Can a propeller hub cause a motor to stall when switching gears?

[bcrock]

Just replaced a spun hub with a new one and took it out to the lake. Now when trying to shift it to forward the motor dies. Engine starts up no problem in neutral and dies again when trying to go forward or reverse. Can the hub be any reason it is doing that now? Maybe it was installed incorrectly? Or can gas be mixed too rich with oil cause this? I searched on here and there are various answers ranging from bad carbs, incorrect idle screw adjustments to bad throttle cable.

 

[Maxz695]

Re: Can a propeller hub cause a motor to stall when switching gears?

What year type and HP is this. Some engines use different oil gas ratios. My 79 70 is 50:1 being 16 onces for 6 gal of gas. If the prop is spinning freely in neutral then it is not binding causig the engine to stall. Incorrect timing Idle too low clogged low speed jets in the carbs incorrect mixture adjustments. Start by checking the porp in neutral to see if there is free motion in both directions. If OK then try readjusting the mixture screws turning out from a light seat to 1 1/2 turns and then in until the engine studders. (Do this for all carbs if more than 1) after the studder turn the mixture screws outward another 1/4 turn. After getting it in the water and starting it, check to see if it runs in gear. If so then when throttling up if it boggs down open the mixture screws a bit more about 1/8th of a turn (Give time between adjustments to burn excess fuel before making another adjustment) until you get a good solid pick up and holeshot. If the engine dies when putting into forwards then bring up the idle a tad at a time but do not exceed 1200 RPM as a base. If you need more than that then timing or reeds may be the issue. Question: Did you have the same prop rehubbed or get a replacement with the same diamiter and pitch?

 

[bcrock]

Re: Can a propeller hub cause a motor to stall when switching gears?

If the prop is spinning freely in neutral then it is not binding causig the engine to stall. Incorrect timing Idle too low clogged low speed jets in the carbs incorrect mixture adjustments. Start by checking the porp in neutral to see if there is free motion in both directions. If OK then try readjusting the mixture screws turning out from a light seat to 1 1/2 turns and then in until the engine studders. (Do this for all carbs if more than 1) after this turn the mixture screws outward another 1/4 turn. After getting it in the water and starting it, check to see if it runs in gear. If so then when throttling up if it boggs down open the mixture screws a bit more about 1/8th of a turn (Give time between adjustments to burn excess fuel before making another adjustment) until you get a good solid pick up and holeshot. If the engine dies when putting into forwards then bring up the idle a tad at a time but do not exceed 1200 RPM as a base. If you need more than that then timing or reeds may be the issue. Question: Did you have the same prop rehubbed or get a replacement with the same diamiter and pitch?

I got a replacement with the same diameter and pitch. I will try to adjust the mixture screws and test it out again next time we hit the lake. Thanks

 

[Maxz695]

Re: Can a propeller hub cause a motor to stall when switching gears?

Post #2 edited for gas fuel oil ratio. depending on the engine the ratio may be different most run 50:1. On rebuilt engines they use 2 X that so I don,t think to much oil is an issue. Also make sure all plugs are firing on all cylinders

 

[bcrock]

Re: Can a propeller hub cause a motor to stall when switching gears?

I dont know what year is it , I made another thread on it so I can buy parts for it when I need to, but it's a merc850 4 cylinder 85 hp motor.I. I been using a mixture of 40:1 oil to gas mix. I will try to adjust the mixture screws and test it out again next time we hit the lake. Thanks

 

[Grub54891]

Re: Can a propeller hub cause a motor to stall when switching gears?

Also make shure the washer/spacer behind the new prop is in there,sometimes they will stick to the old prop,then the new one will bind up on the case........
Grub

 

[Maxz695]

Re: Can a propeller hub cause a motor to stall when switching gears?

That would be the forward thrust washer and yes it would bind without this in place and possibly do some damage.

 

[Maxz695]

Re: Can a propeller hub cause a motor to stall when switching gears?

16 oz per every six gallons or you risk engine failure. Better to have more than enough than not enough. That would be 50 : 1 ratio. Running it without enough oil will wear down the bearings and the rings wristpins etc until KAPOWWWWW!!!

 

[bcrock]

Re: Can a propeller hub cause a motor to stall when switching gears?

The mechanic I took the boat to have it serviced a while back said to use a 40:1 ratio. Was he wrong?

 

[Maxz695]

Re: Can a propeller hub cause a motor to stall when switching gears?

Again the year of the motor would be of help. Can you at least guess if it,s late 70,s in the 80,s 90s 2000s or is it old as in 60,s. If you post the serial number maybe carholme can assist you in finding the year and the mini manual for your engine. I wouldn,t want to recommend the wrong ratio and have something happen to your engine but I am concerned that you may not be using enough oil in the gas. EDIT I see you and Carholme are already working on this on another post. Looking like it might be the 64 so it may well be 40 : 1 ratio

 

[Texasmark]

Re: Can a propeller hub cause a motor to stall when switching gears?

The mechanic I took the boat to have it serviced a while back said to use a 40:1 ratio. Was he wrong?

Again, what engine and what year? Some folks on here like to run 40 when the mfgr. says 50 is what the engine is rated for if it is an engine mfgr'd in the last 30ish years. Might ask him why? If you live in a highly corrosive environment and the engine sits for a long time without running he may have made the suggestion to reduce corrosion.

Problem I have with your problem is that you said that all you did was to change the prop. Seems odd that that would cause a problem all of a sudden with inadequate fuel....aka dies when putting a load on the engine.

One would assume that you replaced the parts you removed when you took the old one off. If you failed to put the thrust washer on the prop would move forward into the gear housing and grind on the alum housing. The prop shaft spline probably would stick out past the rear of the prop and the nut wouldn't be able to go on tight, or if you had an older engine with a drive pin the prop would slide back and forth on the shaft....course as I recall on those, like the OMC engines of the 40's and 50's the prop hub has a notch in it and the drive pin is what stops forward movement and the prop is turned till the pin and notch are aligned and then the cap/nut is installed. Others had a hole in the rear of the prop hub and the pin went through there, locking the prop at the proper position on the shaft.

Only other thing could be that if your new prop had a removable hub, you might have the wrong one or wrong spacer; but again the only problem would be interference between the prop and LU housing and you ought to notice that at the time of replacement.

On the way to get another cup of coffee, I had another thought. Unless the prop is jammed up against the housing tight, aka loose on the shaft, when you went into R it would pull away from the housing and would work, noisy, but would work. So something is fishy about this.

Mark

 

[quicktach]

Re: Can a propeller hub cause a motor to stall when switching gears?

Just doing a straight prop change shouldn't do what you say is happening. What happened to the original prop ....did you hit something ?

 

[bcrock]

Re: Can a propeller hub cause a motor to stall when switching gears?

Again, what engine and what year? Some folks on here like to run 40 when the mfgr. says 50 is what the engine is rated for if it is an engine mfgr'd in the last 30ish years. Might ask him why? If you live in a highly corrosive environment and the engine sits for a long time without running he may have made the suggestion to reduce corrosion.

Problem I have with your problem is that you said that all you did was to change the prop. Seems odd that that would cause a problem all of a sudden with inadequate fuel....aka dies when putting a load on the engine.

One would assume that you replaced the parts you removed when you took the old one off. If you failed to put the thrust washer on the prop would move forward into the gear housing and grind on the alum housing. The prop shaft spline probably would stick out past the rear of the prop and the nut wouldn't be able to go on tight, or if you had an older engine with a drive pin the prop would slide back and forth on the shaft....course as I recall on those, like the OMC engines of the 40's and 50's the prop hub has a notch in it and the drive pin is what stops forward movement and the prop is turned till the pin and notch are aligned and then the cap/nut is installed. Others had a hole in the rear of the prop hub and the pin went through there, locking the prop at the proper position on the shaft.

Only other thing could be that if your new prop had a removable hub, you might have the wrong one or wrong spacer; but again the only problem would be interference between the prop and LU housing and you ought to notice that at the time of replacement.

On the way to get another cup of coffee, I had another thought. Unless the prop is jammed up against the housing tight, aka loose on the shaft, when you went into R it would pull away from the housing and would work, noisy, but would work. So something is fishy about this.

Mark

Im still trying to find what year the motor is built in a different thread. http://forums.iboats.com/mercury-mariner-outboards/what-year-my-merc-850-85hp-motor-588064.html

I didn't change the propeller, I replaced the hub. I will take it apart again and try to reassemble it again.

 

[Maxz695]

Re: Can a propeller hub cause a motor to stall when switching gears?

Not trying to be hard but in post #3 you said " I got a replacement with the same diameter and pitch " Now on the last post you say " I didn't change the propeller, I replaced the hub " We cannot help you if you can,t give us the facts.

 

[bcrock]

Re: Can a propeller hub cause a motor to stall when switching gears?

Not trying to be hard but in post #3 you said " I got a replacement with the same diameter and pitch " Now on the last post you say " I didn't change the propeller, I replaced the hub " We cannot help you if you can,t give us the facts.

Sorry I'm kind of a newbie when it comes to boat part specs. I was assuming the diameter and pitch was reffering to the hub that got replaced not the prop. as in I thought he said if the new hub was the same size of the old hub that got replaced.

 

[Maxz695]

Re: Can a propeller hub cause a motor to stall when switching gears?

OK thanks thanks for that info. The diamiter would be twice the distance from the center of the prop shaft to the outer most part of the prop blade. The pitch would be the offset of the blade itself. Most props have the pitch etched on them after a number (example 55682734a 12 P being a 12 Pitch) So you just changed the hub and therefore put the foward thrust washer (if even ever removed) back on before installing the prop with the new hub. That is good to know and would eliminate the prop as the problem.