RCU Forums - Need information on the K&B 40 size engine

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The K&B 40 engines came in two basic variants, with sub types beyond that.

First were the ones with the small front bearing and the prop drive pressed on the crank.

The earliest of these had a smaller carb mounting spigot and bypass port than the later ones, These were the model 80xx engines. The “xx” was replaced with other numbers to indicate the exact model.

Then came the 83xx engines, still with thed pressed prop drive, but alarger carb spigot and the bypass was machined to a much greater cross section internally. Other than the size of the carb spigot the 80xx and 83xx were identical in appearance.

The hottest K&B ringed 40 was the model 8360, it had a built-in Perry pump and a carb bore more fitting to a 1.20 size engine. This was also known as the “Q40” version.

The second major variant is the current production model 4011. It has a much larger front bearing and the prop drive is on a centering cone, easily removed with your fingers.

In production they have been supplied with carbs from Perry, Irvine, and two different K&B branded carbs. In all there are about seven different carbs that have been used.

Three different crankcases also. Wont go into all the differences beyond saying the early ones had no provision for muffler mounting, the later ones do.

The two engines in the picture are an 8330 on the left, and a 4011 on the right.

Any K&B 40 will be an excellent engine if used as it should be – by current standards it’s a good sport engine, not a screamer. At the same time, if treated nicely your great grand-children will be able to use it – almost impossible to wear out.

Bill.