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Author Topic: Bosch Distributor Mechanical Advance  (Read 262 times)
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capriblu
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« on: October 23, 2017, 03:16:16 PM »

My car is a 1980 2 litre Coupe.   The distributor is a Bosch unit without vacuum advance.   I had ignition issues a couple of years ago and had distributor serviced including replacement of pick-up and original Bosch control unit with small device attached to body of distributor (H&H Ignition) - mid/part throttle flufiness disappeared.  However have noticed difficulty getting timing set that ensures smooth tickover whilst decent punch at higher engine speeds.  Have just replaced cam belt and timing is "spot on" (i.e. timing marks on crank and cam pulley wheels) - car will tick over perfectly at 800 rpm - haven't put strobe on to check exact level of ignition advance but would guess that this is pretty close to the 10 degrees static nominal.  On basis that full advance (from 4K rpm?) is meant to be approx 35 degrees then intuitively would expect to observe at least 25 degrees min mechanical advance available when slowly manually turning distributor rotor cap against spring action to full advance stop.  Rough measurement with protractor and a bit of geometry shows a smidge under 20 degrees total movement in the mechanism?Huh???

Would seem max advance is restricted to 30 degrees or less?   Because of this it would seem that only way I can get car to perform strongly at mid/top end is by having static advance of 15 degrees+  with consequent lumpiness and very mild occasional pinging at tickover.   Guys who originally did work on distributor and control pack replacement are on holiday this week - I will contact them,  but is my train of thought correct?

How easy is it to disassemble the distributor and adjust the maximum advance setting?

Any advice greatly appreciated .........

In mentime off to buy a new timing light

« Last Edit: October 23, 2017, 03:18:32 PM by capriblu » Logged

!980 2.0 Coupe - Owned since 1990
capriblu
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« Reply #1 on: October 23, 2017, 10:28:52 PM »

On closer examination noticed rotor arm wasn't seating perfectly with quite a bit of "angular slop" - possibly causing some issues.  Moulded locating key not the same shape/form as an older spare item I found. Cleaned up spare and fitted, no movement.  

Decided to treat myself to a new (cheapo) timing gun with advance dial - my old one (expired) and was just a fixed strobe.   Adjusted static to just over 10 degrees and then checked advance as engine speed raised. Plateaued at about 4.5K rpm and 37 degrees so a good 25 degrees advance from static.  Seems to match standard advance curve data posted elsewhere in this section.

Will road test car later in week - fingers crossed.  Still cant understand where an additional 25 degrees advance from static comes from if maximum movement of mechanical advance mechanism is less than 20 degrees?  can only assume the control module that was fitted also has some contribution to timing ......  

Was looking at a link that Mark (smithymc) posted last year to dutch company supplying programmable distributors for Fiat T/C engines.  Would probably plunge for one of these if there was something suitable for a Beta.  I'm sure that over 3500 rpm advance could be "pushed on" quite a bit if standard advance settings could be held below this speed.
 
« Last Edit: October 23, 2017, 11:13:08 PM by capriblu » Logged

!980 2.0 Coupe - Owned since 1990
HFStuart
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« Reply #2 on: October 24, 2017, 05:31:52 PM »

Don't forget that the distributor does not rotate at crank speed so 20deg on the dizzy is 40 or 80 crank degrees.

Also though if static is 10 deg BTDC then add 25 degrees advance to get 35 deg BTDC which is pretty much what you've got.
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smithymc
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« Reply #3 on: October 24, 2017, 06:31:48 PM »

Having now had mine set up on a rolling road, am happy to let you have those settings if it will help?

Am away until weekend- remind me if I forget after a week whisky 'testing'in Edinburgh.

Regards

Mark
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capriblu
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« Reply #4 on: October 24, 2017, 08:23:32 PM »

Ahhhhh!   Thanks Stuart, Can't believe I've made such a schoolboy error! - had it factored in to my head that Cams only turning once for 2 full turns of crank but of course same applies for auxilliary shaft and dizzy.   So, what I was measuring on dizzy mechanical advance obviously only equates to half actual advance at crank ......   Embarrassed

Thanks Mark,  would be interested in your settings as and when you have time to dig these out - enjoy the Whisky testing! 

Weather looking OKish for tomorrow afternoon here so road test scheduled .....

Thanks again .....

Andrew
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!980 2.0 Coupe - Owned since 1990
capriblu
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« Reply #5 on: October 26, 2017, 12:05:22 PM »

Finally - With timing light was able to set at 12 degrees static (1000 rpm) and confirmed maximum of 37 degrees from about 4.5 K on.

Car runs well!   Smiley

As with all things Beta having closed one little project another emerges;  nearside bonnet striker pin broke as I dropped bonnet yesterday.  Will survive with some temporary back up on that side - other latch works but will need a neat fabrication/weld repair somehow before next MOT in spring.
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!980 2.0 Coupe - Owned since 1990
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