Distributor advance curves

The forum for all of your technical questions on your classic FIAT autos
bnam2
Posts: 120
Joined: Sat Jan 20, 2018 4:34 am
Last Name: Nambisan
First Name: Byas

Distributor advance curves

Post by bnam2 » Fri Feb 01, 2019 12:09 pm

The distributor on my 1608engine (block mounted) had distorted/stretched springs that limited total advance to only 20deg. I've temporarily replaced the springs with good springs from a spare 2L distributor that I still had. the 2L distributor is specced for 28deg advance while the 1608 one is 24, so I've reduced the initial advance setting to 7deg to compensate.

But, I am looking out for a good block mounted distributor and have seen several for sale on ebay.it. But, I'm not sure of the advance curves of those distributors. I believe I had a link (or a photo) of advance curves of several fiat distributors. But, I'm able to find neither -- and perhaps I'm just imagining it. Anyone know where I can find such info?

The 3 specific distributors that I saw several examples of were
S120 (this was marked as 20deg advance)
S147 -- did not show the markings clearly
S155C -- again, no markings shown in pic

Any info on these distributors and suitability with a 1608. I'm running a 34DCHD carb btw.


Thanks!
Byas
1965 Fiat 1500 Cabriolet with 1600twin-cam
!971 VW 1302LS Convertible in original condition
1965 KG - under restoration
User avatar
rridge
tremila club
Posts: 3471
Joined: Sun Jan 24, 2016 9:18 pm
Last Name: ridge
First Name: richard

Re: Distributor advance curves

Post by rridge » Fri Feb 01, 2019 12:39 pm

These may be useful. The 2 liter curves are from a Fiat service manual. Not sure of the original source of the third plot.
Attachments
advance curves.jpg
advance curves.jpg (45.39 KiB) Viewed 249 times
2L carb advance curve.jpg
2L carb advance curve.jpg (127.14 KiB) Viewed 249 times
2l FI advance curve.jpg
2l FI advance curve.jpg (172.28 KiB) Viewed 249 times
Richard
'81 Turbo Spider
Rockville, MD
bnam2
Posts: 120
Joined: Sat Jan 20, 2018 4:34 am
Last Name: Nambisan
First Name: Byas

Re: Distributor advance curves

Post by bnam2 » Sun Feb 03, 2019 8:45 am

Thanks Richard!

Over the weekend I did find the info I have. But, it was a repeat mostly of what you posted. I've not been able to find any info on the 2 distributors I listed yet.

Here's the info I had from about 15yrs ago.
Advance curves.JPG
Advance curves.JPG (75.35 KiB) Viewed 201 times
Byas
1965 Fiat 1500 Cabriolet with 1600twin-cam
!971 VW 1302LS Convertible in original condition
1965 KG - under restoration
User avatar
davedecker4
Posts: 612
Joined: Sun Jan 24, 2016 11:05 am
Last Name: Decker
First Name: Dave

Re: Distributor advance curves

Post by davedecker4 » Sun Feb 03, 2019 11:07 pm

Why don't you just replace the springs instead looking for a another dizzy?
Dave Decker
a 'couple' Fiats and Lancia's
bnam2
Posts: 120
Joined: Sat Jan 20, 2018 4:34 am
Last Name: Nambisan
First Name: Byas

Re: Distributor advance curves

Post by bnam2 » Sun Feb 03, 2019 11:35 pm

I have (for now) -- replaced with the springs from the 2L carb distributor I had.

Where could I buy new springs? And, when you buy springs, how does one know what curve will result? Or are the spring tensions all the same and only differ in details like -- larger loop to have later engagement, heavier/lighter arms, and profile of the centrifugal advance arm?
Byas
1965 Fiat 1500 Cabriolet with 1600twin-cam
!971 VW 1302LS Convertible in original condition
1965 KG - under restoration
User avatar
rridge
tremila club
Posts: 3471
Joined: Sun Jan 24, 2016 9:18 pm
Last Name: ridge
First Name: richard

Re: Distributor advance curves

Post by rridge » Mon Feb 04, 2019 8:03 am

Byas,

If you poke around old forum posts here and on other Italian marque sites you will find that for years some owners used spring assortments made for GM Delco HEI distributors and found somewhat suitable replacements. NAPA BK 735-4448 is one but there are many others.

The usual problem with worn springs is that there are usually found in worn distributors so adjusting advance for the proper curve can be a frustrating exercise. Years ago distributor rebuilders were relatively common and some specialized in Marelli distributors. With new mechanical distributors available for less than $200 and the price of electronic ones dropping, distributor rebuilding and recurving is probably becoming another lost automotive art.

Here's a related article from an old Alfa website post:
https://www.alfabb.com/bb/forums/spider ... rings.html
Richard
'81 Turbo Spider
Rockville, MD
User avatar
vandor
quattromila club
Posts: 4411
Joined: Sun Jan 24, 2016 10:03 pm
Last Name:

Re: Distributor advance curves

Post by vandor » Mon Feb 04, 2019 8:13 am

Regardless of what the manuals say, the FI distributors are marked '11' at the top, meaning that they have 11 degrees of advance, which translates 22 crank degrees.
IIRC the carbed 2 liter distributors are marked 16.30', which would give 33 degrees at the crank.
Csaba
Parts: http://www.autoricambi.us
Cars: http://italiancarclub.com/csaba/Fiat.html
'71 124 Spider, much modified
'72 124 Coupe, new project, ex-Pete, ex-Eli, ex-Jack car (all Mira members)
User avatar
friedman
mille club
Posts: 1566
Joined: Wed Aug 24, 2016 8:13 am
Last Name:

Re: Distributor advance curves

Post by friedman » Mon Feb 04, 2019 8:26 am

You check your advance curve with a timing light, noting the timing at various rpm. A dialback or adjustable timing light is the best since you always use the zero degree mark and adjust the dial on the timing light to find the advance at any particular rpm.
Carl in Virginia
75 spider
86 Bertone
77 X1/9
bnam2
Posts: 120
Joined: Sat Jan 20, 2018 4:34 am
Last Name: Nambisan
First Name: Byas

Re: Distributor advance curves

Post by bnam2 » Mon Feb 04, 2019 8:26 pm

The carb distributor I have (pulled from a 131 IIRC) is marked 14deg (28crank) which matches the advance curves published for 2L carb distributors.
vandor wrote:
Mon Feb 04, 2019 8:13 am
Regardless of what the manuals say, the FI distributors are marked '11' at the top, meaning that they have 11 degrees of advance, which translates 22 crank degrees.
IIRC the carbed 2 liter distributors are marked 16.30', which would give 33 degrees at the crank.
Byas
1965 Fiat 1500 Cabriolet with 1600twin-cam
!971 VW 1302LS Convertible in original condition
1965 KG - under restoration
User avatar
vandor
quattromila club
Posts: 4411
Joined: Sun Jan 24, 2016 10:03 pm
Last Name:

Re: Distributor advance curves

Post by vandor » Tue Feb 05, 2019 5:26 pm

bnam2 wrote:
Mon Feb 04, 2019 8:26 pm
The carb distributor I have (pulled from a 131 IIRC) is marked 14deg (28crank) which matches the advance curves published for 2L carb distributors.
Sorry, my comments are for US models only, my guess is that you are not in the US?
Csaba
Parts: http://www.autoricambi.us
Cars: http://italiancarclub.com/csaba/Fiat.html
'71 124 Spider, much modified
'72 124 Coupe, new project, ex-Pete, ex-Eli, ex-Jack car (all Mira members)
Post Reply

Who is online

Users browsing this forum: 2Spidertwins and 5 guests