Need advice to see if prop shaft is bent. Mercury 650

[sutor623]

1969 Mercury 650, runs great, moves quickly. I had what seemed to be an unusual amount of vibration on the boat in gear at lower RPMs. Check out the videos guys, they speak for themselves.

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

From the untrained eye, I see absolutely no wobbling at all of the shaft, just wondering if you guys would agree. Sorry that the vid is a little shaky, but I think that I just have a bent prop. I would just buy a prop, but the L/U on here is a 2.3:1 ratio, and the one in the basement is stock but needs a rebuild, and is 2:1. I want to get a 16pitch prop for this unit, or a 17pitch for the one downstairs, so you can see why I need to figure out what unit to use before I order a prop.

 

[Mi duckdown]

Re: Need advice to see if prop shaft is bent. Mercury 650

Pull the prop and check the shaft with a dial indicator.

 

[Texasmark]

Re: Need advice to see if prop shaft is bent. Mercury 650

Agree with Mi, but in looking at both your video's I'd forget the shaft and go after the prop. It looks like it could use some relief. The difference between your 2.0 and 2.3 is 15% meaning that for expected identical response, considering a prop of exactly the same design and material, the pitch would have to be 15% less on the 2.3.

Why don't you install the prop back on the shaft and put your wire next to the rear of the flare on the prop and run your test again, but at idle rpm's.....easier to see a variation if slower.

Mark

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

Pull the prop and check the shaft with a dial indicator.

Okay, haven't really used a dial indicator before, how exactly do I do this. And Texas, thanks thats what I thought. The shaft looks great IMO. Unfortunately, I was running the motor at Idle. Just seems when this girl is out of the water she really moves it.

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

So Texas, you are saying that if the stock runs a 17P, I should run a 14.5P with a 2.3:1 ?

 

[gwukena]

Re: Need advice to see if prop shaft is bent. Mercury 650

So Texas, you are saying that if the stock runs a 17P, I should run a 14.5P with a 2.3:1 ?

You want to run more pitch with a 2.3:1 ratio, driveshaft has to spin 2.3 times to rotate prop shaft 1 rpm, so works out to 19.55, so run a 19 or 20 pitch prop, 19 would probably be better all around

Gary

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

You want to run more pitch with a 2.3:1 ratio, driveshaft has to spin 2.3 times to rotate prop shaft 1 rpm, so works out to 19.55, so run a 19 or 20 pitch prop, 19 would probably be better all around

Gary

Hell, I think you are right man. I always mix up the ratio numbers. This lower unit is actually sucking torque right out of the motor. Guys like Faztbullet have told me that these lower units will take the lower end grunt out of the motor. Do you guys think that a prop change will get some of that grunt back, or should I just rebuilt the "correct" lower unit and slap on a new 17P prop? So right now I am actually underpropping my motor by a bit. Sure glad I didnt over-rev my motor this weekend.......

 

[gwukena]

Re: Need advice to see if prop shaft is bent. Mercury 650

Simple rule of thumb for ratios, first number is the input(drive shaft), second number is the output (prop shaft), the higher the first number the higher the mechanical advantage and rpm and torque multiplication. A higher first number actually means you are running a lower gear ratio. The problem with trying to go with more pitch for a unit wth a lower ratio is typicaly prop diameter also increases which takes more power to spin, kind of a catch 22 situation. Your best bet is probably to rebuild the correct unit and run the recommended prop. What is wrong with the original lower unit?

Gary

 

[Texasmark]

Re: Need advice to see if prop shaft is bent. Mercury 650

So Texas, you are saying that if the stock runs a 17P, I should run a 14.5P with a 2.3:1 ?

You mentioned a prop on another engine you had. I just commented on the fact that unless you were at the extremes of performance for either, with like items you need to increase the pitch of the prop 15% on the 2.3 as compared to what one would run on the 2.0 engine of like capabilities to get the same performance.

Assume water were a solid. For one 360 degree rotation of the prop, and running the same prop, the 2.0 would move the prop 15% farther than the 2.3. So, to make all things equal, you'd have to increase the pitch when running it on the 2.3 by 15% to go the same distance per rev, hence mph. Make sense?

So what are the two pitches of the props mentioned and what are their characteristics? If identical just give me the pitch numbers and which prop is on which engine.

Mark

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

Gweneka, Yeah I simply just get the #'s backwards sometimes, but thanks for the physics lesson.... LOL But seriously the original unit was split cause it had gotten frozen, the unit on there now came off a 150hp, has no fitment issues, just a different gear ratio. It is smoootthh as butter in shifting, and the best part is that I got it from a salvage yard for $25. Anyways, I have a spare unit that is in great shape except for the driveshaft splines have worn a bit, just dont want to slap it onto my motor and strip out the crankshaft splines. So I need to get into the insides and switch out the driveshaft from the unit that froze and split. I have tons of L/U parts to work with, so I dont even need to pull the unit off my motor right now. Honestly I have heard both ways about the whole gear ratio/prop thing. Some say it works fine, others say it is less than stellar. I think the best thing for me to do is get a 19P prop, then rebuild the "correct" unit as time and money permit, switch the units, and then always have a spare. But I will say if the 19P on this unit can pull up a skier, and my top speed isnt compromised too badly, I wont even worry about it. Just dont want to buy a prop and find out that my vibration is coming from a prop shaft.

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

You mentioned a prop on another engine you had. I just commented on the fact that unless you were at the extremes of performance for either, with like items you need to increase the pitch of the prop 15% on the 2.3 as compared to what one would run on the 2.0 engine of like capabilities to get the same performance.

Assume water were a solid. For one 360 degree rotation of the prop, and running the same prop, the 2.0 would move the prop 15% farther than the 2.3. So, to make all things equal, you'd have to increase the pitch when running it on the 2.3 by 15% to go the same distance per rev, hence mph. Make sense?

So what are the two pitches of the props mentioned and what are their characteristics? If identical just give me the pitch numbers and which prop is on which engine.

Mark

Thanks for your time Tex, this is useful info to me. The problem is that I dont have a tach on my boat right now, but I have the stock prop (17P for a 2:1 ratio) on a lower unit with a 2.3:1 Ratio. I think that speaking from a physics standpoint, a 19P prop would do me just fine. Top speed now on the boat is plenty, but I could use a better hole shot. If the prop shaft is not bent Id be happy to put a prop on there and go with it. It would be more than great for me, just dont want to do it if propshaft is bent....

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

Oh and Tex, either way I need a new prop, just want to get the right one for the job and Im not too picky

 

[Texasmark]

Re: Need advice to see if prop shaft is bent. Mercury 650

Thanks for your time Tex, this is useful info to me. The problem is that I dont have a tach on my boat right now, but I have the stock prop (17P for a 2:1 ratio) on a lower unit with a 2.3:1 Ratio. I think that speaking from a physics standpoint, a 19P prop would do me just fine. Top speed now on the boat is plenty, but I could use a better hole shot. If the prop shaft is not bent Id be happy to put a prop on there and go with it. It would be more than great for me, just dont want to do it if propshaft is bent....

I think the number is 200 rpm per inch of pitch reduction. The 17 would definitely improve your hole shot at the cost of about 400 rpm increase.....this is all figuratively speaking. Only an actual test will give you the result. On rpm's with the 17, 2 strokes like the upper end and my Mercs, all of them love to push the envelope. I ran my tower for 6 years at 6k WOT and the current engine runs 5600-5800 unless I am venting then it runs 6000 to 6200. So personally, tach or not, unless the thing sounded like it was going to blow any second don't worry about the upper limit.

Now if you want some performance, get yourself a 19P SS that is ported (Merc Laser II). The ports let you spin up fast in the hole just as if you had a much lower pitched prop (hole size determines the slip), but at WOT the holes are sealed off and you have the 19p propelling you....best of both worlds.

Mark

 

[CharlieB]

Re: Need advice to see if prop shaft is bent. Mercury 650

I doubt if that shaft in the vid is bent beyond spec, to be sure you need to rig a dial indicator then slowly turn the shaft and see just how much deflection the indicator shows, 0.003 if within tolerance.

Using the wire you have rigged, leave the motor OFF and in Neutral, turn the shaft by hand and see if you can tell the shaft is wobbling. Remember a normal sheet of paper is roughly 0.003

Even one blade of a prop dinged can cause erratic vibration at different RPM. I would seriously suspect the prop needs attention, call your local prop shop and ask about reconning your prop vs replacing the prop, benefits of alum vs SS for the waters you boat in.

The shafts should be interchangeable between the two gearcases, you will need a seal kit. Here again, talk to your prop shop about which prop is abvisable for the gear ratio that you will be using.

A lower numerical ratio has the advantage of turning a larger prop, diameter as well as pitch, and can give a quicker holeshot.

A higher numerical may give a higher top speed at the expense of a slower holeshot, but here again, it is all dependent on the prop, diameter, pitch, and the style of blade shape. Your prop shop knows far more about all of these then we cover here.

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

Cool, always a pleasure Charlie B! I tried to buy an indicator locally today on the way home from work, looks like I will have to order one if I want one. Going to be awfully hard to tell if my shaft is bent more than a piece of paper, but thanks for not doubting me. I thought that shaft looked pretty darn straight also! My prop is damaged beyond repair, so it sounds like the best thing for me to do is just order a new prop and see how she turns. If a little ding will cause it to be vibrating, then believe me, this prop is more than the culprit. It is useable, but I dont want to use it for a long time. I wish I knew if my motor was turning within the spec with the 17P that I have. Here she is at WOT, maybe some of you guys can tell by ear if she sounds like she is spinning too fast, seeing as I am underpropping the motor right now.Sounds like she may be at her upper limits to me.

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

Now if you want some performance, get yourself a 19P SS that is ported (Merc Laser II). The ports let you spin up fast in the hole just as if you had a much lower pitched prop (hole size determines the slip), but at WOT the holes are sealed off and you have the 19p propelling you....best of both worlds.

Mark

Wow!! Now that's what I call prop-nicality at it's finest!!

 

[Texasmark]

Re: Need advice to see if prop shaft is bent. Mercury 650

You may have a bent blade to go along with your wear and tear on your current prop. A prop shop could measure it tell you, but again I say: With an aluminum prop, before you are going to bend that stainless steel prop shaft, you are going to have a full dog eared blade, one knocked completely off, or something drastic.

I used to have a '72 125 Johnny and I was "busting" up alum blades all the time; almost every time I went out. One time I hit the concrete railing on a submerged bridge that didn't get removed when the lake was built. Regardless of the how, as soon as I could afford $185 for the new (at the time) OMC teflon coated SS prop, that was the end of the prop problems and she ran smooth as silk.....no bent shaft.

If you don't think SS is tough, try drilling into it. I ported my current prop using my drill press and never used titanium coated bits. I knew SS was tough, but this was amazing.

 

[sutor623]

Re: Need advice to see if prop shaft is bent. Mercury 650

You may have a bent blade to go along with your wear and tear on your current prop. A prop shop could measure it tell you, but again I say: With an aluminum prop, before you are going to bend that stainless steel prop shaft, you are going to have a full dog eared blade, one knocked completely off, or something drastic.

I used to have a '72 125 Johnny and I was "busting" up alum blades all the time; almost every time I went out. One time I hit the concrete railing on a submerged bridge that didn't get removed when the lake was built. Regardless of the how, as soon as I could afford $185 for the new (at the time) OMC teflon coated SS prop, that was the end of the prop problems and she ran smooth as silk.....no bent shaft.

If you don't think SS is tough, try drilling into it. I ported my current prop using my drill press and never used titanium coated bits. I knew SS was tough, but this was amazing.

Cool Tex, good to know. I guess what I really ought to do is order me a tiny tach, take the boat out one more time and measure my hole shot and top speed so I can see what the 17P is delivering. It seems as if I need a prop and that is all, but I just want to get the right one for the job. I wish I could buy a Merc Laser 2, but $400 on a prop when I have $1200 into my entire setup seems a bit unpractical.

 

[Texasmark]

Re: Need advice to see if prop shaft is bent. Mercury 650

Cool Tex, good to know. I guess what I really ought to do is order me a tiny tach, take the boat out one more time and measure my hole shot and top speed so I can see what the 17P is delivering. It seems as if I need a prop and that is all, but I just want to get the right one for the job. I wish I could buy a Merc Laser 2, but $400 on a prop when I have $1200 into my entire setup seems a bit unpractical.

Turning Point Brand Hustler is a good alum prop. It has a lot of the characteristics of SS and sells on here for about $100. Have to order a hub with it to suit your engine. Getting the tach is most definitely the right choice.

Mark