How to test coils on 1968 Evinrude 40HP?

[andreipou]

I am rebuilding 40HP 1968 Evinrude.

It looks like I am not getting sparks. I replaced plugs , points and condensors, tested vacume swithch , etc, but did not help.

I reassembled it again and took coils out.

Is there a way to check them without special equipment?


Thanks.

 

[kbait]

You need a load tester to properly check 'em.. They're normally good unless cracked/arcing to ground. Check the bottom of the coils carefully for a pin hole/burn mark from one/both coils. Also, check for continuity from plug wire boot to wire end that screws into coil.. many times the connector at the boot loses contact.. You may have a faulty or incorrectly wired key switch that leaves the kill circuit connected when you're spinning the motor over.

Top secret files has some great info: http://forums.iboats.com/forum/engi...oards/307224-top-secret-file-updated-8-1-2012

This link from that page is very in-depth about universal magnetos. I think they're talking about a 6hp, but same deal: http://forums.iboats.com/forum/engi...45086-1972-6hp-evinrude-has-no-spark?t=531940

Good luck!

 

[Robert Ellis]

I'm no expert but I've done a few of those exact motor.

Thinking of the coils. First, get an ohmmeter (or a multimeter) and remove the coil. Ok, in the coil, there are 2 windings: a primary and secondary.

The primary winding is pretty much always good but check it any way as follows: set meter to 1000 - attach one lead to the green wire - the other lead to the ground wire - the meter should read off the scale.

The secondary winding is most often where a bad coil will show itself. Keep the meter at 1000 - attach one to the spark output of the coil (don't ground out on the sidewall - you want the centre pin) and attach the other lead to the ground wire of the coil - if the meter reads less than 7 ... it's junk. New ones tend to read just over 10. If you get a reading you're happy with .... attach the spark plug wire and put the lead to the spark connector in the rubber boot - if the reading is pretty much the same as you got from the coil output pin itself you know the spark plug lead and connector is good. If there's a big drop, well ... replace the wire and connector.

I guess I should have said that prior to all this - give the coil a good look when you remove it - if there are any cracks whatsoever ... time to replace it.

Let me know how you make out.

 

[F_R]

Clean those new points!!! All too often lately, they are coming through with an invisible layer of non-conductive film on the contacts. Then use that multimeter (lowest ohms scale) to check the resistance across them (wires disconnected) . Must be ZERO ohms when closed. Not an ohm or two, not more.

 

[andreipou]

Thank you all for replyes.


The coils look new, but this is the thing about this engine:
I got it 10 years ago in dissassembled state.
Only lower unit was assembled because the guy told me he rebuilt it years ago and just abandoned project.

I believe it because when I opened LU now it looks brand new inside.
All the parts looks like very low use on this engine (one of the reason I wanted to restore it).
Compression is also good.

I replaced all rubber parts in this engine , electrical parts, rebuilt the carb, but did not test coils because they looks new (yes, big mistake).

For the primary winding - it looks good.

For the secondary I have a question:
I do not have 1000 setting on my tester. I only have 200 and then 2000 , etc,...
On 200 and 2000 both coils show no connectivity.
It only start to show on 20K as 3.38 on both coils.
Do I need to get tester with 1000 or are they just bad?

I found them available for $23 each. So, shouild I just buy them?

 

[andreipou]

Thank you all for replyes.


The coils look new, but this is the thing about this engine:
I got it 10 years ago in dissassembled state.
Only lower unit was assembled because the guy told me he rebuilt it years ago and just abandoned project.

I believe it because when I opened LU now it looks brand new inside.
All the parts looks like very low use on this engine (one of the reason I wanted to restore it).
Compression is also good.

I replaced all rubber parts in this engine , electrical parts, rebuilt the carb, but did not test coils because they looked new (yes, big mistake).

For the primary winding - it looks good.

For the secondary I have a question:
I do not have 1000 setting on my tester. I only have 200 and then 2000 , etc,...
On 200 and 2000 both coils show no connectivity.
It only starts to show on 20K as 3.38 on both coils.
Do I need to get tester with 1000 or are they just bad?

I found them available for $23 each. So, shouild I just buy them?

 

[racerone]

Cheaper / quicker to buy new ones that to do iffy testing !!

 

[Robert Ellis]

Yep, 3.38 is way too low. Get new ones (wish I could get them in Canada for that price!) Just for snicks, do the same test on the new ones ... you will see.

 

[Robert Ellis]

racerone ....I'm quite puzzled by your 'iffy test' comment. What's iffy about an ohm test on the secondary windings of a coil? Cheaper/quicker to buy new ones? The test is free and takes 30 seconds? If you get a low reading you absolutely know the coil is bad. I agree that if you get a good reading, is still could be a faulty coil but ... that is highly unlikely.
Not everyone has the disposable $$$$ to spend on coils if the ones they have are working fine. Up here in Canada, by the time the dust settles (tax etc, they're $80 a pair plus the hassle of getting them).

 

[andreipou]

Just to check if I understood correctly :

3.38 at 20,000 setting would be too HIGH comparing to 7 at 1,000 setting, right?

 

[Robert Ellis]

I was tempted to say no right off the bat but after a quick web search, it turns out that may be correct. It seems some meters give you the actual value and others require you to multiply the value by the setting.
Mine (a cheapo) gives the actual value with varying levels of precision. I'm just looking at it now and I only have a coil I have rejected. So at 20k I get 6.47, at 200k I get 6.5, at 2000k I get 006 (no decimal point).
I suspect yours is like mine - you could easily test by trying the higher setting and see if you get same (but less precise reading) that you got at the 20k setting or if they are the same after doing the multiplication. Let me know.
One thing I can't explain is why didn't get a reading at the 200 setting - unless this is your diode tester ... does it have an arrow going to a bar symbol beside it? Sometimes the first setting is reserved for this.
Test the new coils when you get them. I always use the sierra ones simply because of availability (like I mentioned they give me slightly above 10). let me know - I'm curious ... particularly if you use a different brand.

 

[nwcove]

id bet that both those coils are fine...if they are indeed the new type. what are the chances of both being bad when the new ones rarely fail? ( i will answer my own question. slim to none.....and slim just left! lol)

 

[F_R]

Andrei, you are not getting a reading on the 200 range because the expected resistance (several k-ohms area) is out of the 0 to 200 ohms range. Same with the 0 to 2000 ohms range. Your reading of 3.38 on the 20,000 range scale is 3.38 k-ohms, or slightly over 3000 ohms. I say that is in the ballpark. Doesn't the meter window say K-ohms somewhere, like in the corner?

Anyhow, you can't look for a specific k-ohms spec because it varies with coil manufacturer. What really matters is the ratio of the number of turns between the primary and secondary. Beyond that, wire gauge and length come into play, and varies with the mfr. Yes, resistance is a valid test but only if you know the spec for the particular mfr's coil.

Hey, did you clean those points yet? Or are you too hung up on the coils to consider it?

 

[F_R]

If I may, let me further explain what I just said. I am going to use round numbers for simplicity. Suppose the electrical engineer at the coil factory decides he needs a 100:1 turns ratio between the primary and secondary. In theory (only), 50 volts generated in the primary would equal 50 X 100 or 5,000 volts available to make a spark across the plug. That is, for every one turn on the primary, he wants 100 turns on the secondary. Furthermore, for 100 turns on the primary, that means 10,000 turns on the secondary. To get that many turns on the secondary, he has to use some mighty fine wire. But lets just suppose he increases the primary by only 10 turns to 110. Now he needs 11,000 on the secondary, an increase of 1,000 turns.

But wait, there is more. To get that 1000 more turns in the same space, he has to use even finer wire. Finer wire means more ohms. Likewise the longer wire to make all those extra turns also means more ohms.

So as you can see, there is a very wide variance in the possible allowance for resistance values in the secondary.

 

[racerone]

Picked up a box with 30 new coils last year while doing a bit of trading !-----------------When I want to test coils I use a MERC-O-TRONIC tester which is the real thing for testing !!!

 

[F_R]

Well of course that is true. I regret selling mine.

 

[kbait]

I buy used/good coils from a salvage that load tests 'em before sending 'em. I always ohm test w/multimeter before installing, and one of 'em just stayed at zero.. I called the salvage, and they said, 'install it, it'll work fine - it's been load tested.' I installed, and it worked fine. What I got out of the deal is, with un-cracked coils, if it ohm tests good, it's good. If it ohm tests bad, it may be good.

Also, I've worked on MANY universal magneto motors, and I've seen exactly 2 bad coils that weren't cracked and arcing out to ground.. I bet your coils are just fine. As stated above, make sure your plug wires have continuity and aren't split anywhere, CLEAN point faces, and points set to .020", kill circuit not engaged, coils installed w/laminations even w/mounting boss, etc.

Good luck!

 

[kbait]

I buy used/good coils from a salvage that load tests 'em before sending 'em. I always ohm test w/multimeter before installing, and one of 'em just stayed at zero.. I called the salvage, and they said, 'install it, it'll work fine - it's been load tested.' I installed, and it worked fine. What I got out of the deal is, with un-cracked coils, if it ohm tests good, it's good. If it ohm tests bad, it may be good.

Also, I've worked on MANY universal magneto motors, and I've seen exactly 2 bad coils that weren't cracked and arcing out to ground.. I bet your coils are just fine. As stated above, make sure your plug wires have continuity and aren't split anywhere, CLEAN point faces, and points set to .020", kill circuit not engaged, coils installed w/laminations even w/mounting boss, etc.

Good luck!

 

[F_R]

A coil with an open secondary (ohm tests bad) can and often will fire the plug and run. It can also pass the merc-o-tronic test. That is the "gotcha". The spark is jumping the open gap in the very fine wire of the secondary winding, and continues on out to fire the plug. Trouble is as it jumps that gap, it burns away at the broken wire ends, making the gap wider. Eventually, it will fail.

 

[Robert Ellis]

Adrea: It seems I have given you some poor advice. Sorry about that! These guys clearly know a lot more than I do about coils so you should listen to them. It’s been an education for sure. Assuming you’ve already ordered the new coils and are going to use them, I think you should still test them and record the results. That way, if you decide to redo the ignition in 5 years or so, you can retest the coils and see if they’ve degraded.
Thinking of my situation … I’ve quite recently pulled the flywheels off about a dozen motors having this same ignition system – some of them Andres’s same year and hp. 2 so far have had what I think are the original coils … badly cracked with an amber colored plastic casing with green colored mounts. I’m sure everyone would agree that these needed to be replaced. All the others have what I think are replacement coils (green plasticy casing with bronzy colored mounts). On the side of the green casing is stamped “to replace OMC 582 370 Made in Germany. OK … when I test these, I get a range of readings … as far as memory serves from around 5 to 8. Presumably, they all have the same number of windings and gauge of wire although it’s impossible to say for sure. Is it reasonable to say that a coil that reads close to 8 is in better shape than one that reads close to 5? As mentioned, what I’ve been doing is replacing the ones that read under 7 and using those that read over. It sounds like its possible I’ve got a little bag of coils that I’ve replaced sitting on my shelf that are actually ok?