OLD K&B 7.5, ~8702 model...square carb OLD...lines/tubes

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OLD K&B 7.5, ~8702 model...square carb OLD...lines/tubes

Postby frd1952 » Mon Feb 23, 2009 8:38 am

http://www.modelengine.org/gallery/deta ... ode=search is where you can see a pic of this motor...where do the lines/tubes go please ?? Top on cone of carb to fuel tank ? bottom of cylinder head goes to where ? Bottom in the lower unit goes where, or is just exhaust or what ? Any help appreciated...thanks. F
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Postby SteveM » Mon Feb 23, 2009 9:14 am

Your motor is a water cooled 2-stroke outboard. The brass tube behind the prop scoops water which is then fed through the pinkish colored fuel tubing into the cylinder head exiting through the curved brass water fitting on the other side of the cylinder head. The fuel tubing on the carb goes to the fuel tank.
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WOW...thanks, a few more ?? now please

Postby frd1952 » Mon Feb 23, 2009 9:59 am

OK, I get the water cooled and 2 stroke (glad to know that....a) what type of fuel should I use, and b) does the water outlet fitting need any tubing on it when it runs (hopefully), and c) what is the fitting for on the lower unit if you know )? Any idea what model this old motor is and where I can get any diagrams, specs, etc ?? Thanks a lot !! F
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Re: WOW...thanks, a few more ?? now please

Postby SteveM » Mon Feb 23, 2009 1:20 pm

frd1952 wrote:OK, I get the water cooled and 2 stroke (glad to know that....a) what type of fuel should I use, and b) does the water outlet fitting need any tubing on it when it runs (hopefully), and c) what is the fitting for on the lower unit if you know )? Any idea what model this old motor is and where I can get any diagrams, specs, etc ?? Thanks a lot !! F


a) I ran 25% nitro in my K&B 3.5cc motors while others ran up to 60% nitro. The 7.5cc motors seemed to like 40-45% nitro fuels

b) the curved nipple where the water exits from the cylinder head does not need tubing. Racers like to see the water squirting out so they know the head is getting fresh cooling water when running.

b) the nipple on the lower unit is a pressure take-off fitting. The lower unit acts as the muffler and most racers use a pressure system for fuel. You setup the fuel tank with one feed to the carb and the other to the muffler nipple. This way the fuel is pressure fed to the carb for better reliability.

Your motor is several years old and looks to be the original 7.5cc outboard. MECOA now own the rights to the K&B line and might have more info for you.
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Thanks Steve...to confirm...

Postby frd1952 » Mon Feb 23, 2009 1:28 pm

Got it...just to confirm, I should have a tube then running from the muffler nipple back to the fuel tank to create pressure in the tank/fuel system...correct ? And my tank should have 2 places on it to connect tubes then ? Not at home by the tank to check Steve, but makes sense and when we opened the box up in my buddies basement there was no tube attached to the muffler nipple, so I would like to confirm. Do I need any special tubing to run the gas lines, water circulating line, muffler pressure lines? I guess all the same size ( I see on hobby sites, S, M, L ??) and for nitro they say use silicone tubing...for everything use this ?? Thanks again.

F
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Postby SteveM » Mon Feb 23, 2009 3:11 pm

Mose airplane fuel tanks use a rubber stopper that allows three pipes, but for a boat you want to use only two. The third must be sealed for a pressure system to work. The vent tube that is normally bent so the brass tube inside the tank points upward is where you attach the pressure to.
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Postby SteveM » Mon Feb 23, 2009 3:13 pm

Medium size fuel tubing should be fine. Large may be a bit too loose.
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Postby frd1952 » Tue Feb 24, 2009 5:47 am

thanks Steve...will do. Took apart the engine last nite...was well lubed 25 yrs ago it seems when stored...EXCEPT for the small section where the flywheel cone and shaft goes down toward the bottom and grabs the hole on the back end of the piston. In that ~ 1-2 inch space where the shaft goes thru a bearing or two, has a shaft that screws in on the top for the cone to sit on and attach to and the pin on the bottom to grab the piston, it seems frozen up. I think that should spin pretty freely, since it would when attaching the starter motor to the cone, and it would need to spin since attached to the piston. Got it soaking in gasoline and will see if I can free it up...any ideas welcomed. I wonder if that entire shaft should be able to be pressed/knocked out downward towards the prop ? seems like it should but a few wraps with the hammer on top of the threaded cone shaft had nothing moving.

Thanks again Steve.
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Postby SteveM » Tue Feb 24, 2009 7:11 am

Sounds like you're describing the crankshaft to me.

The nose of the motor (with the aluminum flywheel) uses a threaded stud with a cone washer and nut to retain that flywheel. The crank is hollow and has a cutout that matches the carb mount in the crankcase.

The pin on the end of the crankshaft inside the crankcase connects to the bottom of the piston rod. If you disconnect the piston rod from the crankshaft you should be able to spin it easily. If it doesn't spin, then perhaps things are gummed up or you may have a rusted or seized ball bearing. The crankshaft rides on two ball bearings.
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Yes, it is the crankshaft...see pics

Postby frd1952 » Tue Feb 24, 2009 7:31 am

Steve, Yep it is the crankshaft that is frozen...pics are at >>> http://www2.snapfish.com/thumbnailshare ... =161727161 >>>.I have it just in the crank housing, with carb off. Soaked in gas overnite, now have it doused in Liquid Wrench. I believe it should turn pretty freely by putting in the threaded shaft for the starter cone/flywheel and turning it there, or by turning it from the bottom with the pin that goes into the back of the piston...correct? Should I be able to knock the entire crank shaft assy out of the housing and thru the bearing at the top, how ? Can I try vice grips or something to turn the crank and if so grab it by the threaded shaft on top (where the cone attaches) , or by the pin on the bottom that goes into the back of the piston ?Neither place can I budge it at all...does look a little rusty/dirty espec when I look close up at the pictures of the inside...see pics. Any ideas on how to free this crank up, assuming it should spin/turn pretty freely ? I have the old model, per the spec sheet, with the set screws that held the carb in the carb body throat (now all removed). Piston moves in the cylinder nicely and some lube in there, and drive shaft well lubed and looks in good shape. Ideas on the crank welcomed...My crank does NOT look exactly like the one in the spec sheet (surely mine is older), and on the bottom has another spacer or bearing and the pin that grabs the piston looks like it is pressed in vs. the spec sheet model, but pretty similar....thanks. F
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Re: Yes, it is the crankshaft...see pics

Postby SteveM » Tue Feb 24, 2009 7:35 am

frd1952 wrote:Steve, Yep it is the crankshaft that is frozen...pics are at >>> http://www2.snapfish.com/thumbnailshare ... =161727161 >>>.I have it just in the crank housing, with carb off. Soaked in gas overnite, now have it doused in Liquid Wrench. I believe it should turn pretty freely by putting in the threaded shaft for the starter cone/flywheel and turning it there, or by turning it from the bottom with the pin that goes into the back of the piston...correct? Should I be able to knock the entire crank shaft assy out of the housing and thru the bearing at the top, how ? Can I try vice grips or something to turn the crank and if so grab it by the threaded shaft on top (where the cone attaches) , or by the pin on the bottom that goes into the back of the piston ?Neither place can I budge it at all...does look a little rusty/dirty espec when I look close up at the pictures of the inside...see pics. Any ideas on how to free this crank up, assuming it should spin/turn pretty freely ? I have the old model, per the spec sheet, with the set screws that held the carb in the carb body throat (now all removed). Piston moves in the cylinder nicely and some lube in there, and drive shaft well lubed and looks in good shape. Ideas on the crank welcomed...My crank does NOT look exactly like the one in the spec sheet (surely mine is older), and on the bottom has another spacer or bearing and the pin that grabs the piston looks like it is pressed in vs. the spec sheet model, but pretty similar....thanks. F


I can't see the pics unless I register with Snapfish.

I assume you've removed the PTO and can see the end of the crank. Have you removed the cylinder head, sleeve, piston and connecting rod?
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OLD K&B 7.5, ~8702 mod, tore down, crank frzn, now what

Postby frd1952 » Tue Feb 24, 2009 8:07 am

Steve, I put the pics here for ya.. http://www.modelengine.org/gallery/sear ... t=1&page=1 , and http://www.modelengine.org/gallery/sear ... t=1&page=2 , ...I did not pull off the head, piston seems to move well in the cylinder...I think you can tell my stage of tear down from the pics...need to push out, or twist, or free up the crank inside of the housing I think is where I am stuck now.
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Postby SteveM » Tue Feb 24, 2009 8:19 am

Can you re-attach the flywheel and use that to gently turn the crank? Once assembled, and you have the nut tightened, hold the flywheel and give the nut a gentle tap with a hammer. This loosens the crank a few thousands of an inch so nothing binds. Use an old toothbrush with the WD-40 to scrub the case and bearings a bit.
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will try ..does the crank actually push out of the housing??

Postby frd1952 » Tue Feb 24, 2009 9:11 am

I will try that tonite Steve...thanks. Does the crankshaft actually push out (towards prop, or towards cone flywheel) of the housing somehow ? I see nothing holding it in and suspect it should just spin in the bearings and should come out of there somehow, and maybe easily if not bound up? correct?

F
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Postby SteveM » Tue Feb 24, 2009 9:37 am

The crank comes out of the nose piece from the back, ie: not via the flywheel. They are a PITA to remove and you often need heat and/or a press to gently remove them.
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little lost

Postby frd1952 » Tue Feb 24, 2009 11:01 am

Steve, I am a little confused. In the pictures titled Old K&B..8, and 9, I think what is shown is the crankshaft inside of the crankshaft housing...in my terms at least, m/b wrong...the housing is a solid piece of alum tubing type piece with the frontal port where the carb slides in. On one end of the shaft is where the treaded pipe/shaft goes that the cone sits on, and on the bottom of the shaft where it sticks out beyond the housing is what looks like a bearing right next to the bottom of the housing (this does spin) and then next to that (as you go down towards the piston & prop) is the crank pin that catches inside of the piston. I am wondering how to get that crank assy out of the housing piece, as I think that is necessary to see how badly it is rusted or whatever and clean it out. Right now neither the cone, nor the final part at the bottom with the pin in it that grabs the piston, will turn. I think they (cone, threaded rod, crank shaft inside the housing, and the part at the very bottom of this little assy, are connected and should all spin inside the housing and the bearing at the top, and what I think is another bearing near the bottom....do I have this correct, and what do you mean about taking the crank out from the back (is this what I am calling the "bottom" ?...as I feel it is lower on the motor as the motor stands up), and are you suggesting if needed to heat up the housing gently with a torch and then trying to tap/squeeze the shaft out by pushing on the top and forcing it to come out the bottom (towards the piston end) ? Thanks, Frank
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Re: little lost

Postby SteveM » Tue Feb 24, 2009 2:44 pm

frd1952 wrote:Steve, I am a little confused. In the pictures titled Old K&B..8, and 9, I think what is shown is the crankshaft inside of the crankshaft housing...in my terms at least, m/b wrong...the housing is a solid piece of alum tubing type piece with the frontal port where the carb slides in.


also known as the nose piece

On one end of the shaft is where the treaded pipe/shaft goes that the cone sits on, and on the bottom of the shaft where it sticks out beyond the housing is what looks like a bearing right next to the bottom of the housing (this does spin) and then next to that (as you go down towards the piston & prop) is the crank pin that catches inside of the piston. I am wondering how to get that crank assy out of the housing piece, as I think that is necessary to see how badly it is rusted or whatever and clean it out.


This is where you may need heat and/or a press to push the crankshaft out. Imagine pushing down on the flywheel as that's the direction you need to push

Right now neither the cone, nor the final part at the bottom with the pin in it that grabs the piston, will turn. I think they (cone, threaded rod, crank shaft inside the housing, and the part at the very bottom of this little assy, are connected and should all spin inside the housing and the bearing at the top, and what I think is another bearing near the bottom....do I have this correct


Yes.....that is all the crankshaft and it all spins together

, and what do you mean about taking the crank out from the back (is this what I am calling the "bottom" ?...as I feel it is lower on the motor as the motor stands up), and are you suggesting if needed to heat up the housing gently with a torch and then trying to tap/squeeze the shaft out by pushing on the top and forcing it to come out the bottom (towards the piston end) ? Thanks, Frank


The circular part with the crank pin that connects to the piston rod is the end of the crankshaft that you must pull to remove the crankshaft.
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to confirm

Postby frd1952 » Tue Feb 24, 2009 3:01 pm

Will that circular part with the pin, actually come off of the shaft by itself, and separate away from the shaft and the lower bearing that I think is just above it, or is it really permanently attached to the shaft going up through the housing to where the treaded rod screws in at the top of the shaft, for the cone to attach to?
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pushing it out..

Postby frd1952 » Tue Feb 24, 2009 3:07 pm

When pushing out the shaft, like pushing down on the cone, should I actually push down just on the rod part in the center (with the threads on it) or really try to push the entire bearing, or sleeve, pin, etc everything inside the housing, out at the same time and use a "pusher" that covers that entire top surface, vs. just pushing/tapping on the center rod portion...sorry to be so slow on this, but how or IF that entire assy, bearings, shaft, etc stays in the housing is not clear to me...seems like it should all be able to push out together, but just me guessing...thanks, Frank
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Re: to confirm

Postby SteveM » Tue Feb 24, 2009 3:30 pm

frd1952 wrote:Will that circular part with the pin, actually come off of the shaft by itself, and separate away from the shaft and the lower bearing that I think is just above it, or is it really permanently attached to the shaft going up through the housing to where the treaded rod screws in at the top of the shaft, for the cone to attach to?


The crankshaft is all one piece and the circular part will not come off. It's part of the crank itself.
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Postby SteveM » Tue Feb 24, 2009 3:32 pm

Click the link below for an exploded view.

http://mecoa.com/kb/48/7510-exp.pdf
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Postby SteveM » Tue Feb 24, 2009 3:34 pm

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got it...push it all?

Postby frd1952 » Tue Feb 24, 2009 3:46 pm

OK, I can tell the shaft, female threaded shaft, pin and circular bottom are all one piece..the crank shaft. Only ? left re this part is should I try to push out just that crank shaft and try to leave the front/rear (or top/bottom as I woulda called them) bearings in place in the housing, or try to push all of that out stuff out at once. Just wondering where to tap when I try to push it out the rear/bottom...thanks for hanging w me on this.

F
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Postby SteveM » Tue Feb 24, 2009 4:04 pm

The bearings will normally stay in the nose piece. Sometimes, the rear bearing closest to the round part of the crank sticks to the crank and can be difficult to remove.
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ok,,,will try to push out shaft only

Postby frd1952 » Tue Feb 24, 2009 4:45 pm

Got it...will advise. I will try to push out JUST the center shaft section and will not be surprised if the bottom bearing comes out with it. Will also heat it up first....either with a torch or in the oven...fingers crossed. Thanks loads.

Frank
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Postby SteveM » Tue Feb 24, 2009 4:52 pm

If you need to add a little force, screw in the shaft stub and put an acorn nut on the end before tapping with a hammer very gently.
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Postby frd1952 » Tue Feb 24, 2009 4:55 pm

got it...will do Steve
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