1966 Lark electric shift slipping out of forward gear at medium revs?

[greggles77]

Hello, I am new here (and to boating) so please bear with me if I posted this in the wrong place.

I have a 1966 Lark 40 hp model 40672B with an electric shift that on our last trip suddenly slips out of gear at just below halfway revs. The result was a very slow trip back obviously at only a few knots. until this time it has ran great considering its age. although I have only had it a few months and it hasn't had a service :redface:

I am wondering if it could be simply a lack of gear oil? I noticed it was possibly leaving a bit more than its normal slick in the water that day. I have also read on similar posts but not the same motor it could be:

*Wiring corrosion (Green or blue) - but not sure where these wires are?

*A damaged clutch dog - no idea what this is, I have the exploded gearbox diagram here that I purchased and I can't see it - is that the clutch spring?

*some other type of spring in the gearbox?

*a spun prop? not really sure what this means but seems common with this sort of problem..

*A damaged gear - although it does find reverse okay and as mentioned travels at low speed, so I am not sure about this.

I know a little about car mechanics but zero about outboards, but I am trying to get some ground knowledge. Any help you could give me would be appreciated. Here is a picture of the old tacker below:

Thank you.

P.S. I also have a spare one of these motors for parts if it helps I can change what I need once I know what it is!

 

[merc20076]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

I have the same outboard except that mine was repainted black.

Do you use Type C oil?

I just hope that I won't have this kind of problems with my Lark.

 

[greggles77]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

I don't know I haven't topped up the gear oil; is the C-oil what I am supposed to use? Up until this happened it ran very well.

I hope somebody here can help answer my question..

 

[F_R]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

OK, let's use a bit of common sense trouble shooting here. greggles, you suggested several things, most of which are a possibility.

The oil: Wouldn't cause a sudden failure as you describe. But low or wrong or contaminated oil will cause problems over the long haul. So it is wise to check it as normal maintenance. Yes, it requires Type C. Evinrude now calls it "Premium blend Gearcase oil". Aftermarket suppliers such as iboats/Sierra still call it Type C.

There is no clutch dog. The springs wrap and grip the clutch hubs. They can slip if abused (back to the oil issue). Low voltage to the clutch coils can also cause slippage. That is why voltage checks at the blue and green wires are appropriate. Green wire is forward gear. Suspect a bad shift switch if low voltage. The wires come up from the lower unit at the rear of the midsection. There are rubber sleeves covering the connectors. Check voltages with the connectors exposed but still connected. DO NOT EVER allow the two wires to contact each other while running. That puts it in both fwd and rev at the same time and will bust something for sure.

The blue and green wires as they go down into the gearcase are becoming a problem with age. But let's not go there yet.

Spun prop??? Yes indeed. My bet is on that, given the symptoms. Make a mark on the prop nut cone, and another on the propeller itself, aligned with the first one. Run the motor till the slippage occurs, then stop and check the marks. If no longer aligned, the prop hub slipped. If they are still aligned, repeat the test run. There is a slim chance it stopped slipping at the same position. The cure is to either have the prop rehubbed, or simply replace it.

 

[greggles77]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

Wow, thank you for such a detailed answer, I appreciate your time.

Well I don't seem to have anything rubber in my hub, but being an old school prop I guess it was all metal, hub and propeller anyway. I have removed it and marked it accordingly, so will test under load. The hub has a number 11 stamped into it, so I have marked the precise spot it is lined up.

Now I will go and have a good look for these wires and hopefully be able to test them as advised.

Thank you again

 

[F_R]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

I'll guarantee that your prop has rubber in it. You just can't see it. It is a rubber donut ring between the bronze hub and the aluminum prop body. When I was doing outboard service work for a living, I had a propeller that I hacksawed in half to show people that there indeed is rubber in there. I have an old beat-up prop in my shop now that I think I'll cut open and take a picture of it.

 

[glassmaster68]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

spun prop,,,shear pin?if you spun your prop ,youll have to replace the shear pin,this model def has a shear pin ,,when you take off the black cap that has cotter key,the prop has a hole that goes through the prop shaft,this is where the shear pin is located there is a washer,call it a thrust washer, between the prop and pin,,,the prop pushes on the washer and the washer pushes on the shear pin,when the prop hits something,log, bottom,whatever,it pushes the washer in to cut the shear pin,thus saving your prop shaft ,,if you scraped the bottom with it ,it will take out the shear pin,,its a precaution to save the prop shaft from getting it,,,i have exactly the same setup,,,i dont think i have rubber inside of my prop either, i could be wrong fr,but i do have a rubber donut between prop and bearings

 

[tx1961whaler]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

There really is rubber between the center bronze hub and the aluminum body. See the small gap between the bronze and aluminum? The rubber is in there. That is the shock absorber for the drive system. The hard stainless steel drive pin (some call it a shear pin) does not absorb any shock. Newer props replaced the drive pin with splines on the prop shaft. Those still have the rubber in the prop to absorb shock.

 

[merc20076]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

I've checked the voltage at the wires while doing the water pump impeller job. I have on FWD and REV 11.5 volts. Is this enough or it can slip?

 

[greggles77]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

F R - If you could show a cut picture, that would be great; although I take your word for it. The wiring is in pretty bad shape so I am going to replace that anyway as a matter of precaution, and will also check the voltage.

 

[greggles77]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

spun prop,,,shear pin?if you spun your prop ,youll have to replace the shear pin,this model def has a shear pin ,,when you take off the black cap that has cotter key,the prop has a hole that goes through the prop shaft,this is where the shear pin is located there is a washer,call it a thrust washer, between the prop and pin,,,the prop pushes on the washer and the washer pushes on the shear pin,when the prop hits something,log, bottom,whatever,it pushes the washer in to cut the shear pin,thus saving your prop shaft ,,if you scraped the bottom with it ,it will take out the shear pin,,its a precaution to save the prop shaft from getting it,,,i have exactly the same setup,,,i dont think i have rubber inside of my prop either, i could be wrong fr,but i do have a rubber donut between prop and bearings

I checked under the shear pin, and there is no washer of any type - although there seems to be enough room for something to go in there. How big is the 'thrust washer' is? Thank you

 

[glassmaster68]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

ok,maybe you dont have that kind of setup,the prop goes on then the washer and then shear pin behind the washer then prop nut ,,,or you have a slot on the front of your prop the shear pin goes in?where the shear pin is in front then the prop goes into it where the slots are,,and the shear pin was ok?

 

[greggles77]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

Wiring okay - Voltage checks out.. I am ruling electrics out for now.

Yes the shear pin was okay, but what I have discovered is NO thrust washer.. I don't know if I have lost it out on the last run when things started going wrong, or a previous owner removed it / did not put it back in.

I guess the correct questions are:
(1) what would be the effect of having NO thrust washer? (apart from not shearing the pin)

Also,

(2) when a thrust washer does take out a shear pin, does it cut it out entirely?
(am thinking perhaps I have hit something now, lots of debris on water last run, could have caused damage)



thanks again, these forums are great and it is wonderful to see others with the same engine as myself.

 

[glassmaster68]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

if you have that kind of setup and the washer wasnt there,then the prop was pushing on the shear pin ,i guess,,,,,,,will the prop spin without the propshaft spinning?

 

[lindy46]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

If the drive pin is ok, replace the dang washer and check for a spun hub. Simple as that.

 

[tx1961whaler]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

Part number for the thrust washer is 304576

 

[wilde1j]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

Have you checked for a spun prop hub yet??? Very easy to do. The fix is take the prop to a prop shop to be rehubbed.

 

[F_R]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

OK, back to the common sense. The washer goes between the drive pin (it isn't a shear pin) and the propeller. It is not vitally important to be there, and in fact probably the majority have been lost by now. Prop thrust is toward the front of the motor--forward. That is AWAY from the washer!

I say again, the shaft with the drive pin turns the bronze hub. The rubber cushion is bonded to the brass hub. The whole assembly is pressed into the bladed porton of the propeller. When the bond between the rubber cushion and the bronze hub fails, the bronze slips in the rubber, which is similar to spinning your wheels on the ice.

There IS a rubber cushion in there, I'll guarantee there is. Unless your prop was made in some unknown remote jungle.

EDIT: While I am at it, I may as well explain the purpose of the thrust washer. The rubber and bronze hub assembly is designed to slip inside the bladed prop part in case of extreme overload conditions--such as if you get tangled up with a submerged tree limb. When that overload conditon exists, the prop wants to spin right off the hub assembly. The washer, against the drive pin, stops it from spinning off. After all, that slip-on plastic nut certainly isn't going to stop anything.

 

[glassmaster68]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

sorry i called it a shear pin,,,,my seloc[repair manual] refers to it as a shear pin,it does refer to it as drive pin in other places in the book,thats all i had to go by,yeah the push would be to the front ,i guess unless youre in reverse,,,,thanks for clearing that up fr,experience speaks for itself

 

[F_R]

Re: 1966 Lark electric shift slipping out of forward gear at medium revs?

I wasn't picking on you, just pointing out the difference between a shear pin and a drive pin. A shear pin is made of a soft material and is intended to break if an obstruction is hit. A drive pin is made of stainless steel and is not intended to break. The rubber cushion is there to absorb impacts. Yes, it is possible to break a drive pin if you severely, mortally whack something very hard.