It is an
often asked question as to which frames Jim Lee made for the production Yamaha 2stroke
race engines. Many times frames have been incorrectly identified through a lack
of knowledge and falsely attributed to his hand. The following blog is an
attempt to catalogue his work in this field.
Jim was
clearly born with a welding torch in his hand, but had a wonderful ability when
it came to all aspects of fabrication. His skill was not only in the actual
joining of the parent metal, but also in the visual effect of the finished
product. It had to both ‘look right’ and be easy on the eye. Unless requested
by a customer to do things differently, the former qualities gave his work a
distinct feel and have left a signature for all to see.
By the mid
1960’s Jim had fabricated racing frames suitable for a huge variety of race
engines. In fact it was his ability and willingness to take on ‘one-off’ jobs
that had attracted his services to people such as Reg Orpin, Peter Williams,
Dave Simmonds, Bill Bancroft and Paul Dunstall to name but a few.
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| Series 1 frame |
These frames
were made using 17 SWG Renolds 531 tubing and were fillet bronze-welded at the
joints. Jim used a gas-fluxer fitted in the acetylene hose to the torch and it
is fair to say he was generous with the bronze fillet applied. The frames were generally
of a simple duplex design and as Jim used a thinner gauge tube than the
accepted norm, were considerably lighter than proprietary units. Jim’s constant
quest to save weight resulted in him using brackets and gussets that were
minimalistic in design and in many cases barely up to the job required. As a
consequence his frames suffered badly over time, with fatigue and fracture
cracks limiting their useable life. It is often said that no two similar frames
are identical, as Jim did not use a complete frame jig, the tubes being bent to
chalk markings on the workshop floor.
Four distinct
series of frame were made from the period 1965 to 1970 and are described in
detail below.
Series 1
This was
Jim’s original design for an improved race frame which could be fitted with a
Yamaha TD1B/C or Suzuki TR250 engine. The frame was supplied along with
clip-ons, footrests and swinging arm at a cost of £65.
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| Series 1 frame modified by Jim Lee to fit a Bultaco 250 engine |
The
distinguishing features in this series of frame are as follows:-
The frames
are fabricated in 1” diameter x 17 SWG Renolds 531 tubing.
The frames
are bronze-welded throughout.
Single
thickness plate to SA pivot gusset.
Steering
head brace tube is near to being in line with the main frame tubes from the SA
gusset plate.
Single
thickness plate to front engine mounting gusset.
Stud brazed
into seat tube for upper suspension mounting.
Splayed seat
tubes at upper suspension mounts return slightly beneath the seat.
Tubular
footrest support brackets.
Fabricated
‘D’ section swinging arm with ‘pull back’ adjusters to the rear wheel spindle.
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| Short steering head brace |
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| Splayed seat tubes and upper suspension mounts |
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| Fabricated 'D' section swinging arm with pull-back adjusters |
Series 2
This was the
later version of Jim’s race frame and was intended to be fitted with a TD2/TR2
Yamaha engine. Although the attention to bracketry and ‘boxing in’ of the SA
pivot and front engine mounts were sorely needed, the overall design of the
frame is not as good as the original series 1 version. Quite simply the more
‘open’ layout of the main frame tubes and general lack of triangulation meant
there was no longer the same degree of stiffness between the steering head and
SA pivot. This change in frame design however allowed a taller engine to be
fitted and removal for maintenance was considerably easier. Jim by now had expanded his business considerably and no longer made every frame himself. He was ably assisted by both Neil Procter-Blain and Brian Earnshaw in the fabrication of his frames and it is clear to see that the grey frame shown below is not of his hand.
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| Seies 2 Yamaha TD2 Jim Lee frame |
The distinguishing features in this series of frame are as follows:-
The frames
are fabricated in 1” diameter x 16 SWG Renolds 531 tubing.
All joints of the frame are bronze welded.
Fully welded boxing
of SA pivot gusset to frame
The steering
head brace tube extends halfway along the top tubes and is not in line with the
main frame tubes from the SA pivot gussets.
Fully welded boxing
of front engine mountings.
Double-sided
plate support at upper suspension mounting.
Seat tubes
splay after the rear cross-brace and widen towards seat mounting.
Fabricated
plate footrest support brackets.
Fabricated
‘D’ section swinging arm with ‘snail-cam’ adjusters to the rear wheel spindle.
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| Long steering head brace |
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| Fabricated 'D' section swinging arm with cam adjuster location |
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| Splayed seat tubes above upper suspension mounts |
Series 3
These frames
were manufactured by Jim Lee and supplied as a frame-kit to Padgetts of Batley.
The frame was similar to the Yamaha factory unit, but with a 1 ½” longer
swinging arm and could be fitted with Yamaha TR2, TD2, TD1B/C engines. The
complete frame kit included forks, tank, seat and rear dampers. It was priced
at £179 and purchased direct from Padgetts.
Jim had
taken the brave step to invest very early in MIG welding equipment and was one
of the first of the ‘bespoke’ frame makers to go down this route. Primarily it
was because he wanted to increase the production of frames for Dalesman and
Wassell. Following a series of tensile welded-sample tests carried out at Aston
University, it was clear that Renolds 531 could not be reliably MIG welded.
This prompted the move to Cold Drawn Seamless Tube as the frame material to be used
with this welding technique. Mick Grant assisted in the jigging and welding of these frames.
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| Series 3 Jim Lee fabricated Padgett Yamaha frame. |
The distinguishing features in this series of frame are as follows:-
The main
frame is fabricated in 1” diameter x 16 SWG CDT (cold drawn seamless tube)
The seat
sub-frame in 7/8” diameter x 16 SWG CDT (cold drawn seamless tube)
The frame was
MIG welded throughout.
The frame
was fully bracketed to accept all STD Yamaha ancillary parts.
Fabricated
box-section swinging arm, similar design to STD Yamaha item but 1 ½” longer in
length.
The main frame
tubes from SA pivot gussets are not of uniform radius as on STD Yamaha frame.
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| Swinging arm gusset and Yamaha ancillary mounting points |
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| Steering head brace and tank restraint mounting |
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| Rear seat hoop and upper suspension mounts |
Series 4
These were ‘spine’
frames and of a completely different design to anything that had been seen or
done before. Jim built a special Yamaha TR2 as a 'works' bike for Mick Grant to ride during the 1970/71
seasons. This was built as a 'one-off'' with 'no expense spared' and at that time Jim had no plans to market or sell replica versions to paying customers. It was innovative in using a large diameter straight tube as the spine
of the machine. This was bored at the correct angle and the now usual long
steering head tube passed through and brazed in position. The same was done at
the swinging arm pivot, ensuring that both steering head and swinging arm
remained in their relative positions at all times. A pair of tubes ran from the
massively braced steering head, beneath the engine and returned to join the
seat rails at the top suspension mounts. An extended swinging arm pin passed
through the main spine, swinging arm bushes and a brazed clamp on either of the
cradle side-tubes. This arrangement greatly increased the stiffness of the
frame.
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| Mick & Jim with his Yamaha TR2 |
As it turned out, the combination of Mick Grant and the Jim Lee Yamaha were an outstanding success and
because of this Jim offered to build replica frame kits for interested parties.
The price of the rolling frame was approximately £200 depending on the actual
specification.
The
distinguishing features in this series of frame are as follows:-
The main
spine is fabricated in 3” diameter tube.
The engine
support tubes are 1” diameter x 17 SWG Renolds 531.
The seat
rail tubes are ¾” diameter x 17 SWG Renolds 531.
The frame is
bronze-welded throughout.
The engine
is rubber mounted throughout.
An extended
swinging arm pin passes through the main spine and is clamped to cradle side-tubes.
Tubular
swinging arm fabricated in 1 3/8” diameter x 16 SWG Renolds 531.
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| Heavily gussetted down-tubes |
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| Main spine and diverging seat rails. |
