B33/M33 rear mudguard

[Rog1]

Is there much difference between the rear mudguard on a plunger B33 (or B31) and a plunger M33? They do have different part numbers so are not the same. Is much involved in modifying a B33 mudguard to fit an M33 bike?

What about the two flanges on the front of the mudguard; are they for the battery/oil tank mounting plate?

[Rog1]

Err... anybody got an answer for me?

[Derek996]

A B31/33 mudguard could probably be fitted to an M21/21 and vice versa but they are not the same.
The B series mudguard has a removable rear section to facilitate easier wheel removal and the stays are different. They both attached with the lugs at the front to the oil tank \ tool box and frame and with a single bolt at the bottom to frame cross member behind the gearbox.

[Rog1]

A B31/33 mudguard could probably be fitted to an M21/21 and vice versa but they are not the same.
The B series mudguard has a removable rear section to facilitate easier wheel removal and the stays are different. They both attached with the lugs at the front to the oil tank \ tool box and frame and with a single bolt at the bottom to frame cross member behind the gearbox.

Both the mudguards you show seem to have a hinged rear section, but which is the M series and which is the B series mudguard?

[Derek996]

Both the mudguards you show seem to have a hinged rear section, but which is the M series and which is the B series mudguard?

Sorry,the M series mudguard is on the left and the other, showing the toolbox and part of the oil tank is the B series mudguard.

[Rog1]

Okay thanks,Derek999.
Now, just to boggle the mind here are two frame dimension drawings overlaid. In a sort of pale red with outlines filled in is the M series frame, and as a black outline is the B series frame.

There is some distortion in the original diagrams so not everything lines up or is all quite to the same scale, but there are a few differences. The front down tube and the tube from between the crankcase and gearbox up to the seat nose (the seat tube?) seem to be a bit more substantial.

The cross tube on the M frame below the rider's seat is shown in a different place compared to the B frame, though looking in parts books the drawings there say otherwise.
The casting that holds the plungers looks a bit beefier on the M frame and of course there's an additional piece of frame below the crankcase.

But the frames seem pretty similar where a rear mudguard would sit.

[GLENN]

Assuming the M and B series plunger mudguards are similar to a M and B series rigid, then I'd say the B series mudguard is quite a bit narrower than the M series.  I can measure the width of both tomorrow if that helps? 

Glenn

[Rog1]

Assuming the M and B series plunger mudguards are similar to a M and B series rigid, then I'd say the B series mudguard is quite a bit narrower than the M series.  I can measure the width of both tomorrow if that helps? 

Glenn

Thank you, that would be very helpful.

[GLENN]

OK, the measurement really depends on were you take it, for example they both flair out slightly towards the end of the tailpiece.  overall the M20 mudguard is more substantial in every respect.  at a comparable width the rigid M20 mudguard is 1/2 to 3/4" wider than then B31.  I didn't check the depth, but the M20 is clearly wider.  I have a plunder M20 mudguard (but couldn't get to it to measure it tonight), but it definitely resembles the larger M20 rigid mudguard.  So while a B series mudguard (at least rigid) might be made to fit, it would always look "light" in the frame. 

Best,

G

[Rog1]

OK, the measurement really depends on were you take it, for example they both flair out slightly towards the end of the tailpiece.  overall the M20 mudguard is more substantial in every respect.  at a comparable width the rigid M20 mudguard is 1/2 to 3/4" wider than then B31.  I didn't check the depth, but the M20 is clearly wider.  I have a plunder M20 mudguard (but couldn't get to it to measure it tonight), but it definitely resembles the larger M20 rigid mudguard.  So while a B series mudguard (at least rigid) might be made to fit, it would always look "light" in the frame. 

Best,

G

A belated thanks!

[GLENN]

No problem!   If you need anything else just let me know! 

Glenn