timing question

[mrcrsr]

use the dial indicator as stated, it is way more accurate to what is really going on w/ piston position in the bores. remember also that each trigger(3) does a pair of cylinders, so in theory if it was a trigger issue you would have a pair that was off by the same amount. maybe someone will chime in w/ what the pairs are, i'd have to go dig out a book

[ChrisCarsonMarine]

1/4,3/6,5/2

[patchesII]

wasn't my switchboxes. i swapped some more i had and it did the same thing. moving to the trigger next. also while swapping switchboxes i found a very loose ground screw(backed out about 3 turns) on the eletrical mounting plate just below and right of the starter solenoid that had 3 ground wires on it. one going to the stator, one going to the main engine harness, and one going to the ecu harness. no telling the gremlins that thing was throwing into the works

just tested the trigger with an ohmmeter according to the mercury high performance manual and it tested perfect.

one reason i'm going into some of these details is for people that are doing a search in the future. i find when i do searches alot of times the originator of the thread doesn't go back and update the thread to describe things that worked and didn't work. thanks everyone for the input

[scc82]

TDC has dwell. That's why Mercury gives the .464 to set the pointer.
By using a degree wheel you are setting the timing marks for each cylinder exactly 60* apart. Now when you check each cylinder you will see exactly where the timing falls. If the ignition fires at 60* of rotation each time you know the ignition is correct. It has no bearing where the piston is. If the timing fires erratically then you know it is an ignition problem. As Lightnbug said it is a way to differentiate between a mechanical and an electrical problem.


Some engines do fire a little off of exactly 60*, it may be #2 is slightly more advanced than the others so do your timing to #2, the most advanced cylinder, and you won't have a problem due to advanced timing on a cylinder.

A piston can be mechanically off due to machining errors, twisted crank, main bearing slop, etc.

V6 mercs use a .462 mark to set timing pointer, inline6 uses .464

[Jeff_G]

Boy is that splitting hairs!

[patchesII]

after putting my original switchboxes back on and tightening the loose ground screw i found i reshot the timing and found that the only two cylinders that are out now are 3 and 6 that are both at 30-31 while the rest are at 25. i talked to ronnie(way2slow on h20) today and he was very helpful. although the trigger tested perfect i think everything points at it. mrcrsr alluded to a pair being out of line with the rest and chris confirmed that 3 and 6 are one of these pairs. i'll update tomorrow. thanks again to everybody for the help

[Ranger976]

Eric, I'm interested to see what you find and how you have corrected 3/6....

[lpugh]

Eric I am a automotive driveability tech, meaning I do a lot of very technical diagnostic work with electronics. I do not know why but I have never heard of marine techs using DSO (Digital Storage Oscilloscope) A must have to diagnose this type of problem accurately. With a DSO you can watch the voltage at various points at the same time to determine where the problem lies. Not just any automotive tech can do this for you, but I am sure someone in your area can, How ever the cost to diagnose it may exceed the price of the parts to repair it. If you can beg, borrow or steal a 4 channel DSO I will be glad to walk you thru the process.
My Ph is 916 333 4105

[chad202]

It could be coils, wires, or a number of things. If it were my motor, which every cylinder timed the highest, I would set that one at 25*. Yes, the other would be lower but you'd be safe.

[lpugh]

Sorry chad coils and wires do not have any effect on timing, with the exception of power & ground issues for control units. I would not leave it that way, that would cause quite a bit of torque loss at lower RPM

[sschefer]

Someone asked what the share was: It's 1 and 4, 2 and 5, 3 and 6. I spent the last two day's with a unrelated problem but the tests were the same.

I think the advice of indexing the flywheel every 60 degrees and then finding the most advanced cylinder is a good approach at making the engine last the longest. In my simple mind it's the most economical and the most likely to succeed.

It seems the only other alternative would be to blue print the engine to total perfection and then hope you can find electronics that are equally perfect.

Personnally I'd time if off of #1 and make sure I had it jetted correctly so I didn't lean it out. I have a feeling that was what merc had in mind when the engine was designed.

[lpugh]

LightnBug I do not want to sound like a jerk, I am only trying to help others understand how it works. I do agree with earlier post that you need a decreed flywheel marks as well as piston tdc marks to determine mech. or electrical. If it checks out with DSO then it has to be a mechanical issue.
When the power transistor in the module has a closed circuit the current is flowing thru the primary coil windings to ground creating a magnetic field in the core of the coil. When the transistor is commanded open by the module the magnetic field collapses creating a high voltage low current into the secondary windings thus firing the spark plug. The voltage rise is extremely fast far less than one millisecond. You would have to have plug wire long enough to go around the world several times to retard the timing. Now the recovery time is more than ample. Resistance in the circuits will cause the available voltage to be lower, but the time will remain the same. Voltage level does not effect the speed of electron flow. This is a simple explanation there is more to it especially with cd type ignition.

[patchesII]

I just got around to changing the trigger and it fixed the timing issue. All the cylinders are right where they need to be. Thanks for all the help and insight on this issue

[gmacrae]

I learnt a lot from this, great thread. I'm going to use this info to check my engines 'mechanical' timing in the next few days - it never occurred to me that it can vary like has been mentioned.