Stearman starting woes

[bob turner]

Lately the darn thing has become recalcitrant. Once in a while we get no sign of life at all.

Details - Continental W-670 - Bendix SF-7 mags overhauled within the last three months. Carburetor overhauled same time frame. New fine wire plugs. Good Concorde RG35A XC. Really good primer system.

only thing not checked is the mag switch and the spark plug wires, which we will do manana.

Can those old mag switches go intermittent? Do we need "shower of sparks"? Is there a way to flood these things and not start even with wide open throttle?

Help?

 

[cubdriver2]

Good fuel flow? Check for spark, if none unhook the mag wires at the mag would be a good starting point

Glenn

 

[wireweinie]

When you say 'no sign of life' do you mean it cranks, but does not fire off, or do you mean it does not crank at all?

Web

 

[bob turner]

Cranks really good. A sign of life is a puff of smoke or a kickback. On kickback we go to full throttle and it starts right away.

 

[wireweinie]

Do like cubdriver said. Pull the P-leads from the mags. If it starts good, problem is in pleads or switch. If it still does not start well, it's probably fuel. Shouldn't be same issue with both mags.

Web

 

[silflexer]

We had a problem recently with ours where the mags would not shut off. The control rod between front and rear seats that connect the actual mag switch on the firewall and the cockpits had worn one of the joints. This wear created enough slop that the mag switch would not turn the mags all the way off. It is plausible that your mag switch is not actually being positioned to on with the connecting linkage.


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[flagold]

Lately the darn thing has become recalcitrant. Once in a while we get no sign of life at all.

Details - Continental W-670 - Bendix SF-7 mags overhauled within the last three months. Carburetor overhauled same time frame. New fine wire plugs. Good Concorde RG35A XC. Really good primer system.

only thing not checked is the mag switch and the spark plug wires, which we will do manana.

Can those old mag switches go intermittent? Do we need "shower of sparks"? Is there a way to flood these things and not start even with wide open throttle?

Help?

The key others have keyed in on is "no sign of life." Trace that down (and probably is a grounding switch) before flying because that kind of thing can let you down fast. Once you get that handled you won't need a "shower of sparks" mag unless you simply want that option. It started before fine and will again. Yes, you can certainly flood anything if determined - if it ever catches fire keep cranking and suck the fire back into the engine.

 

[Farmer Hank]

I had this exact problem with my R-975 this spring. Normal start procedure, absolutely no go. I contacted a friend (Forrest Lovley) and he said the points can “fog over”. I stuck a little strip of 400 sandpaper between the points, rotated the prop to close the points, and pulled the sandpaper out. Did this to both mags. Voila! Perfect start!

 

[Farmer Hank]

Double over the sandpaper strip so both points get cleaned at the same time.

 

[AKjurnees]

Check E-gap and timing. I bet your E-gap is off, when’s the last time anyone worth their salt look at the points?

 

[bob turner]

Brand new overhauled mags - maybe 12 hours. Ya think the points fogged over already? Maybe they replaced the platinum with something cheaper?

Single mag switch in rear. I dislike the WWII mag switches, but they are considered traditional.

 

[AKjurnees]

If you have the maintenance manual, check the timing and then read it real good on setting the points. Sometimes people forget that they need to oil the mag every so often, the cam blocks could over heat and wear down without lube causing the points to not open. Seen it a few times on hard starting W670’s.

 

[wireweinie]

But did you do the mag work yourself? Did you observe the work? If not, then you don't know the extent of the actual work. Example; a bunch of slick mags were shipped with no lube on the points follower. The result was slow failure at 50 to 100 hours.

Trouble shoot and let us know what you find.

Web

 

[Wingwrench]

Check the mag timing, 29 and 31 BTC. The timer will tell you if the points are breaking and also the operation of the mag switch. If the timing is way off, check the point gap. No need for a booster coil on a 670 with a starter, it's a bandaid for other problems. Check for moisture in the mags. Who did the mags? Very few shops today have the parts or know how to do those mags. Fine wires in a 670? REM37BY work the best if you have 5/8" leads, especially if it's an oil burner.

 

[Farmer Hank]

Twell us what worked for you.

 

[bob turner]

Started it twice today. It still doesn't start like a good 670. I don't know if the mechanics checked the points - I asked them to. It got new brakes and tires, tho . . .
23 landings today. Cubs just sat in the hangar looking sad.

 

[AKjurnees]

Next time, as soon as you start cranking, give it 2-3 QUICK full strokes on the throttle. Like fast strokes. Then retract throttle to Cracked. All while cranking. I’m Just curious to see if that works. It did for me on my old ride hopper.

 

[bob turner]

Yes, that is the way I start most carbureted engines. My experience is these things should start on about the fourth blade using your technique. My Cubs all start on the first blade with impulses.
Yes, we are getting it started almost every time, but it sure takes way too much cranking. I am leaning toward carbon tracks inside that ancient mag switch.