Logo
FULL SITE MENU

Setting Timing Followup

P

paw2000

Contributing Member
I had posted earlier about double checking my timing on my engines after install, as I had moved the dizzy during install. Well it was checked and was off, I had a buddy check while I ran the engine. He set for 12 btdc, motor sounded fine, set idle and revved up the engine total advance was 24btdc. full advance came in early after 2000 rpms. Now my question, is the total advance too soon? or am I safe? also I rechecked timing tonight and got a different value then my buddy. The balancer has different marks, One was labeled vertical, has anyone seen this. I set the timing to 8btdc, and the motor sounded better, better (smoother) idle, revved well. I used the mark that appeared closest to the timing tab, when I moved the dizzy It was noticable, so I'm hoping I used the correct mark. Without pulling the #1 plug is there a way to determine which mark I need to use?
 
You can TDC your motor by removing # 1 plug and inserted a piston stop in its place. The stop is adjustable, and you set it to stop the piston about 10 degrees BTDC in both directions (marking where that is on the damper). True TDC will be between the two marks.



With that done, you can select which mark is actually your 8 ' BTDC and time it.

Jeff

PS: All in at 2,000 rpms seems a bit too soon, but only 24 ' total advance seems a bit soft: I've seen 26 to 28 on several Crusaders.
 
Depends upon which "model" you have...v-6's and 502's have different timing curves and they have changed over the years due to fuel changes.

Typically, max advance is dialed in and the at idle value is used 'as-is' assuming no start/restart issues occur. Aftermarket distributors usually permit full tailoring of the timing curve.
 
This morning I checked TDC and and the only mark near the timing tab was a mark that was painted white and had a large dot of paint, guess the builder did this to mark the correct mark. The painted mark at TDC was lining up with the bottom of the timing tab. Which wasn't zero but showing 8btdc on the scale. Now maybe I'm over thinking this, this engine is a reverse rotation, the balancer turns counter clockwise (looking from the front), the timimg mark moves clockwise (down from tab). Which is off the scale of the tab. I don't want to ruin an engine. When I rotate the dizzy counter clockwise, the rpms will increased. How much is to much?

Why I'm getting grey hair over this, today went for a shake down cruise, the reverse engine needed a lot more throttle in relation to the other. I'm thinking the timing is low. the port motor was 1/2 to 3/4 throttle but the starboard was pushing 3/4 throttle for the same rpm's. So the starboard motor is working much harder.
 
Ideally we be using a balancer that is professionally marked off, as shown here for a Std LH rotation engine.
(note that this one is also marked every 90*..... most likely for using the 8 stop cam follower adjustment procedure)

images


Or something like this where the numbers are actually machined into the surface.
images


The reverse of this would be used for a REV RH rotation engine.

With these markings, we don't need anything other than the ZERO notch at the tab.

As for the PPS procedure....... rather than using 10* in either direction, try using something closer to 30* (could be 29*, could be 31*, 33* ... doesn't actually matter as long we adjust the pointer to come up with the same crank angle in either direction)
This gets us further away from top of stroke, and will give us a more accurate true TDC when the PPS is removed.

See post #12 in this recent thread on the PPS method.

The entire purpose of having these markings available, is to allow for higher RPM setting/checking of ignition advance.
We fire these on BASE advance, and we idle these on BASE advance... and that's about it.
Past this, our greatest concern will be our Ignition curve and Full-In RPM.
With the balancer marked off correctly, the Digitally Advancing type timing light now becomes Un-Necessary (a good thing in my book).
We can now use an ordinary strobe type timing light and see this in "Real Degrees" in "Real Time". :D


In particular, take heed of Jeff's comment regarding your "24 btdc full advance came in early after 2000 rpms"
I agree...... this is too early for most V-8 gasoline Marine engines.


Timing a Marine gasser is nothing to roll the dice on, as an incorrect advance can cause Detonation.
Detonation can take out the tops of several pistons in a matter of minutes, and it not always audible, such as pre-ignition may be.
I'd find your OEM TA spec, and follow it.

As a rule only.... and for a SBC Marine Engine fitted with the full dished pistons, they can generally handle 26*-28* @ 3.2k RPM.
If Q/E built, this can be bumped to approx 28*-30* @ 3.2k RPM.
Again.... see your OEM specs to be safe, and always time your engine for TA.
BASE advance means little compared to this.

*************************************
I'll be bold here and stick my neck out some......, but if we're using a mechanic that sets BASE advance only, and calls it a day, he's not the right guy to be tuning your Marine Engine.
Find someone who understands Marine load Detonation and Marine Ignition Timing, and have them do this for you.

.
 
Last edited:
The difference in throttle settings could be the timing difference - could also be the control cables. Not uncommon for the throttles to be 'different for the same rpm.

that said, you really need to get a stop and find TDC on your engines to know what is really going on. The factory mark on the balancer is a deep grooved mark that runs across the circumference of the balancer, parallel to the crankshaft. Also, an unbutchered crusader will have the proper timing tab installed, based on the engine's rotation. the counter rotating tab has the correct marks for Before and After. I'd suggest ignoring any old existing markings unless you have documentation describing them.

You may also consider a small investment in a pair of timing tapes. they last a long time and will be of significant value if you really want to optimize your engines' timing adjustments. They will also make having the correct timing tab irrelevant - all you use on the tab is the TDC (zero) point to read the tape under it.

You may also want to invest a few minutes researching some of the recent posts on timing adjustments on this board. Many details and a few had some decent pictures.
 
The mark on the damper was a factory mark, it was filled in with paint, there are 2 other marks on the damper, 1 labeled vertical so the paint dot was used to identify the correct mark. Ouch on the butchered crusader comment.
 
Back
Top