Stuck cylinder/head screws on K&B Sportster 45

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Stuck cylinder/head screws on K&B Sportster 45

Postby Chucky » Mon Jun 17, 2013 5:58 am

An R/C buddy gave me an older Sportster 45 with the needle valve mounted on the carburetor. Although it will run, the compression is not what it should be and the piston shows visible signs of wear, so I'm considering replacing the piston and cylinder. Unfortunately, I have not been able to break the head screws free and do not want to strip them out or something worse trying. The engine is in otherwise good shape with no visible signs of corrosion. Is there a recommended method of dealing with stuck steel screws in an aluminum engine such as this?
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Re: Stuck cylinder/head screws on K&B Sportster 45

Postby max hansen » Mon Jun 17, 2013 9:24 am

Some of those screws go all the way though the head & cylinder & into the crankcase. I use a LPG torch & a oven mitten . Get the engine hot in the head & case areas & then try your screws. I have always found that works. Good luck , Max
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Re: Stuck cylinder/head screws on K&B Sportster 45

Postby Chucky » Tue Jun 18, 2013 6:43 am

Applied heat with a propane torch and got the stubborn screws out. These go clear through the cylinder into the crank case and the threads were full of old castor varnish. The heat apparently softened the varnish enough to allow the screws to be removed. Thanks for the tip.
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Re: Stuck cylinder/head screws on K&B Sportster 45

Postby chiefss » Thu Jun 20, 2013 12:34 pm

A new piston and cylinder, if you could find one, would probably cost more than the engine is worth.These weren't the greatest engines ever made and the ones that put K&B out of business.
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Re: Stuck cylinder/head screws on K&B Sportster 45

Postby SteveM » Fri Jun 21, 2013 5:17 am

The K&B Sportster motors do not use a traditional ABC piston and sleeve setup, but instead used an AAC setup that uses the upper portion of the cylinder as the sleeve itself. These are bushed motors and did require some break-in to seat the parts properly. My Sportster 20 remains a strong runner and also worked well for me with a Davis Diesel Head. The simplicity and low parts count of these motors makes them ideal for beginners. They may not have been as powerful as a twin ball bearing ABC motor, but they were priced right and were user friendly. I believe that K&B had other issues that saw them fold as a company and I don't think you can blame their demise on the Sportster line.
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Re: Stuck cylinder/head screws on K&B Sportster 45

Postby chiefss » Fri Jun 21, 2013 9:52 am

Oh but I can as did several other big time engine gurus. Even George Aldridge called them "Modern Slag Engines" in reference to the old GHQ and other junk of the past.

They had a crankshaft that ran on the plain aluminum crankcase, no bronze bushing, and were prone to wear there. They also chromed the piston and NOT the cylinder. They were huge compared to their counter parts in size and wouldn't fit any commercial motor mounts. The 45 was as big as most 60's.

As stated, finding parts at a reasonable price is going to be difficult if you can find them at all. Not worth the cost. Another problem the early ones had was too much cooling fin in the head so they ran cold and didn't idle well. They finally chopped off the fins and the engine looked so weird with the plug sticking up a mile. that's when they first got the bad name and it went down hill from there. Well documented. Even Mecoa's web site states that. Parts and engine no longer available from mecoa.
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