Removing piston

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Removing piston

Postby Kevink8 » Thu Aug 28, 2014 4:14 am

Hello, someone gave me a Boat with a K&B 8906 outboard engine on it and it has been standing still for many years my guess 10-15+ but I'm trying to remove the piston from the crankcase but 1-2mm before it would come out it gets stuck also when I turn it by rotating the prop or flywheel it gets kind of stuck at the same point. I can't see any damage on the crankcase so I don't know if it's supposed to come out or if there's another way?
I hope someone can help me with this.

Thanks,
Kevin
Kevink8
 
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Joined: Thu Aug 28, 2014 4:04 am

Re: Removing piston

Postby SteveM » Thu Aug 28, 2014 10:54 am

That model number is for the K&B 3.5cc outboard and these are great little motors. It will be virtually impossible to remove the piston by pushing it through the sleeve. These motors use ABC construction which refers to an Aluminum piston running in a Brass sleeve that is Chrome plated. The sleeve is tapered such that it narrows at the top of the stroke. This taper creates the seal so that combustion works properly and is completely normal. Sounds like your piston and sleeve is in great condition and some motors even squeak because of this taper.

What you need to do is remove the sleeve from the crankcase first. The best method to do this is to remove the assembled power head from the lower unit and remove the cylinder head and combustion head button. Take the brass compression washer from a new or used glow plug and with the piston at the bottom of its stroke drop in the washer on top of the piston. Next, carefully slide the washer to the exhaust side so that it hangs over the edge of the piston and can be seen in the exhaust port. Then gently rotate the crankshaft pushing the piston up so that the washer engages the edge of the sleeve. Continue rotating the crankshaft until the sleeve is raised out of the crankcase so that you can use your fingers to remove it. Once the sleeve is out, you can remove the connecting rod from the crankshaft and the piston and rod assembly will drop out.
SteveM
 
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Re: Removing piston

Postby Kevink8 » Thu Aug 28, 2014 12:46 pm

Thanks alot for the quick response Steve also made everything clear eventhough my brother got it all out after some more toying with it.
Now I put everything back together after cleaning everything properly and checking for rust etc and everything looks good just when i put it back together there is a small gap between the Head Button and the crankcase it's about 0.5mm or less.
I don't remember if it was like this or not but i'm hoping on trying it out this weekend could you tell me what kind of fuel I need? and is there anything else that I have to do or know before I start it up?

Appreciate the help,
Kevin
Kevink8
 
Posts: 2
Joined: Thu Aug 28, 2014 4:04 am

Re: Removing piston

Postby SteveM » Thu Aug 28, 2014 2:43 pm

Outboards require an electric starter, good glow plug and mid to high nitro content. When you use an electric starter, be sure to connect the starter in reverse polarity. The outboard motors have a reverse rotation crankshaft so you need to spin them clockwise to start them. Spin it in your hand and watch the prop when you spin the motor to see what I mean.

I raced the K&B 3.5cc in IMPBA District 1 races for over 15 years and primarily used Byron 25% nitro fuel with one extra ounce of SIG AA castor added to each jug. Nitro boat racing can be challenging and to finish first, you must first finish. The higher nitro fuels in the 40% to 60% range will give more power, but you rick blowing glow plugs and the high nitro is tough on motors and bearings. Racing 3.5cc outboards is tricky enough due to the hull type which is why I went with the lower nitro and extra oil. I used to run between 12 and 20 thou head clearance depending on the brand and nitro content of fuel as well as the weather.
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