MECOA's Model Engine Forum & Swap Shop

by **chuckstarck** » Tue Jun 02, 2009 5:40 am

What is the normal end gap for the ring at top of stroke for the KB 40 sportster. Just wondering how worn out mine is. Mine measures 12 thousands. I don't have a ridge at the top of the cyl so assuming the cyl is still in good condition.

by **stunter** » Tue Jun 02, 2009 10:44 am

I don't know were I heard this but, ideal is .003 to .005
with a maxium of .008 for most engines. Maybe one of
the experts will give us their view.
George

by **chuckstarck** » Tue Jun 02, 2009 3:06 pm

I think somewhere I remember .0005 per inch diameter is practical for all engines up through 455cuin. BUT I didn't know what it should be for this type of engine, might change with heat.

by **chiefss** » Wed Jun 03, 2009 5:49 pm

K&B never made a Sporster 40. The Sportsters were 20, 28, 45, and 65's. None of them had a ring. They were AAC's in the sense that the cylinder was aluminum as was the piston and the piston was chrome plated.

by **loucrane** » Fri Jun 05, 2009 10:37 am

Chiefss,

Correct!

Chuck may have that later version of the classic 4011 that was aimed more for sport fliers than the early CL Rat /RC Pylon howler versions. The one with bolt-on front and back ends, came in shaft rotary and rear disc rotary versions... and of course, you could switch exhaust stack left or right on those (preferably before running them in.) Those had Dykes rings.

I don't know the nominal gap spec, but if it is a 4011-based engine MECOA/K&B should still have replacement rings.

by **chiefss** » Fri Jun 05, 2009 10:55 am

I have a box full of broken K&B 4011 engines. Probably enough parts to make one good engine. Most hit the pavement. Bent rods, broken crankcases etc. I've had them for years. Just couldn't bring myself to throw them away. There are good piston/cylinders and rings in the pile. Maybe someone can use them. let me know.

by **chiefss** » Mon Jul 27, 2009 11:30 am

Still have a few broken K&B 40 parts engines.

by **Frank Klenk** » Tue Jul 28, 2009 5:21 am

10%
Edit your posts. Anything not related to the topic being discussed please delete.

Frank

by **chiefss** » Tue Jul 28, 2009 11:04 am

Frank, the last post has nothing to do with K&B engines. It's just reference to another site.

by **10%_nitro** » Sat Aug 01, 2009 1:18 am

This link to RCU has a very interesting thread on K&B cylinders, which started as a OS FSR thread.

http://www.rcuniverse.com/forum/m_48276 ... coa/tm.htm

by **10%_nitro** » Sat Aug 01, 2009 1:24 am

Another link on the K&B, interesting read on the Sportster. I suppose the .61 certainly had a better design.

http://www.rcuniverse.com/forum/m_44438 ... tm#4443842

by **chiefss** » Sat Aug 01, 2009 8:46 am

All my K&B40's and parts have been sent to Dedaddy007.

by **kersplat** » Tue Nov 14, 2017 9:37 am

1.5 -2 thou.

MECOA's Model Engine Forum & Swap Shop

K&B 40 Sportster ring gap

K&B 40 Sportster ring gap

size matters

Re: K&B 40 Sportster ring gap

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