Help with Ignition Timing on a 2455-gctid341083

[Guest]

I am seeking advise on setting the ignition timing on a 5L GM engine for a 1988 2455 Sundbridge with an OMC outdrive.

I have seen someone comment on a different post that the timing should be 8 degrees BTDC but it is unclear what increments each mark represents. I would assume that the deepest saw tooth is TDC (Top Dead Center) and BTDC are increments above.

I have set timing on cars in the past but have not adjusted the timing on a marine engine. Is there an optimal rpm the timing should be set too? Would there be any different setting for different pitch props? Can someone help to clarify the gauge pictured?

Many Thanks in advance.

Attached files [img]/media/kunena/attachments/vb/643646=23349-0102121313a_2.JPG[/img]

[2850Bounty]

This should help explain the OEM harmonic balancer TDC and timing tab markings.



Note that the tab markings limit the advance to the BASE advance range only..... perhaps a bit more, but certainly not enough for TAT (total advance timing).

We need more degree markings in order to set/adjust TAT......., or a digitally advancing timing light (that I won't use for this type of ignition system).

The balancer can be marked off up to approx 35*, or so, then we'd use the ZERO notch ONLY on the tab!

This one is HP auto, and goes up to 60*..... we don't need anywhere near 60*.



When these degree marks are used, engine rpm is increased to 3.2K (+ or - ), and the timing marks are strobed with a timing light in "standard mode".

Very simple to do!

Is there an optimal rpm the timing should be set too?

Well, yes.... but this requires some clarification, and that should be covered in the thread that I link you to further down here.

Nut shelling this:

BASE Advance RPM will be below 1K rpm.... or should be. IOW, we should see NO mechanical advance until .9k or 1k rpm or later.

As for the "Progressive Advance"...... you'll need to see your OEM Ignition Timing specs, and more than just BASE advance.

All too often (when searching on line) we'll see BASE advance specs mentioned ONLY...., and nothing further.

In fact, it can be quite difficult to find anything past this...., so keep looking if you don't have the OEM manual.

https://"http://www.baylinerownerscl...the procedure.

If you have some automotive experience, it should make sense to you.

Post back if any questions and we can take it from there.

[Guest]

Thank You 2850Bounty for your detailed and insightful answer. I have to admit that before your answer my understanding was only limited to the base advance timing and I was unaware of the progresive advance timing. Your information helps. I will look for this specification so that I can atleast check this.

I may come back to this topic in that I am in the process of gathering the informaiton to do this when the weather warms up enough for me to undo the winterization and get ready for the next boating season.

[2850Bounty]

You are welcome, and yes... come back if need be.

You are not alone. I've spoken with, and read forum posts from some allegedly well seasoned marine mechanics who post regularly on boating forums.

Not all, but some of these gentleman seldom bother to look past BASE Advance.

What you're looking for, will be something very similar to this, and will be tailored to your engine.

(note that the vertical scale does not include BASE.... BASE must be added if doing the math. While strobing, BASE is automatically included)



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