Buying used K&B engine

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Buying used K&B engine

Postby coosbaylumber » Tue Jan 30, 2007 5:11 pm

Buying used glow engine


How do I go about buying a used (and elderly) K&B .40? In a few days from now, I will be over at the residence of old friend's place looking over his stock of old glow engines. I have a need for one of the older K&B .40 of the 1960's, the type with a baffled exhaust port, no muffler. Eight bolt crankcase, and stud type prop shaft.

The son isn't too solid on condition, but he and some expert went and made an assessment for valuation from an estate. Before I agree or not to the selling price, I'd like to know (perhaps) what failed or wore out before ultimate age on these. Compression is springy, but then again I see what looks to be scars on the piston. Maybe a loose conenecting rod. The son assures me a rod will tighten up once hot, and long as there is sufficient compression it will fire off good.

What do I look for?



Wm.
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Postby gossie » Wed Jan 31, 2007 10:15 pm

A very little 'slop' in the con. rod is probably fairly normal.
Hold the piston at TDC until all the air is out of the combustion chamber and rock a prop. back and forth to get a feel of how loose it is.
It would also be very easy to take off the backplate to check out both big end and little end as far as how much slops there.
I truly can't see a rod coming good when the engine warms up though.

Have heard full size auto engines with piston slap that goes when things warm up and expand, but I doubt that would apply to slop in a con.rod.
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Postby Jim Thomerson » Sat Feb 03, 2007 4:21 pm

That is a Dykes ring engine, and you can't tell anything about compression by turning it over by hand. New rings are available from several sources. There are abundant later models out there, 4011's, at reasonable prices. One of the things that wore out in the earlier 40's was the piston holes for the piston pin, which would go egg-shaped. The 4011 has brass bushings there. Personally, I'd look for a 4011 rather than the earlier model. I have several of them flying CL stunt and I really like them.
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Postby propwobble » Sun Feb 11, 2007 9:20 am

You're right Gossie when you have an aluminum piston in a steel or iron bore the piston will expand faster than the cylinder and tend to close up the clearances. As a rod gets hot and the metal expands, the big end hole gets larger. With a cooling incoming fuel charge, does a crankcse in a two stroke get hot enough to make the rod expand? Probably not much but I sure doubt it has the affect of cooling the rod enough tho make the big end hole contract.
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