Crankcases magnesium

Hi Ian,

The magnesium crankcases were first used on the works racers in 1934 and the first public appearance was probably the NW200 in Ireland. There may have been proto-type ones around in 1933for testing. All the pre-war 350s had a seperate set of numbers which ran from 1000 in 1929 to 10700 in 1939. At a guess I would think 8000 would have been later 1937 probably for the Manx GP. For 1937 there were probably around 60 350magnesium enginesmade that year, but if you can attach a photo it might be easier to indentify them. Regards, Richard.

You just posted that picture to make the Manxmaid whimper!

Previously ian_bradley wrote:

Hi Richard

Thanks for your reply you are correct its April 1937 when this bike was despatched as full Manx spec according to the records..Do you know if CJ flywheel ect is a strait swap over into these magnesium crankcases ,I think they do but are the bearings different?

I tried to up load a photo of crankcases but instead

some how I've attached a photo of me and my 1932 inter special and I can't remove it sorry.

Hi Ian,

See your bike on JDK's site, looks like there is lots of history behind it. In answer to your question.......Snap.... I am looking at doing the exact same myself ! Off the top of my head the drive side mainshaft and bearings are the same but the timing side is quite a bit different. The Manx bearing is a double row self-aligning ball bearing and is a metric size, even back in 1937. The standard Inter and CJ bearing is a fixed single row ball in imperial size. That means the mainshaft is longer and slightly smaller diameter where the wider Manx bearing fits. The Manx flywheels are slimmer than the standard ones where thebig-end crankpin fits sothe pin is different and the conrod is webbed on the Manx and is the 7.5 inches between centres compared to 7 inches and plain on the standard OHC. If I get time this week-endI will try the standard crank in the Manx cases and see what they look like but I think the barrel height and shorter conrod will be the main problem. Regards, Richard.

Previously ian_bradley wrote:

Hi Richard

the bike in the photo is a CS1 bottom end with manx barrel and head,the only thing I had to add was 4spacers under the magnesium cam box. The con rod was the right length could this be that the CS1 bottom end was built to Manx spec as it does have stamp on it to say it's been through the race shop.

I have just bought a CJ that has the same race stamp on and was built to Manx spec ,I thought every thing was the same except the material parts were made from and bits shaved off for weight .I think a Manx or race con rod has three oil holes in the top to oil the Gudgen Pin and road going inter has four(I may have that the wrong way round)

at some point I'm going to clean up the Magnesium cases pull down the CJ bottom end and swap it into the magnesium cases.I have an aluminium 350 barrel that goes with the crankcases does any body know what head would have been on this type of engine?

Photo of race stamp attached.

ps you haven't got a set of girders have you?

cheers Ian

Hi again Ian,

Go toBennett CNC and see Ian Bennett's parts for sale which will give you the applications and yearsof the different components he makes and is a good reference. Most of the 500cc parts are similar dimensions, hence your Inter/Manx all fitting together O.K.All 350 Inters andCJshave smaller crankcases than the 500s and the magnesium versions are likewise up to 1950 after which they were the samesize. Compare your different cases side by side and you will see there are several differences. Your 1937 engine should have the bi-metal ( alloy head/bronze skull ) small fincylinder head. The CS1 and the CJ were the touring versions, so not sure wether they would be race tuned. Sorry only have forks for my own bikes, but could help to identify the various types if that's any help. Regards, Richard.

Ian that stamp is of a lot of machines including my Australian "36 modelCS1 which was definitely just a tourer. As I know, no one has ever come up with a definitive on this mark, however your understanding may be valid, how did you come by it?

BtW what progress with the CJ etc...? Also; If you have any Manx Spec items going spare there is a member in France seeking parts to rebuild his machine. see "Pre war Norton" thread.

How come all the good stuff is in the antipodes????

Cheers

Jon

Just to say that the Manx 350 magnesium crankcases were a common casting - the same size as the 500 - from 1948. It's an absolute parts minefield - especially with 350s - the relevant parts books can be a good place to start. Ian Bennett is a big help as is Stu Rogers also Ken McIntosh.

Cheers,

Ian.