B33 Plunger cylinder barrel

[bruce.craig]

I would appreciate your help please.

I have a 1952/1953 B33 plunger and my query is about compatibility of cylinder barrels.

I understand the cylinder barrel part number 65-1707 is listed in the 1954-57 BSA parts book and has square'ish fins.

However cylinder barrel part number 65-1229 is listed in the 1949-52 BSA parts book.

Can anyone please advise if these two cylinder barrels dimensionally and functionally compatible ?

I also understand that the 65-1707 cylinder barrel would use the short con rod whereas the 65-1229 would use the long con rod 66-482 ?

Cheers for your help, much appreciated.

[neil1964]

The functional parts of the two different barrels are completely the same and, like the B31 versions, are completely interchangeable.

I have made back to back comparisons with these before.  The later barrels just have larger and thicker fins, you can mix and match heads and barrels, just looks a bit odd.

The shorter rod makes no real difference as it is the same stroke and compensated for by a taller piston crown above the gudgeon pin.

B31 kept the same long rod (7 3/8") lengths all the way through. 

[bruce.craig]

Neil, cheers for your response which confirms my own research, thanks, and this is s huge help.

So I gather from your response that for the B33 it is possible to use either a short or long con rod with either cylinder barrel ?  Reason is I can find a replacement long con rod but finding a replacement short con rod is "mission impossible".  Your feedback would be appreciated.

And I would appreciate any information you may have if a Hepolite 11341/STD (6.8:1 compression ratio) or 11744/STD (7.5:1 compression ratio) piston is recommended with the 65-1707 cylinder barrel and long con rod configuration ?

Cheers for your help.

Bruce

[neil1964]

The Hepolite 11341  6.8:1 is for long rod engine
The 11744 @ 7.5:1 is for short rod.
You can tell which is for long rod as the gudgeon pin hole almost abuts the lowest piston ring land whereas the 11744 has some meat above the gudgeon pin hole and bottom ring. 
I had the search looking for an approx 7.5 to 8.5 CR piston for both B33 and later my ZB34 which is also a long rod motor.
I used a 020 NOS BSA piston in my B33 like this:

To my shame I don't know the exact piston in my ZB34 as Phil Pearson built it from my box of bits but he did not use my piston and supplied a new one and fitted a fat compression plate (I thought to allow for facing/squaring off the alloy sleeve before relining it).  However the CR is about 7:1 (by oil burette method).
I've since obtained a spare 8:1 020 for it (ever so slightly more crown height than the one above. 
Typically the later pistons (ie gold stars) have similar ring/gudgeon pin look but have a rounder crown edge c/w early ones.