Engine width

[Tazmantic]

Probably a silly question but do 500cc cases vary in width between years eg are 1940 narrower than 1950 ? because I know they do with 350 engines as I have a 1954 350 engine and that is wider than the 1941. So next question if all 500 engines are the same width are there spacers for the early 1940 frames and CP gearbox so as to make them the same width as the engine so the engine plates line up.

Hope this makes sense

[Reynard24]

My 1937 500 has narrower cases, they are 2 1/2” wide as are the mounting lugs on the CP gearbox. The rigid frame lugs are also 2 1/2” wide so everything should line up.

[Tazmantic]

My 1937 500 has narrower cases, they are 2 1/2” wide as are the mounting lugs on the CP gearbox. The rigid frame lugs are also 2 1/2” wide so everything should line up.

Many thanks yes my frame and gearbox which I both believe to be 1945/46 are that wide so is the 1941 350 engine I have but the 1948 500 cases are wider 3 1/2” same as my 1955 350 engine but the 48 cases have part numbers that match the 1939 parts list so would of thought the cases would of all been the same width. It’s all very confusing.

The width of the cases seem to match up with the width of a sprung frame.

[clive]

Mixing and matching overs the years is never quite as simple as it seems. However the 48 parts list notes a change in crankcase at engine number 8000. Before that 350 had cases starting 37- and 500 had 39- . After 8000 all engines had crankcase 39-... So it looks like the change in crankcase size for the 500 came in in 39 and eventually part way through 48 the 350 got the same crankcase.
I have changed a 350 wd motor on my rigid to a 1950 350 motor. I think the frame is 1948 (although I have reg docs which show it as both 1948 and 1952!) The front engine lugs on the frame are 3 3/4 and that part of the engine sloted straight in. When I had the earlier 350 motor in I think I had to have spacers between the front engine plate and the crankcase on the primary drive side. The other problem was that the rear engine plates are closer together with the earlier enging so I must have moved the spacers backwards. I also had to get the later dynamo strap to fit the wider spacing of the rear engine plates. Finally a point to note is that the later crankcases have a scallop to allow the dynamo to be pulled up against them. With the earlier cases the dynamo was pulled against the cutout in the rear engine plates. I had previously converted my plates by opening out cutout because I had an Alton alternator fitted and the spun cap of the early model meant it needed to be pulled against the crankcase. Sadly West London section members do not read the forum or they would be reassured to know that I achieved this by packing between the crankcase and alternator with a piece of aluminium cut from a saucepan! I think you may still be able to use the earlier rear engine plates with the later engine if you have a dynamo fitted but it will need checking if it is the shorter body type.

[Tazmantic]

Thanks for all the info Clive and my 1948 engine number is in the 6000 so suggests before the change and I thought I read in Mr Bacons book it was only the timing side that was changed. I’m positive the CP box is 1945 as it’s stamped C1 K 45 and the frame is 1@@1 so that puts that at 1946 according to Mr Bacons book.

The 1940s 350 engine I have would probably drop straight in as that’s the same width as the frame and Gbox so maybe the question now is is the Gbox and frame actually from a 350 where they narrower and was the 500 frames wider I’ve not looked that up yet but I thought they were the same.

Cheers Neil

Just looked one frame and Gbox for both 350 and 500 though the 1948 frame has a different part number

[Duncan]

Have you looked through the various pre and post war parts lists to identify stud lengths and spacers for engines and gearboxes?

[Tazmantic]

Not yet that will be the next port of call was just hoping someone on here would have a pucker 1946 and could out right say yep the cases are narrower or no cases the same and there are spacers on the frame down tube and gearbox.

[SPRIDDLER]

...... was just hoping someone on here would have a pucker 1946 and could out right say yep the cases are narrower or no cases the same and there are spacers on the frame down tube and gearbox.

My chum 'Thrifty Peter' has a '46 G80 Rigid which I believe is 99% original which he bought around 40 years ago from the first local owner.
If he doesn't spot this post and you think it would be useful I'll nip round and get some pics and measurements. Hopefully tomorrow afternoon as he's local to me.

EDIT............
It's just ocurred to me that at the moment he has a '47 engine in it but has the '46 engine in the shed. I'll measure both but from memory the '47 engine dropped straight into the '46 frame without needing different bolts or spacers.

Thrifty's '46 80.jpg

[Tazmantic]

Hi Spriddler that would be amazing thank you any pics and measurements would be a god send it’s a lovely looking bike and after a long day your mates name “Thrifty Pete” did make me chuckle Thanks again.

[SPRIDDLER]

Hi Spriddler that would be amazing thank you any pics and measurements would be a god send it’s a lovely looking bike and after a long day your mates name “Thrifty Pete” did make me chuckle Thanks again.

It's a nickname in our section which he has hard-earned over the past 30 or so years. I probably shouldn't tell you this, but just between you and I..........I bumped into him this morning when I called round to Resto Ray's shed to sort out the issues of global warming, high energy bills and unsatisfactory denture adhesives, etc. He was telling us how he had bought a carrot (just the one) for 8p at Tesco to have with his steak pie.

This is a winter photo but summers are much the same.

Wrinkly caff.jpg