Hi,

I have a 1955 BSA M33 Plunger. I am trying to workout how to get the most extra MPH out of the old girl. Its got a standard 4 speed gearbox that I rebuilt but didnt think about the internal ratios. Things can improve the speed include.

1. Larger engine sprocket
2. Smaller Gearbox Sprocket
3. Gearbox ratios.

Attached to this message is the 1955 BSA Sales Brochure with the gearbox ratios for both BSA B and BSA M, with and without side cars. Can someone explain how the gearbox ratios relate to the internal gears, number of teeth, and layshaft number of teeth etc. People advertise the 4 speed gearboxes as Goldstar's but may not have the right ratio's

Ideally someone out there will have a standard 4 speed gearbox with higher ratios that the one I have at the moment and might sell me them?

Thanks

Chaps,

Will Hogan at Stainless steel classics has kindly and beautiful supplies a new brake rod. It’s for an A7/10 so is too long but I will adapt for my 1955 BSA M33 Plunger. The old brake rod is pretty bad and while it works to a fashion is not good. Can anyone measure their plunger brake rod and tell me their kink angles and dimensions. A couple of photos to explain how it gets around the plunger units would be superb. I have said to Will I will send these onto him to aid his supply specifications.

Many thanks
Hamish

Hi,

Bike has had a new engine rebuild, magneto rebuild, fitted with Amal concentric with 260 main jet (middle position needle) 19cc Idle jet 1 1/4 turned back. Oil getting to top of engine and back down on return pipe. Running Mineral SAE40 oil. Sits between advanced and retard even warm, doesnt like to advanced or too retarded. Carb has 10mm of heat protection with heat insulting plate... mildly warm to the touch after 20 min, not in any shape or form hot. Choke is fully open from the start and doesnt need any at all.

After 20 minutes of riding - getting up to 50mph, it slowly and surely starts to lose power to the point I have the throttle wide open it chugs along... sounds more throaty. Still idles well, but when hot gets slow, loss of power. When cooled it back to normal and will run quickly.

Any advice gratefully recieved.

Hamish

BSA M33 Plunger - 1955 - New Lucas Wiring Loom - diagram followed religiously, new battery 6v positive earth, refurbed, Lucas Magdyno, new solid state rectifier.

Lights switch off / off from the battery, all good.
Run the bike, get it night are warm running for about 20 min, all good... except the lights have died....
Leave the bike for 30 min or more to cool down... lights come back on.

Its a standard off the shop floor 6v positive earthed system, the magdyno was professionally rebuilt... I am so confused... any ideas?

Any ideas warmly welcomed!
Modify message

Hi,

My bike is now up and running... sounds awesome, and is looking great. One issue I do have is the rear stays. The offside rear stay is a creative Burmese fixer and is wrong.

1. What is the length from bracket to mudguard, rear, and what height to the top of the mudguard (in the middle)

2. Does anyone have any spares? I am not buying the India stuff as 100% it will be wrong. I bought a chain guard and rear mudguard and they were a mile off!

Many thanks
Hamish

Guys,

Nearing completion of my 1955 BSA M33 Plunger bike and its getting fired up this weekend. Will post video...anyway, the final thing to do is the final drive chain.

Kidderminster BSA have supplied a new chain, Japanese which looks very tidy, but its too long and will be shortened.

Its a 5/8th inch x 1/4 inch. Gearbox sprocket is 19T and the rear wheel drum is 42T.

Clearly this is somewhat subjective as you need to balance the gearbox primary drive and the rear final drive, but approximately how links will be in the final drive chain?

Many thanks and kind regards
Hamish

Hi Guys,

Quick Q. Following the power coating of my BSA M33 Frame I need to thread clear my frame in a couple of places.

There are a couple of threaded lugs on the Saddle down to gearbox...I think the battery and the rear mudguard will connect to them. Does anyone who what tap / thread I should buy?

Ta
Hamish

Hi Guys,

I am sure this a common thread as it seems to be a common problem. The inner case of my BSA M Plunger gearbox is worn around the kickstart quadrant and speedo drive area... Its grinding metal. I have managed to get a new inner case for the gearbox part which is in amazing condition but I am worried about it getting damaged.

Does anyone know what is causing this e.g. which part or parts are worn that are causing this internal damage and how I fix it.

Many thanks for all your help.
P.S. I managed to get plunger columns from Baxter cycles in the USA... last pair and the bike is coming together nicely.