flex shaft clearance

[Ken Webb]

Usins .187 flex. How much clearance should I leave between the strut and prop drive dog? Is 1/4 inch too much?

 

[Ted buckley]

I believe up to 3/16" is the going rate.

 

[RodneyPierce]

a good rule of thumb is, leave the same amount of space as your cable size. So if its a 1/4 inch cable, leave 1/4 inch, 3/16 cable, leave 3/16, etc...

 

[Rigged]

IMO it depends on the cable, and how long it is. Ive had some cables that would tighten up alot, and 1/4" gap wasnt enough.

At a minimum, should be what the diameter of the cable is though like said.

 

[Ken Webb]

Thanks guys.Big help. Someone needs to write a how to book for boaters.

 

[Ted buckley]

Thanks guys.Big help. Someone needs to write a how to book for boaters.

Don't think this will ever happen, because everybody seems to have a different view-point. But that isn't neccessarily a bad thing. B)

 

[Rigged]

Thanks guys.Big help. Someone needs to write a how to book for boaters.

Don't think this will ever happen, because everybody seems to have a different view-point. But that isn't neccessarily a bad thing. B)

never say never

 

[Ted buckley]

Thanks guys.Big help. Someone needs to write a how to book for boaters.

Don't think this will ever happen, because everybody seems to have a different view-point. But that isn't neccessarily a bad thing. B)

never say never

I'll be there for your "Book Signing".. It'll give me a reason to go out to Blue Ridge, GA. and race with you guys - some day.

 

[Ken Webb]

I know Alan Hobbs and John Finch both had some books out years ago. I've got some of them. These books probably need to be updated now. How about it guys?

 

[Craig dickson]

Usins .187 flex. How much clearance should I leave between the strut and prop drive dog? Is 1/4 inch too much?

Hi Spider

In my opinion, your topic raises some good questions.

What is the ideal clearance gap?

If the gap is too small it will result in the flexi cable winding in and combined with the propeller thrust causing excessive friction at the strut end potentially leading to a snapped over stressed flexi cable.

Okay, what if the clearance gap is sufficiently big enough such that when at full throttle the flexi shaft has plenty of room to wind in but still leaving say a 3mm gap between the strut end bearing and the drive dog?

In that scenario, I see several potential draw backs or problems:

1) The thrust from the propeller will be delivered to the engine. If the throttle linkage to the carb is of a fixed rod type from the servo it could affect the set up should the engine move bodily forward at full power.

2) The flexi drive shaft (even after its natural winding in) is with a further strut end gap going to be further compressed within the stuffing tube. I’d suggest that this might cause some snaking within its confines causing loss of power and potential vibration plus undue wear on the stuffing tube and flexi shaft.

Personally I am still experimenting with the ideal gap.

I am aiming for a gap that will at full throttle result in just a little wear on the washer that sits between my strut end and the drive dog.

Regards

Craig

 

[TimothyJones]

Some cables wind up more than others so a judgement call will have to be made at some point.

This may not be the best way but I hold the flywheel, twist and push the prop for a feel on what is close and then a hard run will tell you if you if needs more.

3/16" gap should be plenty on a 3/16" cable unless it has lost its temper and or the stuffing tube is bigger than it should be.

Usins .187 flex. How much clearance should I leave between the strut and prop drive dog? Is 1/4 inch too much?

Hi Spider

In my opinion, your topic raises some good questions.

What is the ideal clearance gap?

If the gap is too small it will result in the flexi cable winding in and combined with the propeller thrust causing excessive friction at the strut end potentially leading to a snapped over stressed flexi cable.

Okay, what if the clearance gap is sufficiently big enough such that when at full throttle the flexi shaft has plenty of room to wind in but still leaving say a 3mm gap between the strut end bearing and the drive dog?

In that scenario, I see several potential draw backs or problems:

1) The thrust from the propeller will be delivered to the engine. If the throttle linkage to the carb is of a fixed rod type from the servo it could affect the set up should the engine move bodily forward at full power.

2) The flexi drive shaft (even after its natural winding in) is with a further strut end gap going to be further compressed within the stuffing tube. I’d suggest that this might cause some snaking within its confines causing loss of power and potential vibration plus undue wear on the stuffing tube and flexi shaft.

Personally I am still experimenting with the ideal gap.

I am aiming for a gap that will at full throttle result in just a little wear on the washer that sits between my strut end and the drive dog.

Regards

Craig

 

[Al Hobbs]

This the reason so many boaters use square drive systems. It doesn't matter how much the cable winds up, the engine collet can absorb the cable length differences and the prop load is always on the strut.

When you use a full length cable, the load is normally transferred to the engine and can cause some side load on the bearings.

Either cable system sure beats the old solid shafts and u-joints. How is that for dating myself?

Al Hobbs

 

[LarryConrad]

Thanks guys.Big help. Someone needs to write a how to book for boaters.

John Finch wrote several of them.

 

[Tom Foley]

Bottom line from a few years of doing this ..if you leave an honest 1/4 " it's all good ...to small ..no good . It's not really a complex issue ..1/4 " works for ANYTHING !

 

[Andy Greene]

Bottom line from a few years of doing this ..if you leave an honest 1/4 " it's all good ...to small ..no good . It's not really a complex issue ..1/4 " works for ANYTHING !

Yep

I liken it to a 4 page thread about flex shaft lube

And NO I wont read it

Andy

 

[Rigged]

This the reason so many boaters use square drive systems. It doesn't matter how much the cable winds up, the engine collet can absorb the cable length differences and the prop load is always on the strut.

When you use a full length cable, the load is normally transferred to the engine and can cause some side load on the bearings.

Either cable system sure beats the old solid shafts and u-joints. How is that for dating myself?

Al Hobbs

i still have a old 60 sport hydro that used a solid shaft in a box in the garage somewhere

 

[Hydro Junkie]

You're not dating yourself too much Al. My first two or three boats all had a 3/16 threaded shaft with a U-joint running through brass/bronze bushings(first boat) or needle bearings(next few) in the strut and stuffing box. Heck, I still have a boat with a Dumas needle bearing strut and teflon bushed rudder bracket :huh:

 

[Walt Barney]

I was just digging thru some stuff looking for some parts I knew I had an just ran across two new 3/16 hard shafts. Man what a surprise.

Walt Barney

 

[LarryConrad]

You're not dating yourself too much Al. . Heck, I still have a boat with a Dumas needle bearing strut and teflon bushed rudder bracket :huh:

And it's most likely never been in the water.

 

[brett english]

Bottom line from a few years of doing this ..if you leave an honest 1/4 " it's all good ...to small ..no good . It's not really a complex issue ..1/4 " works for ANYTHING !

ive followed that theory that tom says(1/4 gap works on anything) for the past 25 years...worked great and never had any issues..Right up til late last year..with my new twin having these new cmb vac"s 91 with brand new shafts i left my normal 1/4 gap and big mistake!! theres so much torque with these motors that the drive dog pushed against the back of the struts and changed the strut angle, i know several other people with the same set up happening to them..so now i leave a bit over 3/8 gap..