Mariner 60 - Spark shooting from coil.

[Richardnpat]

Hello all:

I have a 1988 Mariner 60. I had the power head rebuilt (twice now), black box replaced, carb rebuilt, etc...

It has now blown the top cylinder twice in the same way - pitting on top of the piston. The shop I have been taking it to is aparently unable to diagnose and is only taking responsibility for rebuilding the power-head because I apparently didn't make it clear that I wanted a boat back that runs for more than a few hours without blowing up.

The second time I got the boat back after it had been sitting in the shop for 4 months, I put it in the water and it was idleing rough again and I could hear what appeared to be the snapping noise of a spark. I pulled the cowling and sure enough, there was an occasional spark jumping from the boot of the #2 coil to the ground for the three coils. I called the shop that did the rebuild and they said it was a cracked coil. Being that they had already replaced the #1 coil as part of the second rebuild and "diagnosis" I had them just go ahead and send me the other two. I replaced both of the other coils and now they are all new. Put it in the water - same problem.

So the coils are all new, plug wires are new and test out fine with practically no resistance, plugs are clean, the grounds seem to be ok but haven't messed with them to be sure. Does anyone have any idea why this might be happening?

I've been 6 months without my boat now. I would really like to get out.

Thanks for any help.

 

[j_martin]

Re: Mariner 60 - Spark shooting from coil.

I would hazard a guess that it is hitting way early, or multiple times on #2. Could be a cracked magnet in the flywheel. Could be extreme lean on that cylinder.

What you need to do is put a timing light on each cylinder and verify that it is firing at the right time under all conditions. This would involve calculating where TDC, and the firing timing is on the flywheel and marking it for each cylinder. It's a simple math and measuring task.

If the cylinder routinely pre-ignites, the extreme pressure would raise the secondary voltage to the limit, encouraging it to find another way to ground.

When a motor melts down, it is imperative to find out why, before you put a rebuild into operation. I would think that would be part of the shop service.

hope it helps
John