SB chevy timing retarding

[sdroadster]

I have a Small Block Chevy in #352 Studebaker that I run at the Dry Lakes and Bonneville. The motor is a stroked 350 (368) and has a wet sump. The first pass at Bonneville was faster than we had ever been, 223 mph. Then the speed started to detoriate. We found that the ignition timing is retarding about 20 degrees at 5000 rpm. It has 36 degrees of initial advance, and a locked out MSD distributor. When free reving it in the garage you can see the timing begin to retard. At 5000 rpm there is a difference in the exhaust note as the timing falls off. It has had 2 new MSD digital 6al ignition boxs, 2 new distributors, a new MSD timing light and I pounded a paint paddle between the water pump and the timing cover to address possible cam walk. I have spoken to MSD Tech several times. They haven't been much help. The next thing I'm going to do is install an old points distributor and abandon the MSD electronics. If it still retards and falls off we will tear into the motor. Any ideas or suggestions? Thanks Terry

[johnneilson]

have you checked the end play of the shaft in dist or lower bushing in housing?

J

[SPARKY]

What is the exact model of the MSD box do you have? If you have a "Digital" box it is most likely is programmable to the RPM timing curve!

[sdroadster]

The car has real basic ignition parts. MSD 6AL Digital box (no adjustments, just a rev limiter). Haven't checked end play in the distributor because I bought it brand new. The motor is really a circle track hand me down. Crower bottom end, Dart cast iron heads, Crower roller cam, Crower valve springs, and roller lifters. About 13 to 1 compression, and 850 Holley carb. No Nitrous, no start retard, simple motor that used to always run well. We shift at 7200 rpm. Car ran 185 at El Mirage, and 223 on the salt. We are not record contenders, just geezers that want to see how fast we can go in CG/CC. Thanks

[jdeleon]

Reverse the two wires from the the msd dist to box. This should retard the base timing on your lite... if so, Then reset the timing...  then you should be go to go.

[Milwaukee Midget]

So does it the sound fall off precisely at 5k, or does it vary a few hundred rpm?  If it varies, I'm thinking mechanical - if it's precisely at a given number, I'm thinking electronic.

[sdroadster]

The engine falls off and "lays down" give or take a few hundred rpm after 5000. Sometimes 5200, 5600 etc. I ran at El Mirage in November. The motor reved to 5200 or so, and quit pulling. I never shifted to 4th gear, and went through at 117 mph. I ran 185 in July...

[Sumner]

223 is a good run, congrats.

Have you checked the valve train, the springs in particular?  Has something happen where it is now going into valve float?

Sum

[SPARKY]

More and more folks are going to valve spring oilers to prolong valve spring life---T&D rockers even have them built into their rocker arms if you want them.

My guess is Sum and MM is on the right track.  If you have  restricted oil to the top of your eng to make it live at B'ville you might want to consider "spring oilers" if you find your valve springs weaken.

[sdroadster]

Thanks for the info on the valve springs. Although this was a new stroker motor in July, the valve springs were reused from a previous season. The owner of the engine said they tested fine. The motor started laying down at Bonneville. It didn't float it's valves (when is used to rev to 7600 or so) and doesn't shoot ducks. I agree the valve springs are getting old, but how would they affect the timing? You can watch the advance detoriate as the engine revs. It's loosing 16 degrees, maybe more.

In the next few days I'm going to install an old points distributor, and run it off the white wire on the MSD box. If the timing still drops off, I'm going to abandond the MSD, and run the distributor with a coil, and a ballist resistor like any old car. If the timing still goes away the owner will be pretty much convinced the motor needs attention. A friend loaned me a Vertex Mag I will probably install at the end of the testing. I wonder if putting a new Vertex in the motor is an option. I have been pouring money into MSD parts, and even MSD doesn't know whats wrong. It seems like a mag would be simpler. Thanks

[SPARKY]

I am guilty of having an old one track mind that tends to get tunnel vision  you did mention that you had watched it back track on the timing light---

YOU are not alone with problems with MSDs---I sent a 7-AL  2 back and they told me nothing was wrong with it but with no other change but replacing the box--- solved the problems--

Andy next door has had a 6 al quit him sent it back  told nothing was wrong but we didn't get the same box back---this one works--something may be going on would not be the first one---check the HR article about bogus MSD parts you may be a victim!

[jimmy six]

SD. If you put in a points dist make sure every thing is top notch. Stock points float at 5500 and good racing points may be hard to find today. Have you tried what jdeleon said.....I go to the ez stuff first....good luck JD

[tauruck]

Sparky is spot on.

It's the MSD.

[Sumner]

Sparky is spot on.

It's the MSD.

I'd have to agree and withdraw my earlier diagnosis as I forgot that he said he could see the retard and the springs aren't going to do that  ,

Sum

[Milwaukee Midget]

Why the MSD? 

Provided the wiring is solid and there are no ground faults or physical issues (leaky capacitor, poor solder joint that's sympathetic with engine vibration, etc.) an electronic error would tend to repeat at the same rpm - or event parameter - every time.

You could test it by putting it in a different car.

I'm not saying that there aren't physical conditions that effect electronics, but my experience has been that an electronic failure - even one that seems sporadic - is usually repeatable and/or absolute, if the test is performed with care.

If the symptoms occur in a range of event parameters - sometimes 5200, sometimes 5600 - I'm thinking that's heat, expansion, centrifugal force - elements that are more widely variable than the flow of electrons.

Conditions change more readily in an engine than they do on a circuit board.

20 degrees of timing at the crank, your turning motion takes a right hand turn at the dizzy drive.   So that's really only 10 degrees at the base of the distributor.  Stack up some tolerances with the gear on the cam, maybe a loose cam bearing.  What kind of run out and end play are you seeing at the gear?  The base of the distributor? 

Jack Gifford pointed out that he was able to do adjustable cam timing of 16 degrees with as little as .001 change in gear mesh on a gear drive cam.  It stands to reason that that kind of change on a helical gear could create similar changes in timing at the distributor.

I think this sounds like a combination of bushings and worn gears riding up as centrifugal force and oil temperatures and pressure changes. 

But I would start with the box.