Johnson opposed twin questions

[adam1961]

Hi,
I am working on a Canadian OK10. This motor is common to most of the Ok series and shares parts and specs with the OK75.
It looks like this engine has seen some hours. It has a few issues.
The upper keyway on the crank is worn. Is this worth welding and re-cutting, or can the motor be put back into service with just the lower key in place?

One rod journal is scored up. It is about .005 undersized right now. The rods also have some brass tabs between the rod and cap. I have never seen these, but can’t imagine why someone would want to increase the size of the ride bore in that dimension. Are these original?

Lastly, can anyone tell me how the drain in the bottom of the crankcase works? It looks like it might be plugged.
See the photos below.
Adam

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[lyks2tinkr]

Good morning.
As long as the metal is not raised around the out side of the top keyway , a tight key in the bottom and a key in the top albeit loose should be OK IMHO. The key is just for proper flywheel alignment . It’s the taper fit and the proper flywheel nut torque that hold it all together.
You can check the taper fit and lap it in if needed.

I would guess the rod shimming is not original. I’ve run into the same thing on other make motors.
I’ve polished out light to medium scoring on rod journals in the past and closed up the rod and reamed them to fit. You could also try and find a donor motor with a decent powerhead.

Not sure on the crankcase "drain". If you spray some carb cleaner in you may be able to see where it comes out. It might be it recirculates back into the crankcade.
Hope this helps some.

[Mumbles]

The shims are an original Johnson item. The trick on reassembling them is to keep them square to the crank so they aren’t dragging. For the wrist pin retainers, I just used some cut down stainless cotter pins.

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[bill-loveland]

Do you make your own gaskets mumbles, or do you have a supply?

[adam1961]

Interesting that Johson used the shims. What is the reason for this design? I have not seen them before.

I was planing to remove some material from the rods and caps an then ream them to fit the undersized crank pin.

Mumbles,
Those parts cleaned up nice. What model OK is that? Mine is an early 10 and has a crank with female splines at the bottom.

[bkrsdoz]

Cushman motor scooter engines used to use these type shims. They were very thin. When the rod clearance became over the limit, and started to knock, you would peel away a layer or two from each side until it was tight enough to return for service.
Bob

[Mumbles]

Bill: No readily available gaskets here. I had to cut them. The thickness of the bottom one controls the amount of end play on the crank.

Adam: I believe the photos are of my OK-15 but I also have a 20, 75, and 60 in various states of repair. You say your crank has female splines on it? Interesting. I’ll bet the shims can be replaced with thinner ones as the rod wears and then the rod can be resized to fit the crank.

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Attachments:

Johnson OK 15 60 75 10 15 Motors.pdf

[bill-loveland]

That’s one shiny Eskimo motor!

[wbeaton]

quote Mumbles:

Adam: I believe the photos are of my OK-15 but I also have a 20, 75, and 60 in various states of repair. You say your crank has female splines on it? Interesting. I’ll bet the shims can be replaced with thinner ones as the rod wears and then the rod can be resized to fit the crank.

Beautiful motor, Mumbles. I think its an OK-20 since it has removable heads.

Wayne
Upper Canada Chapter

uccaomci.com

[adam1961]

I seem to have a mystery on my hands. The parts list that mumbles posted states that the OK 55, 60 and 75 up to 1939 used the internal spline crank and that all other OK models used the external spline crank. My motor has the internal splines, but has a 1940, OK 10 rope plate. It was built in the first batch of OK10s that came out of the plant. I wonder if they were just using up parts?

My crank seem s to be bent. When spun in a lathe, I have a noticeable wobble on the other end.

Is the crankcase head supposed to be a very tight fit in the case? I have a hard time getting mine in and out even after cleaning it up.

Might be time for another parts motors LOL

[Author]

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