500cc Pistons Wanted

[Orgasmatron]

Does anyone have a pair of 500cc pistons that they would like to sell? Current pistons are +40 (and they rattle about a lot), so +60 would be best.
The pistons are for a 1930 blind head barrell TT Rep.
Chris.

[BRIAN MARSHALL]

As I mentioned the other day, do make sure that the rattle is not being caused by the gudgeon pin holes in the piston/s being worn oval due to the pins being seized or partly seized in the little-end eye of the conrod, which makes the pins turn in the pistons rather than the conrods. (They are supposed to be an interference fit into the pistons). If you do have this problem it is MUCH cheaper to get the piston gudgeon pin holes bushed back to being round, and a good fit onto the pins. Even if only one is worn get them both bushed so that they are the same weight.
In any event, new 498 pistons are not currently available, but may be, (from the Spares Scheme), in a few months time.
It might be possible to find a good pair of used oversize pistons, at perhaps plus 50 or 60 thou”, and then get them turned down to fit your bores. The bores themselves of course, will need checking for wear and ‘tramline’ damage, plus honing to remove any ‘glazing’. All this really needs doing by a Scott specialist repairer, rather than a local engineering company.
Brian

[Orgasmatron]

Brian,
There is no wear on either little end, although one gudgeon pin (RHS) is seized into the piston (but not the little end, which is free and has no wear otherwise – all nice and solid with no movement – slides easily sideways on the gudgeon pin).
If I move the flywheel backwards and forwards, there is a loud clacking noise, possibly from the RHS barrell/seized piston.
Both pistons are very loose in the barrells.
The bottom end is very good, with no wear apparent ; everything appears to be still as Tom Ward put it together in 1963 (not much use at all since then). Pity he didn’t do the top end as well, at the time.
I am seriously thinking of Mr Shermer’s 530cc conversion with turned down 600cc pistons. I would really like to keep it standard (either 500cc or 600cc) but if I cannot locate some +40 or +60 500cc pistons or locate a good 600cc barrell, then that’s what I might well go for ; I’m a bit worried that the 530cc rebore might not allow for any further rebores though.
Chris.

[chris wastell]

Think about the mileage you are likely to do on a new set of 530 pistons, carefully riding an 80 year-old bike. Not many of us ride our Scotts as they were “back in the day”, so to my way of thinking the need for a rebore is going to be unlikely. If you do have a mishap and wreck the barrels you haven’t really lost anything. Just a thought 🙂

[BRIAN MARSHALL]

A ‘clacking’ noise as you move the flywheel backwards and forwards is usually caused by the drive tongues on the crankcase sealing glands having worn slots into the sides of the flywheel keyway. It is of course a full bottom-end stripdown job to repair this, but actually it is of little detriment to the running of the engine, just an annoying noise.
Brian

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