E Mod shear pins??

[bh/]

With your set up, ie; 9/16" shaft and 3/16" pin, you will have more problems than most, keeping a pin in there, and what works for others will not always work for you.
11/16" shafts are what most have under their 44"s, some times with bigger 5mm , and even 1/4" pins. 15mm shafts are also common.
I also expect that you must be bushing 11/16" and/or 15mm props
down to the 9/16" shaft to make them fit. Some times the fit
of the bushing can cause a problem.

To clarify, 9/16" is about 14mm, 11/16" is 17.5mm.
AB&C stock Mercs were 9/16", 40" Ds were 11/16"
Motors from Europe use 15mm.
Factory Yamatos are 16mm.
Would it not be nice if we picked one size, and stuck with it

[blueskyracer]

With your set up, ie; 9/16" shaft and 3/16" pin, you will have more problems than most, keeping a pin in there, and what works for others will not always work for you.
11/16" shafts are what most have under their 44"s, some times with bigger 5mm , and even 1/4" pins. 15mm shafts are also common.
I also expect that you must be bushing 11/16" and/or 15mm props
down to the 9/16" shaft to make them fit. Some times the fit
of the bushing can cause a problem.

To clarify, 9/16" is about 14mm, 11/16" is 17.5mm.
AB&C stock Mercs were 9/16", 40" Ds were 11/16"
Motors from Europe use 15mm.
Factory Yamatos are 16mm.
Would it not be nice if we picked one size, and stuck with it

No lie..I hope I can find something and not have to buy a bigger gear foot..And folks wonder why people give up on boat racing...Da

[Yellowjacket]

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..

Where on the pin was the failure? From the way you described it, it appears that it didn't fail while it was running, but you took it out and found it was broken in half.

Does that mean it was broken into two pieces and the break was about in the middle, but it hadn't sheared???

[Dave M]

Easy Answer

Mike,

Get some from Dudley, you won't have these issues to deal with then. Also, Larry M is probably one of the best Merc people around. He has been involved in the sport longer than I have, and I use some of the parts he makes. If he thinks it will work, I would trust his judgement over just about anyone.

[blueskyracer]

Where on the pin was the failure? From the way you described it, it appears that it didn't fail while it was running, but you took it out and found it was broken in half.

Does that mean it was broken into two pieces and the break was about in the middle, but it hadn't sheared???

It was a very clean break at about the 2/3rds mark and I did not know it had broke till I took the prop off and like I said earlier it was on our C Mod not the E mod.

I know something will work so I will try the wire next year and I will try the Nas623 screw that Ric Montoya sent me this weekend..Use to use them on Boeing aircraft so I have confidence.

[Yellowjacket]

Interesting... The problem isn't just weak material, it is something else....

What appears to be happening is one side is failing and then the other. You are using only half of the pin at a time, and then that side fails. After that it uses the remaining side until the second surface fails.

Odd that it would fracture all the way through, and then load up the second shear surface. I would have thought that before it got that far the second surface would start to contact and the load would be shared between the surfaces. That isn't happening for sure.

I suspect that the hole in the prop or the hole in the shaft isn't correctly aligned, or it could have yielded and one side is loading before the other. Or, in drilling out previous pin failures, the hole in one end of the shaft is buggered up, and could be a bit bigger than the other end. If the prop hole is a bit off center, or if the hole has yielded, it would only load one surface of the pin. For the shear pin to work right the pin has to be a close fit in the shaft hole and the prop.

The NAS623 screw is rated at 160ksi ultimate strength, as opposed to the 133 that you had in there. Thats about a 20% improvement. If you are failing one side of the pin that may get you a bit more life, but it may not fix it. Going to stronger materials is usually better, but sometimes increasing strength results in lower ductility. If the strength is high but the material isn't ductile enough you will end up just chasing your tail.

I'd look at the hole in the prop and shaft and if necessary, redrill the prop hole at a machine shop where it can be done properly, and you can insure it is square and in the right place. Also carefully inspect the hole in the shaft, make sure it is round and true and isn't bigger at one side than the other.

[Larry M]

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?

Yes that is the right stuff. Dudley does have some good shear pins reminds me of the music wire. The only problem is they are 5 mm which is .197 to big for a lot of props and shafts.

Larry Mac

[blueskyracer]

I will also add that the problem is happening on two different gear feet and two different sets of props so the hole being a problem I really cannot buy.. I have the NAS to try and 3/16 grade 8 bolt to try..I cant get the piano wire by Wednesday night so that is till next year

[Fast Freddie]

Use The NAS Bolt

We have been using the NAS bolts for quite a few years and rarely have problems on our D (44) Mod. I would try that this week and then go with the music wire when you get it. The NAS bolt will yield a little (it is ductile) when you tighten the nut - very similar to the rivets.

Also, use a lock washer under the nut. That is very important.

Make sure the edges of the pin hole in the shaft are "broken" as a sharp edge will easily shear the pin.

If you cannot solve the problem at the shaft or pin - drop the engine down a bit as surfacing puts more load on the prop (and pin).

My 2-cents.

[ram95]

Here ya go.. be a hero. Do the following:

Drill yer prop and propshaft shearpin hole out to 1/4 (.250"). Use a new drillbit and drill slowly.

Buy two reamers from McMaster-Carr. A .250 and a .251" straight reamer. Grind a flat on the shank so's you can grip it with a nice pair of US made vise-grips. Never turn a reamer backwards.. always clockwise... always!

Ream all your prop shearpin holes to match your propshaft.. do a nice job... clean things of tailings when you're done. Oil your reamer and wrap it up nicely.

Motor on down to your local hardware store and buy a handful of grade five .25dia bolts about 3 or 4 inches long not threaded all the way. Get out yer hacksaw and cut them to length.

Test them for a slide-thru fit. If you have done the job correctly the pin will slide right thru. I have not had one fail. And after three or four heats, I loosen the nut and the pin usually slides right out. Almost zero deformation. Inspect the pin and re-use it if you wish. Toss it away if in doubt.

And... if you dont want the advantage of a 1/4 inch pin.. by all means, use the piano wire for those little 3/16" holes.

Alex

[blueskyracer]

Here ya go.. be a hero. Do the following:

Drill yer prop and propshaft shearpin hole out to 1/4 (.250"). Use a new drillbit and drill slowly.

Buy two reamers from McMaster-Carr. A .250 and a .251" straight reamer. Grind a flat on the shank so's you can grip it with a nice pair of US made vise-grips. Never turn a reamer backwards.. always clockwise... always!

Ream all your prop shearpin holes to match your propshaft.. do a nice job... clean things of tailings when you're done. Oil your reamer and wrap it up nicely.

Motor on down to your local hardware store and buy a handful of grade five .25dia bolts about 3 or 4 inches long not threaded all the way. Get out yer hacksaw and cut them to length.

Test them for a slide-thru fit. If you have done the job correctly the pin will slide right thru. I have not had one fail. And after three or four heats, I loosen the nut and the pin usually slides right out. Almost zero deformation. Inspect the pin and re-use it if you wish. Toss it away if in doubt.

And... if you dont want the advantage of a 1/4 inch pin.. by all means, use the piano wire for those little 3/16" holes.

Alex

Alex, can a 9/16 shaft handle a 1/4 inch shear pin hole in it?? I have used a couple thousand reamers during my years at Boeing so that will not be a problem but I am worried that the shaft is awful small for a 1/4 hole thru it.

[ram95]

Oooops! Does not apply

Alex, can a 9/16 shaft handle a 1/4 inch shear pin hole in it?? I have used a couple thousand reamers during my years at Boeing so that will not be a problem but I am worried that the shaft is awful small for a 1/4 hole thru it.

I got carried away thinking that no FE's run 9/16 shafts. A bad assumption. For the 9/16" shafts, that 'piano wire' is certainly a 'the' safe bet. And doing the reamer fit exercise just makes it better.

Thanks for your attention.

Alex

[pops67g]

Mountains from molehills?

The great majority of us run fairly ordinary pins with no trouble. On a typical race weekend we run four different gearcases and at least that many propellors. We have not sheared/broken a pin in decades. It is obvious that your shaft or prop has an issue yet to be determined. You don't need a pin with the tensile strength for lifting an aircraft carrier. A pin hole in the shaft that is not champhered(sp.) can eat up a pin. A sloppy fitting prop can do the same. Going without a lock washer is not the best idea. Years ago we ran a 125hp D Looper on a Merc D gearcase and did not shear the 3/16 pins. As a matter of fact the gears failed before the pins did.

[Mr_dirt]

Geeze! This whole problem coming from a guy who thought that Y-80 was going to be enough fun for him.

[blueskyracer]

Geeze! This whole problem coming from a guy who thought that Y-80 was going to be enough fun for him.

Y-80 is to slow and for us old guys the ride of a bigger boat is so much nicer