Old Merc Question

[Roger Stouff]

The plug wires in my 1958 Mark 55 need to be replaced.

The ones in it are clearly automotive. The distributor ends look like they've been trimmed (in diameter) with a razor knife to fit.

Should this vintage engine have wires with metal ends at the distributor, or can I use auto plugs and cut to length? Will they fit the distributor hole?

Thanks from the Rez,
R

[Paul Scheuer]

There must be an antique motor BB somewhere, Roger, where the experts in that field hang out. I thought you'd have a dozen answers by now. I'm certainly no pro about motors, but the good news is that the old ones are simpler, and tend to tell you right away when something isn't right. It's not like there's some computer in there making decisions based on some CO ratio. Try it and see, before you get too heavily invested in the correct "factory replacement part". You'll know right away if it ain't sparking right.

There seems to be some reluctance for anyone to come forward on this board when someone suggests a crude and rude solution. From my experience pushing the old '84 pick up it's third 100,000 miles, sometimes you need to postpone the "right" solution, and get somthing in there that has a chance of working for a little while, and keep an eye on it.

[Memphis Mike]

Roger, When it comes to plug wires,
you have to take into consideration
the lenght of wire and condition of the
wire. The longer the wire, the more
resistance to electrical current flow.
The older the wire, the more resistance
to electrical current flow. If you have
a bad connection at the plug or
distributor, that also can create
resistance and cause bad performance.

Automotive plug wires shortentened to the
correct lenght should be fine as long
as you take into consideration the above.
if you cut them to the correct lenght,
do it at one end or the other and don't
create a break in the wire in the middle.

[Roger Stouff]

Thanks for all your replies.

Mike...copper or that silicon graphite stuff?

[Memphis Mike]

IMO, copper would be the best conductor.

[Wayne Jeffers]

The downside to copper plug wires: the engine will create radio frequency interference if copper wires are used. It will be weak RFI, so it will only cause problems for radios in or near the boat, but you could still annoy your neighbors without realizing it.

That's why copper plug wires are almost never used in cars. The silicon wires used to be called "supression" because it supressed the RFI. I don't think I've seen them labeled this way in decades. You'd probably have to make a special point of requesting copper wire.

I'd probably go with the silicon. They are long-lived, probably cheaper, and you won't have to worry about the radios around your boat popping and cracking every time you go past.

Wayne

[On Vacation]

Over here in never never land of modern weapontry, auto parts stores have single plug wires. We match them up and get about two years out of them before the engine hickups.

[Roger Stouff]

Thanks again for all your replies. My mechanic INSISTED on metal wires, shielded, so that's what we went with. He was adamant about not using anything else on these older engines. I don't know what the radio interference level will be, but most the times I'm off in remote areas, anyway.

As it happens, I put it over this afternoon after I got back from the shop, and noticed a little better acceleration and performance. I think that's just because the old wires were so bad, not the difference between the types.

The plug wires merely poke into the distributor, no metal ends. You just strip back about a quarter inch of core and it seets itself nicely.

Now that that's done, I have to get out tomorrow and fiddle with the carbs to try to get that slight idle miss out of it. Onward!