TR6 PI starts with a bang, then dies

[Guest ntc]

Good man

Two or three wrongs do not make it right you tinkered with it as many do and things go downhill Martin will have set the dizzy right.... so where are you now?

Edited August 19, 2016 by ntc

[MortenHoyseth]

Neil, I marked of the position on the pedestal/distributor driveshaft (when not on the block) for when the dizzy is opening the point and the nose on the rotor is approaching #1.

[Guest ntc]

So you have the dizzy and ped in your hand?

[Peter Cobbold]

 

A couple of extra pictures taken at random from USA TR6 sites showing the retard dissy and the position of the retard spring pin in relation to the body.

 

Alan

anotherusdissy1.jpg

anotherusdissy2.jpg

Back to square one.

So Morten's points are in the correct rest position when a vac retard unit is fitted. But the cap contacts dont match,when the cam and timing is correct fro a PI engine at static 12BTDC ( #61).

The answer is in the timing curves, the PI and carb/vacret are very different:

The vac retard was only operative at tick-over, it was designed to delay the spark to help burn hydrocarbons,to meet early emissions. So those photos show the plate's position of a loaded engine during driving. (Little manifold vacuum : no retard)

Now we compare carb and PI timing curves:

At tickover the vac ret unit takes 16 crank deg off the timing, bringing it to 4 ATDC:

http://s381.photobucket.com/user/saffrontr/media/img225-1.jpg.html

- this puts the spark 8 disy deg anticlockwise and into rotor-contact alignment.

When the throttle is opened this vacuum declines and we'd expect the alignment to be lost.

However the carb disy c/f brings in a lot more advance at 1500rpm than the PI:

http://s381.photobucket.com/user/saffrontr/media/img227.jpg.html

Compare disys F-L ( carb) with PQ (for PI)

Summary: So the carb disy on tickover has the firing point delayed, allowing the rotor and cap to align.

And as the vacuum drops the c'f advance also moves the firing point anticlockwise and into rotor/contact alignment.

 

What Morten has is static set at 12BTDC not 4 ATDC, because the vac capsule is disconnected. Rotor and contact don't align ( #61).

And the PI advance curve is nowhere near as much as that of the carb, so as the PI cenfrigal comes in the rotor mismatch is still there. (But note Morten said earlier more rpm help his engine to run - some c'f does help cure the mismatch)

 

Mortens solution is still to move the points plate closer to the lug on the body. The above merely explains why the vac ret disy works with the points plate apparently with a rotor phasing issue. And why a disy with vac ret unit fitted wont work with 1) the vac ret inoperative and 2) the PI c'f curve. And it wont work because of "rotor phasing"

 

Peter

@Morten: send this post to Martin, see what he thinks.

Edited August 19, 2016 by Peter Cobbold

[MortenHoyseth]

Neil, no I'm away, but back in two hrs.

[MortenHoyseth]

Peter, I sent a few questions/pictures to Martin, with a link to this thread

[Peter Cobbold]

Peter, I sent a few questions/pictures to Martin, with a link to this thread

Morten, Hope you dont ask him to read the lot!! Just point him to #61 and #154.

You need to know the rest position of the points plate for a PI disy- Martin will know.

Peter

[Guest ntc]

Peter

I hope you can type up how to time the whole lot

[GT6M]

Im meb,e gonna bung a spanner int works here, IF it aint ign.

 

did ye get the engine wid new duplex sprokets, top n bottom, !!

if so, were they a matched set,!!

 

sprokets of a TR5/6 are indexed diff to a Salloon, or a 270, 110 deg cam

bung a salloon bottom wheel ona TR 5/6 {280 } top wheel, and timings 10 degs oot

BUTT,timing marks say its correct

the cam bolts holes are indexed diff, for diff cams 270 - 280

 

meb,e some thing to consider too.

 

M

Edited August 19, 2016 by GT6M

[oldtuckunder]

So those photos show the plate's position of a loaded engine during driving. (Little manifold vacuum : no retard)

 

 

No they show static position engine not running timed at 10/12 BTDC, the retard when running would pull it to 4deg ATDC.

 

NB the retard mechanism doesn't use manifold vacuum, it uses a special port on the carbs not covered by the butterfly at idle, but covered by the butterfly at cruise.

 

There is a good description somewhere I'll see if I can find it.

 

The bottom line is that with a retard dissy you still set the static the same at 10/12 BTDC.

 

Alan

[oldtuckunder]

 

There is a good description somewhere I'll see if I can find it.

 

 

 

Cant find original, but copy in this on-line pdf

 

http://www.mntriumphs.org/Archive/2014-04-Apr.pdf

[Peter Cobbold]

 

No they show static position engine not running timed at 10/12 BTDC, the retard when running would pull it to 4deg ATDC.

 

NB the retard mechanism doesn't use manifold vacuum, it uses a special port on the carbs not covered by the butterfly at idle, but covered by the butterfly at cruise.

 

There is a good description somewhere I'll see if I can find it.

 

The bottom line is that with a retard dissy you still set the static the same at 10/12 BTDC.

 

Alan

Alan, When the engine is loaded there's not enough manifold vac to operate the retard unit - so the photo shows the non-tick over position.

The vac retard does not work at cruise. The throttle edge take-off you refer to is for vac advance that does work only at cruise.

Yes you do set the static at 12 with vac ret unit,then the tickover manifold vacuum pulls the point to deliver 4ATDC. But Morten does not have the unit connected to the manifold, so the timing stays at 12 BTDC and in rotor mismatch.

Peter

[Peter Cobbold]

 

Cant find original, but copy in this on-line pdf

 

http://www.mntriumphs.org/Archive/2014-04-Apr.pdf

Useful link, thanks.

Example 1 agrees with what I said.

'Points to remember' summarises

 

The point I make is that Mortens vac ret is not connected up so that USA disy is trying to work without 16 crank deg retard at

tickover.

Peter

Edited August 19, 2016 by Peter Cobbold

[oldtuckunder]

The throttle edge take-off you refer to is for vac advance that does work only at cruise.

 

 

No, two! different take off ports 1 for advance and one for retard!

[Guest ntc]

 

No, two! different take off ports 1 for advance and one for retard!

+1

[John L]

Morten

We need the Lucas part number from the distributor, it should start with 4***** and a date code day month year, and photo would be good. Not sure the numbers you quoted, perhaps DD'S numbers.

 

@ Oldtuckunder your second picture of the dizy on a test stand is one that rotates in a clockwise direction, we need ones that rotate in anticlockwise, perhaps thats the difference.

 

John

[MortenHoyseth]

I'm in the garage in 30 min, and post some pictures then. And ready to work on it

[Peter Cobbold]

 

No, two! different take off ports 1 for advance and one for retard!

Of course, I know.

The vac advance port located above the butterfly top=leading edge when the throttle is part-open sees a very high venturi depression at cruise, that disappears at tickover and at wide throttle openings. It advances the arpk only at cruise.

The vac retard port does not see that venturi depression. It senses static manifold depression mcuh lika vac gauge. The vac is high enough to actuate the capsule ony at tick over (and over-run if an air valve is absent from the buttelrfy.

 

Theres a lot of fluid mechanica at play

The difference between the location of the ports to the butterfly motion is crucial,

The buttlerlfy edge moves away from he vac retard port as the throttle is opened, and the port sees less vacuum:

http://s1105.photobucket.com/user/PLHuckels/media/Jolly%20Green%20Triumph/Front%20Carb%20Vacuum%20port%20cleanout/DSC00009_zps6b3fe5fe.jpg.html

By contrast the vac advance port sees only choke tube depression ( b888ar all) at tick over. As the buttlerfly is opened its top edge gets closer to the port and the fast air flow ( which can be sonic) creates a large vacuum through the venturi effect.

http://static.triumphexp.com/phile/8/12522/_T2eC16Z_ykE9s7t_2bmBQtnlp_5r_60_57_1_copy.jpg

- this is often referred to as the 'ported vacuum' take-off

 

At part-throttle the manifold vacuum feeding the retard capsule will be much less than the vacuum feeding the vac advance capsule. One pressure is statci the other a dynamic pressure. At closed thottle the retard capsule see high vacuum, while the vac adv capsule sees almost none. Neither port is blocked by the butterfly.

 

Peter

Edited August 19, 2016 by Peter Cobbold

[oldtuckunder]

@ Oldtuckunder your second picture of the dizy on a test stand is one that rotates in a clockwise direction, we need ones that rotate in anticlockwise, perhaps thats the difference.

 

 

I think you can ignore the arrow, it was one being built for a TR6, here are the links to the two

 

http://www.74tr6.com/distributoradjustable.htm

 

http://www.74tr6.com/distributor.htm

 

Alan

[MortenHoyseth]

Attached is the dizzy housing with number printed on.
The vacuum unit - hard to get a picture of that, but code on it is: 3-10-7R .54424200

Edited August 19, 2016 by MortenHoyseth

[Peter Cobbold]

Attached is the dizzy housing with number printed on.

The vacuum unit - hard to get a picture of that, but code on it is: 3-10-7R .54424200

3-10-7R

Standard code, means:

R is for Retard

actuation starts at 3 inch Hg 'vacuum'

ends at 10 inch Hg

and gives 7 disy degrees of retard (at vac= 10in Hg), which is 14 crank deg.

 

But its not operational.....

Edited August 19, 2016 by Peter Cobbold

[oldtuckunder]

 

The point I make is that Mortens vac ret is not connected up so that USA disy is trying to work without 16 crank deg retard at

tickover.

 

 

Exactly! he has it timed at 12 BTDC, but the points are in the position they would be with about 16 crank vac advance!

 

In normal operation the retard vac doesn't pull them back and past neutral at idle it pulls them further back so that 4 ATDC is achieved.

 

I'm using the same dissy timed at 12 BTDC static (without vac connected) at idle I have 12 BTDC. If I hooked up the vac unit I would then have 4 ATDC at idle, unplug it and it would swing back to 12 BTDC.

 

My rotor is nicely over #1 in the cap at 12 BTDC just as the points are breaking if I apply vacuum retard the cam and rotor and cap don't move all that happens is that the whole points are just pulled anti clockwise, so the spark occurs late i.e the rotor is further past #1 in the cap when the points break. If I had and applied vac advance it pulls the points clockwise so the spark occurs earlier and the rotor is less advanced on #1 in the cap.

 

Morten's points are being held at max vac advance position when timed static at 12 BTDC, so the rotor is in the wrong place, now add in a bit of mechanical advance (remembering that this works in the opposite direction to vac advance) and the cam and rotor advance anti clockwise so whilst the rotor advances a bit more to #1 in the cap (and maybe also stops arching back to #4?) this also has the effect that the points hit the cam earlier so the net effect is that the rotor is as far away from #1 as it was with no mechanical advance.

 

Alan

[oldtuckunder]

Attached is the dizzy housing with number printed on.

The vacuum unit - hard to get a picture of that, but code on it is: 3-10-7R .54424200

 

Ok its a 41385A USA TR6 distributor, and that is the correct numbers for the vacuum unit.

 

By luck it is also exactly the same distributor and vacuum unit that I have manufactured within a few weeks of each other in 1973 so they should be identical!

 

So the question is why aren't they?

 

Mine is an unmolested NOS Lucas unit with a couple of thousand miles on it.

 

Alan

[Peter Cobbold]

 

Exactly! he has it timed at 12 BTDC, but the points are in the position they would be with about 16 crank vac advance!

 

In normal operation the retard vac doesn't pull them back and past neutral at idle it pulls them further back so that 4 ATDC is achieved.

 

I'm using the same dissy timed at 12 BTDC static (without vac connected) at idle I have 12 BTDC. If I hooked up the vac unit I would then have 4 ATDC at idle, unplug it and it would swing back to 12 BTDC.

 

My rotor is nicely over #1 in the cap at 12 BTDC just as the points are breaking if I apply vacuum retard the cam and rotor and cap don't move all that happens is that the whole points are just pulled anti clockwise, so the spark occurs late i.e the rotor is further past #1 in the cap when the points break. If I had and applied vac advance it pulls the points clockwise so the spark occurs earlier and the rotor is less advanced on #1 in the cap.

 

Morten's points are being held at max vac advance position when timed static at 12 BTDC, so the rotor is in the wrong place, now add in a bit of mechanical advance (remembering that this works in the opposite direction to vac advance) and the cam and rotor advance anti clockwise so whilst the rotor advances a bit more to #1 in the cap (and maybe also stops arching back to #4?) this also has the effect that the points hit the cam earlier so the net effect is that the rotor is as far away from #1 as it was with no mechanical advance.

 

Alan

Where is the points plate pin in relation to the casing in your disy? (engine off) If its same as Mortens then its not the disy, as yours works.

I thought the cam timing had checked out OK, equal positions of 11and12 at 12BTDC on 1.

So whats causing # 62, the rotor phasing fault?

#62 suggests the rotor is half-way between two cap contacts so about one twelfth of a full rotation out.

How many gear teeth mesh between the disy and cam gears?? Ans.: 14

http://s233.photobucket.com/user/poolboy_album/media/100_0337.jpg.html

Maybe Morton has been relying upon the pump drive slot to dictate where to best insert the drive shaft.

Moving the meshing one cog either way should correct the rotor phasing

 

Peter

Edited August 19, 2016 by Peter Cobbold

[John L]

Morten

Thanks for the photos now we know which one it is.

Can you look at the cap, are the plug lead contacts on the inside equally spaced by the notch close to the Distributor Doctor label on the dizy body, and will be the same on the other side where the U cutout is, I'm sure there is more than one part number for the caps.

I still think we need to know the relation between the drive dog at the bottom of the dizy to the rotor arm position, picture in the Brown manual.

Also when you have timed the dizy to #1 firing what position is the rotor arm in?

John

Edited August 19, 2016 by John L