Priya

I bought the MSD 8428 distributor recurve kit which has springs of three different strengths.

The heavy spring has 0 degrees advance at 1000 rpm and 8 degrees advance at 1500 rpm and maxes at 18 degrees at 5500 rpm

The medium spring has 8 degrees of advance at 1000 rpm and maxes at 22 degrees at 4500 rpm

The light spring has 8 degrees of advance at 500 rpm, 12 degrees at 1000 rpm and maxes at 24 degrees at 3000 rpm

The initial timing spec for my stock '79 L82 is 12 btdc at 900 rpm

According to what I've read for best performance I should have 36 degrees total timing (12 set at distributor +24 centrifugal) all in by 3000 rpm which would be the lightest spring but if I use that one the centrifugal advance will already be near 12 degrees at 900 rpm so if I use the timing light to set it there I essentially have no built in iniital timing at 900 rpm, and will only have 24 total degrees total at 3000 rpm

If I use the medium spring it'll have nearly 8 degrees of centifugal advance at 900 rpm, my built in initial timing will only be 4 degrees to hit the 12 btdc @900 spec and my total timing will only be 26 degrees at 4500 rpm

If I use the heaviest spring there will be no centrifugal advance at 900 rpm so my built in initial timing at 900 rpm will be 12 degrees and my total timing 30 degrees at 5500 rpm

Should I just use the heaviest spring to make sure I get the proper 12 degrees BTDC at 900 rpm even though that will give a less than optimal advance curve? Or do I use either the light or medium spring but put a rubber band around the distributor weights so they can't move to set initial timing at 12 degrees at 900 rpm which after I remove the rubber band will result in 20 degrees of advance at 900 rpm (medium spring) or 24 degrees of advance at 900 rpm (light spring)?

MelWff

are you using a dial back timing light? If so, remove both stock springs, install one light spring, set the dial back to 36, raise the engine speed to 2,000, turn the distributor so the timing mark on the balancer lines up with zero on the timing tab. Install the 2nd light spring and check what your timing is at idle. If you dont have a dial back light than you need either a scribed balancer or a stick on timing tape.

http://www.msdignition.com/instructi...pdf?terms=8428

Shark Racer

You could experiment with a light and medium spring.

I recommend reading Lars' paper on the timing re-curve. It explains it all very well; better than I ever could.

Priya

I do not have a dial back timing light. On the light and medium springs I could put a rubber band around the centrifugal weights so they can't add any centrifugal advance at 900 rpm and set the base timing timing to 12 degrees, or I could install the light or medium springs without the rubber band and set total timing (centrifugal +distributor position) to 12 degrees at 900 rpm.

Priya

My question is not so much about what the total advance will be at higher rpms, I trust the sheet MSD included, my question is about where do I set the initial timing if I am going to use the light or medium springs - 12 degrees total at 900 rpm(any spring) , 20 degrees total at 900 rpm (medium spring), or 24 degrees total at 900 rpm (light spring)

Shark Racer

The light spring @ 12 degrees *sounds* right. You should verify that you make 36 degrees, don't exceed it, etc.

A dialback timing light is worth it for this. Or timing tape that will let you measure mechanically with your current light. You can make your own by measuring the circumference of the balancer, divide that number by 10 and making a mark on the balancer where 36* would be.

Priya

I'm not following you. Are you suggesting I install the light spring and set timing to 12 degrees at idle even though all 12 degrees will be centrifugal advance and total timing will be 24 at 3000 rpm, or are you suggesting I install hte light springs, put a rubber band on the weights so there will be no centrifugal advance at idle, set ignition to 12 degrees btdc at idle, then remove the rubber band from the advance weights which will give me roughly 24 degrees total ignition timing at idle and 36 degrees total at 3000 rpm?

Priya

Shark racer, thanks for the tip on making my on 36 degree timing tape - I can do that.

Shark Racer

OK, I get where we're disconnecting.

What's important is that you have 36* total.

Do not rubberband the weights. That won't last.

Start by running the light springs, set the car to get 36* total, you may end up w/ too much initial advance (hard starting, pings, dieseling, etc). If that's the case, then switch to a light spring and medium spring and try again.

The ultimate answer is up to your testing... hope that helps.

Priya

I didn't mean to leave the rubber band on the weights, just to do it to set initial timing at idle to 12 degrees and then remove the rubber bands.

I think I'm following you now - aim for 36 total degrees advance at 3000 rpm which if I trust the MSD installation sheet I can get by installing the light springs, putting a rubber band around the advance weights to prevent any centrifugal advance at idle, setting initial timing to 12 degrees at idle, removing the rubber bands, and then I should have my high performance ignition advance curve.

I think I'll make my own timing tape as you suggested so I can check precisely for 36 degrees total advance at 3000 rpm.

Thanks for your help!

cv67

I have 2 of those kits and am throwing them out they were worthless
So were the dist bushings (brand new)

The bushings werent accurate to start with..could not get a curve to get mine to make good power no matter what I did. Timing light said all was kosher but never "ran"

Bob Jennings (any of you guys remember him) took it all apart did his own tweaks what a difference!!

Maybe yours will be Ok, hopefully. If youre not happy send it to Bob
Gotta be coming up on 8o yrs old, has a number of old sun machines/water brake dyno can make any carb or dist run hard


https://plus.google.com/112827651439...ut?gl=us&hl=en

Shark Racer

No rubber bands, they're basically making the springs act heavier. Hook everything up as normal, set the timing to hit a maximum of 36 degrees (at whatever RPM it peaks at), then see what you have at idle.

If the car runs fine with whatever you have, leave it alone, otherwise start to experiment with heavier springs.

A Sun distributor machine is nice because you don't have to use the car as a test bed, but hey, that 350 under the hood works.

Priya

I wasn't really looking to recurve my distributor. I had checked the timing about a month ago and it was set at 2 degrees BTDC. The distributor hold down bolt was stuck and hubby was afraid if he pushed on it any harder it would break so I spent 18 days soaking it day and night with a 50/50 mix of ATF and paint reducer. I tried it after that and it still wouldn't budge. A few days later I thought maybe if I bring the motor up to operating temperature the aluminum manifold should expand more than the steel hold down bolt and it'll come loose. I did that and it was just barely able to get it to turn.

Tried setting the timing and when I moved the distributor to 12 degrees it stayed there for a few seconds and then continued advancing off the scale as the rpm increased. Tried turning the distributor back, it came back to 12 degrees and then a few seconds later kept going to 4 degrees as the rpm slowed down. I tried and tried but couldn't get it to settle on 12 degrees so I figured the centrifugal advance springs were weak and allowing the timing to fluctuate. After much alternating between adjusting the distributor and idle speed I got it to hold somewhat steady at about 13 BTDC but the idle still fluctuated between 1300 and 900 rpm when I was driving.

So, that's how I came to buying the distributor recurve kit - my initial motivation was just to restore the car to stock working order. I just finished installing the springs and weights and decided to put on the heaviest springs to start out with and get the base timing to 12 but I buggered up one of the heavy springs so put on one heavy and one medium. The weight with the heavy spring has tenstion from the start, the one with the medium spring has some play in it before the spring starts to limit its movement so I'm pretty frustrated right now. Hubby's bringing home the timing light tonight so I'll see how this all works out.

bluedawg

What I did on my l48was to take the springs off and reassemble the distributor and start the engine. Set the total at 36. Install either both light weight springs or one medium one light weight spring. Having both light weight springs will give you the best throttle response and as long as it don't ping while power breaking at the highest rpm you can with out spinning the tires. Going one medium will keep the in tial lower but won't allow you timing to be all in by 3000 rpm.

DucatiDon

Using the rubber bands is ONLY to try to determine what your advance is without any mechanical weights adding in, so you can determine what the springs are giving you. Useful only for setting the advance curve, really, and useless if you already know what your springs do.

You do have the vacuum can disconnected and plugged? right?

Sounds more like a vacuum leak than a advance weight/spring issue.

Put your desired springs in, mark your balancer at 36*, put the light on the mark and run it up....note where the 36* mark lines up at. You want it at 0 on the tab when it finally stops moving. Adjust it so that at full advance the 36* mark lines up with the 0 on the tab. Then check again at idle and note where the factory timing mark is....should be around 12-15.

Priya

Yes, I have the vacuum advance disconnected and the hose plugged. I was planning to use the rubber bands only to determine what my advance was without any mechanical weights adding in.

If I for example was to use the lightest spring according to MSD if I had 36 degrees maximum advance at 3000 rpm I would have 24 degrees of advance at idle because the lightest spring allows 12 degrees of mechanical advance at idle and 24 degrees of mechanical advance at 3000 rpm.

If I was to use the lightest spring and set initial timing to 12 degrees without rubber bands to prevent mechanical advance I'd only have 24 degrees total maximum advance at 3000 rpm and above.

bluedawg

I dont even use rubber bands. It will only advance what it mechanically can. 36 degrees at idle with no load won't hurt anything.

Neil B

As others have said, you need to set your timing based on total advance and let your initial fall where it falls. Furthermore, if you are using the 2 lightest springs, you might be idling on the centrifugal advance curve a few degrees. But if I'm not mistaken, you can use 1 light silver and 1 light blue spring and the centrifugal advance curve doesn't start until 1,500ish rpm (look at the MSD graphs and you'll see what I mean). And I can guarantee you you won't have 24 degrees initial with the MSD supplied advance stop bushings. I recently had to use a custom advance stop bushing to get my initial timing in that range with only 10 degrees of centrifugal advance for a race motor setup.

Priya

According to the instructions MSD gave me the heaviest springs have 0 advance at 500, 0 at 1000, and 8 at 1500 and the lightest springs have 8 degrees at 500, and 12 degrees at 1000 which is pretty much my idle speed. Use the medium springs and you get 0 at 500 and 8 at 1000. I'm going to take MSD's word on the spring specifications rather than yours.

There are no blue springs in my advance kit. There are copper coloured springs (light), silver springs (medium) dark grey springs (heavy).

PeteZO6

I don't understand why you have your idle speed at 1,000" R's. That seems high unless you have a really big cam. Also, having any mechanical advance at idle just seems wrong. Advance should start above idle rpm, and max out at ~36* at the speed your build does best with.

Pete