Robbins piston

[MikPowl]

Does anyone know anything about 'Robbins' pistons from the US?  Any good? Avoid?

[groily]

Company has its main focus on kart racing it seems. Hard to find much useful comment but a drag-race motor builder of Indians says they're 'soft as butter' and 'no good' - along with a few others similarly condemned - before praising some Taiwanese ones as being fit for his purposes.
Where were you thinking of putting them? The fact that no-one has replied to your query suggests to me that they're not a known option, be they good or bad, for As.

[MikPowl]

Hi, Thanks for replying.   There's a pair of nos bare A10 pistons I've seen for sale that might be great for my A10 rebuild. I managed to find out that the company who made them were in LA in the States and that manufacture (of this piston anyway) stopped a long time ago - these are n.very.o.s.!   But they're bare so I'd have to take a punt that they were machined to fit standard/Hepolite rings and I'd also have hefty postage to pay. I'd also found the 'soft as butter' remark but I think it applies to a more recent product - these would have been made 50yrs ago at least. I wondered if anyone here had direct experience of these items. On the plus side, they're the correct o/size and are 8.5:1  which is more or less correct for my model. OTH, the low c.r. pistons 'as found' in the engine would probably clean up and just need rings. This bike will never see serious rock'n roll riding so I think maybe I'll give Mr Robbins product a miss.

[groily]

Ah - with you now.
Don't know about rings etc, but FW Thornton is one good place to ask if/when dimensions are known should you want to go that way.
But if you're not looking for ultimate performance, I'd look seriously at IMD for the pistons. Probably cost no more than the ones from the USA, and come with all the necessary.
Personally - just me - the recipe for long and trouble-free running when I had my second A10 (a scruffy de-tuned SR with an iron head) for a dozen and more  years of heavy use, was 'large-journal crank, thick-flange barrels and flat-top pistons'. Latterly, IMD +40s fitted to lightly-worn but high mileage bores after just a hone. Happy I was with them, and so's the current owner who's also a highish-mileage daily-user sort of bloke.

[Swarfcut]

 If the motor was found with low compression dished pistons, the original cam would have been a 334. This works fine with flat top pistons, but these really need a 356 cam for any benefit in performance. Higher compressions mean more power and spirited performance, but may produce a motor with a harsher feel and more vibration. Standard ring grooves were 1/16" for compression rings, 1/8" for oil rings.

 Drags have a piston chart to compare Hepolite stock with original BSA part numbers, along with wrist pin dimensions and ring sets specs.

 Somewhere on the Forum is a whole summary of what's what pistonwise, reckon it was down to Col a couple of years ago....

 Swarfy.

 

[MikPowl]

Thanks for that info.  The bike's a SuperFlash, so was originally fitted with the 365 cam and (I think) 8:1 slightly raised pistons. I got hold of it after it had been dumped on the street - the bores were out to +.060, and the crank had one grind left on it - during all these previous 'rebuilds' it seems the sludge trap was never cleared - totally blocked!!  The cam is still useable and the pistons (standard A10 compression) seem to have had very few miles before the bike packed up and wad dumped. I'm completely with the philosophy of keeping the motor soft if it isn't going to be used in a sporty fashion, which, after thinking about it, has ruled out going with the Robbins jobbies.  Thrashing around in today's traffic on a plunger framed BSA isn't really feasible and the country roads round here would be just as deadly!  After owning the beast for ~40 years I'm finally doing something about putting it back together. The scariest bit is the price and availabilty of fasteners, chroming, etc. I've just bought two stainless bolts w/nuts that, after VAT & postage, have cost nearly 4 times what I paid for the bike (the equivalent of a tenner!)  Can't find stand spigots anywhere - on order with Draganfly.  The plan is to put it together as I would have wanted it back in the day - not as it came out of the factory. So it'll be a red & chrome tank, alli rims, etc. The originality cops can take a hike.

[muskrat]

G'day MP.
You have one of only 577 produced, a rare and desirable model. Most were exported to the US.
 Try to keep and repair as much of the original parts as possible. Finding replacements will be difficult as quite a few parts were specific to that model.
Plunger models handle quite well in my opinion. Mine is/was used as a commuter, tourer and bush basher (even spent time on the race track). Don't underestimate it's capabilities. A bit of tweaking of the front forks will help.
Best of luck with it. https://classicavenue.com/product/1953-bsa-650cc-super-flash-serial-no-001-copy/
Cheers

[MikPowl]

This old fellow was one of the last batch of 20 made and sold off to a distributor, not to the US. It ended up in Hong Kong where maintenance was done mainly in hole in-the-wall shops and where spare parts were very scarce. It's been bodged around to keep it on the road, but the only major SF-specific bits missing are the rear guard & stays and the toolbox. The fasteners are anything that fitted at the time! The rear frame section was badly butchered but that's now in a usable form. It's a '54 bike so a number of parts differ from the '53 parts list - big-fin barrel & head, Rocket yokes, 4-1/4 gallon tank - so it was 'non-original' even when it left the factory, if that makes any sense. (I found a US spec 'small' tank on-line so that's going on the bike). But as I say, this is going to be what I'd have liked to ridden if i'd bought it as a teenager. It's value doesn't mean anything to me.   Expect a few more queries on here as I get into the rebuild!  Thanks for your help, Mike

[muskrat]

G'day Mike.
Your questions are welcome (in the right board). There a few SF owners here and a few very knowledgeable fellas with a lot of info.
Pictures are a must 
Cheers