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Rusty Triumphs in Scotland - Acclaim ignition woes - 23/02/21


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8 hours ago, GingerNuttz said:

If it had 4 carburettors then you could have driven to work on 3 cylinders... 

Not untrue. I could have driven there with 4 cylinders if I'd kept the revs above 2,500rpm. However that's bad for my shagged clutch. 😂

Also:

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Saab has a new quirk whereby it seems you have to tug the key upwards a bit while turning it or it just cranks the starter and doesn't fire. Cheers for @320touringfor suggesting the solution, otherwise I'd still be stuck at Tesco...

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First sunny day for a while so went to try and diagnose the Acclaim's running issue.

153228736_10226410160099525_5690975707419938427_o.thumb.jpg.4bba295d45bc084cdb4572f163b9896c.jpg

Naturally the battery had gone flat again so I had to bump start the car down a hill to drive it round to the flat while it ran like arse. Once it was parked it stalled and the battery wouldn't restart it, so I swapped it's battery for a spare I had upstairs. Annoyingly this had Japanese standard terminals and one of the adaptor rings was missing, so ingenuity was applied.

152503152_770923956882467_8627152595094310663_n.thumb.jpg.d2a2412c604446ea55c8a3cb7cba9c97.jpg

I replaced the ignition control module, which did nothing.

I tried revving the car up and covering the intakes to try and suck any shite out, this also did nothing.

When trying to restart after stalling it kept backfiring through the carb and kicking and then immediately stopping dead like it was out of time. Checked the dizzy and that was tight and hadn't spun loose, so unscrewed the cap to have a look inside and found the issue.

The rotor arm had a good centimetre plus of slop on the shaft. The shaft itself was tight and the advance mech all seemed alright but the arm was loose as buggery. So I whipped out the spare from the boot that was known working when removed and... That was exactly the same. Somehow my dizzy shaft has worn in such a way the rotor arms won't hold true. I wedged a bit of thin carboard between the flat of the shaft and the rotor arm to test the theory and was rewarded with a car that would rev smoothly but not idle and was taching down far too slow.

It's hard to say if the lack of idle and slow return after revving is connected to the dizzy issue, I suspect I've just disturbed something in the throttle linkage while fucking about.

Gonna' try TIGing the dizzy shaft and file it down, 'cause I can only find one place that lists the dizzy as in stock and it's £150.

 

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  • captain_70s changed the title to Rusty Triumphs in Scotland - Acclaim ignition woes - 23/02/21

The whole shaft should have a degree of movement in it for the ignition advance, but it should snap back under spring tension. As it does.

The arm itself should be unable to spin independently of the shaft though, as that'll just throw the timing out at random as the arm rotates back and forth as the engine tachs up or down.

I doubt adhesive would last due to how hot the dizzy gets, I imagine it'd work for a few miles though.

New arm and cap ordered, so I'll try that first to make sure it's not just 2 duff rotor arms.

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At about 0:37 in your video above, when revving the engine up, that is unmistakably a single-cylinder misfire, meaning it absolutely has to be ignition rather than fuelling, and if I were a betting man, it's somewhere from the rotor to the spark plug, (IE components specific to one cylinder only) most likely the rotor arm not aligning with the pick-up in the cap, as you've identified.

The shaft on the distributor doesn't look worn.  Usually the first thing that happens is that the rotor becomes loose on the shaft, which yours isn't.  What's more likely is that the rotor arm isn't the right one for the car, and its D-flat is too small, meaning it can move about on the shaft.

I'd look to see if you can get a better quality/better fitting rotor arm.  Also whip all your spark plugs out and check them.  How new are the HT leads?  Do they all fit with a good "snap" onto the plugs?

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Leads are about 2 years old, still click onto the plugs fine, the plugs are all good, light brown deposits.

Main oddity is that the 2 rotor arms I have are identical and have done at least 10,000 miles between them with no prior problems.

This running issue only appeared when the car left the workshop after being repaired. Hence my assuming it was a gummed up carb from sitting and only running in a dusty garage. It's not something you can really miss as it rendered the car essentially undrivable. 

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Tried a timing gun on each lead to see which cylinder it's misfiring on? (Or if all)

Surely when the engine is running, the rotor arm probably won't be moving that much on the shaft? The rotor arm isn't that heavy with a lot of mass. Especially as it looked like it had a fair amount of friction holding it.

Also, does it matter if it does move? The Rotor Arm doesn't define ignition timing, unless wildly out that it isn't in roughly the right place to create a circuit. Hard to tell from the video how much play is there as the rest of the shaft is moving against the weights + springs.

Have you tried bending the spring out inside the rotor arm to make a stiffer fit? Is the wiper on the top of the cap making good contact?

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I had issues with my Skoda 135 Rapid where the rotor arm refused to fit properly - it was absolutely fine until you went north of 4000rpm at which point it would ride up the shaft and knock the timing about 45 degrees out.  Usually mid overtake.

I wound up wrapping a bunch of that self adhesive aluminium foil around the distributor shaft to make it a tighter fit.  Took a couple of tries but did work.

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2 hours ago, SiC said:

Also, does it matter if it does move? The Rotor Arm doesn't define ignition timing,

Usually the width of the end on the rotor and the "contacts" for each cylinder is enough to allow for the ignition advance mechanism to do it's thing while maintaining the proximity of the arm and contact.  The fact that the point of ignition changes as the ignition advance changes is a good thing, as it distributes the electrical pitting/burning over the whole rotor rather than always being the same point.

However, the ignition advance curve might be upwards of 30 degrees.  That means the rotor arm and contact have to be close enough to each other over a 30 degree arc of the rotor arm.

Start adding in another 20 degrees of movement, and I can well believe that the rotor arm is far enough away from the contact to get a reliable "connection".

To confirm this, I'd fit the rotor arm exactly in line (flat on the shaft in line with the flat on the rotor arm) and see how well it runs.  Also, see if it moves in service.  It could well be that the last 10k miles have been achieved with the arm in the right location, and friction has meant it's not moved.  As it's since been "twiddled with" it could have been at an extreme of travel, hence beginning to not transfer spark when needed to, as it's simply too far away from the correct contact in the cap.

If the plugs are all good and the HT leads in fine fettle, the only remaining area is the distributor.  Nothing else (other than something deeply mechanical) affects one cylinder only.

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Usually the width of the end on the rotor and the "contacts" for each cylinder is enough to allow for the ignition advance mechanism to do it's thing while maintaining the proximity of the arm and contact.  The fact that the point of ignition changes as the ignition advance changes is a good thing, as it distributes the electrical pitting/burning over the whole rotor rather than always being the same point.

Yes I know that and you cut out the bit in my quote where I mention providing it's not wildly out. Hard to judge on that video on how much movement is going on there without the rest of the mechanism slack in there. 

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There looks to be at least an extra 20 degrees of movement there, which could easily be enough to push the rotor out of range.

It sounds a lot like it was too far in the retarded position, meaning that when the engine is idling with a big dollop of vacuum advance, it would run on 4.  As soon as you step on the accelerator, kill the vacuum and retard the ignition further, it splutters.

Then as the engine speeds up and you get some dynamic advance happening, it runs on more cylinders again.

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There is an easy 20 degrees of play on top of whatever the mechanical advance is (around 30 maxed out at 4k IIRC). Vac advance is irrelevant really as it's disconnected!

As I said a few posts ago with the slop taken out and the rotor arm firmly locked in place with a bit of card (whether dead straight or not) it ran considerably better and started first turn of the key whereas before it was kicking back. The floaty rpm return and lack of idle the car developed I'm 90% was me knocking something in the throttle linkage which is mega sensitive to being bent/knocked out of adjustment.

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The mechanical advance doesn't change the rotor arm to cap spark position as the rotor and ignition trigger are floating but fixed reference to each other, the vacuum advance does have a small effect on the rotor arm to cap position but it's a small range of movement.

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21 hours ago, captain_70s said:

First sunny day for a while so went to try and diagnose the Acclaim's running issue.

153228736_10226410160099525_5690975707419938427_o.thumb.jpg.4bba295d45bc084cdb4572f163b9896c.jpg

Naturally the battery had gone flat again so I had to bump start the car down a hill to drive it round to the flat while it ran like arse. Once it was parked it stalled and the battery wouldn't restart it, so I swapped it's battery for a spare I had upstairs. Annoyingly this had Japanese standard terminals and one of the adaptor rings was missing, so ingenuity was applied.

152503152_770923956882467_8627152595094310663_n.thumb.jpg.d2a2412c604446ea55c8a3cb7cba9c97.jpg

I replaced the ignition control module, which did nothing.

I tried revving the car up and covering the intakes to try and suck any shite out, this also did nothing.

When trying to restart after stalling it kept backfiring through the carb and kicking and then immediately stopping dead like it was out of time. Checked the dizzy and that was tight and hadn't spun loose, so unscrewed the cap to have a look inside and found the issue.

The rotor arm had a good centimetre plus of slop on the shaft. The shaft itself was tight and the advance mech all seemed alright but the arm was loose as buggery. So I whipped out the spare from the boot that was known working when removed and... That was exactly the same. Somehow my dizzy shaft has worn in such a way the rotor arms won't hold true. I wedged a bit of thin carboard between the flat of the shaft and the rotor arm to test the theory and was rewarded with a car that would rev smoothly but not idle and was taching down far too slow.

It's hard to say if the lack of idle and slow return after revving is connected to the dizzy issue, I suspect I've just disturbed something in the throttle linkage while fucking about.

Gonna' try TIGing the dizzy shaft and file it down, 'cause I can only find one place that lists the dizzy as in stock and it's £150.

 

OMG I didn't know Ewan Mcgregor was on Autoshite!!!!!!!

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48 minutes ago, Dick Longbridge said:

Now you've said it, I can hear what you mean. Maybe some celeb* voice-over work could help pay for future rust preventative fluids? 

first few seconds had me like......Really!!! Is it??

PMSL

Hmmmm not a Triumph...but tis shite!!! 

Ewan McGregor Keeps 30 Vehicles From His Collection in Divorce Settlement -  autoevolution

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23 hours ago, Jikovron said:

The mechanical advance doesn't change the rotor arm to cap spark position as the rotor and ignition trigger are floating but fixed reference to each other, the vacuum advance does have a small effect on the rotor arm to cap position but it's a small range of movement.

Both the mechanical and the vacuum advance units will change the relationship between the rotor arm and the cap positions.  It's very clear to see in the Captain's video above that the ignition trigger ring is fixed to the same shaft as the rotor arm, so anything that moves the relationship of the trigger ring to the engine timing will also move the rotor arm.

The fact that the Vacuum advance is disconnected does throw my theory above out somewhat though, as the misfire sounds quite regular as the engine is revved up, despite the fact that the ignition timing will be changing as the engine speed increases.

It's definitely ignition related though.  Fuelling misfire sounds very different to that.

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41 minutes ago, Talbot said:

Both the mechanical and the vacuum advance units will change the relationship between the rotor arm and the cap positions.  It's very clear to see in the Captain's video above that the ignition trigger ring is fixed to the same shaft as the rotor arm, so anything that moves the relationship of the trigger ring to the engine timing will also move the rotor arm.

The fact that the Vacuum advance is disconnected does throw my theory above out somewhat though, as the misfire sounds quite regular as the engine is revved up, despite the fact that the ignition timing will be changing as the engine speed increases.

It's definitely ignition related though.  Fuelling misfire sounds very different to that.

The vacuum advance will move the plate that the pick up for the trigger is mounted to. It won't move the rotor arm.

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15 minutes ago, GeorgeB said:

The vacuum advance will move the plate that the pick up for the trigger is mounted to. It won't move the rotor arm.

WHS ^^, the when the trigger tooth passes the pickup the rotor arm is always at the same position when it sparks however due to mechanical advance the engine is put further behind , when the vac advance pulls the pickup plate advanced the reference that the trigger/rotor arm sees has moved around the dissy body and thusly the cap .

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9 hours ago, GeorgeB said:

The vacuum advance will move the plate that the pick up for the trigger is mounted to. It won't move the rotor arm.

You're right.  My description above was poor... when the ignition is advanced by the vacuum advance, the rotor arm relationship to the engine position won't change, but the spark timing does, meaning the relationship between the spark timing and the rotor arm does change.  If the spark was already on the limit of being able to jump from rotor arm to cap pick-up, some vacuum advance could make the difference between it getting to the plug or not getting to the plug.

... but as the vac advance is disconnected on this car, makes no difference from a diagnostic point of view.

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