Timing a 3.0 mercruiser ?

[capecodtodd]

Hello
I have been having issues with my 1998 3.0 mercruiser running very rough now it is to the point of stalling repeatedly. The other day in the yard trying to start it up it was backfiring through the carb and I even saw flames. I could not get it started. A friend suggested a timing issue, maybe the chain skipped or is worn out but the 3.0 doesn't have a chain just gears. The gears by the way are in like new shape with no play and no chinked teeth. Yes I did yank the front cover off the engine. The timing marks on the gears line up and #1 cylinder is at the top and the timing marks on the gear cover match up to "0". When I remove the dist. cap the rotor is pointing dead center at where the #4 plug wire goes. #4 cylinder is also at the top. But if I rotate the engine to move the timing marks 180 degrees then have a look under the dist. cap the #1 spot is off maybe 1/8 an inch.
Maybe the trouble is in the distributor?
Maybe what I think is #1 on my cap is actually #4 and the whole thing is screwed up?
Any thoughts or suggestions? The timing cover is still off.

 

[Bt Doctur]

Re: Timing a 3.0 mercruiser ?

got to be on #1 COMPRESSION STROKE, not just at the top.

 

[frank246]

Re: Timing a 3.0 mercruiser ?

Remove the #1 sparkplug, cover the plughole with your finger and manualy ratch turn (cw) the engine untill air blows out under your finger.
Now gently turn on until the mark on the balancer reads 0, this is tdc at compression! Now check the distributor again. Rotor to cable terminal one on the cap and 1342 is the sequence of firing clockwise.
Carb popping can be ignition timin but also gas mixture!
Good luck.

 

[capecodtodd]

Re: Timing a 3.0 mercruiser ?

This may be a silly question to some but I am not very familiar with the internal workings so how can I tell which is the compression stroke?
If the timing marks on the gears line up and the #4 and #1 piston is at the top maybe I have mixed up the #1 plug position so the firing order of 1 3 4 2is all screwed up right from the start and that is why it is running so poorly or not at all.
How do I make sure it is in fact a compression stroke?

 

[frank246]

Re: Timing a 3.0 mercruiser ?

This may be a silly question to some but I am not very familiar with the internal workings so how can I tell which is the compression stroke?
If the timing marks on the gears line up and the #4 and #1 piston is at the top maybe I have mixed up the #1 plug position so the firing order of 1 3 4 2is all screwed up right from the start and that is why it is running so poorly or not at all.
How do I make sure it is in fact a compression stroke?

The piston is up twice in one revolution of the ignition rotor in a 4 stroke engine.
One is the compression stroke, the other when the exhaust gasses are pushed out... you ll see that the compression stroke is on the #4 at that time.
Good luck!

 

[Bt Doctur]

Re: Timing a 3.0 mercruiser ?

The valve in the head are laid out like this.E= exaust, I=intake
E I I E E I I E, cylinders numbered 1(front),2,3,4(rear)
watch the 2nd rocker arm to open the valve and then close the valve, this is the compression stroke, keep turning untill the timing marks line up, this is #1 top dead center. match #1 plug wire to the post the rotor is pointing to, then clockwise 3,4,2 wires

 

[Fishermark]

Re: Timing a 3.0 mercruiser ?

Just to add to what the others have written... instead of simply lining up at TDC - once you find the TDC of the compression stroke, go ahead and line up the mark to what it should be - 8 degrees before TDC for example, (or whatever your timing is supposed to be set at).

 

[ibrw1]

Re: Timing a 3.0 mercruiser ?

Just to add to what the others have written... instead of simply lining up at TDC - once you find the TDC of the compression stroke, go ahead and line up the mark to what it should be - 8 degrees before TDC for example, (or whatever your timing is supposed to be set at).

I have a question, 1991 3.0 alpha one, guy who owned it before had no clue, I set plug gap from .010 to .035, set points replaced installed proper timing springs into the distributor, repaired lots.

Now all I have left to do is the timing. I see the timing marks but no clue as to what each mark is, not stamped. Anyone have an idea?