Name	ETA 29 Mk 6	Designer	Ken Bedford, ETA Instruments Ltd
Type	Glow ignition, two-stroke	Capacity	0.29 cuin
Production run	6 (or 7) marks	Country of Origin	England
Photo by	Van Richards-Smith	Year of manufacture	1949..1968

 

Background

The ETA 29 was designed by Ken Bedford and produced by the Bedford family company, Eta Instruments, located initially at 5 Hempstead Road, Watford, Herts, England. It made its first appearance on the market in April 1949 and continued in production and development through to 1968. The company logo seen here uses the Greek character/symbol that is used in science and engineering for efficiency--a particularly apt choice for a manufacturer of high quality instrumentation and racing engines. There were six "marks" produced, known appropriately as the "Mark 1" through "Mark 6" (even though ETA referred to them as "Series", not "Mark"). The Mk 6 alone had a variant called the Mk 6C, and the 6C itself underwent a significant crankcase casting change partway through its life to further complicate matters for us.

A very well researched and presented article on all the various marks of the engine by Mr Martyn Serginson appeared in issues 65 and 66 of Model Engine World [1][2]. Martyn's piece gives the differences, dates, rarity and background for each in great detail. Back issues of most editions this publication are still available from then editor/publisher, John Goodall. See the Suppliers Page for contact details.

Models and Marks

Alltogether, six "Marks" of ETA 29 were produced, although as we shall see, the Mk 6 underwent a significant revision to the "6c" that could be considered a seventh version. The "Mark" was not recorded on the engine, so telling them apart requires some extra knowledge. First indicator is the serial number [1][2]:

Mark	Serial Number
Mk I	All start with "3"
Mk II	All start with "3"
Mk III	All start with "29"
Mk 4	All start with "429", or "0429"
Mk 5	All start with "5"
Mk 6/6c	End with production year (58-68)

So far, so good, but how to tell a Mk I from a II? The Mk I is the only engine to have the glow plug set at an angle. From the Mk II, the plug was vertical, but offset from the center of the head. This may help identification, but be aware that many engines were modified with parts from later engines in pursuit of more speed, sometimes at the factory. This makes definitive identification tricky indeed.

The engine pictured here is a Series 6--a fact that we can verify from the original guarantee registration card--even though it is fitted with the small, conical, plain aluminium spinner nut which Serginson's article states was fitted only to Mk 6C's. Note the serial number stamped on the bypass in this photo. Mr Serginson's research states that for the Mk 6/6C, the last two digits are "highly likely" to be the year of manufacture. This is preceded by the month as one or two digits. Hence we see serial numbers like "058959" and "0641059" indicating (probably!) the 58th engine produced in September 1959, and the 64th engine made in October 1959. We might then assume that Van's engine is the 280th engine built in September 1962. Martyn did not specify if the engine count was wound back to zero for each month, although this seems unlikely to me. The numbers he was able to gather tend to indicate that the numbering sequence was sequential for the 6/6C [2], incrementing up until a crankcase change was introduced in 1965 for the fitting of an exhaust silencer. At this time, mid-way through the 6C series, the numbering was restarted with the month/year suffix assuring uniqueness.

Description

Technically speaking, the ETA 29 Series 6 is a cross-flow scavenged, rear-rotary induction, twin ball-race design with an aluminium piston fitted with two conventional Meehanite piston rings, running an a hardened cast-iron liner (Meehanite). The liner's port shape, placement, number and style varied over the engine's lifetime, as did the conrod, piston baffle, and some details of the crankcase casting around the top fin area and bypass flare. The needle/spray bar also underwent some detail design change. All marks used a two-piece spray bar so that only the needle itself projected into the air inlet flow. The basic design was introduced by the McCoy and Dooling racing engines where the needle screws into a stub carrier on one side of the venturi, and seats against a fuel connection nipple on the other side. On the Mk I and II, the needle used a large, knurled, split thimble with a 3BA thread. Subsequent engines threaded the needle itsely and fitted a gland-nut that locked the setting and prevented air leakage.

Conclusion

When introduced, the Mk I ETA 29 was quoted as delivering 0.54 bhp @ 14000 rpm. This performance continually improved with the 6/6C producing 0.82 bhp @ 17000 rpm. In England and Australia, this was THE engine to have in your "B" Class Team Racer.

Van's engine has been run and flown in a control-liner (a Mike Ware "Carioca" published in the Dec/Jan 1957 issue of Australian Model News) but is original in all respects and he has respected to this very day the strong warning stamped by an unknown hand inside the box top that bears the designer's signature. Now, a quiz: there was an cuckoo in the nest when Van took the box contents photo, and one piece of the documentation is not from Eta Instruments. For 1 point, which piece is it? For an extra 4 points, who is it from? NB that 5 points and $3.40 will buy you a cup of coffee. Hover here for the answer.

References:

[1]	Serginson, M: ETA 29 Story, Part 1, Model Engine World, Volume 6, Number 65, Jan/Feb 2000, p12.
[2]	Serginson, M: ETA 29 Story, Part 2, Model Engine World, Volume 6, Number 66, Mar/Apr 2000, p20.