Technical bob weight springs

[randomspeedfreak]

where can i get some?

i think i have made my car not start by streching/bending the end off, the bob weight springs :bang:

is this possible?

the symptoms are loads of turning over but no starting and occasional backfire through the carb

 

[EssexUno]

Are you positive you put the HT leads in the right order?

Just a minor overlook you might not of checked??

Dan

 

[randomspeedfreak]

yeah im pretty certain - i didnt remove the ht leads form the plugs or the cap.

i would have to have rotated the cap 180 degrees, as there is one clip either side.

This would have put all of the ht leads under tension so it would be obvious that it was wrong.

im positive its not that

 

[CLXCraig]

i'm so lost with were you are on this Matt. I guess it still doesnt start? Did your mate fix the last bit that was broken? I'm gonna have to look for all your threads now! Make a big main one god damn you!

 

[randomspeedfreak]

i'm so lost with were you are on this Matt. I guess it still doesnt start? Did your mate fix the last bit that was broken? I'm gonna have to look for all your threads now! Make a big main one god damn you!

yeah man not starting - i sorted that last bit,

yeah sorry about that im real tired and laggy ill look for my project thread 4 ya

 

[EssexUno]

I don't understand how messing with or even breaking the bob weights is going to stop the engine starting because I thought that bob weights were for advancing the timing.

When they spin faster they pull outwards because of the inertia forces acting on them, like a seat belt does, and when they move out they advance the ignition, i don't quite remember how, but anyway that should not stop the engine running (maybe not properly but should at least start up (Will misfire at higher revs)) unless you have moved them soo much that the ignition is too advanced to begin with which may be why back firing though the carb?

Just wondering why you were stretching them in the first place?

Dan

 

[alexGS]

Thanks Dan - I believe that's exactly right. Broken/faulty springs won't make a jot of difference to getting the engine started, as long as the timing is somewhere near TDC.

To go further with the diagnosis, I think we need to know which engine this is - e.g. 999cc FIRE?

If it is the FIRE, then the distributor drive (from the camshaft) is an offset 'dog'. However, it's possible for this to be fitted to the distributor shaft 180-degrees out (it has a pin pushed through to secure it).

So, if it's been taken apart, you have to get back to basics and (again, assuming the FIRE engine) check that the rotor points to the small hole on the plastic shield under the rotor - when the engine is turned to the TDC mark on both the flywheel AND the camshaft. Remember that the cam turns at half crankshaft speed, so when the crankshaft is at the TDC mark, the cam may not be - turn the crankshaft one more turn. The mark for the cam pulley is a fine line on the outside that lines up with a notch in the aluminium casting behind the pulley, somewhere near the join between the cylinder head and the cam cover.

'Backfiring' usually indicates that the timing is out, so I think you'll get somewhere if you check it all again from scratch, and check that the plug leads correspond to the numbers on the distributor cap.

Best of luck,
-Alex

PS. Forgot to answer the original question
As far as I'm aware, the easiest way to replace the bobweight springs is to find a replacement distributor. If the replacement is first stripped of its electronic module and the magnetic pickup inside, it's not worth much to anyone else and therefore should be cheap

 

[Chas Uno]

RSF has the Lampredi ohc engine in his car Alex, not the FIRE

Regarding the bob weight springs, I wonder if Matt has noticed that one seems to be more stretched than the others and is thinking that it is damaged? From what I remember of taking a FIRE dizzy apart they're ALL like that! And I assume that the Lampredi ohc dizzy would be the same too.

My understanding is that at lower revolutions only the first (tighter) spring takes up the tension with the weights. However, as the revolutions (rpm) increase the bob weights pull apart and the first spring starts to run out of tension, but this then overlaps with the looser second spring so at higher revs BOTH springs now tension the bob weights. This effectively allows a large amount of initial advance at lower engine revs but then reduces the amount at higher revs.

I'm sure there's something in physics to do with inertia and forces increasing exponentially with increasing revolutions that would explain this!

The only other thing I'd suggest is that as Matt has been having problems with the aftermarket Lumenition system fitted to his car then perhaps changing this would help. I would try and find a standard electronic distributor from a Uno/ X19/ Strada/ Regatta/ Lancia Delta etc. and put the ignition system back to standard. That sould help rule out any doubt over the current system.

Good luck!

 

[randomspeedfreak]

I don't understand how messing with or even breaking the bob weights is going to stop the engine starting because I thought that bob weights were for advancing the timing.

When they spin faster they pull outwards because of the inertia forces acting on them, like a seat belt does, and when they move out they advance the ignition, i don't quite remember how, but anyway that should not stop the engine running (maybe not properly but should at least start up (Will misfire at higher revs)) unless you have moved them soo much that the ignition is too advanced to begin with which may be why back firing though the carb?

Just wondering why you were stretching them in the first place?

Dan

i read up on bob weights and your correct - it advances the ignition.
the bobweights are (i think) connected to the 'plate' that the optical trigger sits on, this is the same plate that the vacum advance is connected to, and so when they move out due to rotational inertia they move the plate clockwise meaning the beam cutters hit the trigger later than usual.

why were they streched - good question!
basically the chopper (which is non standard) means you cant remove the plate with the trigger on, which stops you from disconnecting the bob weights in a careful manner, as to get it all off you have to pull it.
very difficult to explain, so sorry if thats not clear, but essentially it has been caused by my nievaity/enthusiasm :bang: (probs spelt wrong too, just to put the cherry on the cake lol)

ill take loads of pics next weekend that will show you whats what.

oh and it wouldnt it missfire at low revs rather than high? the higher revs have more advance anyway so it makes sence to me for it to be that way round?

Thanks Dan - I believe that's exactly right. Broken/faulty springs won't make a jot of difference to getting the engine started, as long as the timing is somewhere near TDC.

To go further with the diagnosis, I think we need to know which engine this is - e.g. 999cc FIRE?

If it is the FIRE, then the distributor drive (from the camshaft) is an offset 'dog'. However, it's possible for this to be fitted to the distributor shaft 180-degrees out (it has a pin pushed through to secure it).

So, if it's been taken apart, you have to get back to basics and (again, assuming the FIRE engine) check that the rotor points to the small hole on the plastic shield under the rotor - when the engine is turned to the TDC mark on both the flywheel AND the camshaft. Remember that the cam turns at half crankshaft speed, so when the crankshaft is at the TDC mark, the cam may not be - turn the crankshaft one more turn. The mark for the cam pulley is a fine line on the outside that lines up with a notch in the aluminium casting behind the pulley, somewhere near the join between the cylinder head and the cam cover.

'Backfiring' usually indicates that the timing is out, so I think you'll get somewhere if you check it all again from scratch, and check that the plug leads correspond to the numbers on the distributor cap.

Best of luck,
-Alex

PS. Forgot to answer the original question
As far as I'm aware, the easiest way to replace the bobweight springs is to find a replacement distributor. If the replacement is first stripped of its electronic module and the magnetic pickup inside, it's not worth much to anyone else and therefore should be cheap

know how to do it on the 1301?

whats this hole in the distributor? i dont know if i have said hole...
maybe a picture?

RSF has the Lampredi ohc engine in his car Alex, not the FIRE

Regarding the bob weight springs, I wonder if Matt has noticed that one seems to be more stretched than the others and is thinking that it is damaged? From what I remember of taking a FIRE dizzy apart they're ALL like that! And I assume that the Lampredi ohc dizzy would be the same too.

My understanding is that at lower revolutions only the first (tighter) spring takes up the tension with the weights. However, as the revolutions (rpm) increase the bob weights pull apart and the first spring starts to run out of tension, but this then overlaps with the looser second spring so at higher revs BOTH springs now tension the bob weights. This effectively allows a large amount of initial advance at lower engine revs but then reduces the amount at higher revs.

I'm sure there's something in physics to do with inertia and forces increasing exponentially with increasing revolutions that would explain this!

The only other thing I'd suggest is that as Matt has been having problems with the aftermarket Lumenition system fitted to his car then perhaps changing this would help. I would try and find a standard electronic distributor from a Uno/ X19/ Strada/ Regatta/ Lancia Delta etc. and put the ignition system back to standard. That sould help rule out any doubt over the current system.

Good luck!

ok thanks for your help chas - i didnt know that the springs work in that way, i thought mine were just uneven lol.
not knowing what the springs were, to fit the tighter of the two springs back on i bent the loop back a little :bang:, i definately remember it being a little bit slack putting it back on and me thinking 'that little spring cant do anything important' !!!:bang:

i dont know about changing back to standard, the lumenition system is a sealed/tamper proof system, so it will either work or not, its quite simple really, and i understand it (i would probs have to have a learning curve all over again if i went back to standard) and it improves performance im told (if it actually runs!lol )

the annoying thing is that it HAS run and started last month (and it was amazing ) and ive changed not a lot and now not even a glimpse of sucess

ill have a look at the bob spring thing next weekend, ive battery on charge so it will be fresh and ready for when i get home friday.

if you guys could maybe help me out on how to do the timing from scratch?
(in karts you have a gauge that you put in place of the (only) spark plug. Turn the engine over, it tells you where your ignition is, to ajust it you losen 4 allen bolts and rotate a magnet a little bit! why cant it be that simple eh?! )

thanks for your help so far guys, you're tops

 

[alexGS]

Thanks for the correction Chas I forgot which Uno was being talked about.

if you guys could maybe help me out on how to do the timing from scratch?
(in karts you have a gauge that you put in place of the (only) spark plug. Turn the engine over, it tells you where your ignition is, to ajust it you losen 4 allen bolts and rotate a magnet a little bit! why cant it be that simple eh?! )

Happily, it's almost that simple

On the yellow plastic cambelt cover, look for three raised lines (ridges in the plastic) near the crankshaft pulley. If you have them, good - you should also find either a small notch in the rim of the pulley, or a much larger pointer cast into the pulley itself. When the notch/pointer aligns with the first of the three raised lines, that means the engine is at 10 degrees BTDC (before top-dead-centre) which is when the ignition should fire for cylinder number 4 (not cylinder 1).

If there are no ridges on the cambelt cover or if the motor is a 1498cc or 1580cc, use the flywheel marks instead. On the gearbox bellhousing, there is a rectangular window above the clutch. The window has four lines scribed in it - 0, 5, 10, and 15 degrees. The flywheel has either a radial square-shaped groove about a centimetre long, or a round 'dint', which lines up with the window again when cylinder 4 is ready for ignition. Don't be mislead by numerous shallow stamping marks on the flywheel that are a byproduct of its manufacture.

With the engine set at 10 degrees BTDC, you would then align your distributor (by turning it) so that the points/reluctor, or in your case Lumenition pickup, is just at the trigger point and the distributor rotor arm is pointing to cylinder 4. (not 1 as it would be for most non-FIAT engines). That will be good enough to get the engine started, after which you can use a timing light to get the timing exactly right.

Sadly I don't have any pictures, as I don't currently have a non-turbo 1290/1299/1301cc engine to photograph.

The hole that I referred to earlier is a tiny (<2mm) hole in the grey plastic shield that lies below (behind) the rotor arm in the FIRE distributor and indicates where the rotor arm should point to when the engine is timed to the marks. I doubt that your non-FIRE distributor still has a similar plastic shield, but it might.

Hope that gives you something to go on.

-Alex

 

[randomspeedfreak]

Thanks for the correction Chas I forgot which Uno was being talked about.



Happily, it's almost that simple

On the yellow plastic cambelt cover, look for three raised lines (ridges in the plastic) near the crankshaft pulley. If you have them, good - you should also find either a small notch in the rim of the pulley, or a much larger pointer cast into the pulley itself. When the notch/pointer aligns with the first of the three raised lines, that means the engine is at 10 degrees BTDC (before top-dead-centre) which is when the ignition should fire for cylinder number 4 (not cylinder 1).

If there are no ridges on the cambelt cover or if the motor is a 1498cc or 1580cc, use the flywheel marks instead. On the gearbox bellhousing, there is a rectangular window above the clutch. The window has four lines scribed in it - 0, 5, 10, and 15 degrees. The flywheel has either a radial square-shaped groove about a centimetre long, or a round 'dint', which lines up with the window again when cylinder 4 is ready for ignition. Don't be mislead by numerous shallow stamping marks on the flywheel that are a byproduct of its manufacture.

With the engine set at 10 degrees BTDC, you would then align your distributor (by turning it) so that the points/reluctor, or in your case Lumenition pickup, is just at the trigger point and the distributor rotor arm is pointing to cylinder 4. (not 1 as it would be for most non-FIAT engines). That will be good enough to get the engine started, after which you can use a timing light to get the timing exactly right.

Sadly I don't have any pictures, as I don't currently have a non-turbo 1290/1299/1301cc engine to photograph.

The hole that I referred to earlier is a tiny (<2mm) hole in the grey plastic shield that lies below (behind) the rotor arm in the FIRE distributor and indicates where the rotor arm should point to when the engine is timed to the marks. I doubt that your non-FIRE distributor still has a similar plastic shield, but it might.

Hope that gives you something to go on.

-Alex

you legend that, really is as clear as day -

Ill have a crack at it this weekend when i get home, and i think i owe you guys an update on the project thread so ill get some pics in there and sort it out

thanks mate thats gunna help me loads,
whens your next trip to the UK?