E Mod shear pins??

[blueskyracer]

This weekend was the best for me in my first year of D/E mod..but not perfect.. Now that I have the bigger engine a new problem has come to light..I am using props that have a 9/16 shaft hole and a 3/16 shear pin hole..I am using aircraft clevis pins and they are failing or so close to failing that one more lap would of done them in. I am tired of drilling them out. Any suggestions? I would like to find something that can handle the loads without going to a 1/4 inch set up..The only other thing I can think of right now is to replace the pin after every heat..That would suck!

[reed28n]

Shear pins

Craig Dewald always knows these answers........call him

[David_L6]

I used the pins that Steve Litzel sells.

[Larry M]

This weekend was the best for me in my first year of D/E mod..but not perfect.. Now that I have the bigger engine a new problem has come to light..I am using props that have a 9/16 shaft hole and a 3/16 shear pin hole..I am using aircraft clevis pins and they are failing or so close to failing that one more lap would of done them in. I am tired of drilling them out. Any suggestions? I would like to find something that can handle the loads without going to a 1/4 inch set up..The only other thing I can think of right now is to replace the pin after every heat..That would suck!

I never had any luck with aircraft clevis pins either. You can go to Mcmaster Carr and buy 3/16 music wire and cut it up for shear pins. It is the best thing I have found. It is super tough and I don't think I have ever had one to shear.
Larry Mac

[pops67g]

What pin to use???

The fit of the prop on the shaft is important as is the fit of the pin in the prop. If everything is just a little loose you have to overtighten the prop nut and this in itself will bend up the pin. I use the aircraft pins with no trouble and often will straighten them and use them more than once. I also use a slightly modified lock washer behind the nut to help keep the tension constant on the pin.

[DeanFHobart]

Tacoma Screw

Mike,

I use Tacoma Screw 1/4" dowel pins for the 45...... they also have 3/16".

They are Alloy Steel Heat Treated Precision Ground.

Here are the part numbers:

032-211-1 3/16" 1-1/4"

032-212-1 3/16" 1-1/2"

After use on the 45's there is not a mark on them.

Good Luck,

Dean................................

[krazy karl]

Shear Pins

I use hardened pins that are available from McMaster Carr. Some guys say not to use them but I have never had a problem. A box of 100 is less than $20. I don't remember how much. One pin will last a whole season and then some. This way you will always have a spare for a fellow boat racer when he loses his last one in the grass.
kk

[Yellowjacket]

There's a wide variation in strength for "aircraft" clevis pins. If you look up Ms20392, these pins can be made of either AISI 4037 (149ksi ultimate), or 4130 (81 ksi ultimate), or 13-8 stainless (215 ksi ultimate). So depending on the material you can have more than twice the strength depending on the pin. My guess is that the pins you are using are likely 4130 and that is the problem.

You want the pin to break before the shaft. The pin has a shear area of .054 square inches (.027 x 2 shear surfaces), and the shaft has .146 square inches (the 9/16 shaft - the pin area). For now I'm simplifying it by ignoring the complex stress in the shaft at the edges of the holes where there is a combinatio of shear and bending.

So the shear stress in the pin is ~ 3x the shaft shear stress. If the pin material were to be close to three times as strong as the shaft material the shaft would break before the pin, and you lose the prop. This isn't likely, with even the strongest clevis pin, so you can use a tougher material and not have an issue.

Music wire from McMaster-Carr has a strength of 230-399 ksi. I'm sure you would never shear the pin, but if you hit something with the prop, and the shaft is made out of something like 4130, you will probably break the shaft before the pin. This is also why boring the pin hole out to 1/4 is a bad idea.

You will see a lot of 18-8 stainless pins out there, but these aren't nearly as strong as a 13-8, so you want to stay away from them.

If you are going with a aircraft pin, make sure you get the 4037 material and not the common 4130, and you should be fine, or you could get the 13-8 stainless and be good too.

Look around for some rod stock that has a tensile strength in the 140-160 ksi range and you probably won't have any pin problems, and you won't have worry about damaging the shaft. Be careful in that a lot of bar stock comes annealed and isn't very hard, but if you heat treat it (like 4340) it can get really tough.

[Dave M]

Solved

Call Dudley Malone. He has your answer. They will hold up to any race engine we run today. First time in our 20 plus years in the SEH class (850CCMH) (FEH) that we run something other than the bolt. The bolt will hold if you buy the right one, but these pins... Dudley has nailed it. The three holer won't spit them, with stock shear pin hole size. And I doubt there is a 44 in the country that can out torque a decent three holer. I think they cost around a buck a pin, pretty cheap.

[blueskyracer]

There's a wide variation in strength for "aircraft" clevis pins. If you look up Ms20392, these pins can be made of either AISI 4037 (149ksi ultimate), or 4130 (81 ksi ultimate), or 13-8 stainless (215 ksi ultimate). So depending on the material you can have more than twice the strength depending on the pin. My guess is that the pins you are using are likely 4130 and that is the problem.

You want the pin to break before the shaft. The pin has a shear area of .054 square inches (.027 x 2 shear surfaces), and the shaft has .146 square inches (the 9/16 shaft - the pin area). For now I'm simplifying it by ignoring the complex stress in the shaft at the edges of the holes where there is a combinatio of shear and bending.

So the shear stress in the pin is ~ 3x the shaft shear stress. If the pin material were to be close to three times as strong as the shaft material the shaft would break before the pin, and you lose the prop. This isn't likely, with even the strongest clevis pin, so you can use a tougher material and not have an issue.

Music wire from McMaster-Carr has a strength of 230-399 ksi. I'm sure you would never shear the pin, but if you hit something with the prop, and the shaft is made out of something like 4130, you will probably break the shaft before the pin. This is also why boring the pin hole out to 1/4 is a bad idea.

You will see a lot of 18-8 stainless pins out there, but these aren't nearly as strong as a 13-8, so you want to stay away from them.

If you are going with a aircraft pin, make sure you get the 4037 material and not the common 4130, and you should be fine, or you could get the 13-8 stainless and be good too.

Look around for some rod stock that has a tensile strength in the 140-160 ksi range and you probably won't have any pin problems, and you won't have worry about damaging the shaft. Be careful in that a lot of bar stock comes annealed and isn't very hard, but if you heat treat it (like 4340) it can get really tough.

This is great info and the light just went on..I just started using this latest batch of shear pins and that is when the problem started when I went from the 40 to the 44 all at the same time.. But I am ordering some pins fro TS also just to be safe.. Thank you everyone and anyone who says this site does not help is ..................!!!!!!!!!!!!!!!!

[Yellowjacket]

McMaster-Carr has a hardened steel pin that has a material strength of 133ksi, which should be perfect. For the 1.25 inch pin the cost is $10.85 for 50 pins. The part number is 98381A512 for the 1.5 inch pin the part number is 98381A514. The nice thing about these pins is that it is rated for a specific shear strength as noted in the description, so you know what you are getting.

Either one is a bargin at twice the price.

[blueskyracer]

McMaster-Carr has a hardened steel pin that has a material strength of 133ksi, which should be perfect. For the 1.25 inch pin the cost is $10.85 for 50 pins. The part number is 98381A512 for the 1.5 inch pin the part number is 98381A514. The nice thing about these pins is that it is rated for a specific shear strength as noted in the description, so you know what you are getting.

Either one is a bargin at twice the price.

Just ordered 100 of these puppies so if anyone needs a few let me know..For the price can't beat it and if I never drill out another shear pin that will be fine with me especially in 100 degree temps. Plus I don't like tow ropes!!

[blueskyracer]

Just ordered 100 of these puppies so if anyone needs a few let me know..For the price can't beat it and if I never drill out another shear pin that will be fine with me especially in 100 degree temps. Plus I don't like tow ropes!!

Tried one of these new pins in our C mod. Took it out after 3 heats and was snapped in half..I guess we will try the aircraft screw that Ric sent us next..Have one more race this next weekend..

[Larry M]

Tried one of these new pins in our C mod. Took it out after 3 heats and was snapped in half..I guess we will try the aircraft screw that Ric sent us next..Have one more race this next weekend..

This is a case of what looks good on paper but in the real world doesn't stand up. I will take first hand knowledge every time. Try music wire you will like it.

Larry Mac

[blueskyracer]

Larry so I went and it looks like what I want for next year is Part #8907K18 Carbon Steel in one foot lengths .187 diameter?