Evinrude 35 HP Bigtwin weak spark resistance in coil?

[trigger-trainer]

Hello to all!<br />This is my first post to this forum, thanks in advance to all who reply!<br /><br /> I'm currently working on a 1957 Evinrude 35 HP Bigtwin. The engine has a solid 120 pounds of compression and ran long enough to give me a real good tease. I'm having trouble with weak spark on the motor.<br /> The points are sparkly clean,resistance in plug wires,condensers, and all connections are correct. Magnet edge gap on coils is set correct.<br />I took the coils off of the engine and visually inspected them. They have no cracks and an OHM reading of 6.52 at the 20K setting on my mulitmeter. Resistance through plug wires to coil and back to ground is still in the 6.XX. I read at www.fluke.com (mulitmeter manufacture) that resitance should be between 3k OHMS and 15 K OHMS, so it would be within spec according to them.<br />Two part question, Is this resistance reading two high for the coils(indicating that they are bad), and does anyone know the correct part number? There are two different coils in the engine, one has a number of 580-418, and the other is 582-370. <br />The ignition system is the same as on a 50's fastwin besides the flywheel being larger if that helps.<br />One more thing, the original keyway on crankshaft has been reset right next to damaged keyway. It appears to be a sucessful repair to me though. A spark plug gap would be appreciate to if anyone knows it!

 

[Paul Moir]

Re: Evinrude 35 HP Bigtwin weak spark resistance in coil?

Welcome to iboats, Trigger Trainer.<br /><br />Someone replaced your coils in the past. Those ones arn't terribly old. Are they the black plastic ones? 6K ohms seems right; it'll vary with tempurature some. As you probably read, these coils, especially the older ones, are known for cracking as their typical failure mode.<br /><br />Where the flywheel magnet is in relation to the coil when the points open is critical; the points must open just as the field reverses. Otherwise you will get what you're getting - a weak spark. The flywheel key needs to be in the correct place.<br /><br />I don't know what your crankshaft looks like, but there's a loctite product made for fixing this sort of thing. I think Miata owners use this fix a lot. Hang on and I'll look it up.<br /><br />PS - that ignition system, with the same parts, was used up into the 80's<br /><br />EDIT: Use Loctite 660 <br />Remember, it's the taper that's supposed to hold the flywheel, not the key. The flywheel nut must be tightned to 105 ft/lbs exactly. They flywheel taper must be perfectly free of oil and dirt. Since you have a damaged key, I would lap the flywheel to the taper if I where you.<br /><br />Gap is .030, on a set of Champion J4C (was J4J) plugs.

 

[trigger-trainer]

Re: Evinrude 35 HP Bigtwin weak spark resistance in coil?

One of the coils is red, and I think the other is green if I recall correctly. I figured they had been replaced too. I have a 1952 Mercury KG-4 where I repaired the cracked coils with RTV silicone sealant and havn't had any trouble out of it since.<br /><br /> I'm new to checking things with an ohm meter but am seeing how this can be a very valuable tool in the shop. I tested resitance through the plug wires on my 15 HP Fastwin and it can up with a reading of 4.53, and this engine has very good spark. I really appreciate the "ok" on the spec of 6.5x for the 35 HP engine I'm working on.<br /><br />The keyway on crankshaft is gobbled up pretty bad. It's about two keyways wide, with the original keyway being partially filled in with a poor weld. The flywheel's keyway is a little widened, but I think it will still be usable. What kind of tolerance would you guess I have when attempting to re-set key to original postion? <br />I marked the magnets postion on the flywheel, and noticed that they were close to being on the oposite side of the set of points that were opening on a given rotation and wasn't for sure if it would affect it. I was just guessing though, and guessed wrong. Thanks for the input. Problems like this aren't covered in any of my books. I've got some JB Kwik out in the shed and I'll try to do something with it in the AM. It might be just as easy to get the welder and files out through. Either way it's going to be a permakeyway.(per ma key way)

 

[Paul Moir]

Re: Evinrude 35 HP Bigtwin weak spark resistance in coil?

Hmm, let me think about this.<br />I messed around with this ignition system a while ago. It seems to me that if the breaker opened more than about 10° out of ideal, then spark suffered pretty bad. If you look at where the magnets are when the points just open (initiating the field collapse and creating the spark), the smaller magnet is just passing over the center pole of the ignition coil. By the way, there's timing marks on the flywheel and two on the armature plate. The flywheel mark should be between the two lines on the armature plate when the points open.<br /><br />Anyway - if I were you, I'd remove the sparkplugs and flywheel key, and eyeball the flywheel down onto where the key used to be. Then tighten down the flywheel nut well (making sure the crank doesn't spin) and see if the spark doesn't improve. Then you'll know for sure it's the magnet position. If worse comes to worst, a new crankshaft shouldn't be hard to find; it seems to me that crank was used on a number of outboards for a number of years. Of course it would be a near complete teardown & reseal.<br /><br />As for coil resistance, the only pair I have handy read 5.5Kohms (the others don't read at all ). It seems to me I've seen higher. When water intrudes them, naturally the resistance drops. I remember this from my (unsuccessful) coil baking experience. That was before I learned iboats has em for ~$15 each.

 

[Paul Moir]

Re: Evinrude 35 HP Bigtwin weak spark resistance in coil?

I just ran a little experiment on one set up here. <br />If the magnets were retarded 1/2 keyway width, spark got weaker, but not terrible.<br />If the magnets were retarded by 1 full keyway width (ie, the keyway directly along side of where it should be), the spark got very weak.<br />If the magnets were retarded by 2 full keyways, the spark was about as good (seemed a little better perhaps) as when it was 1 full keyway away.<br />If the magnets were advanced by 1/2 keyway width, the spark got very weak.<br /><br />I was able to eyeball the keyway pretty good though, by marking its location on the top of the taper, beneath the threaded part.<br /><br />PS - RTV sealant is keeping the sparks inside the flyback coil of the monitor I'm looking at. And it's not a little one.

 

[trigger-trainer]

Re: Evinrude 35 HP Bigtwin weak spark resistance in coil?

Now you've got me really excited about the project I'll tear back into first thing in the morning and post asap.<br /> thanks<br /> tt

 

[trigger-trainer]

Re: Evinrude 35 HP Bigtwin weak spark resistance in coil?

Opened the old workhorse back up today. <br />It turns out the "rewelded key" was actually a sheared key. Got a good chuckle out of it. Looks like the repair is going to be much simplier than I previously thought. <br />I'm looking for a key now, I'll post again as soon as she's running. I can't begin to thank you enough for words of wisdom.

 

[Paul Moir]

Re: Evinrude 35 HP Bigtwin weak spark resistance in coil?

I've got one of those keys myself; good for advancing or retarding the timing. <br /><br />Remove the key bits, put a little lapping compound on the taper and spin the flywheel a few time. Take it off and make sure you've got a good, even seat. Then clean all surfaces very well. If there's any oil on the taper, it will cause the hub to spread (may crack) when you torque down the flywheel nut. Torquing the flywheel nut is a pain without a flywheel holder. Jamming the starter pinion has worked for me though. As has making a holder that uses a couple of the starter ring gear bolt holes.<br /><br />Get an key from a Johnny/Rude dealer. They have a marking on them which must face down when it's installed. Why is really beyond me - otherwise it looks like a normal woodruff key.<br /><br />Hope this helps!

 

[trigger-trainer]

Re: Evinrude 35 HP Bigtwin weak spark resistance in coil?

HI!!!!!!<br />I finally got the key in the mail, and installed. The old workhorse wound up starting/running like a dream!!! THANKS A BUNCH