K&B 16.4cc Flex/Drive Cable

[BradSpencer]

Hi All,

Awesome forum with lots of info.

I have read all the previous topics regarding Flex cables, and have learned some excellent tips.

I have recently put together a K&B 16.4cc OB on a 1/4 scale tunnel(50").

It has been running great, however I am chewing through the flex cables very quickly(1 every 2 runs)!

Here is what I have checked/tried to extend the life of the cable:

- Checked PTO bearing for wear/play.

- Using copper flex liner.

- Used different lubricants (marine grease, ATF, graphite grease).

- Tried both K&B prop shaft and Hyperformance Products prop shaft(currently using HP).

- Tried both K&B flex and Hyperformance Products flex(currently using HP).

- Checked in and out play of Flex cables (approx 4mm)

- Tried Hyperformance Products Bullet Drive lower unit. Currently using K&B lower unit.

- Have tried different probs(prather 260, propshop 6017/3, 5519/2, 5521/2) - balanced.

Never brakes under load(under throttle). More often than not they brake when returning to the bank(off throttle).

The engine does seem to splutter slightly when washing off speed from full throttle.

They are braking at the PTO end of the cable.

Anyone had experience with 16cc OB?

Any one have any suggestions?

Any input is appreciated.

Or is continuous flex cable problems just nature of the beast?

-----------------------------------------------

Just added the below pictures of the last one that broke - All have been similar to this.

On inspection, it appears it has unraveled in reverse (anti-clockwise) to the drive direction????? Not sure if this can happen?????

 

[Richard Anthony Hernandez]

hey,i,ve been running outboards for 20 yrs & just recently i drilled & tapped my lower right at the & b on the lower & put a grease fitting in & after every run i shoot 2 or 3 squirts of grease in & away i go hav,nt broke a shft all season & i run 3 times a week 3 hrs at a time ,hope this helps [email protected]

 

[John Kubitz]

Hi All,
Awesome forum with lots of info.

I have read all the previous topics regarding Flex cables, and have learned some excellent tips.

I have recently put together a K&B 16.4cc OB on a 1/4 scale tunnel(50").

It has been running great, however I am chewing through the flex cables very quickly(1 every 2 runs)!

Here is what I have checked/tried to extend the life of the cable:

- Checked PTO bearing for wear/play.

- Using copper flex liner.

- Used different lubricants (marine grease, ATF, graphite grease).

- Tried both K&B prop shaft and Hyperformance Products prop shaft(currently using HP).

- Tried both K&B flex and Hyperformance Products flex(currently using HP).

- Checked in and out play of Flex cables (approx 4mm)

- Tried Hyperformance Products Bullet Drive lower unit. Currently using K&B lower unit.

- Have tried different probs(prather 260, propshop 6017/3, 5519/2, 5521/2) - balanced.

Never brakes under load(under throttle). More often than not they brake when returning to the bank(off throttle).

The engine does seem to splutter slightly when washing off speed from full throttle.

They are braking at the PTO end of the cable.

Anyone had experience with 16cc OB?

Any one have any suggestions?

Any input is appreciated.

Or is continuous flex cable problems just nature of the beast?

-----------------------------------------------

Just added the below pictures of the last one that broke - All have been similar to this.

On inspection, it appears it has unraveled in reverse (anti-clockwise) to the drive direction????? Not sure if this can happen?????

Is it possible that the exhaust timing is to high and the engine will reverse rotation when you slow down?

 

[jydracing]

Hi John I ran in to this once Mount each half to the engine and check the alignment of the flex shaft to the engine. Also as stated before if there is no lube hole at the top of the lower unit drill one and lube every run. I can not say that the engine is not kicking over backwards at slow speeds but it is unlikely. If you let the engine iadle to low while on the stand the force of the prop spinnng than the engine going into compression stroke can couse a twist in the other direction. Hope this helpe Jimmy

 

[topfuel443]

John, what everyone else said, plus to re-iterate, lube the crap out of it every time you throw it in the water. Try a Lawless shaft, they are a little stronger. A little stiffer, but stronger. In reality, that big motor on that small of a flex is bound to chew them up sometimes. Once I switched to an onboard oiler (gravity fed), I havent had any problems with shafts. You may also want to look into that. They are quite easy to make, just do a search on here for them.

Here are a few pictures of them, you can do them many ways. Mine are just gravity fed, and usually last the whole run. You can also pressure feed them from the exhaust. It just has a small hole in the top, and you fill it every time before the run.

~James

 

[jetpack]

Try rounding the square lobes a little bit better at the tip of the flex shaft.

My experience showed me the swaged end of the shaft at the prop stub hole does not go straight into the hole, instead rides at a pretty good angle and makes the flex shaft notch around. Try and remove that notch without hurting it too much. If you use a black marker and color the tip and rotate it a few times in the lower unit assembly, it will tell you where it is hitting hard at the square tips. Ease that section a little at a time and see if it helps. There is usually plenty of square that is engaged with the broaching in the prop stub to not worry too much about enough contact, just be sure you dont get over generous with the grinding that you leave a strand that can fray on you. Try and develop somewhat of a ball-end on the flex. Break in a flex shaft easy the first couple runs also helps to give everything a chance to bed in a little. Both the cable and the stub shaft are hard materials.

 

[BradSpencer]

Thankyou for the all the great info guys. Genuinely appreciated.

Apologies for not responding earlier, but wanted to make sure the fix stood the test to time.

I have Soldered each end of the a flex shaft. Where it changes from the square end to a round spiral(where it's been braking).

So far I have had it out 3 separate occasions with a total of about 10 x 5 minute runs. All looking good! Hasn't broken! And no signs of excessive wear.

Will setup a lubricant feeder bottle over the next week to assist with longevity.

I will take a photo of my flex shaft mod and post it.

Brad

 

[BradSpencer]

Below is a pic of the soldered flex shaft. Might not be a fix for some, but has diffidently worked for my application.

On the left is a new flex shaft, on the right is my soldered one.

I have soldered each end and then filed so that the solder doesn't foul on the prop shaft or PTO fitting.