Decent prop shafts

[poolschool]

Is there any decent prop shafts out there to suit both 3.5 and 7.5 o/b's

Yes, OS IMO is the best 3.5 shaft, but what about 7.5?

I run a CMB45RS/Lafleur combo and the 3 types of shafts I have tried are all no good or could be better

K&B - 2 runs and its all over

Nitro water sports - somewhat better but still looking for more

last one which name I can't remember, the bearings locked up

I do run an oiler system.

Gino

 

[robertpickard]

Get a hold of John Otto at technology hobbies 813-651-1840

 

[Marty Slater]

i asked the same thing 8 10 mounths ago

an got about the same thing <_<

you would think there would be more on this h34r:

any body got any thing else

Marty

 

[Tim leyde]

Kris Flynn makes a hell of a shaft for the OS 3.5. Contact him and see if he makes a 7.5, if so you will not be disappointed.

Tim

 

[David Moyle]

Kris Flynn makes a hell of a shaft for the OS 3.5. Contact him and see if he makes a 7.5, if so you will not be disappointed.

Tim

Hey Tim! I believe Kris makes flex shafts only, not the bushed prop shaft. But I agree, they are awesome flex shafts that he makes!

Regards,

Dave

 

[HTV Boats]

The reason there is little responce here on 7.5 prop shafts is there are no options. The K&B which is a larger version of the 3.5 sucks for the same reason. Too short a bearing surface and materials that don't wear well. The Nitro Water Sports version used better materials but achieved marginal improvement in longevity. Hyperformance shaft bearings are an improvement as the load is supported by a longer bearing distance and better materials. Unlike the OS 3.5 shaft that puts the length into the lower with a longer threaded area, the Hyperfomance adds length to the rear away from the threaded area which allows rotational forces to pry the unit out of the lower unit housing. I have lost too many props on Hyperformance shafts backing out. Locktight helps but creates other issues. Until someome totally comes out with a lower that will accept a longer shaft bearing surface into the lower like the OS were just going to keep replacing prop stubs. Part of the reason OS lowers handle better is the prop runs so much truer than a K&B shaft.

Mic

 

[lohring]

You are all missing Hyperformance. Their prop shafts are the equal of OS in both the 3.5 and 7.5 size. They make good cables as well.

http://hyperprod.bizhosting.com/psa35.html

Lohring Miller

 

[RonShaw]

I hear all of the suggestions and reflecting on the lack of any viable bullet-proof option, for now I would suggest keeping extra K&B's in your parts box and changing them out every couple of races. Keep the used ones for running at the pond and when they show excessive end play and wear, throw them away. Hopefully someone will come out with a solid option soon.......

 

[RonShaw]

You are all missing Hyperformance. Their prop shafts are the equal of OS in both the 3.5 and 7.5 size. They make good cables as well.

http://hyperprod.bizhosting.com/psa35.html

Lohring Miller

Lohring,

I have never tried these shafts but have heard many people, including Mic above, have had issues with them backing out.

 

[BradSpencer]

The shafts from John Otto have worked well on my mod 7.5.

The first one only lasted surround 20 minutes before developing to much play. But the second shaft has lasted for more than 3 gallons, still with near no slop.

 

[Jim Allen]

It is easily possible to modify the K&B 7.5 lower unit's prop shaft, bushing & Cable housing to make the unit bullet proof.

1. Remove the 1/4" wide leaded teflon bushings. Machine a Bearium metal bushing that extends beyond both ends of the housing. If you are using the stock K&B prop shaft, the bushings ID should be .2472" X .694" long. A .031" thick surface is machined on the back end for the teflon washer to bear against. Use a light press fit & #609 Loctite to hold the bushing in the housing.

Note: The original new leaded teflon bushings will allow a .251" shaft to pass through. Since all the K&B shafts measure .247"- OD, a brand new unit already has .004" total clearance before you run it.

2. Machine a new stainless steel drive dog that fits the .185" OD prop shaft. Use two 6-32 cone point set screws with #271 Loctite. The cone points should match cone shaped cavities on the prop shaft. I never use a flat surface.

3. Machine .062" thick teflon thrust washers that fit the .185" prop shaft. Assemble all the pieces.

4. Replace the teflon cable housing with a rigid wall brass tubing. Rigid wall brass tubing can be bent without annealing by using Cerro Bend metal. Cerro Bend, which can be melted at 212 deg F in a small container, is poured into the tubing that has been plugged on one end. Before pouring, coat the inside of the tubing with mineral oil. The Cerro Bend will not adhere to the inside of the tubing when it is melted out after bending. The Cerro Bend does not shrink when it hardens. This allows bending without any kinks, even if the radius is very small.

5 Add a grease fitting to the lower unit which matches a hole in the rigid brass tubing. Use a #2 white grease with a minature grease gun to lubricate the cable, prop shaft & the bearing at the upper end of lower unit.

6. Close off the front two holes in the bullet of the lower unit. When the engine is running, grease will travel down the cable & lubricate the prop shaft assembly.

If you desire to replace the soft shaft with a hardened shaft, use O-1 tool steel. Machine to size, harden by wrapping in stainless steel & then temper at 550 deg F. Tempering can be done by color providing the steel has been physically & chemically cleaned. The correct temper color is gold.

Note: A broach to make the .1562" square hole in the front of the prop shaft will cost approximately $125.00.

 

[big_makdaddy]

It is easily possible to modify the K&B 7.5 lower unit's prop shaft, bushing & Cable housing to make the unit bullet proof.

1. Remove the 1/4" wide leaded teflon bushings. Machine a Bearium metal bushing that extends beyond both ends of the housing. If you are using the stock K&B prop shaft, the bushings ID should be .2472" X .694" long. A .031" thick surface is machined on the back end for the teflon washer to bear against. Use a light press fit & #609 Loctite to hold the bushing in the housing.

Note: The original new leaded teflon bushings will allow a .251" shaft to pass through. Since all the K&B shafts measure .247"- OD, a brand new unit already has .004" total clearance before you run it.

2. Machine a new stainless steel drive dog that fits the .185" OD prop shaft. Use two 6-32 cone point set screws with #271 Loctite. The cone points should match cone shaped cavities on the prop shaft. I never use a flat surface.

3. Machine .062" thick teflon thrust washers that fit the .185" prop shaft. Assemble all the pieces.

4. Replace the teflon cable housing with a rigid wall brass tubing. Rigid wall brass tubing can be bent without annealing by using Cerro Bend metal. Cerro Bend, which can be melted at 212 deg F in a small container, is poured into the tubing that has been plugged on one end. Before pouring, coat the inside of the tubing with mineral oil. The Cerro Bend will not adhere to the inside of the tubing when it is melted out after bending. The Cerro Bend does not shrink when it hardens. This allows bending without any kinks, even if the radius is very small.

5 Add a grease fitting to the lower unit which matches a hole in the rigid brass tubing. Use a #2 white grease with a minature grease gun to lubricate the cable, prop shaft & the bearing at the upper end of lower unit.

6. Close off the front two holes in the bullet of the lower unit. When the engine is running, grease will travel down the cable & lubricate the prop shaft assembly.

If you desire to replace the soft shaft with a hardened shaft, use O-1 tool steel. Machine to size, harden by wrapping in stainless steel & then temper at 550 deg F. Tempering can be done by color providing the steel has been physically & chemically cleaned. The correct temper color is gold.

Note: A broach to make the .1562" square hole in the front of the prop shaft will cost approximately $125.00.

That is pretty cool B) . How could I get some. I do not have a machine shop :blink: . Very good info.

John Maki

 

[poolschool]

Very good info Jim and MIc

Thanks to all that replied.....keep em coming if anyone else has something to add

Gino

 

[lohring]

Several of us have been running the Hyperformance shafts for over a year with no problems. They haven't developed any play like the K&B shafts do.

Lohring Miller

 

[Kris Flynn]

Gino,

Can you post a picture of your outboard setup, specifically the oiler system you are using?

Cheers

Kris

 

[moparbarn]

the issue with the hyperformance shaft backing out is because the tapered undercut on the shoulder of the shaft housing shaft is too shallow & does not match the angle of the taper on the k&b lower where it screws into the housing. the design is intended to squeeze the lower housing halves together against the prop shaft housing as you tighten it, clamping the prop shaft in place. as the 2 tapers are forced together, the clamping pressure is generated. if the tapers don't match, not enough clamping pressure is generated, allowing the prop shaft to come loose. compare it to a k&b shaft & the differance is easy to see. 2 options, either tighten/check it EVERY run, or cut the taper in the shaft housing to match the k&b unit. the one that i have had the taper modified on to match the k&b lower has NEVER come loose. it has nothing to do with length & leverage, imho. worth modifying, as the bearings are FAR superior to anything k&b offers.

i love it when jim says things are "easily done" . while he has a lifetime of experience as a machinist & tool/ die maker with a VERY nice setup in his garage, he forgets most of us could screw up a concrete block with a nail file :lol: :lol: . but to watch him do what he does, he makes it look easy. very talented & knowledgable man, when he talks about machining & metalurgy, pay attention B) !

 

[poolschool]

Gino,

Can you post a picture of your outboard setup, specifically the oiler system you are using?

Cheers

Kris

Kris,

I don't use an oiler as such, rather I have a nipple drilled into the leg and just inject oil prior to a race with a syringe.

I could post a picture of the syringe if you would like, but I guess you get the drift

Gino

 

[Kris Flynn]

My Point exactly. Yeah a pic of the syringe would be good, need to make sure the ID of the opening is letting enough oil through, how long are you squeezing the oil in for exactly? B) h34r:

You are running 25K + RPM for 3,4,5 mins with basically just a squirt of oil. That definately can't help the poor little bearings.

 

[moparbarn]

kris, i'm doing the same thing with my lowers as gino. i squirt oil in until it comes out the holes by the stub shaft in my k&b lowers. i'm using a bel-ray chain &cable synthetic lube, fairly thick & very tacky. consistency is similar to chainsaw bar&chain lube. no failures in the 2 years i've been doing it. the k&b prop shafts still wear out like always, but the nitro water sports ones seem to last longer, & i have 2 hyperformance shafts that are 2+ years old & still tight. i run either brass or the old "friction free" brand stainless liners with flex's made by some cod down under :lol: . only 1 shaft failure to date since i started using the bel ray lube 2 years ago. that was on my mod boat, in fairly rough water, i think the prop unloading & biting again contributed there.......

 

[Tim_Duggan]

Note: The original new leaded teflon bushings will allow a .251" shaft to pass through. Since all the K&B shafts measure .247"- OD, a brand new unit already has .004" total clearance before you run it.

Jim,

Would it be feasible to have the K&B shaft hard chromed then ground down to a more appropriate diameter / clearance, as opposed to having a new shaft fabricated from better material & requiring the broach?

Tim