Ignition help

[77GlastronMT]

Ok, getting ready for boating season. Went to start it up and no fire. I still have the points and condenser, haven't worked with these for about 20 years. I'm pretty sure it's time for a new set. One of my questions is can I use automotive parts (its a Mercruiser 165, same as a Chevy 250) or should I go with marine? What's the difference? Another thing I noticed is I have 12V on the + side of the coil, I thought it was supposed to be around 9V or is that bypassed during starting? Thanks!

 

[UncleWillie]

I don't see an issue with Automotive Points. Others may have a different opinion. But why not just use OEM parts?

If your coil is matched with a Ballast Resistor/Wire, You may see ~6-9 volts if the engine stopped with the points closed, or 12 volts if it stopped points open.
If the coil is a direct power type, 12 volts will be the norm.

 

[achris]

Uncle Bill ^^^ has the right advice... The important thing is to know if the points are open or closed when you do the voltage reading.

But either way it does point to a points problem. I would first try the old-timers trick (yes, I'm an old-timer now :facepalm). Just get a piece of newspaper (that other old thing before the internet) and run it through between the contact surfaces... That should be enough to remove any tarnishing... Or, try this other OT trick. Points open. A wire connected to the coil negative. With the key ON, tap the other end of the wire on a good earth of the engine block... You should get sparks from the coil.... If you do, replace the points....

Chris.......

 

[77GlastronMT]

Thanks for the replies. Uncle Bill, the reason I'm thinking of the automotive parts is I can go pick them up right away, I'd have to order the marine stuff and I don't want to wait. I noticed there was a lot of wear on the block that rides on the distributor shaft and I can't find my remote starter cable so I can't watch the points actually open and close so I have to go pick up one of those (I've never been a fan of the screwdriver across the starter). achris, I'll try your suggestion with the coil. Thanks again.

 

[Silvertip]

There is no issue using auto-based points in place of the Mercruiser parts -- that is provided the distributor on your engine actually has a distributor that uses the same points. Don't waltz into a parts store and buy a set of points for a 250 Chevy Six without verifying the distributor can actually accept those points. It's a physical thing, not an electrical issue. All bullets go bang but not all bullets fit your gun.

 

[stonyloam]

If the cam follower on the points is worn, then the points may not be opening correctly, time for a new set of points. Points is points, your local auto parts store should be able to cross reference your engine for the correct parts.

 

[Bt Doctur]

Blue-Streak DR-2240X for the points

 

[Villain lll]

Uncle Bill ^^^ has the right advice... The important thing is to know if the points are open or closed when you do the voltage reading.

Chris.......

Correct me if I'm wrong but wouldn't he see 12v on the positive side of the coil regardless if the points are open or closed. Doesn't that side get voltage directly from the battery once the key is in the on position?

 

[UncleWillie]

Correct me if I'm wrong but wouldn't he see 12v on the positive side of the coil regardless if the points are open or closed. Doesn't that side get voltage directly from the battery once the key is in the on position?

Some coils will be damaged if 12 volts were to be directly applied to them.
There will be a `Ballast' device, either a resistive length of wire, or an actual resistor in series with the coil.
When the points are closed the current through the resistor will drop a few volts and only 6-9 volts will appear at the coil.
Lowered voltage and current equals lowered Power. No Damage
When the points are open, there will be no current, and so no voltage drop, and the full 12 volts will be present.
12 volts and zero current equals zero power. No Damage.
Other coils are designed to withstand the full 12 volts without and Ballast devices.
Very generally speaking, older ignitions used the Ballast method, Newer ignitions do not require it.

 

[77GlastronMT]

Thanks all for your responses, it really helps out those of us without lots of knowledge/skills. I used to deal with point type ignitions years ago, still have the dwell meter and timing light but can't find my remote starter and will definitely have to read the directions on setting dwell. This is an old boat, '77, I've never had it in the water but hopefully this year. Thanks again.

 

[achris]

Correct me if I'm wrong but wouldn't he see 12v on the positive side of the coil regardless if the points are open or closed. Doesn't that side get voltage directly from the battery once the key is in the on position?

Voltage at the coil + must first travel though the resistance wire, which has a resistance slightly less than that of the coil. Using the rules of a voltage divider will see slightly more than half the voltage at the junction of the 2 resistances (coil and wire), provided the points are closed to 'complete the circuit'. If the points are open, everywhere along the route from battery to the connection on the points will be 12volts, as the circuit is not complete, it's open.

Chris........