Prop removal, first time.

[FishMagnet]

I hate to ask what is probably an easy beginner question, but I've had to many "Oh shoot!" times when removing things from motors etc... <br /><br />I'm getting ready to remove the prop off my Johnson Sea-Horse 40hp (rd-22) and was hoping someone could walk me through it to make sure I don't damage anything. Also, is a prop wrench required, or will a 1/16" socket (not positive on the size) work fine?<br /><br />Thank you,<br /><br />Matt

 

[Paul Moir]

Re: Prop removal, first time.

You hardly need anything but a pair of pliers normally. Actually, this is a real simple task on a Big Twin.<br /><br />1) Remove the black plastic 'cone' behind the prop by pulling out the cotter pin. It just pulls straight off.<br />2) Remove the drive pin that runs through the hub of the prop (which you just uncovered) through the prop shaft. If it's stuck, tap it out with a hammer and punch.<br />3) Observe or remove the thrust washer on the hub behind where the drive pin ran through. This is often found missing.<br />4) Pull the prop straight off. If it seems to be stuck, put the engine in gear to hold the propshaft. Then rotate the prop about 180° and pull. <br /><br />When reassembling, grease the prop, thrust washer and pin with marine grease. If the drive/shear pin has marred the shaft where it runs through making removal of the prop difficult, file the pushed out metal down so the prop slides on easily.<br /><br />I hope that's clear!<br /><br /><br />EDIT: Ah, a picture's worth a 1000 words:<br />

<br />There they are in the order of assembly. The first hole in the driveshaft is for the cotter pin for the cone, the second is for the drive pin.

 

[CATransplant]

Re: Prop removal, first time.

Paul's absolutely right. There is no prop that's easier to change than the one on a Big Twin. But do buy and keep a couple of spare shear pins and cotter pins in the boat for emergencies. That's a must.

 

[Paul Moir]

Re: Prop removal, first time.

Or like me you can be an unbelievable cheapskate and cut your own out of a piece of 1/4" stainless (ie, an old Big Twin shift-shaft). They're 1-7/16" long.

 

[MYTJC]

Re: Prop removal, first time.

You might want to invest in a repair manual for your boat motor. I just bought one and its full of information about my 1985 Johnson 40hp. The fella's here always suggest obtaining one.

 

[CATransplant]

Re: Prop removal, first time.

Yeah, Paul, but not everyone has a pile of shift shafts lying around. I noticed the other day that someone had recommended using roll pins. I can't remember if I advised against that at the time, since I was kind of busy.<br /><br />The shear pin's SUPPOSED to shear. Those spring steel roll pins won't shear. Good way to bust a gear or something else.

 

[FishMagnet]

Re: Prop removal, first time.

MYTJC, I've got a service manual coming in the mail. (FINALLY!) I didn't want to shell out the $75 for one on the Ken Cook website so I patiently waited on eBay and got one for $14 (thats with shipping!). Took 3 months of waiting though.<br /><br />Paul, you're pretty hardcore. Making your own pins, and your custom brass throttle shafts. <br />Thanks for the walkthrough and the pic. The prop comes off tomorrow. If the thrust washer happens to be missing, do you happen to know the size so I can pick up a new one? Is it just a regular washer, or is there something special about it?<br /><br />Matt

 

[Paul Moir]

Re: Prop removal, first time.

Now to get really off topic...<br /><br />Those Big Twin "shear" pins, just what does it take to shear one? Well, ultimate shear strength of a material is around 75% of the ultimate tensile strenght, which for 304 stainless is 90,000 psi. The drive pin is 0.25" in diameter, so it has a cross-sectional area of 0.05 square inches. Since there's two sides of the pin to shear, that means you've got to go through 0.1sq-inches of material. Which would require the application of about 6700 lbs of force (90000 x 0.75 x 0.1).<br />So what sort of torque are we talking about here? The drive shaft is 0.75" thick where the pin runs through, so applying 6700 pounds on a 0.375 torque arm (radius of the 0.75" shaft) works out to about 2500 inch/lbs, or about 210 foot/lbs.<br /><br />Worst case, the Big Twin puts out 40hp with the prop shaft spinning about 2300 RPM (4000 motor RPMS). Theoretically, that puts about 90 ft/lbs on the prop shaft.<br /><br />So, how about other materials?<br />Nails (low carbon steel, I'm guessing 1020) 160 ft/lbs<br />Brass - about 120 ft/lbs<br />316 stainless - 197 ft/lbs<br />1/4" Grade 8 bolt - 350ft/lbs.<br />Hardwood dowel - 16 ft/lbs. <br /><br />I have no idea what a roll pin would do (other than rust ) since I have no idea how much cross-sectional area there is.<br /><br />EDIT: Thanks for noticing the throttle links. The thrust washer is brass, 1-5/8 OD, 1-3/16 ID about 0.060" thick. It is supposed to allow the propeller to spin properly when the drive pin shears. I think you could find them easily at any J/E dealer or wrecker, but they're a little weird so you're not likely to find one at the hardware store.

 

[FishMagnet]

Re: Prop removal, first time.

Well, the prop is off. You weren't kidding about how simple it was. Everything looks good, and the thrust washer was there. Found a massive amount of old fishing line behind the prop so I took that out.<br /><br />Did a light grind on the prop to smooth out a few nicks, nothing major. Sanded the rest by hand and am now waiting for the primer to dry.<br /><br />Its still the old prop, but it will look nice.