Mr Cox

I made a nice deal (I hope) on a NIB K&B .21, with lots of parts, including a diesel head. I don't know if it is DDD head or not. Does anyone have any experiences with these engines on diesel?

controlliner

These engines are screamers! the crank and port timing are more advanced than a sport engine. They were king in Free Flight back in the day. The ABC pinch is real big, should heat cylinder before starting the first few times. Definitely break it in as a glow before using diesel. The connecting rod is bushed and made out of 2024-T3 and of generous dimensions.

1QwkSport2.5r

I'm pretty sure they are timed for using a full wave tuned pipe. I know someone that has a non-R/C K&B .21; it is incredibly tight. +2 on preheating.

AMB

Mr Cox I did pick up a used K and B 20 sportster a few years back Davis head, nice runner quiet ,not a screamer however easy hand flip on a few flicks
it does have a pressure tap on the muffler where it is attached to the engine note the Davis head looks nothing like the one on the 21
just a nice easy running sport engine think plain bush in shaft must be a bunch out there many posts on the glow site on the 20

controlliner

These worked good with a Mini pipe although very loud. The version with the venturi, the size of a toilet bowl needs crank case pressure to run, and wear ear plugs.

Mr Cox

Thanks for the info and advice here, and yes it is squeaking tight at TDC. A heat gun is enough relive the pinch though and it fired right up on a little prime.
Here are two pictures of the engine and diesel head. The diesel head appears to have an aluminium counter piston running in an aluminium head, seems a little odd to me, are DDD heads made like that?

1QwkSport2.5r

The sportster .20 and the K&B 3.5/.21 engines are totally different. In fact, they are on opposite sides of the port timing spectrum.

Dan Vincent

The K&B 3.5cc was a high-performance schneurle-ported powerhouse with BB shaft. It was the basis for the K&B 3.5cc outboard engines and also available for inboard boat installations.

dennis

My Feedback: (90)

I ran a K&B 21 as a diesel for some time back in the 80's on a lot of things that certainly wern't high performance. With fond memories of upgrading the performance of the lowly Sportster 20 when it was a Bridi kit. It is a predictable good running engine with more latitude in it"s running characteristics then most people realize. I still have the engine and it still performs well

AMB

The Diesel head is not the typical Davis construction, his compresion screws are black and run in a helicoil and I notice the screw appears to have teflon tape around the threads
doubt if any commercial head looks like a one off some one made also quite thin also the 20 a 4 bolt head not 6 as on the 21 martin

dennis

My Feedback: (90)

I still have the Davis head for the K&B 21

buzzard bait

I do too. It doesn't look like the one in the picture.

AMB

Buzzard bait whatever it is in the pix no way is it a Davis head martin

controlliner

It's no a DDD head, it looks like a one off.

Mr Cox

Yes, it is probably another source than the DDD then (I don't have any DDD head to compare with though). I know there were swedish makers of conversion heads in the 80-ties, so that is probably where it comes from. It doesn't really look like a "one off", it is a three piece head and the part with the cooling fins has been sand/beed blasted for a matte finish, so someone has made quite an effort on it.

buzzard bait

I have a friend who does work just like that, but I don't know what was available in Sweden.

I was amazed to get a DDD head on a K&B .21. I didn't even know the engine existed before I got it in an estate, and I had never seen an exhaust manifold like it. I'm still trying to figure out what I could do with it and how I might mount it. As a diesel those exhaust ports could really make a mess. I think it would have to be inverted with extension tubes. Still not sure it makes any sense to do it.

If anyone has a report on how this runs as a diesel with the Perry carb I would be very interested.

Jim