BSA B33

[Guy Wilson]

I have a B33 plunger (1952/3 - not 100% sure. The barrel bore is 88mm. Could anyone tell me how much oversize that is from the standard 85mm bore? Is it +60 thou to mix measures...
Feked list Bore Size: 3+3/8" (85mm) Standard, also available as +.020, +.040, +.060 oversize - please select.
thank you
Guy

[RDfella]

.060" is roughly 1.5mm so .060" oversize would take you to 86.5mm Your bore is 3mm oversize or roughly 1/8"

[KiwiGF]

I have a B33 plunger (1952/3 - not 100% sure. The barrel bore is 88mm. Could anyone tell me how much oversize that is from the standard 85mm bore? Is it +60 thou to mix measures...
Feked list Bore Size: 3+3/8" (85mm) Standard, also available as +.020, +.040, +.060 oversize - please select.
thank you
Guy

If its 88mm it may have been bored out for a liner? Which is not yet fitted?

[Guy Wilson]

Thanks RD, Kiwi, I doubt it was bored out to fit a liner, It came in bits and all goes together except for the piston and barrel. I suspect it may have had VW piston in a some point (the 1600 engine) was an 88mm bore.. I shall investigate more now I know its not a BSA oversize,
All the best
Guy

[Guy Wilson]

Question: the bore on the B33 barrel is 88.3 or .4mm ...what would the appropriate diameter of a piston be to fit this bore? what are the tolerances?
Guy

[muskrat]

G'day Guy.
At that size I'd give it 0.004" = 0.1 mm but depends on the piston type (cast/forged). I can't find any BSA/Triumph/Norton pistons that size.
I know a fella put a Dihatsu piston in a Yamaha. Lots of things need to line up. Crown height, pin diameter, skirt length etc.
Would certainly be easier to throw a sleeve in it.
Cheers

[Guy Wilson]

I agree, sleeving is the easiest.. may go that way... Guy

[chaterlea25]

Hi Guy,
An available liner that is cheap and will do the job is one from a Ferguson 35
4 cylinder diesel engine . I got one for about €15 
I turned down the bottom end of the liner and stepped the cylinder bore to suit as  additional security

John

[Guy Wilson]

Thanks John, there are certainly enough tractors here.. I have a look around
Guy

[Rocket Racer]

After sleeving it back to standard, make sure you look for a long rod piston. the later BB series changed the rod length and the gudgeon pins moved accordingly, so you'll need the right piston to suit your rod type which if early (ZB?) should be the long rod.

Have owned my ZB33 since the mid 1980's, it will the last bike I'd ever sell.

IMHO avoid JP pistons for these, they grow too much and seize. try and find a hepolite or equivelent, preferably flat top

[Guy Wilson]

Thanks RR, I have a standard piston which I'll check to see if its correct for the rod. Good advice,
I've just had an enjoyable weekend on a sort of socially distanced DGR https://advrider.com/f/threads/kenyas-kinda-dgr-just-our-cup-o-tea.1469171/ Here's Hunter's write up. Many up and down hills and at altitude..
Guy

[Rocket Racer]

Thanks RR, I have a standard piston which I'll check to see if its correct for the rod. Good advice,
I've just had an enjoyable weekend on a sort of socially distanced DGR https://advrider.com/f/threads/kenyas-kinda-dgr-just-our-cup-o-tea.1469171/ Here's Hunter's write up. Many up and down hills and at altitude..
Guy

enjoyed the link, thankyou .