for the vacuum advance not working ?

 

The advance capsule is connected to the distributor base-plate by a spring which is looped over a pillar. A visual inspection will show whether it is in place and connected.

You can check whether the vacuum advance capsule is working without the engine running, by connecting a pipe to the distributor and sucking on it. (You might get a nasty taste of petrol doing that). With the top off the distributor you should see the base plate rotate a bit clockwise as you suck. If it doesn't move, its stuck. If you can't get a vacuum there is a hole in the operating diaphragm. If that checks out OK then the pipe to the carb might have an air-leak.

Rob,

The vac advance wont be operating at tickover - not enough suction. Most va capsules start to pull at 2 to 6 inch Hg. At tickover an SU will only generate about 0.25 psi at the take-off, which is 0.4 inch Hg, too little.

I dont have data for 4 pots but doubt the capsule will be any different.

Peter

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The instructions you attached are to set static timing, which is consistent with original factory recommendations and still done by many folks (including Mark Macy, whom you referred to earlier). If you're going to do it this way you don't need your timing light at all. And a child could make a test light -- you certainly don't need an electrician. Do you know how to solder a couple of wires? That's all it takes to make a test light to be honest. Alligator clips are a useful upgrade but aren't required for it to work.

 

I'm not a big fan of static timing, although it does give an adequate result. You can also rotate the distributor as the car's running by loosening (just enough) the baseplate clamp to adjust timing and check with the strobe gun. That's what I do.

 

But tell me, why do you spend hours and hours fooling with the car and asking countless questions here if in the end you're afraid to do anything? :) It's only a TR -- it'll take a lot of abuse!

Don,

I've worked with postdocs who threw a wobbler at being asked to re-solder a dry joint......had never seen a soldering iron.

Schools these days....(sigh)

Peter.

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Ah yes Peter - good point.

 

 

My feeling now is that Camilo should do as he has suggested and set the timing statically to get things near the standard setting, and then re-check with the strobe to see whether the dynamic reading is more sensible.

Edited by RobH

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+1 for Peter's comments.

As it happens I was checking my timing today, & found that removal of the vacuum pipe had no effect on the timing at tickover, & yes the vacuum advance diaphragm is OK & the timing moves if I suck on the pipe.

 

Oddly my timing was also rather too advanced at around 20° BTDC although I have not experienced any pinking. it is now 15° BTDC at 600 RPM.

 

Bob.

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+1 for Peter's comments.

As it happens I was checking my timing today, & found that removal of the vacuum pipe had no effect on the timing at tickover, & yes the vacuum advance diaphragm is OK & the timing moves if I suck on the pipe.

 

Oddly my timing was also rather too advanced at around 20° BTDC although I have not experienced any pinking. it is now 15° BTDC at 600 RPM.

 

Bob.

 

 

Thank you all.

 

This brings me back to a question I posed but did not get answered: what is the consequence of running too advanced? Me at 24º; Bob at 20º.

 

Does it explain high consumption, or just pinking, in my case? Or could it be just due to the quality of petrol (95 octane regular plus lead additive)

Edited by qim

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Thank you all.

 

This brings me back to a question I posed but did not get answered: what is the consequence of running too advanced? Me at 24º; Bob at 20º.

 

Does it explain high consumption, or just pinking, in my case? Or could it be just due to the quality of petrol (95 octane regular plus lead additive)

Sparks that happen too early make the peak gas pressure above the piston occur too early, when the geometry of the conrod and crank are not optimal. The best crank angle is about 16 degrees after top dead centre (ATDC), for almost all engines not just TRs.

If the sparks are too early ( timing over advanced) or too late ( retarded) both economy and power will sufffer. But an error of say 5 crank degrees only takes off about 1% of power, so timing is not supercritical. The pinking occurs on some strokes when the gas burns rather slowly leaving a pocket of 'end-gas', usually under the exhaust valve, which then explodes - that 'detonation' is pinking. Higher octane fuel will abolish it, but it is more elegant, in my view, to retard the spark a bit until you just don't quite get pinking.

 

There is lot of information on the processes going on during combustion in the talk I gave at IWE Lincoln last year:

https://supertrarged.files.wordpress.com/2016/07/combustion-talk-iwe-2016-v2-ppt.ppt

 

There is a second, very common, cause of pinking that happens for maybe a second or two after suddenly flooring the throttle. Slides 91 onwards expalins why this happens - stiffer oil in the SU daspot will cure it. See also this years talk on SUs.

 

Peter

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Sparks that happen too early make the peak gas pressure above the piston occur too early, when the geometry of the conrod and crank are not optimal. The best crank angle is about 16 degrees after top dead centre (ATDC), for almost all engines not just TRs.

If the sparks are too early ( timing over advanced) or too late ( retarded) both economy and power will sufffer. But an error of say 5 crank degrees only takes off about 1% of power, so timing is not supercritical. The pinking occurs on some strokes when the gas burns rather slowly leaving a pocket of 'end-gas', usually under the exhaust valve, which then explodes - that 'detonation' is pinking. Higher octane fuel will abolish it, but it is more elegant, in my view, to retard the spark a bit until you just don't quite get pinking.

 

There is lot of information on the processes going on during combustion in the talk I gave at IWE Lincoln last year:

https://supertrarged.files.wordpress.com/2016/07/combustion-talk-iwe-2016-v2-ppt.ppt

 

There is a second, very common, cause of pinking that happens for maybe a second or two after suddenly flooring the throttle. Slides 91 onwards expalins why this happens - stiffer oil in the SU daspot will cure it. See also this years talk on SUs.

 

Peter

Hi Peter

 

I am surprised that you say that 16º is optimal when Triumph stated 4º, but then maybe I am not talking about the same thing. From your post, I gather also that I should not stay awake at night because my timing is 24º

 

Thanks

 

Camilo

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Hi Peter

 

I am surprised that you say that 16º is optimal when Triumph stated 4º, but then maybe I am not talking about the same thing. From your post, I gather also that I should not stay awake at night because my timing is 24º

 

Thanks

 

Camilo

Camilo,

16 degrees After TDC is the crank angle at wich the gas pressure shodl peak. The gas does not burn instantly at the spark. Thats why a distributor is needed.

 

24deg Before TDC is wrong. For a normal compression ratio 9 to 10 to 1 it should be nearer 10 or 12 BTDC static. I would set it to that with the light bulb across the points and see if it stops pinking.

Another method that does not assume the pulley mark is correct is to turn the disy anticlockwise to retard the spark unitl it just stops pinking when driving. Turn it about 2 to 3 mm anticlockwise ( measured at the rim of the cap) at a time. Do not forget to retighten the clamp-bolt before driving.

 

Peter

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I am sorry to come back to this, but...

 

My timing mark, according to my fingertip is exactly where the hole in the pulley is located.

 

Now, my poor understanding is that correct timing should be a number of degrees BEFORE TDC. If the hole (and so, the white mark) serve to mark TDC it does not allow for the number of degrees before. What I mean is that I get 24º with a strobe when the mark is lined with the pointer; but should the desired angle not be some degrees before?... which accounts for the high result?

 

Camilo

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NO.

If, when the hole lines up with the pointer your strobe is set to read 24°, then that is your timing at those revs.

The only way the hole will appear to the left of the pointer (BTDC) is if you alter the strobe to read less than 24° i.e. 0°

 

Bob.

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Camilo - as you say, the plug actually fires some degrees before TDC which means it will not occur when the mark is in line with the pointer. If the flash from your timing gun happened at exactly the same time as the plug firing you would see the timing mark to one side of the pointer where the firing actually takes place but it would be difficult to estimate the advance angle from that.

 

To make measurement easy, the gun works by allowing the flash to be delayed some time after the plug fires, and during this delay the mark has rotated towards the pointer. if the plug fires at 24 degrees before TDC, and the gun waits 24 degrees before flashing, you will see the marks apparently lined up. You are varying the delay with the +/- buttons and the gun is displaying the delay that you have set. This makes the measurement more accurate as you can easily see when the marks are in line whereas trying to estimate the angle if they are apart is difficult.

 

As Bob says, if you set the gun readout to 0000 which means there is no delay between the plug firing and the flash occurring, you will see the actual firing point.

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