a better 3.5 k&b flex shaft?

[chunkt]

a better 3.5 k&b flex shaft?

Looking for some help here.

Any ideas on a better flex shaft for a K&B lower unit other than the K&B made ones?

I'm breaking them on a regular basis, between 15-20 tanks of fuel I'll lose one. im running a wet .21 on a stock lower unit, 50% nitro and either a mod X437/3 or a mod X440. They always break near the middle. I've tried everything I can think of - replaced the teflon tube, tried different lubes even gone to reduced diameter props or reduced pitch props with no change to this problem.

I'm compleately stumped on this one. Let me hear your two-cents worth.

chunk t

 

[synthon]

Re:a better 3.5 k&b flex shaft?

Chunk

FWIW, I have been running the same flex shaft (from K& B) for the last two seasons in my MOD boat (48-49 mph) on a K&B lower, and this is how I treat it: (1) throw away any teflon liners you have...all they are good for is as a drinking straw. (2) Replace that liner with a brass one, there was an article in RCBM a while back by Mr. Tunnel himself on how to make these, (Jerry jump in here anytime), it's easy even for me who sucks at soldering! Make a bunch, not only will your friends appreciate you, but when yours wears out, just pop in a new one! (3) Trim the flex shaft! I cannot stress this enough! You want the shaft to float, not touch the bottom of either the prop shaft or the PTO. The K&B shafts are too long...usually 1/8" will suffice. A good way to check for this is to push in your prop shaft...if it pops back out, its too long! (4) Lubrication! I use 1:1 STP/40 WT and I lube BEFORE AND AFTER each run.

I'm sure there are other suggestions out there, like trying the Lawless shafts (see Tim at PBR) but IMHO, the K&B's are fine when treated properly!

Later,

Rick

 

[nitrotoys]

Re:a better 3.5 k&b flex shaft?

I have had good luck with the 3.5 lawless shaft.

it seems to be stronger than stock K&Bs.

I ran with a semi mod 3.5 K&B engine for a season, and it seemed fine, Lubed it up and am ready for this one. Put different powerhead on and will see how it holds up now.

That Brass tube seems on here more than its worth, but sounds pretty simple to do.

 

[chunkt]

Re:a better 3.5 k&b flex shaft?

Rick,

The length currently isn't a problem, and I don't think it was in the past (can't seem to recall one at least). Haven't tried the brass tube yet on the o/b, but that's how I run my i/b set-ups, just as you described but with a heavier lube.

Nitro,

How much stiffer is the Lawless than the K&B? The K&B lower unit has a pretty sharp bend.

chunk t

 

[chunkt]

Re:a better 3.5 k&b flex shaft?

Regrding set-up - I have the prop shaft center-line set a touch less than 5/32 above the sponson bottom. So, no I'm not running too deep.

Just incase any of you were wondering.

chunk t

 

[nitrotoys]

Re:a better 3.5 k&b flex shaft?

Hey Chuck,

I dont think the lawless one is stiffer, I beleive its made better, and stranded better. If you are breaking them that much, eather your doing something wrong, or you should go to the lawless all tougher.

talk to Tim at PBR, He will help you out.

Very Good guy, and will get your parts to your door FAST.

 

[chunkt]

Re:a better 3.5 k&b flex shaft?

Nitro,

Believe it or not, I really do go through that many. I break about 5 a summer. It kills me, because I'm religious when it comes to maintenance. Haven't had a problem with any other set-up I own.

Everyone can blame me for K&B always being out of flex shafts ;D

I'll wait for some of the other tunnel guys to weigh-in before I deside, but you are making a good case for the Lawless.

chunk t

 

[nitrotoys]

Re:a better 3.5 k&b flex shaft?

I SWEAR By the LAWLESS.

See the K&B Lower makes a 90 degree bend in a short amout of space, and i think thats why its breaking in the middle. The lawless seems just STRONGER than the K&B, and the lawless shaft is like 10 bucks. what is the K&B shaft run?

I went with the lawless shaft, because that lower is MADE to handle HIGH HORSEPOWER and HIGH RPMs.

So hope this all helps, and wish you luck.

Now I am going to try a different lube for a bit and see how it works. At work we use this caliper lube, its a high temp grease made for brake systems. I figure i will try that out and see how that works. It doesnt seem to fling off or water doesnt wash it away.

 

[synthon]

Re:a better 3.5 k&b flex shaft?

Nitro & Chunk,

Just wanted to make sure we are all on the same page. I think Chunk should try the strongarm flexshafts before even thinking about buying an entire Lawless lower unit, especially given the powerhead.

I should also mention that the K&B shaft quality can vary widely...the "new" ones I have are about 5 years old! I also think you will see a large difference in using the brass tube to support the shaft. Especially since you are breaking them in the middle.

It all comes down to taste, the Lawless units are beautiful, but I have yet to see the justification in the expense. We have a mix of lower units in our district and shaft breakage occurs equally as often in all units.

Rick

 

[waterbug]

Re:a better 3.5 k&b flex shaft?

Nitrotoys,

Is that the blue teflon grease in a can ?? I know Ford has it in a pint paint can . There is also a blue waterproof synethic bearing grease for boat traliers . You can get it at any WalMart store in the automotive section .

Tim at Precision Boats Racing has a prop shaft bearing for the foot that helps also , you might try a teflon thrust washer instead of the brass one behind the drive dog.

 

[Ron Olson]

Re:a better 3.5 k&b flex shaft?

I've had pretty good luck with the K&B's myself. I have had both the 3.5's and 7.5 motors. I used what K&B calls for, a 50/50 mix of STP and 20w50 racing oil. I've also tried regular flex cable grease, high-speed bearing grease, Marvel Mystery Oil and probably a few other things. I've only had one flex cable failure at a race but I will change them normally if they start looking bad. I have friends that seem to go through more than their share so I don't know what's going on. Most of them have broken off near the powerhead.

 

[Kris Flynn]

Re:a better 3.5 k&b flex shaft?

The debate on the brass tubing, as opposed to the teflon one seems to some good points on both sides...

One for the teflon being that it would have less friction in it, on the shaft, compared to a brass one...also it wouldnt be metal on metal so the actual shaft surface wouldnt wear as much...correct me if i am wrong, but i thought i would point some things out

Maybe someone should manufacture a brass tubing with a teflon liner sitting snug inside it to be the perfect liner with the best of both??

Kris

 

[Kris Flynn]

Re:a better 3.5 k&b flex shaft?

Also i am sure the type of oil you use for lubrication would be important for shaft wear...but i suppose it is just the nature of the beast.

Could an in-correctly aligned or worn prop shaft cause shaft breakages?

Kris

 

[chunkt]

Re:a better 3.5 k&b flex shaft?

Kris,

My thoughts on the Teflon vs. Brass...

As long as the Teflon is kept clean I feel it's as good as a brass tube. The trick is keeping the Teflon tube clean. I personally like to use brass w/o the Teflon liner on my i/b set-ups, I think it's better, but with an i/b the stuffing tube doesn't back up against an engine back plate & bearing like it would on an o/b. I'm unwilling to put a brass stuffing tube that close to an exposed bearing. You're always going to get little brass flecks from inside of the tube no matter how well you lube (nature of the best). (Rick, please don't take my comment as nocking your method, that's just my feeling on using brass in the lower unit).

Ron I've tried the 50/50 mix STP & oil, I prefer a grease, I thought it was more work than I wanted, relubing after every run.

chunk t

 

[billr]

Re:a better 3.5 k&b flex shaft?

One of the biggest problems I have found out is that breakage is not usually torque alone. If you do not flush out the outdrive shaft, water will stay in there. Now there are those who will are that water does not go in the tube from either lube or drain hole. That is a load of BS. Open one up after a good days run and you will find water. Point being is that if you do not flush it out with oil, or in my case automatic transmission fliud; rust will set in and start its magic. Eventhough it may be on a micro scale at first, it does effect the strength. Once I started using ATF for lube along with an oil mix, and flushing it with the same at the end of the day, I never lost another 3.5 shaft in my lawless. Rust kills flex shafts!!!!!!

 

[Propjockey]

Re:a better 3.5 k&b flex shaft?

I've had good luck with a mixture of Slick 50 'One Lube' ( a green grease with teflon in it) and ATF. Takes a bit of patience to mix, but it has the consistancy of Cool Whip...tastes different though.

 

[chunkt]

Re:a better 3.5 k&b flex shaft?

Rick,

Where would I go looking for a Strongarm flex shaft?

chunk t

 

[_laxmasta2039]

Re:a better 3.5 k&b flex shaft?

PJ,

ahhhh...good.....for a while there i though i was the only person out there that enjoys tasting different types of engine oils. wait, you were being serious, right?? :-X :

lol,

hope ya wern't to shocked when you started reading!! ;D

Rebel Racing- high quality, fresh-tasting grease at low prices!

 

[Propjockey]

Re:a better 3.5 k&b flex shaft?

 

[Mark Anderson]

Re:a better 3.5 k&b flex shaft?

Do you remove the cable from the lower unit after a days running? K&B cables will last alot longer if you use a brass tube and a bearing prop shaft. Since you are breaking them in the middle and not at the lower end your prop shaft is probably good. I have seen alot of guys just lube the cable and motor after running and call it good. If you remove the power head after doing this I will guaranty you will find water still in the cable and rear bearing of the pto. Remove the power head and flush the rear bearing good with wd40 then oil it. Remove the cable and spray it with wd40 and store it straight. You are probably getting rust in the cable which makes it want to stay bent. Your cables and rear bearing will both last longer. I have cables in my tool box that have the outer wrap of wire worn flat from running so long. Another good lube is chain saw bar oil. A couple of guys can split a gallon and have a life time supply for cheap.