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TR6 PI starts with a bang, then dies


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Hi dear fellow TR drivers,

 

I'm back with my TR6 PI CP running problems. Sadly. My previous post was "TR6 PI not starting" and I guess this is kind of related.
Hope somebody have some ideas to what cause this problem.

Problem:

I get the TR6 engine starting after a few tries. It's does not sound happy and dies after 10 secs, running very rough until it dies. It also seems to be petrol firing in the exhaust, as a get a few bangs with afterburner out of the exhaust. Pretty effective for gathering the neighbours.

Here is what I've checked:

  • Plugs get a spark. I have installed the Pertronix coil and adjusted the plug gaps to 40 thou. Spark seems ok. (same result with the lucas sports coil btw).
  • Timing of ignition probably not perfect, but at about 13 dgr BTDC low rev.
  • Metering unit timing checked. Eye on rotor for cylinder 6 opening (about 50% open and increasing) when cyl #1 fires.
  • Voltage at the coil positive (and ground on battery) 11,7v when cranking the engine. Battery voltage without load 12,7v.
  • Voltage at Bosch fuel pump tested good. Injectors producing a good cone of fuel. All injectors seems to be working fine. Tested when spark plugs removed.
  • Ground checked for all major points - all good it seems.
  • I've checked that when cylinder #1 is firing, the distributor rotor points at #1, Metering unit timed as described, and both valves for #1 are fully closed. Vents for cylinder #6 are on the rock.
  • The screw for idle running on the air manifold, I've screwed all the way in, then opened five turns. The CP link rod has new poly bushes. The butterfly rods (or whatever they are called) are new. The adjustment rods for each butterfly are new. It looks fairly tight and good. I've managed to use a (carb) air flow meter and seen that the airflow for each port are pretty much on the same level.
  • Battery in new.
  • Valve gaps checked twice. According to manual. Checked cold.

The engine just in the running-in phase. Proffessionally rebuildt in England (stage II). The Metering unit and Distributor has also both been in England for rebuild. The Starter motor is uprated as well as new alternator (both bought from Moss).

This problem is getting reeeeally on my nerves.
It seems like both sparks are produced and fuel is produced - but it results in the weirdest misfire and it does not feel like it produces any actual powers. I've tried to rotate the dizzy a bit; retarting the dizzy body (ccw rotation) results in no start, advancing (cw) results in a more unhealthy sound from the engine. I tried to turn the it 180 dgr, but that did NOT sound right.

Please help! Why won't it run? I'm running out of ideas?

I have not replaced the fuel filter (paired with the Bosch Fuel pump).

Best regards

Morten

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Hi Morten,

I'm not really up on TR6 but with the backfires etc it sounds like the sparks and valves are out of sync.

 

Go back to basics and check everything to do with spark timing, firing order etc and the valve timing.

 

Roger

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Thanks for your prompt reply, Roger!
I've checked the igition order - 1-5-3-6-2-4 , and that the right lead go to the right plug number. The injection pipes from the metering unit goes from the right port on the M.U. to the right cylinder.

 

The solution is probably something basic, but I've gone blind on it.

Firing on cylinder #1: When look at the dizzy rotor (I'm not able to set the static ignition timing as I've installed the PerTronix Ignitor - same problem with standard capacitor solution), should the rotor, moving CCW, be starting to touch the contact point for lead #1, midway, or at the end/back of the rotor? Or does it not matter?

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Morten,

Do you have the correct order of the plug leads 153624 going anti-clockwise looking down on distributor from above? #1 is the front cylinder. ( I see you have a Jag, didnt they number them backwards?)

 

Check the pulley timing mark for TDC agrees with the #1 piston actually being at TDC. You need to make a piston stop from an old plug to do this. The engine builder should have done that though.

Use a simple 12 v bulb to check when the points open, set static to 12BTDC.

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Has the engine run previously OK with Pertronix?

I would put it back on points and set the static.

If the Pertonix sensor is not in the same position on the moving plate as the points' cam then I would be concerned about the rotor arm/disy contact not matching. As you suspect.

Peter

 

I recall a post where a rotor arm shorted sparks downwards through an electronic pickup device, via a rivet.

Edited by Peter Cobbold
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If you hadn't said MU was professionally rebuilt, I would have guessed it's not correctly set up, not giving the right amount of fuel. Does the MU hold vacum if you suck the hose?

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Hi - thanks! Very good suggestions.

Peter: no, it has never run with the PerTronix setup, but I did get the same problem with the contact points/condenser. However, other things might have changes. I'll certainly go back to the points/condenser tomorrow, and test it out.
Ijonsson: Yes, the MU was rebuild by Malcolm in the UK, which certainly know his things. Haven't tested the vacuum like you suggest, though. I know the vacuum hoses are tight and connected but haven't tested how well they function.

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Morten,

So on points with static set to 12 and it still would not run....it points to the pulley timing marks I think. Assuming the engine builder timed the cam to the crank right....

Peter

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Morton. Not a technical offering, but.....

The problem is there for you to find....and of course you will. You say you are blind to it. I know the feeling. Sometimes best to walk away for a week and let the brain digest and process your effort. Then start from scratch, without any assumptions. Good luck Peter.

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Morten,

Do you have the correct order of the plug leads 153624 going anti-clockwise looking down on distributor from above? #1 is the front cylinder. ( I see you have a Jag, didnt they number them backwards?)

 

Check the pulley timing mark for TDC agrees with the #1 piston actually being at TDC. You need to make a piston stop from an old plug to do this. The engine builder should have done that though.

Use a simple 12 v bulb to check when the points open, set static to 12BTDC.

 

This one..... especially firing order and direction of rotation. Been there, done that......

 

Nick

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just a daft one to try but out worked for me after rebuilding a rover V8.

 

try moving the plug leads 180 degrees in the dissy cap. just take each lead and move it to the opposite position, If it doesn't work put them back where they are now.

 

Gary

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as Peter and Pete suggested, recheck timing starting with removing plug 1 and try to establish TDC (I made a tool suggested in another post by drilling out a spark plug and made a inside thread and screwed in a bolt http://ijonsson.se/triumph/photo_diary.php?day=motor&folder=motor&id=IMG_1321) then turned the engine clockwise until stop, marked the pulley then turned the engine counter cw made another mark and then you have TDC exactly in the middle between those to marks. Then go on from there.

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+1 for valve/cam timing

 

Particularly as you are getting backfiring.

 

Chris

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Hi folks,

Thanks for all suggestions - highly appreciated!

As a start I replaced the PerTronix ignitor and replaced it with known well working condenser/points. Set the point gap to 15 thou. Same problem still.

Just to be sure I understand you correctly - when you say focus on valve/cam timing - I understand it as these would be the appropriate next steps:
* Establish the true TDC (I've been trusting the marks on the pulley done by the engine rebuilder).
* At true TDC, with #1 cylinder firing (counting from front), valves 11/12 should be on the rock, valves 1/2 both fully closed. Right?
* Remove the dizzy and lift of the Metering unit (bracket)
* Re-check that the MU is timed. On the MU, the port on the rotor should be opening (about 50%) when firing cylinder #1. Checked after the MU/bracket is settled, and connected to the oil drive / dizzy shaft.
* Put the dizzy back on. Set static timing.
* Test.

What I do not fully understand is the timing of the MU. Have I got this all wrong? When #1 is firing, it should obviously not get any fuel from the MU. Good. But since port #6 on the MU is opening for fuel spray when the valves are on the rock - couldn't the fuel just be sprayed out?

I would appreciate if someone could verify my steps and understanding above - my head does not seem to work properly :)

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Morten.

Bad MU timing wont be the cause of the problem. It has a minor effect in minimising wall-wetting and pinking. I ran mine with the port closing rather than opening for several years, until I realised the Haynes manual had printed the diagram upside down. So you can ignore the MU timing.

 

I would find true TDC with a piston stop as Inge says. Remark the pulley, set static to true 12 BTDC and see if it runs OK.

If it still backfires then you'll need to set the cam timing by removing the timing chain etc. The engine builder should have done this, so I think we were reluctant to suspect such a fault. Its not impossibel the builder marked the pulley wrong ! - do Inge's check.

 

Peter

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Morten.

Bad MU timing wont be the cause of the problem. It has a minor effect in minimising wall-wetting and pinking. I ran mine with the port closing rather than opening for several years, until I realised the Haynes manual had printed the diagram upside down. So you can ignore the MU timing.

 

I would find true TDC with a piston stop as Inge says. Remark the pulley, set static to true 12 BTDC and see if it runs OK.

If it still backfires then you'll need to set the cam timing by removing the timing chain etc. The engine builder should have done this, so I think we were reluctant to suspect such a fault. Its not impossibel the builder marked the pulley wrong ! - do Inge's check.

 

Peter

 

 

Peter,

 

Out of curiosity, how many degrees out of time do you think a camshaft would have to be to cause the symptoms Morten is experiencing?

 

Richard.

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Peter,

 

Out of curiosity, how many degrees out of time do you think a camshaft would have to be to cause the symptoms Morten is experiencing?

 

Richard.

Richard, Not enough for valves to hit pistons :unsure: . I've no experience of bad exhaust backfiring. It may be that the spark and cam timing are both wrong, which might have happened if TDC was measured wrong on the crank/pulley.

But you set me thinking..... see #23 .Peter

Edited by Peter Cobbold
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Morten,

What do the new pulley markings look like?

Normally the fixed pointer is on the timing chain case. The pulley is marked at TDC and at 2 deg intervals going clockwise from TDC. Because the crank rotates clockwise these marks are degrees BeforeTDC. And when a mark, say 12, is lined with pulley you have the correct static timing: 12 BTDC.

IF the builder has put a single TDC mark on the pulley and marked the timing case every 2 degrees could it be possible he has marked again to the right, but these are now After TDC not BTDC. When you then set the static you'd be setting 12 ATDC and the engine would be retarded, by 24 degrees. That might make it run rough, not sure if it would backfire in the exhaust. Maybe...

Peter

Edited by Peter Cobbold
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Hi folks,
again - very good suggestions! I'll proceed with checking true TDC and take it from there. Quite a nice tool you made there, Inge ! I'll go for that approach.

One thing came to mind. The brown workshop manual (which I am a heavy user of) specifies something 10 thou gap at the valves when closed. In my engine a sprint 90 cam (bought from Moss) was fitted by the engine rebuilders in UK. Since I checked, and adjusted, the values according to the brown bible, could be they are not right - to small a gap, making the exhaust open prematurely, which then again causes the backfire?
I found the sheet for the Sprint90 cam just now (http://www.moss-europe.co.uk/media/pdf/6_cylinder_camshafts_instructions.pdf) and it specifies 14 thou inlet valve clearance and 15 thou exhaust clearance at worm, adding 5 thou each if cold. I'm not able to test before tonight, though.

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