Johnson Starter Nut

[gogittum]

Got a dandy for ya. My '93 Johnson 25 hp was balky on the river a while back and I ran the starter hard. Suddenly the bendix let out a screech and stopped working. The nut on the top of the starter shaft had spun off and flew into the river, along with the spring and cap. Not s'posed to do that.

I hate to spend $10 for a nut, so went to Ace Hardware and their aisle of nuts and bolts. Nada. All Johnsons I've seen are SAE. The "only" nut I can find that's even close is a 10mm x 1.25 pitch and it jams on the threads after 1/2 turn. Close, but no cigar. 3/8 of any pitch is too small and 7/16 is too big.

Metric on an SAE motor ?? I don't really care, but I need to find something that will work. I do have a tap & die set to clean the threads - if'n I can figure out which thread it's s'posed to be.

P.S. I've never even heard of this happening before. Why me, on top of all the other b.s. with these 2 motors ?? How can I prevent it from happening again ??

 

[DaleH]

1) My '93 Johnson 25 hp was balky on the river a while back and I ran the starter hard ...

2) How can I prevent it from happening again??

1) New correct plugs and properly gapped, tune it up, sync & link

2) Red Loktite on whatever nut you can find (no info in my OEM service manuals for the thread/pitch) or I'd drill through it, countersink the hole and would peen the ends of a steel pin or would use one of those 'rolled compression' pins to keep the nut on there. Definitely a Rube Goldberg approach, but hey ...

Hopefully Pappy chimes in with the best advice and answer, 'cuz that's all he knows (or just PM him)!

 

[gogittum]

I was spooky with the idea of a metric nut on an SAE motor, so was very picky and careful on selection. It turned out to be a 10mm x 1.25 pitch after all, but the threads on the starter shaft were mildly buggered my my previous customization efforts. My tap & die set has 1.00 & 1.50 dies and I hate to buy a new die for one job....mainly because - where do I put it ?? Won't fit in the case.`

Going on past Koostum Engineering I've done, I found a grade 8, 10 x 1.25 nut (80¢) and used the 1/16" x 1¼" cutoff wheel in my Dremel tool to cut 4 slots in the nut to act as a sort of threading die to chase the threads on the shaft.

It worked. Took a bit of doing - that shaft isn't "hardened," as in grade 8 or similar, but it Is heat treated and it's harder than mild steel. (with extreme care, patience and cutting oil, a high speed drill bit "will" drill thru it, but it's a near thing) The slotted nut did eventually do the job, with a bit of patience and perseverance. Problem solved.

Now, the starter doesn't want to throw the bendix up into the flywheel against the spring, but that's another problem....one of many, so far.

 

[LDUBS]

Ingenuity = the quality of being clever and inventive! I love these kinds of solutions. Well done!

 

[gogittum]

Thanks. I owned and operated a restaurant service business for years and took care of "everything," but specializing in refrigeration and a/c. You learn to be creative and think outside the box when you have a busy high end restaurant with a problem on Friday night. They don't want to hear anything but "we got it, you're in business again."

Some of the fanciest restaurants in Palm Springs, CA were regular customers.

 

[KMixson]

One thing about thread fit that not a lot people know about is the class of thread fit. It determines how tight or loose the mating parts are. Some fit classes are very loose while others are very tight for the same thread. There are class 1A, 2A, 3A and 1B, 2B, and 3B. 2A and 2B are the most common types that people use in normal situations. Another thing to watch for are lock-nuts that are punched(crimped) that may make them very tight on the bolt or external threaded portion of the bolt. They may be tricky to identify by just glancing at them. Nyloc nuts are easier to identify as a lock-nut with the insert installed on the top of the nut. Some castle nuts are also used as a type of lock-nut if their tips are bent in slightly.

 

[gogittum]

Yep, it's official.....now the starter motor doesn't throw the bendix up into the flywheel when I hit start. Once in a while it will, but that's not good enuf. Most of the time, hit the switch and the starter just spins and that won't get me home. I expected a problem, so used the shorter and lighter of the 2 springs I had and used the thin grade 8 chaser nut turned down just far enuf to have full thread contact. I did secure it with red loctite.

It still has about 3/16" of thread left, so the spring is under the least possible tension I could do. Voltage was 12.8, which should be plenty - it used to start fine at 12.4 volts, but I put the charger on it anyway....and there it sits for the night. Frustration. There was never any problem with it previously.

 

[gogittum]

One thing about thread fit that not a lot people know about is the class of thread fit. It determines how tight or loose the mating parts are. Some fit classes are very loose while others are very tight for the same thread. There are class 1A, 2A, 3A and 1B, 2B, and 3B. 2A and 2B are the most common types that people use in normal situations. Another thing to watch for are lock-nuts that are punched(crimped) that may make them very tight on the bolt or external threaded portion of the bolt. They may be tricky to identify by just glancing at them. Nyloc nuts are easier to identify as a lock-nut with the insert installed on the top of the nut. Some castle nuts are also used as a type of lock-nut if their tips are bent in slightly.

`I've seen that in the field on a practical level, but always thought it was just tolerance variation between different mfg'ers. Interesting. Thanks.

 

[gogittum]

Found it....outside the box, again. This morning, voltage was at 14.3, so hit the switch and the starter just spun. Hmmm....??

Fussing with it a bit, found that if I pried the pinion/bendix up out of rest position just a bit, starter would engage normally, then on try 2 just spin again. Pulled the flywheel - very glad I built that puller setup - and pulled the bendix out of there and seemed like the very bottom of the spiral was chewed up a little bit. I have some tiny burrs for the Dremel flex drive, but a 10,000th" off the wrong spot could toast it. Hmmm....??

No plastic washers, and no others big enuf - need a hair over 5/8" - so I very carefully took a step drill to a smaller inside dia. washer and opened it up. Chewed it up a bit, so had to polish it all nice and smooth.

I installed my Koostum spacer and....wall-lah, we have normal function. It engages every time now. No washer/spacer showing on the parts diagram. Put the whole thing back together properly, permanently, installed the new Racor fuel filter/water separator and hit the start switch.

It went thru no more than 2 compressions - cold - started instantly and idled smoothly. Last time on the river, the lanyard kill switch went south, which caused me to row/paddle 2 miles home. The new, very compact switch will be here Thursday, so will be able to make a test run then. Illegal, the way it is now and would get me a ticket.

 

[gogittum]

In case someone else runs into this:

When the nut, spring and cap flew off the starter shaft, my warning was a loud screech from the starter when I hit it again. From what I saw, without the nut, the pinion went all the way up into the flywheel and was stopped from also flying away by the shoulder below the teeth. This was high enuf to let the spiral at the bottom un-mesh and the shaft spin under the pinion, causing the screech and galling the beginning of the...threads...?? Not sure what you'd call those segments of the spiral.

With the pinion seated all the way down it could hang up "just a bit" and that was enuf to hold it down. With the tight quarters and bad angles, cleaning up that galling without causing a worse problem would be an awful job. Putting my washer underneath lifted it just enuf to where it's already started up, but low enuf to clear the flywheel when not in use. I told several mechanics at a local Yamaha dealership about it yesterday and none had ever heard of such a thing. (yes, I know it's a Johnson motor) This motor has been like that....all along. One thing after another.