Rebirth of a Lightweight Panther. 3. The Game Changer

      A post appeared on the Ebay advertising the remains of a 250 Panther but I missed it until notified by Grahame Sherborne. Close inspection of the photos suggested it was a post-war Model 70 with Dowty forks so I passed a tense week as I watched the auction bids slowly rise. No way could I miss this and I duly won it, picking it up from Oxfordshire. Thanks to Mike Bagshall.

Back home I picked through the pile of expensive rusty bits to find that I had most of a frame, (excluding the pair of saddle down tubes), most of an engine, most of a gearbox, a set of Dowty forks, a saddle, and a front hub without a spindle or bearings. The vendor told me he had brought the bike back from Northern Ireland and it does indeed have an Irish registration number, GZ8428 was registered in Belfast. Ginger (POC registrar) imparted the happy news that the bike was indeed a ‘virgin’ with frame and engine numbers matching the factory data book, having left the Cleckheaton factory together on Tuesday June 17th 1947. The engine number 47DSD338, tells me it is a 1947 Model 70 (D) with new-type timing gears (S) indicates 805 20pa gears and Dowty forks (the second D.) and build number Z1419, so it was built by Mr.Blackburn, (Z). The frame number is 20292, 661 frames earlier than the one sent over by Bruce. Coincidentally my house is number 292! The gearbox is also dated 1947 so the whole (?) machine appears to be right. Production data in the POC Library shows that during 1947 the factory produced 411 Heavyweights, 433 Model 60s and 653 Model 70s, 1497 bikes in total.

It is worth noting again that the frame number on these machines is to be found on the lug under the saddle and is a five digit number. There are numerous other numbers on the frame as each lug carries a casting number, usually proud as cast in the mould, sometimes stamped in place. These are usually only three digits long.

As it arrived.

The rest of it.

Engine (Commision) Number

Gearbox Number

Frame Number

                                        

Lug number cast into headstock web.

The Bottom End.

     I pulled it apart and found that everything was just loosely assembled, presumably for the sale. There were no balls in the headstock but two of the races were in place but upside down, and the headlamp appears to be wrong but there is a good basis there. Now I have to build two bikes but I shall concentrate on one for now using the best parts from both although I must keep the 1947 frame and engine together as they left the factory. The gearbox from the engine/gearbox assembly that started this off is complete and also dated 1947 so I shall use that. I will examine the two sets of Dowty forks and see which one is the best.

      Comparing the two front frames side by side reveals that they are identical; so much for the thought that Bruce's frame was from a Stroud as suggested in the last post.

        I couldn't resist looking at the engines and the first job was to remove the sprocket centre from the crankshaft. These are notoriously difficult to get off and a normal two or three-legged puller wouldn't look at it. Indeed someone had obviously tried this on the engine shown above as parts of the centre was broken away. I set- to to make a puller then half way through that man Rex walked in carrying a split puller just made for the job. A few minutes, some heat and a sideways wack against an anvil had then off both engines. Concentrating on the 1947 engine above I removed the timing cover complete with the camshaft to find that the crank pinion was missing. It looks like one from a Heavyweight will fit and I have several of those but are the tooth forms the same? 

           The standard pressure angle for the teeth of spur gears was 14.5 degrees until the early 1940s. My copy of the Mechanical World Year Book 1942 states that "the standard pressure angle is 20 degrees although gears with a pressure angle of 14.5 degrees (the original standard) are not uncommon." Certainly later Panther timing gears are stamped 805 20PA (805 is a steel alloy specification), these in the Model 70 are not so stamped. The S of the engine number suggests 20PA gears are fitted. Gears of differing pressure angle should not be run together as they will rapidly wear but it is very difficult to tell them apart.

             Another point to watch out for on crankshaft gears is that one from a Model 65 or 75 will fit a Heavyweight engine but they have one tooth more, 25 instead of 24. The engine will only fire every 50 revolutions of the crankshaft!

             I separated the crankcase and withdrew the flywheels, the big end feels ok but needs to be washed out. Now comes the messy job of cleaning the parts.

With the frame stripped into its component parts I removed the crud and paint using a 3Ms disc in the electric drill. The metal was treated with Kurust then given two coats of red primer followed by two coats of  black coach paint. This was slow to dry due to the low temperature but once I fired up the heating it hardened to a smooth gloss. I then bolted the frame together using new stainless steel studs and the pair of saddle stays I had made for the other frame.

 

Frame in coach paint

I shall now turn to the Dowty forks and perhaps the engine.

Rebirth of a Lightweight Panther: 2. First Steps

In early  November 2020 I lifted the rather heavy engine/gearbox assembly down from the shelf for a closer look, guiltily noting it had sat on the shelf for years with no spark plug. With the very rusty primary chain removed it turned over very sweetly. So what is it? 

The Engine number 8D247A is stamped just below the cylinder on the drive side. The "engine number" is the Commission Number used by the licensing authorities for tax purposes.  It was the key number for the bike that was replaced by the VIN for modern vehicles.  The Commission Number was added to the cases at the time that the bike was built. The suffix letter could then be added for changes to other fittings (like rear suspension) as the build year progressed.  Typically for P&M some engines, in fact complete bikes, left the factory and were sold with the same Commission Number.  There were no computers to check for duplicates back then, everything was recorded in hand-written ledgers. The engine (commission) number here, 8D247A, reveals it is a 1948 Model 70 (D) 350cc, the 247th built to the first specification (A).

Engine (Commission) number (315 is a casting mark.)

The build number is stamped on the rear of the timing case and was specific to each engine erector. It was a sequential number, with a letter code, identifying the fitter.  Some of the codes were re-used, especially after the war, which does complicate things.  Generally engine erectors worked on one series of engines, either Heavyweight or Lightweight, but if they built both types during their time at the factory they would continue to stamp the finished engines sequentially.  These numbers were added at the time of the engine build not the assembly of the bike.  The numbers were issued by the shop foreman chronologically as engines were completed to enable traceability to every engine erector in case of future problems. In this case the build number is B2200 which shows it was built by Mr.B Browne in Cleckheaton (ref.Barry Jones’ excellent Panther history). The P&M data books show it left the factory on Tuesday February 3rd 1948. (Thanks to Ginger, registrarpoc21@yahoo.com or pocregistrar@pantherownersclub.com for dating information and Ian Fox for telling me the derivation of the numbers).

Build Number

The gearbox is a four-speed Burman dated 1947.

Gearbos, 4-speed Burman

Gearbox number

The dynamo is a Miller three brush with built-in cut-out. 

Miller 3-brush dynamo, cut-out left.

This along with the main engine plates, the clutch and inner chaincase was all I had. Could I really convert this into a complete bike? 

Clutch and engine sprocket parts.

Basically the 350cc Model 70 is a slightly beefed up and improved pre-war Red Panther, as is its stablemate the 250cc Model 60. Planned during 1939/40 production was postponed by the war, starting in 1946 when the machines were fitted with girder forks. These were replaced by Dowty Oleomatic units for 1947 and 1948 when the model ceased production in favour of the completely new Models 65 and 75 with their vertical engines.

P&M Catalogue photo.

1947 Model 60 (Photo Jacques Ivens, Brussels.)

I wondered what else I could find for this model in my stash of parts which resides on a mezzanine floor in my garage. (That sounds rather grand but it is actually a crawl space over my workshop accessed with difficulty by a ladder and inhabited by a jumble of biscuit tins of unsorted bits, tyres, mudguards and sundry rubbish collected over the years.) Other than the M75 and the Red Panther shown in the last post I had built another M75 from a couple of wrecks Brian and I had bought years ago from a chap who had lots of rusty bikes stored in a row of gazebos. In addition we had bought a dismantled M70 for the POC which I roughly assembled and sold to Rollo Turner who has rebuilt it.

M75 Wrecks used for parts

Another Model 75

M70 Kit of parts

       So there should be some bits hiding in the attic. I found a pair of front engine plates, both parts of one footrest, the bottom forging of the front frame, some steering head races and a fuel tank. Still rather a lot is missing so I put the word out on the POC Facebook page and the POC forum.

Fuel Tank.

What a great club. Bruce Sharman in Australia offered me a front frame for the cost of the postage, Tom Norman offered a set of Dowty forks. Petsch in Germany sent me a top yoke and a front mudguard stay bottom fitting as a surprise!

The frame duly arrived. it has the number 20953 on the lug under the saddle. It left the factory on Friday January 2nd 1948 so is just a month older than my engine. Ginger tells me the original engine with this frame had the build number X2096, 104 engines earlier than the one I have. The prefix X was used for the Experimental Department who built the Stroud competition machines so the frame may have a different steering head angle than production machines.  

Frame number under the saddle

     Bruce had said the frame was in poor condition and even offered to cut it to make packing easier but it looked fine to me. (I know the Aussies build beautiful bikes and are very fussy!) It had clearly been retubed with sleeves into the forgings but was solidly brazed so was clearly usable. I had been unable to find the two saddle tubes I was sure I had somewhere but Fred Baggs provided a drawing and I bought some seamless tube locally, sleeved the ends and pressed them flat in the vice at red heat using a block shaped to form the curve. They came out ok so I turned up some studs in stainless steel and built up the front diamond frame. It was then apparent that the frame was slightly out of line at the back but with a lot of heat it was tweaked straight. Then in walked Rex Norton, ace welder, with a rear frame and four tins of beer. What a great chap.

The frame he brought is pattern-made for a rigid heavyweight and is over-long. However the lower forgings fit the M70 engine plates and the tubes could easily be cut down to fit. This with a couple of minor bits would form a complete frame. I contacted Max Priestley, holder of the POC stock of P&M factory drawings, and soon had drawings for the rear frames of both the Model 60 and the Model 70. (These drawings are dated July 1939.) For Max’s contact details see Sloper magazine. The POC holds a lot of P&M factory drawings but these have to be used with care as many do not correspond to the items actually fitted to the bikes. I checked the drawn dimensions against my Red Panther and they seem to match. The Model 60 and 70 rear frames are dimensionally identical but differ at the bottom fixing to the engine plates. With the M60 the tubular chainstays have been pressed flat and drilled for the fixing bolts, with the M70 a forged lug similar to that fitted to the post-war rigid heavyweights was brazed to the chainstay tube.

Trial assembly; Aussie front frame, new saddle stays,
new stand, pattern rear frame and engine.

Rear frame drawing, timing side.

I still had the factory drawing of a battery carrier which I had used to make one for the Red Panther so I set-to with some steel sheet, shears and a brazing torch and made another one. I also welded up (Rex would say not), a centre stand from metal cut from a piece of box section with an angle grinder. I also made the missing inner footrest. 

Battery Bracket drawing.

  

New battery bracket

    This of course took several weeks during which time someone pointed out that a set of Dowtys was being advertised on the POC forum. I quickly grabbed these. They are a good buy having been stored for 40 years after removal from a Panther. They don’t hold air at the moment but the bushes feel really good and the hard chrome of the sliders is perfect.

Lightweight Dowty Forks

 Then came the game changer!

 

My thanks to reach this stage go to Bruce Sharman, Tom Norman, Fred Baggs, Ralf Petscheleit, Paul Laming, Rex Norton, Ginger Ratcliffe, Ian Fox and Max Priestley.