New member, engine nr \ “hc” mark

[Tors]

The enginenumber is AA7 S 1533 it also features a “hc” mark. Does that stand for high compression?

According to the a list i found it’s a 1952 engine. Didn’t check the frame nr yet.

[muskrat]

G'day Tors.
Yes the engine number is for a Star Twin. HC means high comp pistons. The standard at the time was 6.6:1 so the HC may have been 7.2:1.
Cheers

[a10 gf]

Also looks like accomodating thick flange cylinder ?

[Swarfcut]

 Thick flange cylinder? Not if it is still an A7. Count the fins....there should be 7 and the bore as standard is 66mm.  The A10 barrel has 8 fins and so is a little taller, along with a bigger bore of 70mm. All other external dimensions are the same, so plenty of scope for mix'n match in a previous life. Reckon both bikes are pre'53.

 The nuts and bolt threads are mainly what is termed  CEI or BSCy, based on the system used in the British Bicycle Industry. You won't find these in your local store. Threads into Alloy are the coarser Whitworth thread.

 The taps and dies along with most of the nuts and bolts required are available from specialist suppliers.

 Swarfy.

[Tors]

Thick flange?

My barrel has 7 fins, i added a picture. The bore was 66mm but has been rebored 1mm oversize to 67mm and the top was slightly skimmed.



The head has new valves and guides.

@muskrat… i found a second hand copy of the Roy Bacon book.

[Black Sheep]

Not forgetting that there are a few thick flange/small fin A7 barrels out there. Usually found with a small pile of hen's teeth.