Author Topic: MSD dizzy mech. advance timing (Read 18183 times)

Darylle · « **on:** May 04, 2018, 08:50:54 PM »

Hi all
I have recently replaced my engine with a 383 from engine master and all is great except my new MSD dizzy has too much mechanical advance (around 40 deg total) and I have been told that I need to "modify" the flyweights to reduce their "throw" has any one had similar issues and what measures were taken to rectify?
Thanks in advance.

Lefty · « **Reply #1 on:** May 04, 2018, 09:11:40 PM »

Darryle,
Not sure of the solution. But I've had an msd put in on my 350. It's great but my tachometer reading is high, how did you resolve that?
Best
Lefty

Vettech · « **Reply #2 on:** May 04, 2018, 11:06:58 PM »

I kinda remember in the olden days you could get springs of different lengths or there were holes or posts that the springs could be changed around on, or was it different colour coded spring strength.

In the std GM HEI dizzy, which I just happen to have on my coffee table, these springs are up under the blue rotor cap, but its screwed down.

So, with a flat battery, I'll look tomorrow.

Darylle · « **Reply #3 on:** May 05, 2018, 08:19:08 AM »

HI
Thank you for the replies, I do not have any issues with the tach and the reason I had to replace the stock unit was it had been "welded up"and the "mechanic" did not spot this until we replaced the engine GRRRR!
I do have another MSD dizzy for my torana (which gave me much grief untill I went back to the std. hei) and if I can recall correctly you could interchange the springs but does that limit the total advance?

Vettech · « **Reply #4 on:** May 05, 2018, 03:59:01 PM »

The springs delay the rate of change, at least one will have a large loop, meaning the advance moves a fair way before the loop beds on the post and its tension starts to take effect, the lobes............ look ill get a tool and pull this one apart, but first my cuppa...... back soon......

Vettech · « **Reply #5 on:** May 05, 2018, 04:54:07 PM »

Ok - sorry but I cant send pics. But!.

The HEI springs look identical.

The centre lobe #406 and two outer lobes #139 look non adjustable.

I would imagine they are changed as a set for differing engine needs.

They are held in place by the springs and tinsy circlips on the centre lobe.

The vaccumm advance which for some absolutely unknown reason people rip off, comes into play only when back throttling, ie foot off accelorator.
This changes the advance, and stops back firing, which could result in engine component failure..

As far as changing these bits I cant comment, I've always found std 350 has enough grunt for me.

My 78 runs great on an older std Kettering (points) style dizzy, put the original HEI in, gets me half way to W'pk then stops. That nite Tests ok, put it back all ok drive to work next day and stops in the same stop. Changed everything, but now realise maybe the Hall Effect pickup is the only thing original.
When the 78 runs I'll try again.

rosco · « **Reply #6 on:** May 05, 2018, 05:09:27 PM »

It sounds like you have the heavy springs on it which is what they set them at from the factory. Just change them to the 2 light weight springs this will bring it down so that you should be all in at 3,500.
If it's a good 383 set initial at around 18 to 20 or where your vacuum level is best.
I don't want to get into a timing tuning report here.
But changing to the two light weight springs will get you on the right track

Regards Rosco

RHD.68.l89 · « **Reply #7 on:** May 06, 2018, 07:47:12 AM »

the stock points dizzy has a pin through the plate in the advance mechanism. put a sleeve/tube over the pin and the amount of advance is reduced. Lars recommends a total advance of 36 and all in by 3-3,500 (measured with vac advance disconnected) for best performance with small and Big blocks.

bfit · « **Reply #8 on:** May 06, 2018, 02:19:09 PM »

Quote from: RHD.68.l89 on May 06, 2018, 07:47:12 AM

the stock points dizzy has a pin through the plate in the advance mechanism. put a sleeve/tube over the pin and the amount of advance is reduced. Lars recommends a total advance of 36 and all in by 3-3,500 (measured with vac advance disconnected) for best performance with small and Big blocks.

The amount of advance that an engine we operate with is among other thing directly related to the fuel quality you use, the better the octane rating the more advance that the engine will tolerate , a little lead helps as well , avgas if you have the compressor ratio to utilise it, make good HP

RHD.68.l89 · « **Reply #9 on:** May 06, 2018, 03:01:18 PM »

for pump gas and streetable compression ratios Lars' rule of thumb works very well.

bfit · « **Reply #10 on:** May 06, 2018, 04:55:23 PM »

Quote from: Darylle on May 04, 2018, 08:50:54 PM

Hi all
I have recently replaced my engine with a 383 from engine master and all is great except my new MSD dizzy has too much mechanical advance (around 40 deg total) and I have been told that I need to "modify" the flyweights to reduce their "throw" has any one had similar issues and what measures were taken to rectify?
Thanks in advance.

Darylle why do you think the engine is running to much advance.

Vettech · « **Reply #11 on:** May 06, 2018, 05:19:34 PM »

You may like to look at ebay for.

MSD 8428 DISTRIBUTOR ADVANCE ADJUSTABLE SPRINGS WEIGHTS GM HEI KIT.

Comes up with a pic common to a few adds.

Shows centre lobe, two centrafugal wrights, 4 plastic colour coded bushes and three (3) sets of colour coded springs.

Regards.

bfit · « **Reply #12 on:** May 06, 2018, 05:31:21 PM »

Darylle says he has a MSD distributor that kit will not do the job.
Most of these commercial mass produced 383`s come with a set up with 20 to 22 deg`s advance in the distributor all in by around 4000 rpm .
It’s not logical for then to build engines that run close to the extremes for road use.

Darylle · « **Reply #13 on:** May 06, 2018, 06:41:00 PM »

Hi again
Thank you for the replies, so the ebay kit has the coloured "bushes" which I gather restrict the "throw" of the weights thus reducing the total advance.
Would I be correct?

Vettech · « **Reply #14 on:** May 06, 2018, 07:28:51 PM »

I'd say fairly close, plus the springs are colour coded to their strength.

Matt G · « **Reply #15 on:** May 09, 2018, 10:25:08 PM »

Darylle, Try this link https://www.jegs.com/InstallationInstructions/100/121/121-8464.pdf
I have all of the springs and limiters on my MSD dizzy, and I received essentially the above print with my dizzy, however I didn’t change any of my springs or limiters from standard. I figured that I’d get a good Dino guy to play with it at Dyno time.... one day.... Looks like some good advice from many above. Maybe join the doc with the advice, and you’ll have the full kit :)

Darylle · « **Reply #16 on:** May 10, 2018, 08:58:01 AM »

Hi all
Thanks again for all your replies, with regards to the timing the engine supplier stated that 40 degrees was too much total and warned of potential drama if she gets "hot" She runs well with the 98 fuel but I think she needs a little fine tuning and I was considering a dyno for that purpose. Also I purchased the 8420 kit and I see it has the stop bushings as does the 8464 so if I understand it right these bushings reduce the total advance.

rosco · « **Reply #17 on:** May 10, 2018, 04:12:44 PM »

Okay now that you have the stuff you now need to graph the dissy to your engine.
So you will need to take your cam specs with you to Hume performance and they will graph your dissy up for you correctly.
When this is done take it in for a tune .

Rosco

Darylle · « **Reply #18 on:** May 10, 2018, 10:07:17 PM »

Hi Rosco
As a matter of fact I purchased my quadrajet from Hume and found them very helpful! I was thinking the dyno people would re graph the dizzy when completing the tune.

rosco · « **Reply #19 on:** May 11, 2018, 07:49:33 AM »

They may depends on who does it. Most competent tuners can do this job for u.

Rosco