Resurrecting an old KRAFT .61
Rummaging through my engine drawer I came across a KRAFT 61 pumped engine made in about 1975. In its day, the Kraft 61 was state-of-the-art technology factory equiped with a Perry carb and fuel pump. This engine is a ringed piston type which utilizes Schnurle ports. With some minor updating this engine can hold its own as compared to todays engines. Kraft engines were well designed and supremely manufacturered right here in the United States of America. Kraft, like Fitzpatrick and RJL were ahead of their time and fell to sudden demise sometime in the 80's mostly because of the Imported engine invasion. This included OS, Picco, Rossi, CMB, Irvine, and many more. OS was (and still is) the big winner.
My engine is in perfect condition having smooth bearings and excellent
compression. The internal parts are tight and show minimal wear. Should I need parts, they
are available because the RJL .61 engine parts are identical and still available through
The KRAFT 61 was dis-assembled for clean-up and inspection. The bearings are bad inspite their rolling smooth. It uses the same bearings as an OS 1.20 FS and they've been replaced. This vintage engine utilizes a steel sleeve and a cast iron piston ring. There wasn't any signs of wear so the piston & sleeve assembly are perfect, and the compression is excellent. The crankshaft is good but needs a little clean-up. I won't be using the Perry intergal fuel pump but it needs to stay on the engine as it's part of the backplate. The Perry carb will be stored way in my engine drawer...
The crankshaft cleaned up nicely as well as the remaining parts. Because
the cylinder is steel it required de-glazing in order to re-seat the ring. The engine is
ready to re-assemble and be bench tested. If you look at the head, you will see that it
uses 8 headbolts. This was common in the early engines especially the one's that used
steel liners. As ABC liners became common-place the headbolt count dropped significantly.
Check out this magnificent domed piston!
The Piston & Rod assembly uses an "R" on the rod to be sure
the assembly is properly installed. As depicted by the length of the rod, this is a HIGH
TORQUE engine. The OS .61 SF rod is 1mm shorter. Also notice the thickness of the bushing
and ID! This is one heavy-duty rod. From everything I've seen in this engine I've
concluded that it would make a fantastic micro-gasser!
And here she is READY to run...
I ran it at full throttle for 2 minutes and took a temperature reading. A piddling 172.1 degrees! That was with it turning a 12x6 Master Airscrew Schimitar wood prop at 13,250 RPM. That ain't bad for a 31 year old engine!
You may happen to notice I have by-passed the pump! The engine runs great
without the pump if the tank is in the "normal" location. .The engine is 100%
stock except for the two needle carb that came off my original Thunder Tiger 36. This
engine runs like a top...
I don't know if Kraft would ever be classified as "collectors" engines, but I can assure you that KRAFT made a big step forward in model avaition.
FYI: The early ROSSI 40/45 muffler fits the Kraft engine perfectly, so that gives you some exhaust options.
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