TOPIC: 1961 evinrude 40 h.p lark3 problems.

My lark 3 is running poorly. It won't rev out. I checked the points and they appear to be set at .020. The motor want's to sputter an missfire. When I grab a hold of the flywheel there appears to be a little bit of play from side to side. There is a little bit of metal dust around the stator plate. Looking for advice in how to diagnose my problems with this power head. Thanks for any advice!

dchambers490,

You will find your answers in the famous (among old outboard folk) book: CHEAP OUTBOARDS: THE BEGINNER'S GUIDE TO MAKING AN OLD MOTOR RUN FOREVER, by Max Wawrzyniak.

Copies are often available in public libraries OR new/used on ebay.com/Amazon.com & other places, too.
(I paid 5 bucks for mine, used at a local Goodwill Store.)

With that one book & a handful of ordinary wrenches/pliers/hammer/lubricants/etc. AND about 100 bucks worth of parts by SIERRA from your local NAPA AUTO PARTS store, you can fix most anything on an OMC BigTwin yourself. = ImVho, the OMC BigTwins of the 1955-70 era are the simple to renovate/repair, MOST over-engineered, toughest, longest lasting OBs ever made.
(MY "loony cousin" once borrowed my 16-foot tin trotline boat with a 1958 Johnson 35HP, ran it all day on Lake of the Pines & when he brought it back that night said, "That old motor sure runs HOT. Maybe you oughta have a look at it." = He had run 5 gallons of gas, WITHOUT ANY OIL, in the tank!====> 20+ years later, it still runs fine, btw. - NO other 2-cycle OB would have survived that ABUSE.)

ImVho, ALL old OMC OB motors need the following to run forever: POINTS, SPARKPLUGS, WIRES, COILS, CONDENSORS, CARB REBUILD KIT & WATER-PUMP IMPELLER.

just my OPINIONS, satx

It sounds like you may have excessive crankshaft play; there should be a little end play (up and down), but very little when the crankshaft is pulled side-to-side.

I would remove the flywheel and check the side-play by pulling the crank side-to-side while watching the gap of an open set of points. If can see that gap change, not good! Lots of wear there, and the dust you see is likely flywheel or mag plate rubbing.

Another point of wear on these is the mag plate bushing, which wears egg-shaped and then the mag plate wobbles; coils hit the flywheel; points bounce. With the flywheel off, you can wiggle the mag plate and see if you feel a lot of slop; the points gaps will move about if so.

Failing teardown and crankshaft/bearing replacement, about the only band-aid you can do right now is to open the points gap up to about .022" and then when the "wobble" hits, the point may still have enough gap for proper sparking.

Note it's easy to mistake end play for side-to-side, so make doubly sure that's what you're seeing. Maybe it's just a sloppy mag plate.

HTH..........ed

Thanks for the info! Would doing a compression check give me any insight into bearing wear? How much compression should this motor have?

dchambers490 wrote:

Would doing a compression check give me any insight into bearing wear?

How much compression should this motor have?

1) Nope! The grab it and shake to-and-fro test is gonna tell you that! Plus how much bearing noise the engine has.

2) These are not high-compression engines, the main thing is, that the readings between cylinders are even. Readings are gonna vary anyway, between different compression gauges, cranking speed, atmospheric conditions, etc.

I'd imagine an old Big Twin would pump-up somewhere around 100 psi but would be pretty surprised to see one with way-higher-than-that readings.

If you had readings that were, say, within 5 psi of each other, I'd be pretty happy.

10-20 psi variance, I'd start to worry.

In that case, it might merit a Seafoam decarbonation treatment, and if that didn't help, pulling the head for a look-see at the cylinders.

HTH..........ed

Thanks much for the advice! I need to figure out how to pull the fywheel. sounds like the right way is with the omc special tool. May need to go to the omc shop to have that done. Thanks for your responces. I'm crossing my fingers it's a mag plate problem!

You can also use an automotive harmonic balancer puller with grade-8 1/4-20 puller bolts.

Note that you MUST use grade-8 or better bolts, or you WILL break a bolt or strip out the holes in the flywheel.

When you reinstall the flywheel, the crankshaft taper must be clean, free of burrs, and dry (use no oil or grease on the taper).

Torque to specs, I'm thinking on the old 40's it was something like 105 ft-lbs but don't quote me on that!

Big Caution on this engine, flywheel torque MUST be to spec or the flywheel key WILL shear and damage the flywheel.

HTH & G'luck with the repairs.........ed

You will find your answers in the famous (among old outboard folk) book: CHEAP OUTBOARDS: THE BEGINNER'S GUIDE TO MAKING AN OLD MOTOR RUN FOREVER, by Max Wawrzyniak.

I've put together a complete index of the on-line articles that went into the book (plus some that didn't) at:
www.omc-boats.org/maxw.html

Another great resource for working on old engines is the Antique Outboard Motor Club "Ask a member" forum:
aomci.org/forum/index.php