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 Timing issues 
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Joined: Mon Jan 27, 2014 4:31 pm
Posts: 39
I have a problem with MSD 8365. It is a stand alone HEI with a rev limiter, adjustable mechanical advance; with 21 degrees and light blue springs and a 10 degree vacuum can. It's 406 SBC in a 3700# car with OD and 3,42 gears and 10 -1 compression. The timing jumps around at 1300 rpm and at 3200 rpm. It only shows 17 degrees coming in, where it should be 21. I've checked and cleaned everything the bushing is tight, top bearing is tight and smooth and the end play I .019. The work smooth.
Does any one know how to convert this to a GM module as I think the original MSD is shot or on its way out. My distributer does not indicate that there is excessive cam movement.
Thanks.


Wed Sep 28, 2016 3:06 pm
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Joined: Mon Jan 27, 2014 4:31 pm
Posts: 39
I wasn't too clear in my original post. I'm trying to find out if I need a new module. I have a bushing that limits mechanical advance to 21 degrees; but I'm only getting 17 degrees. Could I be losing it in the module somehow. The question regarding the GM module to see if anybody has tried it.


Thu Sep 29, 2016 11:41 pm
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Joined: Mon Jan 27, 2014 4:31 pm
Posts: 39
This morning I went and started engine and the first thing I did was check the initial timing. It was 14 degrees while the engine was sill cold. I had disconnected the vacuum line and had the timing light ready to go. When the engine was warmed up I checked it again and it had creeped up to 18 or 19 degrees Wasn't steady. Both times the total was at 35 degrees.


Fri Sep 30, 2016 3:16 pm
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
As the engine warms up the idle vacuum will increase as the idle speed increases. Don't expect the MSD advance mechanism to do exactly as the instructions describe. Production tolerance just is what it is. The (color) bushing = xx degrees will vary a few degrees from one distributor to the next. The big green horseshoe shaped MSD module with the rev limiter in it is pretty fast switching (fast slew rate) compared to many others, and it does make more spark energy than most.

What problem is the result of this timing anomaly? If the vacuum advance is dithering the timing and messing with the idle, you can use ported vacuum so the advance is cut off at idle and otherwise normal above idle.


Sat Oct 01, 2016 12:45 pm
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Joined: Mon Jan 27, 2014 4:31 pm
Posts: 39
Tuner, thank you for helping.
This problem is not vacuum advance related as it was not connected when tested. My distributor has a 21 degree bushing in it. It has always been in that range since I bought new and set it up, What I did yesterday was set everything up before I started the engine so I could check the components while they are still cold. First I disconnected and plugged the vacuum advance can hose [manifold].Then I hooked up my .non dial back timing light. [ Now if I have 14 initial and 21 mechanical I should have 35 degrees or close to it,] Now I start it up cold and check initial. It's 14 and total is 35 at 600 RPM. Warmed up it checked at 18-19 initial at 600 and 35 total. I've never checked timing cold so I have no reference to go by.


Sat Oct 01, 2016 3:48 pm
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Joined: Fri Feb 08, 2013 2:37 pm
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This is strange. Perhaps power the timing light with a separate battery.


Sat Oct 01, 2016 4:09 pm
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Joined: Mon Jan 27, 2014 4:31 pm
Posts: 39
Tuner
I did the test again, tried it with the battery that's in the car and an external battery charged to 12.65 volts. I also tried with two different timing lights, One was a sears non dial back and one was snap on dial back set on zero. My results were Cold - Initial-15 degrees @ 575 rpm. Total-35-36. Hot-Initial - 20 degrees @ 575 rpm. Hot - Total - 35-36 rpm. I've never remember timing a motor cold but one day I was checking my car so I had everything set up before I started the car, and just happened to look at the timing at initial and not the total. When it was warmed up I saw a difference, This is where I'm at. MSD says they never heard of this before. Both timing lights gave the same results.


Thu Oct 06, 2016 11:33 am
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Joined: Fri Feb 08, 2013 2:37 pm
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I suppose the greater drag of the oil pump with cold oil could pull the slack out of the chain, but 5 degrees seems a lot. How much slack is there in the chain if you rock the crank back and forth against the drag of the cam? You might pull the distributor and examine the roll pin in the gear. Sometimes a high-volume/high-pressure pump will flex a roll pin enough a section of the outermost wrap will break away. The original GM split pin is tougher because it has more wall thickness than the material in a roll pin. What kind of oil pump?


Thu Oct 06, 2016 2:06 pm
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Joined: Mon Jan 27, 2014 4:31 pm
Posts: 39
The oil pump is standard pressure high volume pump. It doesn't seem to stress the distributor shaft.I recently had it apart and cleaned the top of the shaft as it was causing a slight drag. The roll pin was fine. I might try another distributor when I can get one. I'll let you know what I find out.
Thank you Tuner.


Thu Oct 06, 2016 7:17 pm
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