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Mar 25, 2015, 08:09 PM
DJS Johnny
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Djs 049


First, the name DJS stands for Dub Jett and John Shannon, with the “J” being shared. John and Dub have a very long and wonderful association as friends and model airplane flyers. This association began when they were both teenagers in 1959 and continues today.

The DJS 049 was ahead of its time, being designed in 1976.

The DJS 049 has its genesis as a project to provide Dub with a platform to achieve excellence in his favorite event of 1/2A Speed. John won 1/2A Speed at the 1973 AMA Nationals using a Cox Tee Dee 049 with a homemade chromed 3-port cylinder with a tuned pipe. This is a very good combination, however at RPMs over 30K the rod ball separates from the piston. The DJS 049 is essentially a 0.551 scale model of the DJS 29 with the exception of the bore and stroke. Originally, the bore and stroke were based on the DJS 29 at 0.412 and 0.370 inches. After the design was completed this was changed to 0.406 and 0.386 inches to be the same as the Cox Tee Dee 049 that was very familiar and competitive. Maybe DJS confidence was not as high as it could have been as this provided a path to using the Cox piston and rod assembly, if necessary. It was not necessary!

Dub developed an original design tuned pipe with the correct tuning RPM and volumetric characteristics. His first design was perfect. The real success of this project is not just Dub’s pipe design, but its fabrication. Dub has many things at which he is a wizard. His wizardry is never any greater than aluminum brazing of these thin wall tuned pipes! All John ever managed to obtain while attempting this task was a blob of melted aluminum on the work bench!

The DJS 049 was designed to eliminate high RPM failures and incorporate design features of larger engines including a crankcase with a drop-in cylinder liner, a rear disk valve induction and a piston to rod connection using a wrist pin. The DJS 049 is composed of all original designed and fabricated parts. It is a rear disk valve, three transfer ports, and rear exhaust configuration. The first engine was completed in early 1977, but performance was no better than the Cox based engines. Sometime in late 1977 a simple change was made that made performance spectacular! As is sometimes the way with this type of thing, neither John nor Dub can remember and/or agree on the change. But, it was so simple that no new parts had to be fabricated. Go figure.

Multiple designs of the DJS 049 were fabricated all using the foundation of an A356-T6 investment case aluminum crankcase. The original engines have a bar stock front plate and back plate. Later, cast front plate and back plates were introduced. The front plate housed a full-circle banded crankshaft of 4140 HT steel supported in twin ball bearings featuring a chrome plated crank pin. This chrome plating presented a problem in the first engines. The crank pin surface finish was certainly sufficient for normal operation. However, when chrome plated it made the best abrasive burr know to man and filed out the lower rod bushing in about 10 seconds of running. All the crankshafts were rebuilt and with a highly polished surface crankpin before plating that worked very nicely. Early crankshafts had a reduced diameter crankpin driving the disk valve. This configuration beat out the disk valve driver groove. This problem was solved by changing to a flat blade configuration driver on the crankpin. The disk valve is machined from 4140 HT steel and chrome plated on the back plate mating surface. The rotor pin is made from drill rod and then chrome plated. The piston and liner was originally of the standard meehanite cast iron and steel metallurgy. The cylinder configuration was three transfer ports all angled up at 50 degrees. Other engines were fabricated with the more common straight across main transfers while retaining the steel/cast iron metallurgy. All of these steel/cast iron configurations were, however, chrome plated. DJS 049 pistons were cast in A 390 aluminum by Dub and John. ABC pistons and liners were fabricated in the all high angle and conventional (3 port) configurations with chrome plated C464 naval brass liners. All engines used a Cox glow head reconfigured to a Rossi style “button”. The connecting rods are machined from 7075 aluminum bar stock and have a bronze bushed lower end. The wrist pin is constructed using a case hardened steel dowel pin with the softer inner core drilled for lightening. All wrist pins are retained by using grooves in the piston that house wire clips. The head clamp is machined from aluminum bar stock. Both 8 bolt and 4 bolt head clamps were fabricated, but more than 4 bolts are seldom used. Additionally, the conventional three port configuration sleeves in both steel and brass were fabricated with 15 degree up angled main transfers and exhausts. In all, three configuration crankcases were produced with; three high angle transfers, straight across mains and up angle mains. These are A356 alloy investment castings. Although care was taken to match the ports in the case with the ports in the liner there was no significant change in performance if they were mismatched. Again, go figure.

Performance is outstanding. In May 1978 the AMA national speed record was first set at 124.30 MPH and increased to 128.52 MPH in August in winning the 1978 AMA Nationals. When considered in a historical context, this was probably the first real 049 racing engine.

Johnny
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Mar 26, 2015, 01:02 PM
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Wow, real interesting John to have some insight into that engine development( As a former machinist I can appreciate the work and design involved). I can only imagine you and Dub discussing those matters over Mexican food! The Piston/connecting rod junction was indeed the weak point of the TD .049, never had one come apart but I never pushed mines to the extreme and always resetting the ball joint when it developed play.


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