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K&B 3.5 OB

Old 09-12-2007, 03:30 PM
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500 lb. koolaid man
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Default K&B 3.5 OB

I bought a K&B 3.5 OB for my tunnel hull and received it a couple of days ago(used, ebay). This will be my questions thread since I know I'm gonna have a lot of questions.

The prop nut that came in the mail with it doesn't screw on all the way, it's too small. So I went to ACE today and got a stainless locking nut that fits the threads. Will this be ok to use(no threadlock)?

The engines mount isn't going to fit the "main holes" on the tunnel hull. The "main holes" are medal threaded and had screws in them to be used. There are also two(4 holes each) other spots for engine mount screws, all smaller radius and bare wood. One of the "other sets" fits this mount but the engine mount slightly doesn't clear where it's supposed to go(Top left corner has an edge). So should I use a wood file to grind it flat and smooth so it will fit, then get screws that will fit and use lock nuts on the inside end(toward the hull) to hold them in place since they wont thread into the holes?

Both of my 2(airplane&car) wrenches are too wide to remove the glow plug out of the engine, and they're not even all that wide really, do I need to get a new wrench meant for boats, just one skinny enough to fit, or what? I'm confused as to why the space for a wrench is so darn skinny in the first place.

Is it ok to polish the outdrive with wet sandpaper to shine it up a little?

I'll be running in salt water and don't know what the maintenance is on this motor after each run.

thanks for the help.



Old 09-12-2007, 04:00 PM
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Dan S
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Default RE: K&B 3.5 OB

the 4 existing holes with the screws already in (photo) were made for a different mount than the one you have (Adjustable Dubro mount). you can try to match the holes to your mount, or you can replace the mount you have with a better one, or you can fill all the holes and start from scratch.

The prop nut that you are talking about, is it the bullet nut that we see on the picture?

if it is, it may not screw in all the way to the prop. How many threads can you screw the nut in? if you get 5 or more threads in than its not a problem.

on another note your also supposed to put a prop shock between the prop and the nut, cut a piece of water/fuel line approx 3/8 to 1/4 inch long, put your prop on, than put the prop shock and then the prop nut.
Don't squish the shock flat.

Dan
Old 09-12-2007, 04:50 PM
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dougaldy
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Default RE: K&B 3.5 OB

Koolaid,

Dan is correct in that the mount you have is not the one that the boat was drilled for. You can change these mounts easy enough or like he said you can also redo it if you choose to go that route as well, I would probably change the mount. I was a little unclear as to what you meant where your existing mount didnt quite fit. You want the motor to be centered and you want to be able to move it up and down for adjustment. As for the glo plug, yes you will need a glow plug wrench, or if you have a socket that fits, that will work as well. I have to use a socket and ratchet for my CMB because my glo plug wrench wont fit. The locking prop nut you bought should work just fine.

Scott
Old 09-12-2007, 05:26 PM
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Default RE: K&B 3.5 OB

The prop nut I'm talking about is the bullet nut in the picture, and in the picture it's on tight. It's within 2 or 3 threads of being on all the way, but the problem is the props 2 gaps(whatever you call um') don't even catch the two prong things with the bullet nut on tight. So I'll use the lock nut that I have and use a prop shock with it. Thanks for informing me about prop shocks.

Hmm... I see that both of you recommended either drilling the mount or filling the boats mount holes and start over. But didn't mention trying to use the holes that fit the mount. Maybe I didn't make much sense in the original post. Or the idea of taking a wood file to a small part of the boat(mounting part) is a bigger no no. I'm still a bit confused on this one.

Ok... what I said about the mounts might still be a little confusing. So...
One of the sets of holes does appear to fit this mount perfectly. However the top left corner on the boat(where the mount goes) has an edge just barely stopping the mount from seating nicely as is. I was thinking if I file down this edge, I could get screws and lock nuts to fasten the motors mount and all would be dandy.

Thanks for all the help.

edit: Now I feel dumb. I JUST realized that with the prop shock the bullet nut will work. I think you said that Dan, it just didn't click at first.

Also, is it ok to wet sand the outdrive to make it nice and shiny again? Thanks.
Old 09-12-2007, 08:00 PM
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Default RE: K&B 3.5 OB

I cut a piece of fuel line at 1/4" and put that in between the prop and the bullet nut, then tightened the nut all the way. The prop shock looks smooched but not flattened and it comes over the nut a little. Is it ok like this?

Thanks.
Old 09-12-2007, 08:48 PM
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Default RE: K&B 3.5 OB

Yes,

this is fine like that, just do your check every run and check the prop shock.

you can wet sand if you like or use a dremel with a polishing wheel with jewel rouge to polish the outdrive (thats what I did with my 7.5).

Dan

Edit: with the other pic you have posted you do have the adjustable motor mount, just was not obvious in the first pic. There are better mounts out there but this one is good.

there are way too many holes on that transom, I would fill everything up and start from scratch, and if 1/4" shock is too much you can go 3/8".
Old 09-12-2007, 09:20 PM
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Default RE: K&B 3.5 OB

Koolaid,

will you post a couple of pics with the mount and transon. You can take the mount off the motor and just use the mount for reference. I would like to see what you are talking about. If there are pre existing holes already there and it fits, then yes you can smooth up the transom a bit to make it seat nice and flush.

Scott
Old 09-12-2007, 10:31 PM
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Default RE: K&B 3.5 OB

It fits nice and snug against the left and right "walls". Here's some pictures of the mount lined up against the transoms holes. Where I boxed in red is what I think is making it slightly not fit. BTW I couldn't get the holes to line up perfectly for the picture but it seems they will all fit. It probably wont be until the weekend that I can really start working on it.


Old 09-12-2007, 11:15 PM
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Default RE: K&B 3.5 OB

Are the holes you are planning on using threaded or do they go through the transom? Also keep in mind, whatever holes you use, you are going to want enough room for adjustment to where the center of your shaft is about an 1/8th above the bottom of the sponsons. I would start there and make sure you have room to slide the mount up and down a good 1/8th-1/4". If the holes are not threaded you can easily pick up some 6/32 threaded brass inserts from Ace Hardware for about 50 cents apiece and thread those into the pre existing holes.

Scott
Old 09-12-2007, 11:41 PM
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Default RE: K&B 3.5 OB

That looks like an old Prather OB mount to me, I never liked them. I've used the Du-Bro and Octura adjustable mounts and liked them better.
For a glow plug wrench I really like the one that Dynamite sells as I've got at least 3 of them otherwise try to find a thin-wall 5/16" socket.
Old 09-13-2007, 07:26 AM
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Default RE: K&B 3.5 OB

Dan I think you ment the shock could be 3/16 instead of 1/4.......... correct?
Old 09-13-2007, 07:38 AM
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Default RE: K&B 3.5 OB

LOL

Correct, 3/16.
Old 09-13-2007, 07:42 AM
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Default RE: K&B 3.5 OB

ORIGINAL: 500 lb. koolaid man
Also, is it ok to wet sand the outdrive to make it nice and shiny again? Thanks.
It wasn't shiny when new.
Old 10-06-2007, 10:08 PM
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Default RE: K&B 3.5 OB

I've been rather busy lately so this project has been a slow one...
Anyways, after cleaning the outdrive, I put it all back together today. Here's the shiny pics

Next comes getting the outboard mounted, test running, getting the boat set up, etc...
Old 10-07-2007, 12:12 PM
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Default RE: K&B 3.5 OB

I would change all the fasteners to stainless steel right away before taking it to the water. Screw threads trap water and you will find steel screws will corrode real fast and will break off when you go to loosen them. Even if you have to special order them it is worth it.

Here's a link that I order from. All sizes and types and good prices.

Be sure to order longer ones for the head. For some reason K&B puts too short of screws into their heads so go to the next size longer, and ALWAYS oil the screws before putting them into aluminum.

[link=http://www.fastener-express.com/]Fastener Express[/link]
Old 10-07-2007, 08:09 PM
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Default RE: K&B 3.5 OB

Thank you very much for the info jetpack, I'll look into all that.

Today I got the mounting plate to line up just right with the transom and got the screws to go right into the existing holes, making a tight fit. The screws go directly into the thick wood, is that a definite no no?

A new problem has occurred with the mount. Look at the last two pictures and you will see that there is no way of getting an allen wrench to tighten these two bottom horizontal screws, let alone get them started by hand. I think my only option is to keep trying until I get them in by hand then use needle nose pliers to tighten them, or, buy a new mount($I don't really want to$)

Old 10-07-2007, 10:53 PM
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Default RE: K&B 3.5 OB

I'd go with a Du-Bro motor mount, seriously. You'll avoid all of the hassle that you're running into now with one and they're not that expensive.
BTW, the motor has to go a little higher. That's when you're going to find a mount like Du-Bro's way better.
Old 10-09-2007, 08:59 AM
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Default RE: K&B 3.5 OB

Hey the best mount to go with on that would be the redneck racing hi jack mount . it is all aluminum and has easy ajustments . Check out ebay sometimes there are some for sale on there . Also the mount gives a good amount of offset off the transom which inturn gives more performance ! Also running in saltwater will not hurt the motor . It will need a lot more care after running though . There should be a tiny hole below the flywheel , after running make sure you spray some wd-40 or crc 6-56 lube in the hole this will flush out the upper bearing . also spray in the lower hole right where the motor bolts to the lower unit . Remove the drive flex shaft and lube it good . The pull the glow plug out and put some after run oil in it . spin the motor over several times and install the glow plug . And use all stainless steel hardware !
Old 10-09-2007, 10:07 AM
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Default RE: K&B 3.5 OB

If your gonna stick with that mount for the time being, take the Allen wrench that fits and cut it down. Thats the only way it will fit for now.

Dan.

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