Where is 8* BTDC??
 

I've exhausted my search options on all of the interwebs. I'm setting base timing on my Merc 350 MAG MPI. Its a 0L372*** era motor, year 1999. I found a million threads on how and have the service manual. I though I completely understood how to do this procedure until I went to do it. My issue is that I see my mark on the balancer and see the mark on the plastic timing cover, but doesn't this indicate TDC #1? Shouldn't there be a larger tab on the timing cover to indicate degrees BTDC and ATDC? I looked at google images and could find nothing. The timing cover is just a small "V" shaped notch. The balancer does not appear to have any other markings unless I'm missing them. Please help.

To make sure, what does your distributor cap / rotor look like ?

#1)
http://www.mercruiserparts.com/Merc/...MMON/13723.gif

or #2)
http://www.mercruiserparts.com/Merc/...OMMON/9801.gif

from TDC on the balancer ( should be a line 0 ) there should be small dash lines before and after TDC, if for go back four notches before the TDC line, that is 8* before, each dash line is 2*,

You can use a timing light with an advance knob, or if you don't have one or any marks, 8 degrees before would be about 9/16" to the right of the top dead center mark on the balancer (for an 8 inch balancer).

Thats the easiest way,,,,, but there should be another timing mark on the balancer as well

On some of the Vortec motors, there is not. There is a notch in the balancer for TDC, and a mark on the plastic timing cover, and that is it. I use an advance light and set the ECM to timing set mode with a scan tool to set these motors.

When I've run in to that (on cars), I just use my adjustable timing light to determine degrees (on the light, not the tab).

Doh - looks like I was late to the party.

Buy ya a timing tape. Their available at most auto parts stores. Make sure you get one for the correct diameter balancer. http://www.jegs.com/p/Mr-Gasket/Mr-G...46079/10002/-1

SB, my distributor is picture number 1. It does require that base timing be set for this model. My balancer does not appear to have any hatch marks. I am putting the ECM (MEFI 3) into base timing mode by jumping pins A And B at the diag connector. I don't have an advance timing light. I guess I'll pick up some balancer timing tape. Thanks for the all the advice. This is what I was missing. Funny that so many other threads here and forums ask how to set base timing but nobody asked this question.

hey guys i have the same problem except i have distributor in picture #2

Your distributor does nothing to adjust timing. Timing is controlled by the ECM and the distributor is used as the cam sensor. I'm going off of memory here, but this is what I remember. When setting the distributor in place you line the mark on the crank up at TDC and set the distributor in with the rotor lined up to the mark on the distributor base. From there I would verify cam sensor angle with a scan tool that it is in specification. You don't use a timing light at all with that setup.

^^^Yes. I would also use scan too to verify angle^^^
See #2 here:
http://marinemechanic.com/merc/distr...fi-nostart.PDF


FYI: there where a ton of bad caps out there, even fromMerc, for these distributors. If you run into amostart, or misfiring, or ect condition 1st place to look at are these caps. I guess it is not uncommon for people to change out once a year or so.

What could be the issue when reading the timing that the lines won't line up and look to be sitting still but rather bouncing within a range of say 12-6*?

If the timing is moving around it's either a sloppy timing chain or you don't have it in base mode. Much more likely it's the base mode jumper has a poor ground.

Agreed with base timing mode, you have to put the scan tool in service mode to put the timing into base timing mode or use the Merc timing tool to do so.

ECM 555 and PCM 555 TIMING is NON adjustable. ECM 555 - the HVS needs to be phased properly to provide the proper spark events to the designated cyc's

I have not read all he posts up here so hopefully my answers here helps out whomever.