K&B 3.5 SX question

[racer504]

I'm new to boating and recently acquired a new K&B 3.5 SX. The motor is installed on a Top Speed 2. My question concerns the prop shaft bearing assy. Seems that after just a few runs (6-8) the bearing has become loose allowing the prop shaft to be very sloppy. I was using the recomended oil/STP mix to lube the bearing. I started with a Prather 220 prop but couldn't get any speed so I went to an Octura 440 (I think) Went a lot better with the 440 (sharpened/balanced/polished)prop but when I was cleaning it up I noticed the prop shaft was wobbly. I guess I'll need to order another prop shaft assy but I would like to know how to prevent this in the future. Also what is a good prop for this combination? It still seems like it should be turning up somewhat better than it sounds. What are some of the other guys running on this combination? Any suggestions appreciated. Mike

 

[Kris Flynn]

If you are sure the prop is properly balancd, then your best bet would be to get a prop shaft assembly from www.grimracer.com

Or Brian Nelson on this forum also makes a replacement hub.

Kris

 

[shoboat]

Mike,

The X-440 is just a little too big in diameter and just a little too much cup

for your set up. If you reduce both the boat and motor will be a lot happier.

38.50mm and 3.21" to 3.46" of cup is plenty for a tunnel hull. Oh, I forgot

to tell you the 220 is a great propeller, it just needs a little more work also.

The 220 likes a trailing edge backcut (3 mm) and then the propeller can run real

well.

Good Luck,

Mark Sholund

 

[Brian_Nelsen]

Actually I make the prop shafts Grim Racer sells. Grim is the USA distributor so contact him for the propshaft assembly. It will out last the factory unit even if you never lube it.

The lube you are using is fine its what I use and have for years. With any prop shaft assembly you need to make sure you lube both the flex shaft and the prop shaft. Even with the fine materials we use in our prop shaft assemblies lack of lube is a killer. Remember they run in water which is abrasive. Some people have started plugging the holes in the lower unit at the propshaft end to stop the water from entering the lower unit. This is fine as long as you have some way to lube both of the flex shaft and the propshaft.

Keep it cowl side up

Brian

 

[MarkScott]

The Nelson replacement is the way to go. Make sure the prop you plan to use is balanced/sharpen. Word of warning, if you plan on racing IMBPA, the Nelson unit will make you motor illegal in the Sport 21 tunnel class. Rules state nothing can be altered from factory on the lower unit.

 

[piper_chuck]

The Nelson replacement is the way to go. Make sure the prop you plan to use is balanced/sharpen.  Word of warning, if you plan on racing IMBPA, the Nelson unit will make you motor illegal in the Sport 21 tunnel class. Rules state nothing can be altered from factory on the lower unit.

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Other than a bit of sharpening and polishing below the cavitation plate, right?

 

[Brian_Nelsen]

Ya we gotta work on that part of the rules. I mean we allow anytiller arm. The propshaft does not change the appearance of the lower unit and it certainly does not make it go faster. It just addresses a maintanance issue in regard to the fit of the shaft to the bushing.

Some will argue that oilers should be allowed, my opinion is this. Oilers change the appearance of the engine and lower unit.

We could add the following to the list of exception.

I. Any propshaft assembly provided it does not alter the OEM prop and drive dog location.

Just my thoughts

Oh and People always spell my last name wrong it is spelled Nelsen just for information sake.

Brian Nelsen

 

[Grimracer]

Sport racers,

Im not sure and i need to think about this but adding durability is or might be a performance enhancement... i dunno..

I keep thinking that if one is not durable enough then one would either switch to another brand or let the MFG know of the problem.. I know this does not sound good for a guy that sells a upgrade part but im thinking of all racers and not just what the sale of the part can do for me..

The part... would.... add something (in this case durability) the original MFGs motor.... not to unlike a different tiller arm or throttle arm...?

Im open to talking about this.

Grim

 

[Jerry Dunlap]

I don't see where an after market stub shaft is a performance enhancing addition. Just my opinion.

I get all kinds of spam related to performance enhancing medications, but I think that's a different topic .

JD

 

[piper_chuck]

I see the rules limiting modifications as accompishing several things. Performance is obviously one part of it. Equally important to new boaters is keeping cost and complexity down. Things like oilers add to the cost of the engine. They also increase the complexity of setting up and operating the engine. Since prop shafts do wear out, they fall into a different category. If the aftermarket prop shaft is in the same price range as the original, allow it. If it's significantly more expensive, don't allow it for sport engine. However, once one starts making such changes, the rules get even more complex, so in the end, the more "stock" the engine stays, the better. K.I.S.S. - Keep IMPBA Sport Simple.

 

[racer504]

Thanks for the replies to my questions! The information you all supplied should keep me busy for a while. Mike

 

[Mike Larson]

Hey Mike! Replace the p/shaft assembly and check your props balance accordingly... keep the cable lubricated religiously, save ya in the future, now, since the words of advice seem to have arrived on running the Impba " sport" class... let ya in on the current sport class basics, send the motor to your favorite engine builder of choice, and have him internally modify the works ( staying within the stock appearing rule of course) head clearance, timing, etc, for high nitro ( 60%) solder the left side water outlet shut, drilling a 50 thousandths hole through the water jacket on the right side to shoot water to the glow plug only, leave out any screws that allow better escape of exhaust gases, ( you know, it musta fell out) If Im thinkin the sx has a cannister and there aint much to do there.... i run a lightened flywheel on mine, too, ( looks stock sittin there) ( this may or may not be legal, the flywheel is, stock appearing) make sure the skeg/fin is absolutely perpendicular to the lower unit, ( careful, careful) get a coupla props from Mark, test and trim the boat out to the point you think itll compete, and wha-la! youre racing sport tunnel class! My solution to the nelsen propshaft was to have mine anodized black ( stock appearing, you know) its a nice piece, it should last forever. Good luck, fast racin mike

 

[piper_chuck]

  Hey Mike!    Replace the p/shaft assembly and check your props balance accordingly... keep the cable lubricated religiously,  save ya in the future, now, since the words of advice seem to have arrived on running the Impba " sport"  class...  let ya in on the current sport class basics, send the motor to your favorite engine builder of choice, and have him internally modify the works ( staying within the stock appearing rule of course)  head clearance, timing,  etc, for high nitro ( 60%)  solder the left side water outlet shut, drilling a 50 thousandths hole through the water jacket on the right side to shoot water to the glow plug only, leave out any screws that allow better escape of exhaust gases, ( you know, it musta fell out)  If Im thinkin the sx has a cannister and there aint much to do there....  i run a lightened flywheel on mine, too,  ( looks stock sittin there)  ( this may or may not be legal, the flywheel is, stock appearing)  make sure the skeg/fin is absolutely perpendicular to the lower unit, ( careful, careful)  get a coupla props from Mark, test and trim the boat out to the point you think itll compete,  and  wha-la! youre racing sport tunnel class!  My solution to the nelsen propshaft was to have mine anodized black ( stock appearing, you know)  its a nice piece, it should last forever.  Good luck, fast racin    mike 

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It's always interesting to see the lengths people will go to win. Seems that winning honestly doesn't matter. This is exactly why the engine claim rules need to be changed. Set the price so low that anyone actually doing the above will feel it in the wallet when their modified "stock" engines is taken from them.

 

[Grimracer]

When I took on the job as IMPBA OBD the first question I had was… What was the intent of the sport tunnel class? Beginners? Stock motors? Sport Motors? What did all this mean…

IN IMPBA INTERNATIONL COMPITITION ITS NOT A CHEAP BEGINNERS CLASS and never was.....

It has a hole in and a hole out.. if you are caddy enough to know how or have the money to pay somebody to make changes have at it... The point is that its a bragging rights class for the veteran racer and STOCK is only dictated by the exterior appearance of the motor.. not the class itself.... my favorite thing about this class is that its almost impossible to cheat.. if it looks stock on the outside and its got a bore that’s under .320.. its legal.. END.. the pure act of having the knowledge and or spending money is not cheating...

If you disagree with the rules RACE MOD... sorry to sound so bold..

Now what is REALY FUNNY is that the last two Sport tunnel races at the Internats...2004 and 2005 were won by 100% bone stock bolt it on and lean it out till it shits parts K+Bs...... do most beleave this.. nope and the people that can not catch the leader.. never will..

IMPBA SPORT TUNNEL

Stock appearing on the outside

.320 bore

Its not a beginners class and in IMPBA international competition never was.

If you have the money or the knowledge.. you are one step ahead.. if not you best do your home work..or.. go race mod.. it’s a great class too..

Im not trying to come off so negative and if I am I apologize.. if you want to win in sport tunnel you best do your home work.. it’s a great tuners class..

Grim

 

[piper_chuck]

Forgive me for not being in a position of authority like you are, but I'm having trouble reconciling the rules against what you say about the class:

"Engines must be standard factory production with a minimum of 100 units

available for sale to the general public."

An engine that has internal modifications is clearly NOT a "standard factory production" engine any longer.

and:

"Original carb bore and exhaust configuration will be retained as

manufactured. No modification to the carb bore or exhaust outlets will be

allowed."

If anything goes as long as it can't be seen is truly acceptable in this class then it's obvious that the IMPBA has little interest in beginners. If what you say is not what the originators of the class intended then it's time to fix the class.

I've exchanged emails with people in leadership positions within IMPBA that lead me to believe that your interpretation is WRONG. According to one, the rules were meant to say "the way you got it out of the box was the way you ran it". This is quite a bit different from what you are saying. If this is true then somewhere along the way, the class was hijacked by people who want to win at all costs.

The modified tunnel class leaves plenty of room for people who want to "tune". Why is it so hard for people to allow a few classes where people can run stock engines?

I wonder if any others in IMPBA leadership positions are reading and care to comment. What about those who originated the class?

 

[Grimracer]

Forgive me for not being in a position of authority like you are, but I'm having trouble reconciling the rules against what you say about the class:"Engines must be standard factory production with a minimum of 100 units

available for sale to the general public."

An engine that has internal modifications is clearly NOT a "standard factory production" engine any longer. 

and:

"Original carb bore and exhaust configuration will be retained as

manufactured. No modification to the carb bore or exhaust outlets will be

allowed."

If anything goes as long as it can't be seen is truly acceptable in this class then it's obvious that the IMPBA has little interest in beginners.  If what you say is not what the originators of the class intended then it's time to fix the class. 

I've exchanged emails with people in leadership positions within IMPBA that lead me to believe that your interpretation is WRONG.  According to one, the rules were meant to say "the way you got it out of the box was the way you ran it".  This is quite a bit different from what you are saying.  If this is true then somewhere along the way, the class was hijacked by people who want to win at all costs. 

The modified tunnel class leaves plenty of room for people who want to "tune".  Why is it so hard for people to allow a few classes where people can run stock engines?

I wonder if any others in IMPBA leadership positions are reading and care to comment.  What about those who originated the class?

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Mr, PiperChuck.. Im in no place said this was right or wrong.. It is however the facts...

Hope you understand.

grim

 

[Grimracer]

Forgive me for not being in a position of authority like you are, but I'm having trouble reconciling the rules against what you say about the class:"Engines must be standard factory production with a minimum of 100 units

available for sale to the general public."

An engine that has internal modifications is clearly NOT a "standard factory production" engine any longer. 

and:

"Original carb bore and exhaust configuration will be retained as

manufactured. No modification to the carb bore or exhaust outlets will be

allowed."

If anything goes as long as it can't be seen is truly acceptable in this class then it's obvious that the IMPBA has little interest in beginners.  If what you say is not what the originators of the class intended then it's time to fix the class. 

I've exchanged emails with people in leadership positions within IMPBA that lead me to believe that your interpretation is WRONG.  According to one, the rules were meant to say "the way you got it out of the box was the way you ran it".  This is quite a bit different from what you are saying.  If this is true then somewhere along the way, the class was hijacked by people who want to win at all costs. 

The modified tunnel class leaves plenty of room for people who want to "tune".  Why is it so hard for people to allow a few classes where people can run stock engines?

I wonder if any others in IMPBA leadership positions are reading and care to comment.  What about those who originated the class?

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Chuck.. after doing more reading on this post you understand the rules very well.. SPORT TUNNEL IS NOT FOR BEGINNERS AND NEVER WAS.. again...SPORT TUNNEL IS NOT FOR BEGINNERS AND NEVER WAS... does this mean that the IMPBA does not care about new racers? not at all.. who said tunnels were the door to model boat racing.. not me.. not the IMPBA.. sorry if you do not get it.

Do I have the answer as to what is.. nope.. don’t have a clue.. seems to me that Joe K and Randy R have an idea how to do this so you might want to chat with them..

ROCK ON

Grim

 

[piper_chuck]

Mr, PiperChuck.. Im in no place said this was right or wrong.. It is however the facts...

I realize you were describing the reality of the class as it exists today. What I'm trying to determine is why a class that represents a great entry into the sport does not have adequate rules (perhaps it's just a problem with interpretation and/or enforcement) that would allow it to be such.

I don't know the details of what the IMPBA leadership is doing to encourage beginners. I do know that it's a big problem and I have shared my thoughts with some of them.

I do know that when I was a beginner, years ago, I started with a B tunnel. This was, and remains, a great entry class. The self contained nature of the engine keeps the cost low and installation pretty simple. The recent arrival of the TS2 at such a good price point, and with the advertising weight of Hobbico behind it, presents a great opportunity to grow this sport. However, I can say with certainty that when beginners discover that they are significantly slower because their new $300 engine doesn't have all the internal mods of the seasoned racer's, many of them will leave very quickly. Some of the seasoned veterans will respond that they weren't very serious anyway, and to some extent, this is true. Unfortunately, that attitude leaves out many other people who may just not want, or can't, spend as much money.

In some of the emails I've exchanged about encouraging beginners, one response has come back loud and clear, DON"T CREATE ANY MORE CLASSES! So, if the list of classes is already too full, why not work on making sure that some of the existing classes are defined in a manner that they support and encourage beginners.

Anyway, this has hijacked the original purpose of the thread. I created a new thread for this subject. I invite anyone with an opinion, or ideas, on this subject to join in the discussion over there.

 

[racer504]

Actually I make the prop shafts Grim Racer sells. Grim is the USA distributor so contact him for the propshaft assembly. It will out last the factory unit even if you never lube it.
The lube you are using is fine its what I use and have for years. With any prop shaft assembly you need to make sure you lube both the flex shaft and the prop shaft. Even with the fine materials we use in our prop shaft assemblies lack of lube is a killer. Remember they run in water which is abrasive. Some people have started plugging the holes in the lower unit at the propshaft end to stop the water from entering the lower unit. This is fine as long as you have some way to lube both of the flex shaft and the propshaft.

Keep it cowl side up

Brian

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Brian, Thanks for your info . I've got a propshaft coming form Grimracer as you recomended. I would like to know what the normal life is on these shafts and should I be lubing the shaft before every run? Also, Is lubing the cable after each session sufficient? Thanks, Mike

 

[Jerry Dunlap]

At the 2005 IMPBA Internats, I ran 20 Sport tunnel with a stock O.S. 21 with the head shim removed. I think it now has something like .004 head clearence. I ran an AquaCraft TS2(not a big surprise seeing how I designed the boat), a Props 4 U M440, and O'Donnel 65% Boat Fuel. Even with a "O" round, I ended up 5th out of something like 32 boats in the class. I felt my boat was competitive with other boats in the class. It wasn't the fastest, but I managed to win two rounds. This boat also ran in 20 Stock Tunnel at the NAMBA Nats. It's truly a stock class engine/hull. Granted, 40 years of racing model boats proved benefical. But, I think it proves you can do well in IMPBA's 20 Sport Tunnel Class with a true stock setup.

JD