Timing marks wrong ??

DXN · Jul 18, 2013

86 merc 140 3.0

Its been ruining ok just rough idle when cold and some hesitation on acceleration. so I decided to check timing but if it try to put it at 6 deg BTDC It wont run It seams to idle and start best when the timing mark is straight up 12 o'clock that's like 40 degrees BTDC!

Could the crank pulley be installed wrong? it has a key-way right?

littlebookworm · Jul 18, 2013

Re: Timing marks wrong ??

Have you recently done a tuneup, including replacing the distributor cap and ignition wires? If so, it sounds like you have the wires or the distributor itself out of place. Check that the #1 wire is in the correct position and that the rotor lines up with the at plug wire terminal when you are at top dead center. I doubt very much that the timing marks are off. Hy

sti1471 · Jul 18, 2013

Re: Timing marks wrong ??

When you are trying to set the timing at 6* do you have engine in base timing mode? and are you 100% sure when you were getting your timing readings that the RPM was 650-700 and no higher?

DXN · Jul 18, 2013

Re: Timing marks wrong ??

No I haven't moved the pugs and it doesn't misfire.

RPM 650-700

It's has points so no base timing mode

I did find TDC and It seams like the marks are actually wrong if I put the mark on 0 deg the piston is on its way back down < I got interrupted I'm going to double check this in a little

Don S · Jul 18, 2013

Re: Timing marks wrong ??

Have you tried adjusting the idle mixture?

When was the last tuneup? Have you checked the dwell? How about a compression test?

RogersJetboat454 · Jul 18, 2013

Re: Timing marks wrong ??

DXN said:
I did find TDC and It seams like the marks are actually wrong if I put the mark on 0 deg the piston is on its way back down < I got interrupted I'm going to double check this in a little

Check again. The exterior of the balancer may have slipped in relation to the interior hub of the balancer if this style balancer has the elastomer/rubber ring separating the two pieces.

indybleck · Jul 18, 2013

Re: Timing marks wrong ??

I had a 1979 Chevy Malibu with a 305 that did that, had to time it by ear. The harmonic balancer had spun so the timing marks were off.

bonzoscott · Jul 18, 2013

Re: Timing marks wrong ??

Yes it will start and idle better when advanced but run poor under load. 3.0s inherently run rough at idle, cold especially. If everything is in order, you may just want to let it warm up a bit. Don't know the history and if you just got the boat, that's the way it is.

geo7 · Jul 19, 2013

Re: Timing marks wrong ??

DXN, I just went through this with my 120hp Mercruiser. I borrowed a timing light from my nephew and could not get it running at 8btdc. After about an hour of scratching my head I glanced at the rear of the timing light. The timing light is adjustable for racing and can be advanced by turning a knob at the rear of the light. After turning it back to 0 it timed the motor correctly. I felt pretty stupid for not checking the light!

DXN · Jul 19, 2013

Re: Timing marks wrong ??

Mine light is just a chepo no dial

I confirmed the hub has slipped. Its not actually a balancer on this engine though, is it? It doesn't look like there is enough material to be a balancer. If this is true ill just make a new mark

Its good to know they just idle rough Its been bothering me.

I took it out to test and dial in... but a bigger problem has arose well it's likely to have been what caused the poor performance in the fist place, My manifold is leaking water at the gasket. The plugs are to new to tell if its getting in the intake, but there is carbon on all the cylinders so MAYBE its not in the engine.

Thanks for the help guys!

thumpar · Jul 19, 2013

Re: Timing marks wrong ??

The 3.0 does have a balancer. The 2.5 just has a pulley.

DXN · Jul 19, 2013

Re: Timing marks wrong ??

well I guess its just smaller than Im used to.

Not good to run it if the balancer isn't clocked right. This sucks

frantically relaxing · Jul 19, 2013

Re: Timing marks wrong ??

....

Chef Shawn · Jul 20, 2013

Re: Timing marks wrong ??

bonzoscott said:
Yes it will start and idle better when advanced but run poor under load. 3.0s inherently run rough at idle, cold especially. If everything is in order, you may just want to let it warm up a bit. Don't know the history and if you just got the boat, that's the way it is.

Rough at start-up maybe, but if tuned and timed correctly they will sound like a kitten purring. It takes awhile to dial it in.

Do all the initial tests on the muffs, then take the timing light with you to the water. Warm it up and re-adjust as needed. Everything changes once the prop actually has to push water. Take your time, every engine has a sweet spot.

fishrdan · Jul 20, 2013

Re: Timing marks wrong ??

DXN said:
I did find TDC and It seams like the marks are actually wrong if I put the mark on 0 deg the piston is on its way back down < I got interrupted I'm going to double check this in a little

Yup, sounds like the balancer has slipped.

While at TDC on #1 cylinder, slip a wood dowel (I used an old fiberglass tent pole) into the spark plug hole and rock the engine back-forth to see where TDC is actually at. Pull all plugs, tighten alternator belt really tight and use a wrench on the alternator to rock the engine. Use a small bungee to hold the dowel up, so it's resting on the top of the piston and you don't have to hold the dowel, makes it easier to see when the engine rolls over TDC. Once you find TDC, mark it, file a small spot in the balancer, paint it white and time the engine. That will at least get the engine running right

You'll need to replace the balancer as it's only going to get worse, could throw off how the belt runs, might even slip enough to start hitting the timing cover.....

DXN · Jul 20, 2013

Re: Timing marks wrong ??

Y'all think is safe to run with like this? If the balancer has slipped, the rotating assembly is now out of balance. This doesn't seem ok to me. Its there to dampen vibrations and if the weight is in the wrong place it will do exactly the opposite.

DXN · Jul 20, 2013

Re: Timing marks wrong ??

Well I've been looking at pictures, and judging by the size of the dampener. The 3.0 is internally balanced, and the harmonic dampener dose not act as a counter balance.

Is this right?

RogersJetboat454 · Jul 22, 2013

Re: Timing marks wrong ??

Wasn't too many externally balanced GM engines. 4 bangers are usually internally balanced anyway (not much of a challenge to balance the rotating assembly with bob weights on the crank). You could probably get away with running it until you get a new balancer, but it is best to get a new one. I have seen instances where eventually the outer ring gives up, and falls off. Plus your timing is only a guess with out an accurate balancer.

Timing marks wrong ??

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