flak monkey
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| posted on 20/4/06 at 11:14 AM |
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How to save yourself a few pennies (dizzys)
Some of you will already know this, but thought it might be handy info for those who dont! This is aimed at the pinto, but any car with a bosch
distributor can have this done.
If you have tuned your engine up you will notice that it is recommended that you change your dizzy to a fast road one.
Whats the difference? The fast road one has less all in mechanical advance at above 3500rpm. For example the standard pinto dizzy will end up giving
you well over 40deg total advance if you use it on a modified engine, leading to pinking which can do serious damage to your engine.
Now, you can limit this total advance quite simply but it requires a bit of patience, and pulling the dizzy apart. You will also need to add the
relevant marks to your crank pully for use with the strobe.
Basically heres the procedure:
Set up the engine as normal using a strobe and note the amount of advance at idle. It should be somewhere around 10 degrees to start off. (Make sure
the vacuum hose is disconnected and plugged)
Then take the engine up to around 4500rpm and note the total advance. It will probably be well above the maximum 36-38deg. Turn the dizzy body to
reduce the advance to 36-38 degrees then let the engine idle and see how much advance you have. Subtract the current idle setting from 38 and you will
have the total mechanical advance supplied by the dizzy.
The idle advance depends on your cam duration:
Cam duration Advance
270 10-12
280 12-14
290 14-16
300 16-18
310+ 18-20
Whichever one you have, subtract the advance from 38 to find out the total amount of advance you need. Compare this to the current situation to see
what needs to be done.
Take the dizzy off the engine, and remove the cap, points and condensor. Undo the vacuum advance mechanism, and the screws holding the plate onto the
top of the dizzy body. Carefully withdraw the plate and vacuum advance. You will be left looking at something similar to the picture below. (This is a
Motorcraft dizzy, bosch ones are very similar). You will notice 2 centrifugal weights attached with springs, and a stop pin (2 on the bosch i
think).
All you need to do is bend the pin (circled) in slightly to limit the travel of the weights, until you get 36-38deg total advance. This is a bit trial
and error, and make take several attempts. Its worth it though and will make the car much nicer to drive.
You can even change the advance curve if you like by altering the weights and springs. But thats a bit beyond what most people would bother with.
Apologies if you all already knew this info 
[Edited on 20/4/06 by flak monkey]
Sera
http://www.motosera.com
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02GF74
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| posted on 20/4/06 at 12:49 PM |
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that's quie useful, that is. tink I have seen soemthing similar where the pate is built up by welkding and then filed down insted of bending
the pin(s) - could be interesting if it breaks!!
or maybe one could make a concentric pin and turn it with a screwdriver to adjust or glue on a piece of metal etc....
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NS Dev
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| posted on 20/4/06 at 01:23 PM |
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the curve can be pretty important too though, not just the limit.
certainly limiting the advance can be useful though.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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flak monkey
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| posted on 20/4/06 at 01:26 PM |
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quote:
Originally posted by 02GF74
that's quie useful, that is. tink I have seen soemthing similar where the pate is built up by welkding and then filed down insted of bending
the pin(s) - could be interesting if it breaks!!
or maybe one could make a concentric pin and turn it with a screwdriver to adjust or glue on a piece of metal etc....
There are plenty of ways of doing it. All involve limiting the travel in some way. When there is no pin to bend you can weld it up to add material to
the stops, or I see no reason why you couldnt use some chemical metal to build the stop up.
Infact looking at the motorcraft dizzy you cant bend the pin as its the stop in both directions (the bosch dizzy is different). Its easy enough to add
a pin on the opposite side though.
[Edited on 20/4/06 by flak monkey]
Sera
http://www.motosera.com
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