Reverse timing advance

IDT-572 · Post by **IDT-572** » Tue Dec 13, 2016 6:15 pm

A customer I built a 355 Chevy for carried his truck to the track for me to tune it for him.

I put the timing light on it and the timing is advancing backwards.

I have changed everything I can think of and it's still doing it. When you rev it up it starts taking timing out and motor starts laboring and heating the headers.........

Mechanical Advance is locked out on the MSD distributor. I have changed distributors, MSD boxes, Checked the balancer markings. Wires , coil.

I thought I found the trouble when I found the cam walking back and forth in the block where he had a timing cover leak and left the cam thrust button out.

But put it back together and it's doing the same dang thing.

Any ideas?

Keith Morganstein · Post by **Keith Morganstein** » Tue Dec 13, 2016 6:21 pm

Most likely a polarity issue. Swap/reverse the wires on the pick up.

IDT-572 · Post by **IDT-572** » Tue Dec 13, 2016 6:23 pm

Did that and it showed no change, I'm stumped,

Keith Morganstein · Post by **Keith Morganstein** » Tue Dec 13, 2016 6:29 pm

At this point (for diagnostics), swap out the MSD for an HEI (in good condition) and compare. It's a quick, cheap and easy way to help determine if it's mechanical or ignition problems.

Keith Morganstein · Post by **Keith Morganstein** » Tue Dec 13, 2016 6:34 pm

Have checked with a different and/or self powered timing light?

fatblock · Post by **fatblock** » Tue Dec 13, 2016 6:51 pm

Worn out driven gear on the distributor.

MadBill · Post by **MadBill** » Tue Dec 13, 2016 6:51 pm

You could always unlock the advance and see if it's enough to cancel out the retard..

Also, I'm too lazy to check, but which way does the timing go if there is huge end play in the shaft and the driven gear climbs the drive one under load?

SupStk · Post by **SupStk** » Tue Dec 13, 2016 9:35 pm

Had the same issue with a genuine GM HEI distributor on a SBC. The pickup coil was the problem. Not sure if MSD has different pickup coils based on dist. rotation but GM sure does.

DaveMcLain · Post by **DaveMcLain** » Wed Dec 14, 2016 9:52 am

I've had a problem with an MSD system before when they ran the pickup coil wires too close to the primary coil wires. Multiple spark pulses became multiple pickup pulses and it started to become almost a continuous fire ignition. With a timing light on it the engine seemed to fire all the way around the balancer very weird. It would shoot ducks but once it got above about 3000rpm it would seem to run fine. I wonder if yours is doing something similar but not quite as bad.... thinking that the multiple strikes have to come after the original pickup pulse and are thus retarded.

fdicrasto · Post by **fdicrasto** » Wed Dec 14, 2016 12:21 pm

Please advise at what you have set the timing at. Got to be somewhere between 30-40 degrees or ?

Post by **GARY C** » Wed Dec 14, 2016 5:45 pm

If the clearance between the button and the cover is too big it will still do it, I have also seen this with stock timing cover and the cam pushing the cover out

Kbails · Post by **Kbails** » Wed Dec 14, 2016 7:05 pm

make sure cam is not walking forward. had this problem and there was no button on front of cam. nothing stopping cam from walking forward. I would just check to be sure

Carnut1 · Post by **Carnut1** » Wed Dec 14, 2016 7:18 pm

Kbails wrote:make sure cam is not walking forward. had this problem and there was no button on front of cam. nothing stopping cam from walking forward. I would just check to be sure

Cam button on any cam is a good idea just for this reason.

Post by **Baprace** » Wed Dec 14, 2016 10:03 pm

How many degrees retard are you getting and at what rpm's ?

IDT-572 · Post by **IDT-572** » Thu Dec 15, 2016 10:22 am

Sorry haven't had time to reply. I have changed distributors but not went to an HEI. The cam buttons was left out but it was replaced and put back together, but no difference.
Polarity changed no difference. Checked the timing marks on the damper(new damper when built thought it may have been marked wrong backwards) not the problem.

Start the engine and set the distributor to 35 degrees at an idle and rev it up and it retards to about 5-6 degrees after top dead center when all the timing is in at about 3000 rpm.

I haven't checked the cap to rotor clearance, but I change distributors and use the same cap and rotor so this may be it. I will check that this weekend.

I have rerouted the distributor pick up wires and replaced them too.

Distributor gear is new and in good shape.

Old sears dial back I have had for years and a new MSD light used and a aqutron (spelling) also all the same, just the MSD light the timing marks are very steady and the others are slightly erratic. Marks moving around some.

Thanks for the help guys, an HEI is going in this Saturday.

Welcome to more ideas if anyone has them.

Don Terrill’s Speed-Talk

Reverse timing advance

Reverse timing advance

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