Triumph TR5 Pinking

[DenisMc]

Hi All,

My Triumph TR5 pinks lightly under load. I have checked the static timing using a bulb connected to the distributor low tension connector and earth and it is as close to 11 degree BTDC that I can judge. Using a DTI with an extension piece and magnetic stand to probe the piston crown of No 1 cylinder, I have confirmed that when the crankshaft pulley is at TDC it is actually at TDC. The history file shows that an unleaded head was fitted when it was restored in 2001. I run the car on Shell V-power petrol.

Is it normal to have light pinking under load? If not, what do you suggest as my next steps?

Thanks,

Denis

[John L]

It would be useful to have a bit more information, before any recommendations.

Has this started recently? Is this a new purchase?

Have you done something to the engine?

What sparkplugs are you using?

I'm assuming its a PI and not carbs?

It will give us a better idea of what to suggest.

John

[Tom Fremont]

Denis,

There should be a vernier adjustment on your distributor that gives ~4 degrees of change per turn. If it were me ( and in fact this is what I've always done ) I would back it off a half turn and see how it goes. 

This assumes you have an original 41219 distributor; TRIUMPH supplied very different versions to the run of 6-pot TRs, all others of which gave more centrifugal advance. When I ran a TR250 distributor on my CP spec engine ( on Webers ) the static time setting was 4-6 degrees BTDC. With a 7 degree distributor it's 10-12 degrees BTDC.

I've never found much difference in performance from a few degrees of timing change, but like you hate pinging so set them as far advanced as I can short of that.

Tom

[DenisMc]

Hi John and Tom,

Thank you for your prompt replies. I have owned the car since August 2019 and it has always pinked slightly. It is a PI. The sparking plugs are NGK BP5ES. As far as I know it has the original Lucas distributor but it did have electronic ignition fitted at some point (which I have in the parts box) but the last owner converted the car back to the standard ignition set up. As mentioned, the car was fitted with an unleaded cylinder head back in 2000, but the receipt in the history file doesn't give any details. I'll try retarding the ignition using the knurled wheel to see what effect it has.

Thanks again,

Denis

[elclem1]

Have you set up tappets

Have you checked points gaps

Have you checked fuel pressure at the MU.

Of course its been mentioned on here before but the timing marks on the pulley may not be correct and need to be confirmed. 

Try the knurled nut method to get it running sweetly then i suspect that will stop any pinking. 

Good luck 

[John L]

Denis,

I may help you give it a run and then take out the plugs to see what colour they are, I'm beginning to think it could be a air leak making the mixture very lean, there are several places it could be, or perhaps the MU is just set very lean.

Places I would look at, the o rings on the injector bodies into the manifold, you could spray some brake cleaner at the inlet manifold gaskets to see it that changes the idle speed at idle, may show up a leak there,  if you could isolate the servo pipe and block off the pipe at the manifold, be careful if you drive as the brakes may not be good!

The colour of the plugs will give you a better idea of what going on, posting pictures as well may help.

John

[Tom Fremont]

Denis,

For what it's worth, the plugs you're using are (2) heat ranges hotter than what I've been using in my engines, BP7ES. As John suggests, plug colour will tell a tale and if they're on the white side you could try 6s. Factory specification for plugs was Champion N9Y when new, and that supposedly correlated with the BP7ES in NGK. Hotter UN12Y plugs were spec'd for the emissions cars until they got so leaned out they switched to N9Ys by the end. The 12s supposedly correlated with BP6ES and that's what I used with my stock '250 engine before changing to CP spec on Webers.

Tom

[Rob Salisbury]

It's worth noting that the quoted timing figures are nominal and should be adjusted to cope with the fuel available, these cars were first set up when 5* leaded petrol was readily available, it's anybody's guess what we get in out tanks these days!!

Cheers Rob 

[DenisMc]

Thank you all for your useful suggestions. Not long after I bought the car my local garage put it through the MOT test and for interest carried out an emissions test. This showed the car to be running rich (hc at tickover of 4402ppm) After carrying out a number of checks suggested by Carl Flitchett of Prestige Injection,which found all to be well,  I sent him the MU, pipes and injectors. He replaced a worn linkage in the MU and recalibrated the unit and tested the injectors. The next emission test showed the hc at tickovver to have reduced to 3438ppm). I understand that this is still quite rich. The hc at fast idle was 770ppm. When I refitted the MU and injectors I replaced all of the “O” rings on the plastic adaptors. The last time I looked at the plugs the colour was what one would expect for good combustion. However, I shall check this again and try retarding the ignition slightly. 
Thanks,

Denis  

[ntc]

Denis

Get yourself a good strobe light so you can see what is happening in real time 

[Peter Cobbold]

The PI lacks any 'acceleration charge' such as a throttle pump to richen the mixture upon rapid throttle opening. As a result to prevent unacceptable transient leaning (and thence pinking from octane fractionation)the PI has to be set rich throughout the load range.

Explanation here; https://supertrarged.wordpress.com/2013/06/12/the-lucas-pi-lean-spike/

Peter

[roy53]

Don't worry about the emissions figures .

Thats why America would not accept the PI engines because way to high for them.

Roy

[Andy Moltu]

These cars were intended to run on 5* petrol. 100 octane if memory serves me well.  95 octane, 10% ethanol tractor fuel may need you to retard the ignition a few degrees from the factory settings to minimise pinking. Super unleaded may help as it.may be 98+ octane.

As Pete says, the mechanical Lucas injection doesn't have any means of enrichment when you plant your right foot, so the compromise solution was to run rich. Too many people b****r around trying to get their idle emissions down to those of carbed cars and in the process mess up the mixture for real use. It is not unheard of to find suppliers setting metering units a bit lean. Fine if the car is being used T altitude but not great for sea level.

[Rob Salisbury]

I've always wondered about the notion that Lucas Pi has no means of enrichment when you stamp on the loud pedal, to my way of thinking when you plant your right foot the manifold vacuum drops to atmospheric and the metering unit goes to full fuel delivery then gradually leaning out as the manifold vacuum and engine revs build, so there's your enrichment carefully controlled as Mr Lucas intended.

Cheers Rob    

[Peter Cobbold]

15 hours ago, Rob Salisbury said:

I've always wondered about the notion that Lucas Pi has no means of enrichment when you stamp on the loud pedal, to my way of thinking when you plant your right foot the manifold vacuum drops to atmospheric and the metering unit goes to full fuel delivery then gradually leaning out as the manifold vacuum and engine revs build, so there's your enrichment carefully controlled as Mr Lucas intended.

Cheers Rob    

Rob,  Yes flooring the throttle pedal will send the MU to full flow delivery. Its the state of the wall-wetting of the inlet manifolds that matters just before the thottle is floored. Under cruise the walls will be rather dry, the depression and lowish fuel flow rate ensuring the walls are dry. Then when you floor the throttle the depression goes away and fuel droplet evaporation slows and droplets hit the walls and deprive the inlet valve of mixture. The mixture at the iv weakens. And the engine pinks for a second or so. The reason it pinks is because the high octane components of the fuel are less volatile and end up wetting the walls. The ivs see weak, low octane mixture. Until the walls are fully wetted again.

Peter

[Rob Salisbury]

Ah, fluid flow dynamics is a complete mystery to me, all those horrible looking equations are the stuff of nightmares!!

Thanks Peter,

Cheers Rob 

[Peter Cobbold]

2 hours ago, Rob Salisbury said:

Ah, fluid flow dynamics is a complete mystery to me, all those horrible looking equations are the stuff of nightmares!!

Thanks Peter,

Cheers Rob 

Me too, Rob.  Engineers seem to ditch the equations too, and use test rigs to film the manifold wall-wetting,eg:

https://people.eng.unimelb.edu.au/imarusic/proceedings/9/Milton.pdf

https://people.eng.unimelb.edu.au/imarusic/proceedings/11/Behnia.pdf

Maybe heating the floor of the PI manifold might help avoid transient pinking and allow cruise mixture to be leaned?......

Peter

[DenisMc]

Hi all.

Thanks you for your continuing suggestions and other information. I found Peter Cobbald's articles fascinating and consequently have learnt a lot more about the Lucas PI system. I am a professional engineer (retired) and actually joined Lucas in 1978, albeit Lucas Girling, and not cars but truck brakes and brake control systems. 

Back to the plot, I retarded the ignition timing by 2 degrees as suggested by Tom. On the road this seemed to reduce the pinking although I had just filled up the car with Shell V-Power, which is 99 octane. I also took out No 1 and 2 plugs and to me they appeared to be a good colour. Here is a photo.

I'll see how the car goes on runouts over the summer.

Thanks again,

Denis

 

[Peter Cobbold]

Harvey S Maitland posted his recurved spark timing to allow the PI to run on 95RON without pinking.  It was maybe ten years ago and I have lost the link. But kept a file:

https://prnt.sc/XIwB2eP5a7Zg

(apologies its inverted). He set static to 9 BTDC and fitted a stiffer spring.

He posts on here as HSM.

==

The end-hooks of the disy springs can open up with age and the 'slop' can allow too much advance too soon.

Peter