Early RR-1

Guys,
There's a lot of misinformation on the RR-1 floating around out there and I think this has been posted a year or two back, but I thought with all new members it would be worth posting again. This is from "Mudhen" who I consider to be one of the most (can i say most?) knowledgeable historians, especially the early years of the Thimble-Drome engines.


Cox Thimble-Drome, Initial Issue RR-1
The initial issue RR-1 is unlike any subsequent version of the engine. Even the vacuum-formed box bottom is distinct from later variants. This is one of the most difficult production engines, if not the most difficult to acquire from L. M. Cox Mfg.

RR-1 History
The RR-1 and Babe Bee .049 were developed concurrently over a 15 to 20-month period beginning in October 1954. The Babe Bee was finished by January 1956. The RR-1 was completed by the end of June* that same year. (Re: “*” see below.)

Components of the Initial Issue RR-1
Early advertisements for the RR-1, which were copied directly from Cox-made scratchboards, represent this initial issue version:
01.) Smooth, narrow-conical crankcase.
02.) No oil groove inside the crankcase bore.
03.) Five-fin glow head. (Four cooling fins and one small decorative fin at the base of the glow head core, similar, in appearance, to cat. # 302 Glow heads. [A la Space Bug, Thermal Hopper, Space Bug Jr., and Strato-Bug .049.]) Later versions of the same engine had the fifth decorative fin removed.
04.) 4-piece “302-J” piston.
05.) Larger rotor valve pin.
06.) “STD” engraved on rotor face. (Indicating “standard,” right-hand rotation.) Furthermore, subsequent rotor valves had a smaller rotor pin access hole. Rotor valves fitted to later versions of the RR-1 will not fit on the Initial Issue version.
07.) Tank front is smooth with blue anodizing.
08.) Port is pointed upward. The tank front cannot simply be rotated to situate the port facing down, as found in later versions. This would place the timing 180 out, and the tank front filler tubes would be on the right hand side obstructing the fuel pick-up tube.
09.) Venturi is identical to Babe–Bee .049.
10.) Tank back is identical to Babe Bee .049 except the fill tubes are not tapped.
11.) Tank back has clear iridite plating.
12.) Fuel pick-up tube is black rubber, (or vinyl,) without the .008” spring.
13.) The box bottom has been vacuum formed to fit effortlessly underneath the smooth, initial issue crankcase, (at the wider portion of the crankcase neck.) Later RR-1’s with turned fins had this section of the box bottom enlarged. An RR-1 with turned fins will not fit the initial issue box bottom. This is more than just a passing “bit of trivia.” It must be noted that this vacuum formed bottom was only used on the RR-1. So if this bottom cannot fit a ribbed crankcase then it can only be meant for a smooth crankcase.

When was the Initial Issue RR-1 available to the public?
An article written for American Bicyclist and Motorcyclist dated April 1956 notes, “The ‘RR-1’ is the first rear-rotary valve .049 to appear on the market…” One is left with the impression that by the time the article was published the engine already was available. However, in a letter dated May 24, 1956, written and signed by Roy Cox to Mr. Dale Kirn, he gives a clue to the release of the RR-1. He writes, “The material you requested is being mailed today except the three RR-1’s. We are not yet under way on that item. It will be a few days yet and we will send them as soon as they start to go through the line.” It would seem the initial issue version was released shortly after May 24, 1956. How soon after is not known. Take for granted that the engine was released within one month after the letter was written. This might aptly be considered, “a few days,” thus setting the start of the production run three weeks into June 1956.

How long was the Initial Issue RR-1 in production?
Blueprints for the RR-1 tank front, dated June 7, 1955 note that on November 6, 1956, the following changes were made, “Venturi changed, Fins added, Port turned over.” The amount of time between the changes noted on the blueprints and when these revisions were incorporated on the production line is not known. If the amended version of the engine began one month after the modifications were noted, then assembly for the “finned” RR-1 was set in motion mid-December 1956, or perhaps early in January 1957. If this is true then the production run of the initial issue RR-1 was only six months. Without any other company documentation or original support material, (newspaper articles, business journals, etc.,) the aforementioned is only an estimate. Furthermore, and again without any company documentation, it’s impossible to know the number of engines manufactured during this time frame. Assuming the six-month running time, however, the numbers had to be comparatively few.