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Ignition Timing


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Hi All

Just want to do a quick check on IGN timing for a 72 Pi.

The brown book lists the static timing as 11 degrees but no timing at idle, unless I’ve missed it, though it does for US cars. Now it’s a bit of a pain to slowly turn the engine over to get evrything in the right to check esp when the fan is in place and rad full of water.

So two questions, is there a sneaky way or turning the engine over or what should the dynamic timing at idle, so circa 800rpm.

Cheers  Keith

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With the plugs out I can turn mine with the fan belt.

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Static and 800rpm should  be the same,

The original settings for the 41542 distributor according to the Truimph Repair Operation Manual are static 11 degree BTDC, 0 degrees crankshaft advance at 700 RPM, 0-1.5 degrees advance at 1000 RPM, 0.5 - 3.0 at 1200 RPM, 3.5 - 6.0 at 1600 RPM and 8 -10 at 2200 RPM.

For the original poster who had a 41502 distributor the settings are static11 degrees BTDC, 0 degrees at 600 RPM, 0-1 at 800 RPM, 2.5 - 4.5 at 1200 RPM, 6-8 at 1600 RPM, 13-15 at 2400 RPM.

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I turn my engines with the plastic fan. I'm not sure the fan belt likes the kind of tension it takes to tug the engine round with it, though concede the centrifugal forces they see at 6000 rpm may greatly exceed that - one for the profs here.

I have the CP cam in my Webered '250 as well as a 7 degree distributor. It likes about 12 degrees BTDC of static timing.

 

Cheers,

Tom

 

 

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I initially set mine at 11 degrees BTDC at around 750 rpm with a timing light. Like most PI's I don't have any vacuum advance. After setting the timing I like to creep it forward until I get light pinging under WOT top gear, then retard it slightly.

The timing light also lets me check the centrifugal advance is working smoothly after I set the timing.

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On 12/1/2019 at 3:39 PM, Peter Cobbold said:

Static and 800rpm should  be the same,

The original settings for the 41542 distributor according to the Truimph Repair Operation Manual are static 11 degree BTDC, 0 degrees crankshaft advance at 700 RPM, 0-1.5 degrees advance at 1000 RPM, 0.5 - 3.0 at 1200 RPM, 3.5 - 6.0 at 1600 RPM and 8 -10 at 2200 RPM.

For the original poster who had a 41502 distributor the settings are static11 degrees BTDC, 0 degrees at 600 RPM, 0-1 at 800 RPM, 2.5 - 4.5 at 1200 RPM, 6-8 at 1600 RPM, 13-15 at 2400 RPM.

Hi Peter.

Do you have any idea of the settings for a 41219f type 22D distributor fitted to a CP engine with twin SU’s ?

Thanks in anticipation ! 

Regards

Julian.

 

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25 minutes ago, Julian Mullins said:

Hi Peter.

Do you have any idea of the settings for a 41219f type 22D distributor fitted to a CP engine with twin SU’s ?

Thanks in anticipation ! 

Regards

Julian.

 

Julian, Good question as the PI needed compromised timing that avoided pinking.  With twin SUs you cna use vac advance to improve fuel economy. The TR250 had 9.5:1 compression and:   10 crank deg static plus 26 degrees of mechanical advance + vacuum advance of ca,10 degrees. Total of 46 degrees.  I dont know the spec of your disy but if it needs recurving Disy Dr should be able to advise. The mixture also plays a part, leaner cruise mixtures needing more advance (hence the 46 deg BTDC).

Peter

 

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2 minutes ago, Peter Cobbold said:

Julian, Good question as the PI needed compromised timing that avoided pinking.  With twin SUs you cna use vac advance to improve fuel economy. The TR250 had 9.5:1 compression and:   10 crank deg static plus 26 degrees of mechanical advance + vacuum advance of ca,10 degrees. Total of 46 degrees.  I dont know the spec of your disy but if it needs recurving Disy Dr should be able to advise. The mixture also plays a part, leaner cruise mixtures needing more advance (hence the 46 deg BTDC).

Peter

 

Thanks Peter.

I think you have confirmed my thoughts, a trip to the disy doc is necessary.

Julian

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2 hours ago, Peter Cobbold said:

 The TR250 had 9.5:1  8.5:1 compression 

Peter

 

 

Fixed it for you ^_^!

Mine always needed premium fuel to avoid pinking too ( when I ran the stock setup ). With the higher c/r I doubt more than 30 degrees total advance will keep it under the pinking wire.

With CP cam, 9.5:1 and triple Webers it doesn't like more than ~ 25 degrees total advance. My scheme to incorporate vacuum advance for cruising didn't develop enough vacuum so was discarded, but I do think it could use it cruising.

 

Tom

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I have just gone through this process with my 70 PI. It has a stock (probably the original) 41219D distributor.

The manual says 11deg BTDC static. Idle at 700 rpm should be the same so I set it at idle.

The manual says it should top out at 16 deg BTDC at 2600 rpm. 16 deg, are they kidding. Every engine of this period I have done over 45 years have peaked at 30 or more deg BTDC. The PI system might have something different but not 16 deg max advance.

Mine topped out at 26-28 deg at 2600 rpm.

I have since discovered that the 16 deg is supposed to be added to the 11 deg static. The TR6 manual is the only manual I have seen that describes advance this way.

I've done MGs, Morris Minors, Mini Cooper S, Jag MkII, TR2, Hillmans and they all describe the advance as the total figure, not adding static to the advance at higher revs.

However, that is how it is. I was with the local Triumph specialist today and he confirms that 26 deg at 2600rpm is correct.

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Hi John,

yes, the brown bible states it correct (add the advance to the static for the number you read at engine running.

Took me a couple of reads before I got that:)

Waldi

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On 12/3/2019 at 5:17 PM, Peter Cobbold said:

Julian, Good question as the PI needed compromised timing that avoided pinking.  With twin SUs you cna use vac advance to improve fuel economy. The TR250 had 9.5:1 compression and:   10 crank deg static plus 26 degrees of mechanical advance + vacuum advance of ca,10 degrees. Total of 46 degrees.  I dont know the spec of your disy but if it needs recurving Disy Dr should be able to advise. The mixture also plays a part, leaner cruise mixtures needing more advance (hence the 46 deg BTDC).

Peter

 

Peter, Do not forget that the TR250 had two vacuum capsules, one for advance and one for retard.  The retard was controlled by throttle spindle position I think.

This may be of use to anyone converting a TR250.

Cheers

Peter W

 

tr56_16_07_01.jpg

TR250 Distributor.jpg

Edited by BlueTR3A-5EKT
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7 hours ago, John McCormack said:

I have just gone through this process with my 70 PI. It has a stock (probably the original) 41219D distributor.

The manual says 11deg BTDC static. Idle at 700 rpm should be the same so I set it at idle.

The manual says it should top out at 16 deg BTDC at 2600 rpm. 16 deg, are they kidding. Every engine of this period I have done over 45 years have peaked at 30 or more deg BTDC. The PI system might have something different but not 16 deg max advance.

Mine topped out at 26-28 deg at 2600 rpm.

I have since discovered that the 16 deg is supposed to be added to the 11 deg static. The TR6 manual is the only manual I have seen that describes advance this way.

I've done MGs, Morris Minors, Mini Cooper S, Jag MkII, TR2, Hillmans and they all describe the advance as the total figure, not adding static to the advance at higher revs.

However, that is how it is. I was with the local Triumph specialist today and he confirms that 26 deg at 2600rpm is correct.

Some manuals including mine state static in crank degrees but advance in disy degrees, which of course are half crank degrees. It had me fooled for a long time unitl I read the small print alongside the table.

Peter

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6 hours ago, BlueTR3A-5EKT said:

Peter, Do not forget that the TR250 had two vacuum capsules, one for advance and one for retard.  The retard was controlled by throttle spindle position I think.

 

TR250 Distributor.jpg

From new, vacuum retard was operational only at idle, never above. Throttle linkage incorporated an initial lost motion to release/close a little plastic valve connecting manifold vacuum to the retard capsule, from there it switched from 8 degrees ATDC to 10 degrees BTDC with a corresponding increase in rpm of ~300.

The only TR250 I saw with this feature working properly in 43 years of ownership was mine. I've lost count of examples where the owner had both capsules connected to the same manifold vacuum port.

 

Cheers,

Tom 

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Reading this topic on Ignition timing with great interest and very relevant to me, as never got a definitive answer to my concerns/questions for my car.

I have a 1974 TR6 imported  from USA , (125bhp), converted to PI with a fast road cam, stage II conversion, extractor manifold, sports exhaust and some work done to the head to improve the compression ratio back to 9.5:1.  I dont know all the details or the exact cam that was fitted, but I was told that it would be very similar to an early TR6 PI, if not better which is what I wanted.

My distributor fitted is a  Lucas  22D6, (41558/A) , fitted with a 8 degree base plate, and the static timing set to 11° BTDC.   

Can someone please advise if all this seems logical, and give me some definitive details of what the crankshaft timing curve/RPM should should be for my  car?

Regards, Colin.

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Hi Colin,

You should be good to go with that, though I haven't heard of an 8 degree distributor for these ( 7, 10 and 13 degree I have ).

7 degree distributors were supplied with all P.I. engines I believe; Uncle Bentley can set the record straight.

I run a CP cam in my driver with 9.5:1 and triple Webers, and the 7 degree distributors suits it very well with 11-12 degrees of static time. If yours is not pinking, you can find the max advance by dialing the vernier ( mine have them, not sure about yours ) to the point where pinking starts and back off from there. In my experience, recipes such as yours and mine don't do well with over 30 degrees total advance. 

Regards,

Tom

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OK Tom, thanks for that it confirms and explains all.

I should have explained that I changed over the 41558/A distributor base plate from the 13° to the 8°, 8° was the closest my local friend had at the time.

And yes, I do have the vernier "click adjustment" fitted, so I can do a dynamic timing check and then road test as you suggest.

Cheers, Colin.

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Hi Keith, for turning the engine over, I use a 5/8 Whitworth spanner (28mm might do it, as well?), on the crank pulley retaining bolt.

Hope this helps,

Cheers,

Paul.

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  • 2 months later...

Thanks for all your thoughts on this.

Before sending my disy to the Dr, can someone confirm my thoughts.

I set the static timing to 11 degrees btdc.  At idle (850 rpm), the timing light indicates approx 30 btdc.  and about 38 btdc when I bring the revs up to 1500.

Would this indicate that the advance springs are a bit sloppy ?

Edited by Julian Mullins
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1 hour ago, Julian Mullins said:

Thanks for all your thoughts on this.

Before sending my disy to the Dr, can someone confirm my thoughts.

I set the static timing to 11 degrees btdc.  At idle (850 rpm), the timing light indicates approx 30 btdc.  and about 38 btdc when I bring the revs up to 1500.

Would this indicate that the advance springs are a bit sloppy ?

Could be the spring eyes have opened up. Or some PO fitted weaker springs.

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I think you need to know what cam lever is fitted inside the distributer, it will be stamped with a number, this part limits the full advance, a small amount can be ground off it,  to allow more max movement and so increases the total advance number.

john

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